More Important Topics of Cylinder

older geologic periods, the rock beds that define the start and end are well identified, but the exact dates of the start and end of the period are uncertain by a few million years.

During the Triassic, both marine and continental life show an adaptive radiation beginning from the starkly impoverished biosphere that followed the Permian-Triassic extinction. Corals of the hexacorallia group made their first appearance. The first flowering plants (Angiosperms) may have evolved during the Triassic, as did the first flying vertebrates, the pterosaurs.

Dating and subdivisions
The Triassic was named in 1834 by Friedrich Von Alberti from the three distinct layers (Latin trias meaning triad) —red beds, capped by chalk, followed by black shales— that are found throughout Germany and northwest Europe, called the 'Trias'.
The Triassic is usually separated into Early, Middle, and Late Triassic Epochs, and the corresponding rocks are referred to as Lower, Middle, or Upper Triassic.

The faunal stages from the youngest to oldest are:
Upper/Late Triassic (Tr3)
Rhaetian (203.6 ± 1.5 – 199.6 ± 0.6 Ma)
Norian (216.5 ± 2.0 – 203.6 ± 1.5 Ma)
Carnian (228.0 ± 2.0 – 216.5 ± 2.0 Ma)
Middle Triassic (Tr2)
Ladinian (237.0 ± 2.0 – 228.0 ± 2.0 Ma)
Anisian (245.0 ± 1.5 – 237.0 ± 2.0 Ma)
Lower/Early Triassic (Scythian)
Olenekian (249.7 ± 0.7 – 245.0 ± 1.5 Ma)
Induan (251.0 ± 0.4 – 249.7 ± 0.7 Ma)

Paleogeography
During the Triassic, almost all the Earth's land mass was concentrated into a single supercontinent centered more or less on the equator, called Pangaea ("all the land"). This took the form of a giant "Pac-Man" with an east-facing "mouth" constituting the Tethys sea, a vast gulf that opened farther westward in the mid-Triassic, at the expense of the shrinking Paleo-Tethys Ocean, an ocean that existed during the Paleozoic. The remainder was the world-ocean known as Panthalassa ("all the sea").

All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates; thus, very little is known of the Triassic open ocean.
The supercontinent Pangaea was rifting during the Triassic—especially late in the period—but had not yet separated. The first nonmarine sediments in the rift that marks the initial break-up of Pangea—which separated New Jersey from Morocco—are of Late Triassic age; in the U.S., these thick sediments comprise the Newark Group.

Because of the limited shoreline of one super-continental mass, Triassic marine deposits are globally relatively rare, despite their prominence in Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the west. Thus Triassic stratigraphy is mostly based on organisms living in lagoons and hypersaline environments, such as Estheria crustaceans.

The Triassic climate was generally hot and dry, forming typical red bed sandstones and evaporites. There is no evidence of glaciation at or near either pole; in fact, the polar regions were apparently moist and temperate, a climate suitable for reptile-like creatures.

Pangaea's large size limited the moderating effect of the global ocean; its continental climate was highly seasonal, with very hot summers and cold winters. It probably had strong, cross-equatorial monsoons.

Three categories of organisms can be distinguished in the Triassic record: holdovers from the Permian-Triassic extinction, new groups which flourished briefly, and other new groups which went on to dominate the Mesozoic world.

The climate was also very dry and hot and many dinosaurs had to adapt to the climate.
In marine environments, new modern types of corals

appeared in the Early Triassic, forming small patches of reefs of modest extent compared to the great reef systems of Devonian times or modern reefs. The shelled cephalopods called Ammonites recovered, diversifying from a single line that survived the Permian extinction.

The fish fauna was remarkably uniform, reflecting the fact that very few families survived the Permian extinction. There were also many types of marine reptiles.

These included the Sauropterygia, which featured pachypleurosaurs and nothosaurs (both common during the Middle Triassic, especially in the Tethys region), placodonts, and the first plesiosaurs; the first of the lizardlike Thalattosauria (Askeptosaurs); and the highly successful ichthyosaurs, which appeared in Early Triassic seas and soon diversified, some eventually developing to huge size during the late Triassic.

On land, the holdover plants included the lycophytes, the dominant cycads, ginkgophyta (represented in modern times by Ginkgo biloba) and glossopterids. The Spermatophytes, or seed plants came to dominate the terrestrial flora: in the northern hemisphere, conifers flourished. Glossopteris (a seed fern) was the dominant southern hemisphere tree during the Early Triassic period.

Temnospondyl amphibians were among those groups that survived the P-T extinction, some lineages (e.g. Trematosaurs) flourishing briefly in the Early Triassic, while others (e.g. Capitosaurs) remained successful throughout the whole period, or only came to prominence in the Late Triassic (e.g. Plagiosaurs, Metoposaurs). As for other amphibians, the first Lissamphibia are known from the Early Triassic, but the group as a whole did not become common until the Jurassic, when the temnospondyls had become very rare.

Archosauromorph reptiles — especially archosaurs — progressively replaced the synapsids that had dominated the Permian. Although Cynognathus was a characteristic top predator in earlier Triassic (Olenekian and Anisian) Gondwana, and both Kannemeyeriid dicynodonts and gomphodont cynodonts remained important herbivores during much of the period. By the end of the Triassic, synapsids played only bit parts. During the Carnian (early part of the Late Triassic), some advanced cynodont gave rise to the first mammals.

At the same time the Ornithodira, which until then had been small and insignificant, evolved into pterosaurs and a variety of dinosaurs. The Crurotarsi were the other important archosaur clade, and during the Late Triassic these also reached the height of their diversity, with various groups including the Phytosaurs, Aetosaurs, several distinct lineages of Rauisuchia, and the first crocodylians (the Sphenosuchia).

Meanwhile the stocky herbivorous rhynchosaurs and the small to medium-sized insectivorous or piscivorous Prolacertiformes were important basal archosauromorph groups throughout most of the Triassic.

Among other reptiles, the earliest turtles, like Proganochelys and Proterochersis, appeared during the Norian (middle of the Late Triassic). The Lepidosauromorpha—specifically the Sphenodontia—are first known in the fossil record a little earlier (during the Carnian). The Procolophonidae were an important group of small lizard-like herbivores.

Lagerstätten
The Monte San Giorgio lagerstätte, now in the Lake Lugano region of northern Italy and Switzerland, was in Triassic times a lagoon behind reefs with an anoxic bottom layer, so there were no scavengers and little turbulence to disturb fossilization, a situation that can be compared to the better-known Jurassic Solnhofen limestone lagerstätte.

The remains of fish and various marine reptiles (including the common pachypleurosaur Neusticosaurus, and the bizarre long-necked archosauromorph Tanystropheus), along with some terrestrial forms like Ticinosuchus and Macrocnemus, have been recovered from this locality. All these fossils date from the Anisian/Ladinian transition (about 237 million years ago).

Late Triassic extinction event
The Triassic period ended with a mass extinction, which was particularly severe in the oceans; the conodonts disappeared, and all the marine reptiles except ichthyosaurs and plesiosaurs. Invertebrates like brachiopods, gastropods, and molluscs were severely affected.

In the oceans, 22% of marine families and possibly about half of marine genera went missing, according to University of Chicago paleontologist Jack Sepkoski.
Though the end-Triassic extinction event was not equally devastating everywhere in terrestrial ecosystems, several important clades of Crurotarsi (large archosaurian reptiles previously grouped together as the thecodonts) disappeared, as did most of the large labyrinthodont amphibians, groups of small reptiles, and some synapsids (except for the proto-mammals).

Some of the early, primitive dinosaurs also went extinct, but other more adaptive dinosaurs survived to evolve in the Jurassic. Surviving plants that went on to dominate the Mesozoic world included modern conifers and cycadeoids.

It is not certain what caused this Late Triassic extinction, which was accompanied by huge volcanic eruptions about 208-213 million years ago, the largest recorded volcanic event since the planet cooled and stabilized, as the supercontinent Pangaea began to break apart.

Other possible causes for the extinction events include global cooling or even a bolide impact, for which an impact crater surrounding Manicouagan Reservoir in Quebec, Canada, has been singled out. At the Manicouagan impact crater, however, recent research has shown that the impact melt within the crater has an age of 214±1 Ma.

The date of the Triassic-Jurassic boundary has also been more accurately fixed recently, at 202±1 Ma. Both dates are gaining accuracy by using more accurate forms of radiometric dating, in particular the decay of uranium to lead in zircons formed at the impact. So the evidence suggests the Manicouagan impact preceded the end of the Triassic by approximately 12±2 Ma. Therefore it could not be the immediate cause of the observed mass extinction.

The number of Late Triassic extinctions is disputed. Some studies suggest that there are at least two periods of extinction towards the end of the Triassic, between 12 and 17 million years apart. But arguing against this is a recent study of North American faunas. In the Petrified Forest of northeast Arizona there is a unique sequence of latest Carnian-early Norian terrestrial sediments.

An analysis in 2002 found no significant change in the paleoenvironment. Phytosaurs, the most common fossils there, experienced a change-over only at the genus level, and the number of species remained the same. Some Aetosaurs, the next most common tetrapods, and early dinosaurs, passed through unchanged. However, both Phytosaurs and Aetosaurs were among the groups of archosaur reptiles completely wiped out by the end-Triassic extinction event.

It seems likely then that there was some sort of end-Carnian extinction, when several herbivorous archosauromorph groups died out, while the large herbivorous therapsids— the Kannemeyeriid dicynodonts and the Traversodont cynodonts— were much reduced in the northern half of Pangaea (Laurasia).

These extinctions within the Triassic and at its end allowed the dinosaurs to expand into many niches that had become unoccupied. Dinosaurs became increasingly dominant, abundant and diverse, and remained that way for the next 150 million years. The true "Age of Dinosaurs" is the Jurassic and Cretaceous, rather than the Triassic.

Anthozoa is a class within the phylum Cnidaria that contains the sea anemones and corals. Unlike other cnidarians, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some substrate on which the cnidarian grows.

Some anthozoans can also be reproduce asexually through budding.
All cnidarian species can feed by catching prey with nematocysts, sea anemones capable of catching fish and

corals catching plankton. Some of the species also harbour a type of algae, dinoflagellates called zooxanthellae, in a symbiotic relationship; the reef building corals known as hermatypic corals rely on this symbiotic relationship particularly. The zooxanthellae benefit by using nitrogenous waste and carbon dioxide produced by the host, and the cnidarian gains photosynthetic capability and increased calcium carbonate production in hermatypic corals.

Anemonies and certain species of coral live in isolation, however most corals form colonies of genetically identical polyps; these polyps closely resemble anemonies in structure, although are generally considerably smaller. Most kinds of stony coral live in all parts of the underwater world.

Phylogeny

The two subclasses are divided into a number of orders and a series of orders., extinct orders from the Paleozoic (570-245 m.y.a.) are marked with †.

Subclass Alcyonaria (= Octocorallia) (8-way symmetry)

Alcyonacea (soft corals)
Gorgonacea (sea fans, sea feathers)
Helioporacea (= Coenothecalia) (Indo-Pacific blue coral)
Pennatulacea (sea pens, sea pansies)
Stolonifera (organ-pipe coral, tree fern coral)
Telestacea (soft corals)

Subclass Zoantharia (= Hexacorallia (6-way symmetry)
Ceriantharia (tube-dwelling anemones)
Actiniaria (sea anemones)
Corallimorpharia
Numidiaphyllida †
Scleractinia (= Madreporaria) (stony corals)
Kilbuchophyllida †
Antipatharia (black corals, thorny corals)
Zoanthidea
Heterocorallia †
Rugosa † (= Tetracoralla) (horned corals)
Heliolitida †
Tabulata † (tabulate corals)
Cothoniida †
Tabuloconida †
Ptychodactiaria

Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda, phylum Mollusca. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods.

Ammonites' closest living relative is probably not the modern Nautilus (which they outwardly resemble), but rather the subclass Coleoidea (octopus, squid, and cuttlefish). Their fossil shells usually take the form of

planispirals, although there were some helically-spiraled and non-spiraled forms (known as "heteromorphs"). Their spiral shape begot their name, as their fossilized shells somewhat resemble tightly-coiled rams' horns. Plinius the Elder (died 79 A.D. near Pompeii) called fossils of these animals ammonis cornua ("horns of Ammon") because the Egyptian god Ammon (Amun) was typically depicted wearing ram's horns. Often the name of an ammonite genus ends in ceras, which is Greek (???a?) for "horn" (for instance, Pleuroceras).

Classification
Originating from within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Late Silurian to Early Devonian (circa 400 million years ago) and became extinct at the close of the Cretaceous (65 m.y.a.) along with the dinosaurs. The classification of ammonoids is based in part on the ornamentation and structure of the septa comprising their shells' gas chambers; by these and other characteristics we can divide subclass Ammonoidea into three orders and eight known suborders. While nearly all nautiloids show gently curving sutures, the ammonoid suture line (the intersection of the septum with the outer shell) was folded, forming saddles (or peaks) and lobes (or valleys).

Suture patterns
Three major types of suture patterns in Ammonoidea have been noted:
Goniatitic - numerous undivided lobes and saddles; typically 8 lobes around the conch. This pattern is characteristic of the Paleozoic ammonoids.
Ceratitic - lobes have subdivided tips, giving them a saw-toothed appearance, and rounded undivided saddles. This suture pattern is characteristic of Triassic ammonoids and appears again in the Cretaceous "pseudoceratites."

Ammonitic - lobes and saddles are much subdivided (fluted); subdivisions are usually rounded instead of saw-toothed. Ammonoids of this type are the most important species from a biostratigraphical point of view. This suture type is characteristic of Jurassic and Cretaceous ammonoids but extends back all the way to the Permian.

Orders and suborders
The three orders and various suborders of Ammonoidea are herein listed from most primitive to more derived.
Goniatitida (Devonian to Permian) -- have round saddles, pointed lobes
Anarcestina (Devonian only)
Clymeniina (upper Upper Devonian only)
Goniatitina (Devonian to Upper Permian) -- includes the true goniatites
Ceratitida (Carboniferous to Triassic) -- have round saddles, serrated lobes
Prolecanitina (Upper Devonian to Upper Triassic)
Ceratitina (Permian to Triassic) -- includes the true ceratites
Ammonitida (Permian to Cretaceous) -- have folded saddles and lobes, fractal patterns
Phylloceratina (Lower Triassic to Upper Cretaceous)
Ammonitina (Lower Jurassic to Upper Cretaceous) -- includes the true ammonites
Lytoceratina (Lower Jurassic to Upper Cretaceous)
Ancyloceratina (Upper Jurassic to Upper Cretaceous) -- the heteromorph ammonites

Life
Because ammonites and their close relatives are extinct, little is known about their way of life. Their soft body parts are very rarely preserved in any detail. Nonetheless, much has been worked out by examining ammonoid shells and by using models of these shells in water tanks.

Many ammonoids probably lived in the open water of ancient seas, rather than at the sea bottom. This is suggested by the fact that their fossils are often found in rocks that were laid down under conditions where no bottom-dwelling life is found. Many of them (such as Oxynoticeras) are thought to have been good swimmers with flattened, discus-shaped, streamlined shells, although some ammonoids were less effective swimmers and were likely to have been slow-swimming bottom-dwellers. Ammonites and their kin probably preyed on fishes, crustaceans and other small creatures; while they themselves were preyed upon by such marine reptiles as mosasaurs. Fossilized ammonoids have been found showing teeth marks from such attacks.

The soft body of the creature occupied the largest segments of the shell at the end of the coil. The smaller earlier segments were walled off and the animal could maintain its buoyancy by filling them with gas. Thus the smaller sections of the coil would have floated above the larger sections. Many illustrations make the mistake of placing the larger end of the coil at the top for aesthetic reasons but this is factually incorrect.

Shell anatomy and diversity
Basic shell anatomy

The chambered part of the ammonite shell is called a phragmocone. The phragmocone contains a series of progressively larger chambers, called camerae (sing. camera) that are divided by thin walls called septa (sing. septum). Only the last and largest chamber, the body chamber, was occupied by the living animal at any given moment. As it grew, it added newer and larger chambers to the open end of the coil.

A thin living tube called a siphuncle passed through the septa, extending from the ammonite's body into the empty shell chambers. Through a hyperosmotic active transport process, the ammonite emptied water out of these shell chambers. This enabled it to control the buoyancy of the shell and thereby rise or descend in the water column.

A primary difference between ammonites and nautiloids is that the siphuncle of ammonites (excepting Clymeniina) runs along the ventral periphery of the septa and camerae (i.e., the inner surface of the outer axis of the shell), while the siphuncle of nautiloids runs more or less through the center of the septa and camerae.

Sexual dimorphism
One feature found in shells of the modern Nautilus is the variation in the shape and size of the shell according to the gender of the animal, the shell of the male being slightly smaller and wider than that of the female. This sexual dimorphism is thought to be an explanation to the variation in size of certain ammonite shells of the same species, the larger shell (called a macroconch) being female, and the smaller shell (called a microconch) being male. This is thought to be because the female required a larger body size for egg production. A good example of this sexual variation is found in Bifericeras from the early part of the Jurassic period of Europe.

It is only in relatively recent years that the sexual variation in the shells of ammonites has been recognized. The macroconch and microconch of one species were often previously mistaken for two closely related but different species occurring in the same rocks. However, these "pairs" were so consistently found together that it became apparent that they were in fact sexual forms of the same species.

Variations in shape
The majority of ammonite species feature a shell that is a planispiral flat coil, but other species feature a shell that is nearly straight (as in baculites). Still other species' shells are coiled helically - superficially like that of a large gastropod (as in Turrilites and Bostrychoceras). Some species' shells are even initially uncoiled, then partially coiled, and finally straight at maturity (as in Australiceras). These partially uncoiled and totally uncoiled forms began to diversify mainly during the early part of the Cretaceous and are known as heteromorphs.

Perhaps the most extreme and bizarre looking example of a heteromorph is Nipponites, which appears to be a tangle of irregular whorls lacking any obvious symmetrical coiling. However, upon closer inspection the shell proves to be a three-dimensional network of connected "U" shapes. Nipponites occurs in rocks of the upper part of the Cretaceous in Japan and the USA.

Ammonites vary greatly in the ornamentation (surface relief) of their shells. Some may be smooth and relatively featureless, except for growth lines, and resemble that of the modern Nautilus. In others various patterns of spiral ridges and ribs or even spines are shown. This type of ornamentation of the shell is especially evident in the later ammonites of the Cretaceous.

The aptychus
Like the modern nautilus, many ammonites were probably able to withdraw their body into the living chamber of the shell and developed either a single horny plate or a pair of calcitic plates with which they were able to close the opening of the shell. The opening of the shell is called the aperture. The plates are collectively termed the aptychus or aptychi in the case of a pair of plates, and anaptychus in the case of a single plate. The aptychi were identical and equal in size.

Anaptychi are relatively rare as fossils. They are found representing ammonites from the Devonian period through those of the Cretaceous period.
Calcified Aptychi only occur in ammonites from the Mesozoic era and are normally found detached from the shell and are rarely preserved in place. Still, sufficient numbers have been found closing the apertures of fossil ammonite shells as to leave no doubt as to their intended purpose. (This long-standing and wide-spread interpretation of the function of the aptychus has long been disputed. The latest studies suggest that the anaptychus may have in fact formed part of a special jaw apparatus).

Large numbers of detached aptychi occur in certain beds of rock (such as those from the Mesozoic in the Alps). These rocks are usually accumulated at great depths. The modern Nautilus lacks any calcitic plate for closing its shell, and only one extinct nautiloid genus is known to have borne anything similar. Nautilus does, however, have a leathery head shield (the hood) which it uses to cover the opening when it retreats inside.

There are many forms of aptychus, varying in shape and the sculpture of the inner and outer surfaces, but because they are so rarely found in position within the shell of the ammonite it is often unclear to which species of ammonite many aptychi belong. A number of aptychi have been given their own genus and even species names independent of their unknown owners' genus and species, pending future discovery of verified occurrences within ammonite shells.

Size
Few of the ammonites occurring in the lower and middle part of the Jurassic period reach a size exceeding 23 centimetres (9 inches) in diameter. Much larger forms are found in the later rocks of the upper part of the Jurassic and the lower part of the Cretaceous, such as Titanites from the Portland Stone of Jurassic of southern England, which is often 53 centimetres (2 feet) in diameter, and Parapuzosia seppenradensis of the Cretaceous period of Germany, which is one of the largest known ammonites, sometimes reaching 2 metres (6.5 feet) in diameter.

The largest documented North American ammonite is Parapuzosia bradyi from the Cretaceous with specimens measuring 137 centimetres (4.5 feet) in diameter, although a new British Columbian specimen, if authentic, would appear to trump even the European champion.

Distribution
Starting from the late Silurian, ammonoids were extremely abundant, especially as ammonites during the Mesozoic era. Many genera evolved and ran their course quickly, becoming extinct in a few million years. Due to their rapid evolution and widespread distribution, ammonoids are used by geologists and paleontologists for biostratigraphy. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods.

Due to their free-swimming and/or free-floating habits, ammonites often happened to live directly above seafloor waters so poor in oxygen as to prevent the establishment of animal life on the seafloor. When upon death the ammonites fell to this seafloor and were gradually buried in accumulating sediment, bacterial decomposition of these corpses often tipped the delicate balance of local redox conditions sufficiently to lower the local solubility of minerals dissolved in the seawater, notably phosphates and carbonates.

The resulting spontaneous concentric precipitation of minerals around a fossil is called a concretion and is responsible for the outstanding preservation of many ammonite fossils. When ammonites are found in clays their original mother-of-pearl coating is often preserved. This type of preservation is found in ammonites such as Hoplites from the Cretaceous Gault clay of Folkestone in Kent, England.

The Cretaceous Pierre Shale formation of the United States and Canada is well known for the abundant ammonite fauna it yields, including Baculites, Placenticeras, Scaphites, Hoploscaphites, and Jeletzkytes, as well as many uncoiled forms. Many of these also have much or all of the original shell, as well as the complete body chamber, still intact. Many Pierre Shale ammonites, and indeed many ammonites throughout earth history, are found inside concretions.

Other fossils, such as many found in Madagascar and Alberta (Canada), display iridescence. These iridescent ammonites are often of gem quality (ammolite) when polished. In no case would this iridescence have been visible during the animal's life; additional shell layers covered it.

The majority of ammonoid specimens, especially those of the Paleozoic era, are preserved only as internal molds; that it to say, the outer shell (composed of aragonite) has been lost through fossilization. It is only in these internal-moldic specimens that the suture lines can be observed; in life the sutures would have been hidden by the outer shell.

The ammonoids survived several major extinction events, with often only a few species surviving. Each time,however, this handful would diversify into a multitude of forms. Ammonite fossils became less abundant during the latter part of the Mesozoic, with none surviving into the Cenozoic era. The last surviving lines disappeared along with the dinosaurs 65 million years ago in the Cretaceous-Tertiary extinction event.

That no ammonites survived the extinction event at the end of the Cretaceous, while some nautiloid cousins survived, might be due to differences in ontogeny. If their extinction was due to an meteor strike, plankton around the globe could have been severely diminished, thereby dooming ammonite reproduction during its planktonic stage.

The cephalopods (Greek plural ?efa??p?da (kephalópoda); "head-foot") are the mollusc class Cephalopoda characterized by bilateral body symmetry, a prominent head, and a modification of the mollusk foot, a muscular hydrostat, into the form of arms or tentacles.

Teuthology, a branch of malacology, is the study of cephalopods.

The class contains two extant subclasses. In the Coleoidea, the mollusk shell has been internalized or is absent; this subclass includes the octopuses, squid, and cuttlefish. In the Nautiloidea the shell remains; this subclass includes the nautilus. There are around 786 distinct living species of Cephalopods. Two important extinct taxa are Ammonoidea, the ammonites, and Belemnoidea, the belemnites.

Cephalopods are found in all the oceans of Earth, at all depths. None of them can tolerate freshwater, but a few species tolerate more or less brackish water.

Number of species
There are still discoveries of new species of cephalopods:
1998 - 703 recent species
2001 - 786 recent species
2004 - approximate guess, from 1000 to 1200 species
There are many more fossil species. It is estimated there are around 11,000 extinct taxa.

Nervous system and behaviour
Cephalopods are widely regarded as the most intelligent of the invertebrates and have well developed senses and large brains; larger than the brains of gastropods or bivalves. Except nautiluses, cephalopods have special skin cells called chromatophores that change color and are used for communication and camouflage.

The nervous system of cephalopods is the most complex of the invertebrates. The giant nerve fibers of the cephalopod mantle have been a favorite experimental material of neurophysiologists for many years; their large diameter (due to lack of myelination) makes them easier to study.

Cephalopod vision is acute, and training experiments have shown that the Common Octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects. Cephalopods' eyes are also sensitive to the plane of polarization of light. Surprisingly in light of their ability to change color, most are probably color blind.

When camouflaging themselves, they use their chromatophores to change brightness and pattern according to the background they see, but their ability to match the specific color of a background probably comes from cells such as iridophores and leucophores that reflect light from the environment. Evidence of color vision has been found in only one species, the Sparkling Enope Squid.

Circulatory system
Cephalopods are the only molluscs with a closed circulatory system. They have two gill hearts (also known as branchial hearts) that move blood through the capillaries of the gills. A single systemic heart then pumps the oxygenated blood through the rest of the body.

Like most molluscs, cephalopods use hemocyanin, a copper-containing protein, rather than hemoglobin to transport oxygen. As a result, their blood is colorless when deoxygenated and turns blue when exposed to air.

Locomotion
Cephalopods move primary by jet propulsion, a very energy-consuming way to travel compared to the tail propulsion used by fish. The relative efficiency of jet propulsion degrades with larger animals. This is probably why many species prefer to use their fins or arms for locomotion if possible.

Oxygenated water is taken into the mantle cavity to the gills and through muscular contraction of this cavity, the spent water is expelled through the hyponome, created by a fold in the mantle.

Motion of the cephalopods is usually backward as water is forced out anteriorly through the hyponome, but direction can be controlled somewhat by pointing it in different directions.

Some octopus species are also able to walk along the sea bed. Squids and cuttlefish can move short distances in any direction by rippling of a flap of muscle around the mantle.
Reproduction and life cycle

With a few exceptions, Coleoidea live short lives with rapid growth. Most of the energy extracted from their food is used for growing. The penis in most male Coleoidea is a long and muscular end of the gonoduct used to transfer spermatophores to a modified arm called a hectocotylus.

That in turn is used to transfer the spermatophores to the female. In species where the hectocotylus is missing, the penis is long and able to extend beyond the mantle cavity and transfers the spermatophores directly to the female. They tend towards a semelparous reproduction strategy; they lay many small eggs in one batch and die afterwards.

The Nautiloidea, on the other hand, stick to iteroparity; they produce a few large eggs in each batch and live for a long time.

Evolution
The class developed during the late Cambrian, and were during the Paleozoic and Mesozoic dominant and diverse marine life forms. Tommotia, a basal cephalopod, had squid-like tentacles but also a snail-like foot it used to move across the seabed. Early cephalopods were at the top of the food chain.

The ancient (cohort Belemnoidea) and modern (cohort Neocoleoidea) coleoids, as well as the ammonoids, all diverged from the external shelled nautiloid during the middle Paleozoic Era, between 450 and 300 million years ago. Unlike most modern cephalopods, most ancient varieties had protective shells.

These shells at first were conical but later developed into curved nautiloid shapes seen in modern nautilus species. Internal shells still exist in many non-shelled living cephalopod groups but most truly shelled cephalopods, such as the ammonites, became extinct at the end of the Cretaceous. As for belemnites, descendents of straight shelled nautiloids, some evolved into squid and cuttlefish, while the rest went extinct.

Classification
The classification as listed here (and on other cephalopod articles) follows largely from Current Classification of Recent Cephalopoda (May 2001), plus fossil groups from several sources. The three subclasses are traditional, corresponding to the three orders of cephalopods recognized by Bather (1888b). Parentheses indicate extinct groups.

Class Cephalopoda
Subclass Nautiloidea: all cephalopods except ammonoids and coleoids

(Order Plectronocerida): the ancestral cephalopods from the Cambrian Period

(Order Ellesmerocerida): include the ancestors of all later cephalopods

(Order Endocerida)

(Order Actinocerida)

(Order Discosorida)

(Order Pseudorthocerida)

(Order Tarphycerida)

(Order Oncocerida)

Order Nautilida: nautilus and its fossil relatives

(Order Orthocerida)

(Order Ascocerida)

(Order Bactritida): include the ancestors of ammonoids and coleoids

(Subclass Ammonoidea): extinct ammonites and kin

(Order Goniatitida)

(Order Ceratitida)

(Order Ammonitida): the true ammonites

Subclass Coleoidea

(Cohort Belemnoidea): extinct belemnites and kin

(Genus Jeletzkya)

(Order Aulacocerida)

(Order Phragmoteuthida)

(Order Hematitida)

(Order Belemnitida)

Cohort Neocoleoidea

Superorder Decapodiformes (also known as Decabrachia or Decembranchiata)

(?Order Boletzkyida)

Order Spirulida: Ram's Horn Squid

Order Sepiida: cuttlefish

Order Sepiolida: pygmy, bobtail and bottletail squid

Order Teuthida: squid

Superorder Octopodiformes (also known as Vampyropoda)

Order Vampyromorphida: Vampire Squid

Order Octopoda: octopus

Other classifications differ, primarily in how the various decapod orders are related, and whether they should be orders or families.

Shevyrev classification

Shevyrev (2005) suggested a division into eight subclasses, mostly comprising the more diverse and numerous fossil forms.

Class Cephalopoda Cuvier 1795

Subclass Ellesmeroceratoidea Flower 1950

Subclass Endoceratoidea Teichert, 1933

Subclass Actinoceratoidea Teichert, 1933

Subclass Nautiloidea Agassiz, 1847

Subclass Orthoceratoidea Kuhn, 1940

Subclass Bactritoidea Shimansky, 1951

Subclass Ammonoidea Zittel, 1884

Subclass Coleoidea Bather, 1888

The first mention of Coleoidea appears in (Bather, 1888a) among this article's references.

Cladistic classification

Another recent system divides all cephalopods into two clades. One includes nautilus and most fossil nautiloids. The other clade (Neocephalopoda or Angusteradulata) is closer to modern coleoids, and includes belemnoids, ammonoids, and many orthocerid families. There are also stem group cephalopods of the traditional Ellesmerocerida that belong to neither clade (Berthold & Engeser, 1987; Engeser 1997).

The Queensland lungfish, Neoceratodus forsteri, also known as Burnett salmon and barramunda, is the sole member of the family Ceratodontidae, and one of only six lungfish species that remain.

Olive or dull brown in colour, it grows to about 150 cm in length, more commonly 100 cm.
It is native to the Burnett and Mary River systems of south-

east Queensland, but has been introduced into other nearby rivers, including the Brisbane River. It prefers still or slow-flowing water with at least some aquatic vegetation on the banks, particularly deep pools.

Also known as the Australian lungfish, this creature normally uses its gills for respiration, but is also capable of taking in oxygen from the air when water quality is poor, or there are low dissolved oxygen levels, such as when water temperatures are high during summer. Unlike some other lungfish species, Australian lungfish cannot survive the desiccation of their environment and require permanent water.

This species belongs to a very ancient group Sarcopterygii, the fleshy-finned fishes which is over 400 million years old. Fossils of fish identical to N. forsteri have been dated at over 100 million years which makes this species one of the oldest extant vertebrate species.

Previously lungfish were considered to be the direct ancestors of amphibians, but now a common ancestor is recognised, although lungfishes did appear early in the history of vertebrates.

Spawning involves individual pairs of fish and complex behaviour. However, unlike other lungfish species Australian lungfish do not exhibit parental care. Larvae resemble tadpoles, and are poor swimmers at first. Metamorphosis occurs early, when the fish are only about 2 cm long.

Juveniles are capable of rapid growth, growing at around 1 inches per month if feed well and given ideal water conditions. In several instances, captive reared young grew to 18 inches in little over 18 months of age. They have a long lifespan, however, sometimes living over eighty years.

Primarily carnivorous, the diet consists mainly of small fish, frogs and tadpoles and invertebrates, however they have on occasion been observed to consume some vegetable matter.

Ichthyosaurs (Greek for 'fish lizard' - ????? meaning 'fish' and sa???? meaning 'lizard') were giant marine reptiles that resembled fish and dolphins.

Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 230 million years ago (Mya) and disappeared about 90 million years ago, about 25 million years before the dinosaurs became extinct. During the

middle Triassic Period, ichthyosaurs evolved from as-yet unidentified land reptiles that moved back into the water, in a development parallel to that of modern-day dolphins and whales.

They were particularly abundant in the Jurassic Period, until they were replaced as the top aquatic predators by plesiosaurs in the Cretaceous Period. They belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' - a designation introduced by Sir Richard Owen in 1840, although the term is now used more for the parent clade of the Ichthyosauria).

Description
Ichthyosaurs averaged 2 to 4 meters in length (although a few were smaller, and some species grew much larger), with a porpoise-like head and a long, toothed snout. Built for speed, like modern tuna, some ichthyosaurs appear also to have been deep divers, like some modern whales (Motani, 2000). It has been estimated that ichthyosaurs could swim at speeds up to 40 km/h (25 mph).

Similar to modern cetaceans such as whales and dolphins, they were air-breathing and also were viviparous (some adult fossils have even been found containing fetuses). Although they were reptiles and descended from egg-laying ancestors, viviparity is not as unexpected as it first appears.

All air-breathing marine creatures must either come ashore to lay eggs, like turtles and some sea snakes, or else give birth to live young in surface waters, like whales and dolphins. Given their streamlined bodies, heavily adapted for fast swimming, it would have been difficult for ichthyosaurs to scramble successfully onto land to lay eggs.

According to weight estimates by Ryosuke Motani [1] a 2.4 meter (8 ft) Stenopterygius weighed around 163 to 168 kg (360 to 370 lb), whilst a 4.0 meter (13 ft)Ophthalmosaurus icenicus weighed 930 to 950 kg (about a ton).

Although ichthyosaurs looked like fish, they were not. Biologist Stephen Jay Gould said the ichthyosaur was his favorite example of convergent evolution, where similarities of structure are analogous not homologous, for this group:

"converged so strongly on fishes that it actually evolved a dorsal fin and tail in just the right place and with just the right hydrological design. These structures are all the more remarkable because they evolved from nothing— the ancestral terrestrial reptile had no hump on its back or blade on its tail to serve as a precursor."

In fact the earliest reconstructions of ichthyosaurs omitted the dorsal fin, which had no hard skeletal structure, until finely-preserved specimens recovered in the 1890s from the Holzmaden lagerstätten in Germany revealed traces of the fin. Unique conditions permitted the preservation of soft tissue impressions.

Ichthyosaurs had fin-like limbs, which were possibly used for stabilisation and directional control, rather than propulsion, which would have come from the large shark-like tail. The tail was bi-lobed, with the lower lobe being supported by the caudal vertebral column, which was 'kinked' ventrally to follow the contours of the ventral lobe.

Apart from the obvious similarities to fish, the ichthyosaurs also shared parallel developmental features with dolphins. This gave them a broadly similar appearance, possibly implied similar activity and presumably placed them broadly in a similar ecological niche.

For their food, many of the fish-shaped ichthyosaurs relied heavily on ancient cephalopod kin of squids called belemnites. Some early ichthyosaurs had teeth adapted for crushing shellfish. They also most likely fed on fish, and a few of the larger species had heavy jaws and teeth that indicated they fed on smaller reptiles.

Ichthyosaurs ranged so widely in size, and survived for so long, that they are likely to have had a wide range of prey. Typical ichthyosaurs have very large eyes, protected within a bony ring, suggesting that they may have hunted at night.

History of discoveries
The genus had first been described in 1699 from fossil fragments discovered in Wales.
The first fossil vertebrae were published twice in 1708 as tangible mementos of the Universal Deluge. The first complete ichthyosaur fossil was found in 1811 by Mary Anning in Lyme Regis, along what is now called the Jurassic Coast. She subsequently discovered three separate species.

In 1905, the Saurian Expedition led by John C. Merriam of the University of California and financed by Annie Alexander, found 25 specimens in central Nevada, which during the Triassic was under a shallow ocean. Several of the specimens are now in the collection of the University of California Museum of Paleontology.

Other specimens are embedded in the rock and visible at Berlin-Ichthyosaur State Park in Nye County. In 1977 the Triassic ichthyosaur Shonisaurus became the State Fossil of Nevada. Nevada is the only state to possess a complete skeleton, 55 ft (17 m) of this extinct marine reptile. In 1992, Canadian ichthyologist Dr. Elizabeth Nicholls (Curator of Marine Reptiles at the Royal Tyrrell {"tur ell"} Museum) uncovered the largest fossil specimen ever, a 23m (75')-long example.

rather than as ichthyosaurs proper (Motani 1997, Motani et al. 1998), quickly gave rise to true ichthyosaurs sometime in the latest Early Triassic or earliest Middle Triassic. These later diversified into a variety of forms, including the sea-serpent like Cymbospondylus, which reached 10 meters, and smaller more typical forms like Mixosaurus.

By the Late Triassic, ichthyosaurs consisted of both classic Shastasauria and more advanced, "dolphin"-like Euichthyosauria (Californosaurus, Toretocnemus) and Parvipelvia (Hudsonelpidia, Macgowania). Experts disagree over whether these represent an evolutionary continum, with the less specialised shastosaurs a paraphyletic grade that was evolving into the more advanced forms (Maisch and Matzke 2000), or whether the two were separate clades that evolved from a common ancestor earlier on (Nicholls and Manabe 2001).

During the Carnian and Norian, shastosaurs reached huge sizes. Shonisaurus popularis, known from a number of specimens from the Carnian of Nevada, was 15 meters long. Norian shonisaurs are known from both sides of the Pacific. Himalayasaurus tibetensis and Tibetosaurus (probably a synonym) have been found in Tibet. These large (10 to 15 meters long) ichthyosaurs probably belong to the same genus as Shonisaurus (Motani et al, 1999; Lucas, 2001, pp.117-119).

While the gigantic Shonisaurus sikanniensis, whose remains were found in the Pardonet formation of British Columbia by Elizabeth Nicholls, reached as much as 21 meters in length - the largest marine reptile known to date.

These giants (along with their smaller cousins) seemed to have disappeared at the end of the Norian. Rhaetian (latest Triassic) ichthyosaurs are known from England, and these are very similar to those of the Early Jurassic. Like the dinosaurs, the ichthyosaurs and their contemporaries the plesiosaurs survived the end-Triassic extinction event, and immediately diversified to fill the vacant ecological niches of the earliest Jurassic.

The Early Jurassic, like the Late Triassic, was the heyday of the ichthyosaurs, which are represented by four families and a variety of species, ranging from one to ten meters in length. Genera include Eurhinosaurus, Ichthyosaurus, Leptonectes, Stenopterygius, and the large predator Temnodontosaurus, along with the persistently primitive Suevoleviathan, which was little changed from its Norian ancestors.

All these animals were streamlined, dolphin-like forms, although the more primitive animals were perhaps more elongated than the advanced and compact Stenopterygius and Ichthyosaurus.

Ichthyosaurs were still common in the Middle Jurassic, but had now decreased in diversity. All belonged to the single clade Ophthalmosauria. Represented by the 4 meter long Ophthalmosaurus and related genera, they were very similar to Ichthyosaurus, and had attained a perfect "tear-drop" streamlined form. The eyes of Ophthalmosaurus were huge, and it is likely that these animals hunted in dim and deep water (Motani 2000).

Ichthyosaurs seemed to decrease in diversity even further with the Cretaceous. Only a single genus is known, Platypterygius, and although it had a worldwide distribution, there was little diversity species-wise. This last ichthyosaur genus fell victim to the mid-Cretaceous (Cenomanian-Turonian) extinction event (as did some of the giant pliosaurs), although ironically less hydrodynamically efficient animals like mosasaurs and long-necked plesiosaurs flourished.

It seems that the ichthyosaurs became the victim of their own overspecialisation and were unable to keep up with the fast swimming and highly evasive new teleost fishes, which were becoming dominant at this time and against which the sit-and-wait ambush strategies of the mosasaurs proved superior (Lingham-Soliar 1999).

least fish-like of the Ichthyosaurus, lacking a dorsal fin and fluked tail. It did, however, have an elongated snout like other Ichthyosaurs; although still classified as an Ichthyosaur of the primitive shastasaurid group, its eel-like resemblance have led to speculation as to whether Cymbospondylus was a true Ichthyosaur.

The eel-like tail of Cymbospondylus made up almost half the total body length, and it is possible that the tail was used as a primary swimming mechanism. Like present day Sea Snakes, Cymbospondylus probably swum by wriggling it's body from side to side. The paddle-like limbs Cymbospondylus had were serving use primarily as underwater stabilizers and slowing down the Ichthyosaur's swimming speed.

Cymbospondylus fossils have been found in both Germany and Nevada, and the first species was named by Joseph Leidy in 1868.

In popular culture
Cymbospondylus appeared in Sea Monsters, a spin off to Walking with Dinosaurs. It is portrayed as the top predator in the sixth most deadly sea of all time. It repeatedly strikes at TV host Nigel Marven, the attack ending with the Cymbospondylus still circling Nigel. What happened after that is highly speculative, though it is most likely that Nigel escaped, as he appears later in the Devonian Period, facing the even more dangerous Dunkleosteus.

Mixosaurus is an extinct genus of diapsid reptile belonging to the ichthyosaur order. It was about 1 meter (3 ft 4 in) long. Fossils of Mixosaurus, which means "Mixed Lizard" have been found all over the world - China, Timor, Indonesia, Italy, Spitsbergen, Svalbard, Canada, Alaska, and Nevada. It was named in 1887 by George H. Baur.
Mixosaurus was named so because it appears to have been a transitional form between the eel-shaped ichthyosaurs

such as Cymbospondylus and the later dolphin-shaped ichthyosaurs, such as Ichthyosaurus. Mixosaurus possessed a long tail with a low fin (suggesting it could have been a slow swimmer) but also possessed a dorsal fin for stability in the water.

The paddle-like limbs were made up of five toes each, unlike the three toes found in later Icthyosaurs. Noteworthy however is that each toe has more individual bones than is usual (polyphalangy or hyperphalangy), and the front limbs are longer than the back limbs.
Mixosaurus was a Marine reptile that fed on small fish.

Shonisaurus, which means "Lizard from the Shoshone Mountains", after the formation where the fossils were found.

Shonisaurus lived during the Norian stage of the late Triassic period. It had a whale-like body and long, narrow paddles. Shonisaurus had a long, pointed mouth that contained teeth only at the end.

The first species discovered, S. popularis, was eventually adopted as the State Fossil of Nevada in 1984. Excavations, begun in 1954 under the direction of Dr. Charles Camp and Dr. Samuel Welles of the University of California, Berkeley, were continued by Camp throughout the 60s. It was named by Charles Camp in 1976.

S. popularis specimens reached a length of 15 meters (50 feet). The Nevada fossil sites can currently be viewed at the Berlin-Ichthyosaur State Park.
A discovery in British Columbia in the 1990s made S. popularis the smaller of the Shonisaurus species; a second species, S. sikanniensis, was discovered and has an estimated length of 21 meters (70 feet).
An ichthyosaur found in the Himalayan mountains called Himalayasaurus may be the same animal as Shonisaurus.

Mastodonsaurus was a large-headed temnospondyl that belonged to a group of advanced, mostly Triassic animals called capitosaurs. Originally it was thought that it had a short, massive body, stout limbs, a short tail, and a long-jawed powerful skull. Newer studies showed however that its body was lesser compact and the tail much longer, giving it an overall-appearance much like a crocodile.

Two triangular tusks pointed up from near the tip of its lower jaw. When the jaws closed, these slotted through openings on the palate and projected through the top of the skull. The fossils of some smaller temnospondyls bear tooth marks made by Mastodonsaurus-like animals. It probably also ate fish, as well as land-living animals, such as small archosaurs.

Placodonts ("Tablet teeth") were a group of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. It is believed that they were related to the Sauropterygia, the group that includes Plesiosaurs. Placodonts were generally between one to two metres in length, with some of the largest measuring three metres long.

In appearance, many resembled stout- or barrel-bodied newts, or lizard, while others looked more turtle-like due to large bony plates on their backs. They had short limbs and were highly robust.
Because of their dense bone and heavy armour plating, these creatures would have been too heavy to float in the

ocean and would have used a lot of energy to reach the water surface. For this reason and because of the type of sediment found accompanying fossils it is suggested they lived in shallow waters and not in deep oceans.

Their diet consisted of marine bivalves, brachiopods, and other invertebrates. They were notable for their large, flat, often protruding teeth which they used to crush molluscs and brachiopods, which they hunted on the sea bed (another way in which they were similar to walruses). The Palate teeth were extremely thick and large enough to crush thick shell.

The first specimen was discovered in 1830, and they have since been discovered throughout Europe and the Middle East.
Henodus chelyops ("Turtle-Faced Single Tooth") was a placodont of the Late Triassic period during the Carnian stage.

Henodus was the placodont that had the greatest (albeit wholly superficial) resemblance to a turtle. Like turtles, it had a shell formed from a plastron on the underside and a carapace on top. The carapace extended well beyond the limbs, and was made up of individual plates of bony scutes.

The armor was fused to its spine, and its limbs were situated in normal positions, unlike the turtle, where they are located inside the ribcage. The weak limbs of Henodus suggest it spent little time on land.

Henodus chelyops also had two teeth--one on each side of its mouth, though the remaining teeth were replaced by a beak. These teeth were flat to crush bottom dwelling shellfish. The head was squared-off at the front, just ahead of the eyes. Worthy of note is that Henodus is the only placodont thus far found in non-marine deposits, suggesting it may have lived in brackish or freshwater lagoons.
Fossils of Henodus chelyops were found in Tübingen, Germany.

Proganochelys is the oldest turtle species discovered to date, known only from fossils found in Germany and Thailand in strata from the late Triassic, dating to approximately 210 million years ago. It has several synonymns, including Chelytherium ("Turtle Beast"), Psammochelys ("Sand Turtle"), Stegochelys ("Roof Turtle") and Triassochelys ("Triassic Turtle").

Until relatively recently it was popularly known by the last name.
In life it was about 1 m long, its overall appearance resembling modern turtles in many respects: it lacked teeth, likely had a beak and had the characteristic heavily armored shell formed from bony plates and ribs which fused together into a solid cage around the internal organs. There are some notable differences compared to modern turtles, however: its long tail had spikes and terminated as

each quite long.. Fossils of this creature have been found in Europe and the Middle East. Tribelesodon, originally considered to be a pterosaur by Francesco Bassani in 1886, is now recognized as a junior synonym to Tanystropheus. The best-known species is Tanystropheus longobardicus.

Other currently recognized species include T. conspicuus and T. meridensis.[1] With this incredibly long but relatively stiff neck, Tanystropheus has been often proposed and reconstructed as an aquatic or semi-aquatic reptile, a theory supported by the fact that the creature is most commonly found in semiaquatic fossil sites wherein known terrestrial reptile remains are scarce.

Tanystropheus is most commonly considered to have been piscivorous (or 'fish-eating'), due to the presence of a long, narrow snout sporting sharp interlocking teeth. In several young specimens, three cusped cheek teeth found in the jaw; which might indicate an insectivorous diet, however, similar teeth patterns have been found in Eudimorphodon and Langobardisaurus, both of whom are considered piscivores.

Additionally, hooklets of cephalopods and what may be fish scales have been found near the belly regions of some specimines.

In 2002, fossils of a related genus, Dinocephalosaurus, were collected in Marine Triassic deposits in southwestern China. This new creature was 2.7 meters long, 1.7 meters of which was its neck and head. The specimen was described in 2004.

Possible lifestyles of Tanystropheus
Though the animal is generally considered to have been a sort of 'reverse amphibian', sitting on the shoreline and snatching fish and other marine life from the shallows with its long neck and sharp teeth, the almost disproportionate neck presents several problems for such a lifestyle.

Some scientists have argued that such a disproportionate neck would have placed Tanystropheus' center of gravity in front of its arms- causing it to fall flat on its face every time its neck stuck out. For this and other reasons, David Peters has suggested a primarily terrestrial lifestyle, with the creature rearing up bipedally on its hind limbs, holding its neck vertically, keeping the creature balanced.

Some who subscribe to this theory envision the animal waiting at the base of a tree and snatching small, arboreal animals out of its branches with its lengthy neck and small head. Peters (along with several other scientists) also believes that Prolacertiforms (such as Tanystropheus) were the ancestors of Pterosaurs, and thus assigns prevalently terrestrial behavior to them.

A 2006 specimen discovered in Switzerland by Dr. Silvio Renesto, however, has shifted gears back to the former viewpoint of Tanystropheus' lifestyle. The specimen boasts the first reported soft tissue of the creature to have been found thus far, including traces of skin that show a non-rectangular, overlapping pattern of scales.

But more relevantly, the specimen displays an unusual "black material" around the base of its tail, containing several calcium carbonate spherules, suggesting a quite noticeable amount of flesh behind the animal's hips. In addition to containing powerful hind limb muscles, such a huge backside would have shifted the creature's weight to its rear, stabilizing the animal as it swung and maneuvered its massive 3 meter neck.

Protoavis texensis ("First bird from Texas") is the name given to archosaurian fossil bones from the Late Triassic found near Post, Texas. These fossils have been described as a primitive bird which, if the identification is valid, would push back avian origins some 60-75 million years.

Protoavis is claimed to have been a 35 cm tall bird that lived in what is now Texas, USA, between 225 and 210 million years ago. Though it existed far earlier than Archaeopteryx, its skeletal structure is allegedly more bird-like. Protoavis has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at

the front of the skull, suggesting a nocturnal or crepuscular lifestyle. The fossil bones are too badly preserved to allow an estimate of flying ability; although reconstructions usually show feathers (see link below), judging from thorough study of the fossil material there is no indication that these were present (Paul, 2002; Witmer, 2002).

However, this description of Protoavis assumes that Protoavis actually existed and, if so, that it has been reconstructed correctly. Almost all paleontologists doubt that Protoavis is a bird, or even a good species, because of the circumstances of its discovery, and unconvincing avian synapomorphies in its fragmentary material.

When they were found at a Dockum Formation quarry in the Texas panhandle in 1984, in a sedimentary strata of a Triassic river delta, the fossils were a jumbled cache of disarticulated dinosaur and other bones that may reflect an incident of mass mortality following a flash flood.

The discoverer, Sankar Chatterjee of Texas Tech University, was convinced that some of these crushed bones belonged to two individuals - one old, one young - of the same species.

However, only a few parts were found, primarily a skull and some limb bones which moreover do not well agree in their proportions respective to each other, and this has led many to believe that the Protavis fossil is chimeric, made up of more than one organism: the pieces of skull appear like those of a coelurosaur, while most parts of the limb skeleton suggest affinities to ceratosaurs and at least some vertebrae are most similar to those of Megalancosaurus (Renesto, 2000), which despite what its name may suggest is not a dinosaur but rather an avicephalan diapsid:

Everywhere one turns; the very fossils ascribed thereto challenge the validity of Protoavis. The most parsimonious conclusion to be inferred from these data is that Chatterjee's contentious find is nothing more than a chimera, a morass of long-dead archosaurs. (EvoWiki, 2004)

If it really existed, Protoavis would raise interesting questions about when birds began to diverge from the dinosaurs, but until better evidence is produced, the animal's status currently remains uncertain. Furthermore, paleobiogeography suggests that birds did not colonize the Americas until the Cretaceous; the most primitive lineages of unequivocal birds found to date are all Eurasian.

Certainly, the fossils are most parsimoniously attributed to primitive dinosaurian and other reptiles as outlined above. However, coelurosaurs and ceratosaurs are in any case not too distantly related to the ancestors of birds and in some aspects of the skeleton not unlike them, explaining how their fossils could be mistaken as avian; Archaeopteryx itself was initially believed to be a small theropod dinosaur. Zhou (2004) sums up the matter:

[Protoavis] has neither been widely accepted nor seriously considered as a Triassic bird [... Witmer (2001, 2002)], who has examined the material and is one of the few workers to have seriously considered Chatterjee’s proposal, argued that the avian status of P. texensis is probably not as clear as generally portrayed by Chatterjee, and further recommended minimization of the role that Protoavis plays in the discussion of avian ancestry.

Sometimes it is claimed that Protoavis is a refutation of the hypothesis that birds evolved from dinosaurs (e.g. Feduccia, 1999). But this is not true; the only consequence would be to push back the point of divergence further back in time and possibly cause the dromaeosaurs to be included in the bird clade.

Note that at the time when these claims were originally made, the affiliation of birds and maniraptoran theropods which today is well-supported and generally accepted by most ornithologists was much more contentious; most Mesozoic birds have only been discovered since then. Note also that Chatterjee himself (1997) has used Protoavis to support a close relationship between dinosaurs and birds.

As there remains no compelling data to support the avian status of Protoavis or taxonomic validity thereof, it seems mystifying that the matter should be so contentious. The author very much agrees with Chiappe in arguing that at present, Protoavis is irrelevant to the phylogenetic reconstruction of Aves.

While further material from the Dockum beds may vindicate this peculiar archosaur, for the time being, the case for Protoavis is non-existent. (EvoWiki, 2004)

Eudimorphodon was a pterosaur that lived around present Italy during the Middle Triassic. It had a wingspan of about 100 centimetres and at the end of its long bony tail was perhaps a diamond-shaped flap.

The flap may have helped it steer while in the air. It showed a strong differentiation of the teeth, hence its name "true dimorphic tooth". The species, then the oldest pterosaurian known, was found in 1973 by Mario Pandolfi and described that same year by Rocco Zambelli. Despite its age it has few primitive characteristics.

The prehistoric reptile Peteinosaurus (Peh-TEIN-o-sore-us) was a genus belonging to the Pterosauria. It existed in the late Triassic period in the middle Norian (about 210 million years ago).

The genus name means "flying reptile", the species name, zambellii, honours Rocco Zambelli, the curator of the Bergamo natural history museum. The genus has been desribed by the German paleontologist Rupert Wild in 1978.

Three fossils have been found near Cene, Italy: the first, the holotype MCSNB 2886 is however fragmentary and

disarticulated; the second, the articulated paratype MCSNB 3359, lacks any diagnostic features of Peteinosaurus and thus might be a different species.
An insectivorous lifestyle has been attributed to Peteinosaurus.

The paratype has a long tail (20 cm) made more stiff by ossified tendons stretched along the vertebrae; this feature is common among pterosaurs of the Triassic. Peteinosaurus is trimorphodontic, with three types of conical teeth.

Sharovipteryx ("Sharov's wing", previously known as Podopteryx, "foot wing"), was among the earliest gliding reptiles, from the early Triassic period. It was approximately eight inches long, with an extremely long tail, and weighed about 7.5 grams.

It may have been related — or perhaps even ancestral — to pterosaurs,[1] although this remains controversial. Unlike pterosaurs, its main flight membrane was stretched between long back legs rather than its very short front limbs.
If Sharovipteryx was a relative of pterosaurs, then its

membrane may have stretched to its front legs, or it may have had a separate membrane joined to its front limbs alone. Although front wing membranes have not been seen, the fingers have been traced by Peters and they show similarities to Cosesaurus and Longisquama and to a lesser extent, pterosaurs. Some scenarios have it as a leaping animal, which would spring up in the air and then control its fall with its "wings".

This fits well with the belief that pterosaurs evolved from running, leaping ancestors, because some scientists believe they lacked adaptations for living in trees. However, others suggest that Sharovipteryx would run up a tree on its sharply clawed rear legs (its overall design seems poor for climbing), and then spring into the air. The forelimbs seem too short for quadrupedal running or climbing.

Sharovipteryx was a biped in the manner of living lizards capable of bipedal running, except that Sharovipteryx had a better pelvis, more sacaral vertebrae, longer hind limbs, a shorter torso and a thinner tail than any living lizard. The dimunition of the tail muscles and the increase in the pelvic muscles shows that Sharovipteryx was on its way toward a pterosaur-like metabolism, probably homeothermic.

It was not depending on torso undulations for locomotion and therefore not subject to Carrier's Restraint on breathing while running, something all living lizards are restrained from doing.

In 2006, Dyke et al. published a study on possible gliding techniques for Sharovipteryx. The authors found that the wing membrane, which stretched between its very long hind legs and tail, would have allowed it to glide in a manner similar to delta wing aircraft. If the tiny front limbs also supported a membrane, they could have acted as a very efficient means of controlling pitch stability, very much like a canard.

Without a forewing, the authors find, controlled gliding would have been very difficult (unfortunately, the area around the forelimbs was completely prepared away in the only known fossil, destroying any possible trace of a membrane there). Another membrane, the wrinkled skin of the neck, is preserved 6 times wider than the slender cervical vertebrae.

Slender and long ceratobranchial bones invade the neck from the throat. If the ceratobranchials spread laterally, as they do in some living lizards, then the wrinkled neck skin could expand laterally, forming aerodynamic strakes, as found on modern fighter jets. Together with the canards on the forelimbs, these anterior membranes may have formed excellent control surfaces for gliding.

Sharov in 1971 illustrated the finger tips to the elongated digit IV in both hands. Another study by Peters in 2006 found all the fingers of both hands, and argued that if canard wings were present, they were not as imagined by the Dyke study, which did not observe the fingers.

Longisquama insignis is an extinct lizard-like reptile known from a poorly preserved and incomplete fossil. It lived during the early Triassic Period, 240 million years ago, in what is now Kyrgyzstan. It is known from a type fossil specimen; slab and counterslab (PIN 2548/4 and PIN 2584/5), and five referred specimens of possible integumentary appendages (PIN 2584/7 through 9).

All specimens are in the collection of the Paleontological Institute of the Russian Academy of Sciences in Moscow.
Longisquama has been interpreted differently by different researchers, and is at the center of a large and heavily

publicized debate about the origin of birds. To some, Longisquama is the gliding, cold - blooded, protobird; prophesized by Heilmann's hypothetical "Proavis" in 1927, and it proves that birds are not dinosaurs. To others it is a lizard lying in a pile of fern fronds.
Longisquama means "long scales", in reference to long structures that appear to grow from its skin..

Longisquama's 'long scales'
The Longisquama fossil appears to have feather-shaped structures attached to its body. Investigators have interpreted these structures in a variety of different ways. Haubold and Buffetaut (1987) believed that the structures were long, modified scales attached in pairs to the lateral walls of the body, like paired gliding membranes. Unwin and Benton (2001) interpreted them as a single, unpaired, row of modified scales that run along the dorsal midline.

Jones et al. (2000) interpreted them as two paired rows of structures that are anatomically very much like feathers, and which are in positions like those of birds' spinal feather tracts. Feather development expert Richard Prum (2001) and also Reisz and Suez (2000) see the structures as anatomically very different from feathers, and think they are elongate, ribbon - like scales. Other observers (Fraser, 2006) believe that the structures are fern fronds which were preserved along with Longisquama and misinterpreted.

This last opinion is perhaps reinforced by the fact that several fossils of the structures have been discovered in no association with animal fossils.
Haubold and Buffetaut published a reconstruction of Longisquama with plumes in a pattern akin to gliding lizards like flying dragons and Kuehneosaurus, allowing it to glide, or at least parachute. Though this is now thought to be inaccurate, versions of this reconstruction are still often seen on the internet and elsewhere.

Relationships of Longisquama
The skeletal features of Longisquama are equally difficult to diagnose and, as a result, Longisquama has been placed as a close relative to many different Sauropsid groups. Sharov (1970) determined that it was a "pseudosuchian" (a derived Archosaur) on the basis of two features - a mandibular fenestra and an antorbital fenestra. Jones et al. (2000) see Longisquama as an archosaur, adding to Sharov's two characters a furcula.

Olshevsky believes that Longisquama is an archosaur and, moreover, an early dinosaur - a possibility which could actually dispense with almost all of the debate, were it true. Unwin & Benton (2001) didn't think it was possible to diagnose the crucial fenestrae; the holes could just be damage to the fossil. They agreed with Sharov that Longisquama has acrodont teeth and an interclavicle, but instead of a furcula they saw paired clavicles. These features would make Longisquama a Lepidosaur, and that would mean it is not an Archosaur and, thus, not closely related to birds.

Debate
The debate about Longisquama is one of the most interesting and, certainly, most acrimonious, in all of science. The persistence of this debate raises issues about what are and are not proper methodologies in science, about standards of evidence and credibility, and the inevitable intrusion of emotional investments into human reason. This debate calls into doubt the very objectivity and empiricism of anatomical interpretation. It also shows an uncomfortable relationship between the professional conduct of science and the popular press, where very different standards of evidence are used.

One side in this debate is the vast majority of biologists, all of whom have been persuaded by an increasingly overwhelming preponderance of the evidence, and by continuously refined methodologies, that the consensus is correct. To them, the other side is a small group of deluded, irrational, dissenters whose frequent resorts to the popular press and non - peer - reviewed journals have granted them a prominence that the quality of their work does not justify.

The other side of the debate see themselves as righteous underdogs; the last scientists loyal to classical techniques and logical, beautiful, traditional, scenarios about bird evolution. They see the consensus as a powerful and closed - minded orthodoxy - even a conspiracy - which will impugn and destroy anyone who questions it.

In the consensus view, hundreds of shared anatomical characters support the hypothesis that birds evolved from advanced theropod dinosaurs. Early theropod dinosaurs were probably Endothermic and evolved simple filamentous feathers for insulation, and these feathers later increased in size and complexity and then adapted to aerodynamic uses.

This view is increasingly strongly supported by the fossil evidence (see Feathered dinosaurs). Scientists in his camp usually regard Longisquama as a curious Diapsid with specialized scales, ambiguous skeletal features, and no implications to bird evolution.

In the minority view, birds must have evolved from lizard - like, Ectothermic animals, which lived in trees and adapted to gliding by developing elongated scales and then pennaceous feathers. They later became Endothermic and used the feathers for insulation. To this group, Longisquama is a perfect fulfillment of their hypothetical predictions, with feathers identical to those of birds and skeletal features in common with birds, and it must therefore be an ancestor of birds.

This basic debate is over thirty years old but there is a new twist. For decades Martin maintained that Maniraptoran dinosaurs were not immediately related to birds (Martin, 1983), and that the similarities between them were just superficial resemblances attributable to homoplasy. But in Martin (2004), he said that he was finally persuaded by Hwang, Norell, Qiang and Keqin (2002) that Maniraptorans are the closest relatives of birds.

He now believes that Longisquama evolved into birds, and that some of the birds then became flightless and radiated as the Maniraptora. Thus, in his new view, maniraptorans are not dinosaurs, and the similarities between them are the homoplasies. He credits this hypothesis to Gregory S. Paul, but it is closer to the one been advanced by Czerkas, (2002); Czerkas, 2002; Feduccia, 2005).

Though it is rarely acknowledged, there is one more aspect to this debate. Longisquama could have feathers without challenging the hypothesis that dinosaurs evolved into birds. Instead, it might simply show that feathers evolved far earlier than suspected. If Longisquama is a derived archosaur, perhaps even an Ornithodire or dinosaur, then it might be plausible that it inherited the genes to make feathers or protofeathers from a common ancestor with more advanced dinosaurs.

One of the earliest known dinosaurs, Coelophysis (see-low-FYS-iss) meaning "hollow form" in reference to its hollow bones (Greek ??????/koilos meaning 'hollow' and f?s??/physis meaning 'form') is a small, carnivorous biped from North America.

It first appeared in the Mid Triassic Period, around 228 million years ago.

Description
Coelophysis bauri is the earliest dinosaur known from a number of complete fossil skeletons. C. bauri was a lightly built dinosaur, between two to three meters in length, and less than a meter tall at the hips. The name Coelophysis means "hollow form" or "hollow process", so named because of its hollow limb bones.

Despite being an early dinosaur, the evolution of the theropod body form had already advanced greatly from creatures like Herrerasaurus and Eoraptor. Coelophysis had an elongated snout with large fenestrae which helped to reduce skull weight, while narrow struts of bones preserved the structural integrity of the skull. The neck had a pronounced sigmoid curve.

The torso of Coelophysis conforms to the basic theropod body shape, but the pectoral girdle displays some interesting special characteristics: C. bauri had a furcula (wishbone), the earliest known example in a dinosaur. Coelophysis also preserves the ancestral condition of possessing four digits on the hand (manus). It had only three functional digits, the fourth embedded in the flesh of the hand.

The pelvis and hindlimbs of C. bauri are also slight variations on the theropod body plan. It has the open acetabulum and straight ankle hinge that define the Dinosauria. The hindlimb ended in a three-toed foot (pes), with a raised hallux.

The tail of Coelophysis had an unusual structure within its interlocking prezygapophysis of its vertebrae, which formed a semi-rigid lattice, apparently to stop the tail from moving up and down. This may have let the tail act as a rudder or counterweight when the animal was maneuvering at high speeds.

Coelophysis was very slim and it could have run either on two or four legs. The neck and tail were long. The hands had only three fingers, but they were strong. Coelophysis had a long narrow head, and its sharp, jagged teeth show that it ate meat - probably the small, lizardlike animals that were found with it.

Paleobiology
Coelophysis was probably opportunistic, catching live prey and scavenging. The teeth were typical of predatory dinosaurs, blade-like and recurved with fine serrations on both anterior and posterior edges. They were rooted in the jaws in sockets, and were continually replaced throughout the animal's life.

Since our knowledge of Coelophysis comes mainly from the specimens excavated at Ghost Ranch, there is a tendency to see this massive congregation of animals as evidence for huge packs of Coelophysis roaming the land (as seen in the television series Walking with Dinosaurs).

There is no evidence for this. What the deposit does tell us is that large numbers of Coelophysis, along with other Triassic animals, were buried together. Some of the evidence from the taphonomy of the site indicates that these animals may have been gathered together to feed or drink from a depleted water hole or to feed on a spawning run of fish, then became buried in a catastrophic flash flood.

It has been suggested that C. bauri was a cannibal, based on juvenile specimens found "within" the abdominal cavities of some Ghost Ranch specimens. However, Rob Gay showed in 2002 that these specimens were misinterpreted (several specimens of "juvenile coelophysids" were actually small crurotarsan reptiles such as Hesperosuchus), and there is no longer any evidence to support cannibalistic behavior in Coelophysis.

Gay's study was corroborated in 2006 in a subsequent study by Nesbitt et al. There may be other evidence coming to light that may show stomach contents from some of these specimens, which might bring greater resolution to the subject.
Two forms of Coelophysis have been found, a more gracile form and a slightly more robust form. Opinion among paleontologists is now that these were female and male variants (see: sexual dimorphism).[6][7][8][9]

History of discovery
Edward Drinker Cope first named Coelophysis in 1889 during his competition to name species with Othniel Charles Marsh, known as the "Bone Wars". An amateur fossil collector, David Baldwin, had found the first remains of the dinosaur in 1881. The type species, C. bauri was named for Baur, one of the many fossil collectors who supplied Cope. However, these first finds were too poorly preserved to give a complete picture of this new dinosaur.

In 1947, a substantial 'graveyard' of Coelophysis fossils was found in New Mexico, at the Ghost Ranch, close to the original find. So many fossils together were probably the result of a flash flood, which swept away a large number of Coelophysis and buried them quickly and simultaneously. In fact, it seems such flooding was commonplace during this period of the Earth's history and, indeed, the Petrified Forest of nearby Arizona is caused by a preserved log jam of tree trunks that were caught in one such flood.

Edwin H. Colbert made a comprehensive study[6] of all the fossils found up to that date, and it is from him that we take most of our information about Coelophysis. The Ghost Ranch specimens were so numerous, including many well-preserved specimens, that one of them has since become the diagnostic, or type specimen, for the entire genus, replacing the original, poorly preserved specimen (see Classification below).

Since the Ghost Ranch specimens were discovered, more skeletons have been found in Arizona, New Mexico and an as-yet unconfirmed specimen from Utah, including both adults and juveniles. The deposits where Coelophysis has been discovered date from the late Carnian to the early Norian faunal stages of the Triassic Period.

Classification
Coelophysis is a distinct taxonomic unit (genus), composed of a single species, C. bauri. Two additional species were originally described in addition to C. bauri, C. longicollis, and C. willistoni, however they are not diagnostic and are considered synonymous with C. bauri. C. rhodesiensis is probably part of this generic complex, and is known from the Jurassic of southern Africa (see below for more). In phylogenetic taxonomy, Coelophysis is treated as a clade within the Coelophysidae.

In the early 1990s, there was debate over the diagnostic characteristics of the first specimens collected, compared to the material excavated at the Ghost Ranch Coelophysis quarry. Some paleontologists were of the opinion that the original specimens were not diagnostic beyond themselves and, therefore, that the name C. bauri could not be applied to any additional specimens. They therefore applied a different name, Rioarribasaurus, to the Ghost Ranch quarry specimens.

Since the numerous well-preserved Ghost Ranch specimes were used as Coelophysis in most of the scientific literature, the use of Rioarribasaurus would have been very inconvenient for researchers, so a petition was given to have the type specimen of Coelophysis transferred from the poorly-preserved original specimen to one of the well-preserved Ghost ranch specimens.

In the end, the International Commission on Zoological Nomenclature (ICZN) voted to make one of the Ghost Ranch samples the actual type specimen for Coelophysis and dispose of the name Rioarribasaurus altogether (declaring it a nomen rejectum, or "rejected name"), thus resolving the confusion. The name Coelophysis therefore became a nomen conservandum ("conserved name").

Sullivan & Lucas (1999) referred one specimen from Cope's original material of Coelophysis (AMNH 2706) to what they thought was a newly discovered theropod, Eucoelophysis. However, subsequent studies have shown that Eucoelophysis was misidentified, and is actually a primitive, non-dinosaurian ornithodiran closely related to Silesaurus.

In addition to all of this, there is a competing controversy with another coelophysoid, Megapnosaurus, which many regard to be congeneric with Coelophysis. To make matters more confusing, Paul suggested that Coelophysis should be placed in Megapnosaurus (then known as Syntarsus) to get around the above-mentioned taxonomic confusion.

In a situation affecting many dinosaur genera, many specimens were originally classified as new species but were in fact species of Coelophysis. For example, Prof. Mignon Talbot's 1911 discovery which she labeled Podokesaurus holyokensis, may be related to (or is) Coelophysis. In addition, C. posthumus, named by Friedrich von Huene in 1908, also needs reclassification and is tentatively titled Halticosaurus longotarsus at the moment.

Trivia
Coelophysis was the second dinosaur in space. Although Maiasaura had been taken into space three years earlier, a Coelophysis skull from the Carnegie Museum of Natural History was aboard the Space Shuttle Endeavour mission STS-89 when it left the atmosphere on January 22, 1998. It was also taken onto the space station Mir before being returned to Earth.
Coelophysis is also the state fossil of New Mexico.

Cynognathus was a metre-long predator of the Lower Triassic. It was one of the more mammal-like of the "mammal-like reptiles", a member of a grouping called Eucynodontia. The genus Cynognathus had an almost worldwide distribution.

Fossils have so far been recovered from South Africa, South America, China and Antarctica.
The genus Cynognathus ("Dog jaw") has been given several different names over the years. It has also been known as Cistecynodon, Cynidiognathus, Cynogomphius, Karoomys, Lycaenognathus, Lycochampsa, Lycognathus,

and Nythosaurus. In addition, according to the records of the Peabody Museum of Natural History at Yale, Richard Owen used the name Nythosaurus for this animal in 1876. This usage seems to be unconnected with Cynognathus. Cynognathus is presently the only recognized member of family Cynognathidae. Opinions vary as to whether all remains belong to the same species.

The species Cynognathus crateronotus is also known as Cistecynodon parvus, Cynidiognathus broomi, Cynidiognathus longiceps, Cynidiognathus merenskyi, Cynognathus beeryi, Cynognathus minor, Cynognathus platyceps, Cynogomphius berryi, Karoomys browni, Lycaenognathus platyceps, Lycochampsa ferox, Lycognathus ferox, Nythosaurus browni.

Fifteen different names for one Mesozoic creature might be regarded as excessive, but it's by no means a record. The dinosaur Plateosaurus engelhardti, has been named well over 20 times.

The genera Karoomys, Cistecynodon and Nythosaurus are known only from tiny juveniles, while Lycognathus cucullatus seems to be a misidentified snake from the Balearic Islands, although confirmation is elusive.

Fossil locations
Fossils have been found in Karoo; the Puesto Viejo Formation; Fremouw Formation, in South Africa/Lesotho; Argentina; Antarctica; and China.

Age
The Cynognathus lived between the Spathian (Lower Triassic) and the Anisian (Middle Triassic)
The dentary was equipped with differentiated teeth that show this animal could effectively process its food before swallowing. The presence of a secondary palate in the mouth indicates that Cynognathus would have been able to breathe and swallow simultaneously.

The lack of ribs in the stomach region suggests the presence of an efficient diaphragm: an important muscle for mammalian breathing. Pits and canals on the bone of the snout indicate concentrations of nerves and blood vessels. In mammals, such structures allow hairs (whiskers) to be used as sensory organs. All of these features indicate that Cynognathus was an endothermic animal: a "warm blooded" creature with a relatively high metabolic rate, which needed to be able to process food and oxygen quickly.

Eoraptor was one of the world's earliest dinosaurs. It was a two-legged meat-eater that lived between 230 and 225 million years ago, in what is now the northwestern region of Argentina. The type species is Eoraptor lunensis, which means 'dawn plunderer [from the Valley] of the Moon', denoting where it was originally discovered (Greek eos/e?? meaning 'dawn' or 'morning' and Latin lunensis meaning 'of

the moon'). Paleontologists believe the Eoraptor resembles the common ancestor of all dinosaurs. It is known from several well-preserved skeletons.

It had a thin body that grew to about 1 meter (3 ft) in length, with an estimated weight of about 10 kilograms (22 lb). It ran digitigrade, upright on its hind legs. Its fore limbs were only half the length of its hind limbs and it had five digits on each 'hand'. Three of those digits, the longest of the five, ended in large claws and were presumably used to handle prey. Scientists have surmised that the fourth and fifth digits were too tiny to be of any use in hunting.

Eoraptor probably ate mostly small animals. It was a swift sprinter and, upon catching its prey, it would use claws and teeth to tear the prey apart. However, it had both carnivore-type and herbivore-type teeth, so it could possibly have been omnivorous.

The bones of this primitive dinosaur were first discovered in 1991, by University of Chicago paleontologist Paul Sereno, in the Ischigualasto Basin of Argentina. During the Late Triassic Period, this was a river valley but is now desert badlands. Eoraptor was found in the Ischigualasto Formation, the same formation that yielded Herrerasaurus, a very early theropod.

By 1993 it had been determined to be one of the earliest dinosaurs. Its age was determined by several factors, not least because it lacked the specialised features of any of the major groups of later dinosaurs, including its lack of specialized predatory features. Unlike later carnivores, it lacked a sliding joint at the articulation of the lower jaw, with which to hold large prey. Furthermore, only some of its teeth were curved and saw-edged, unlike those in a later predator's mouth.

Eoraptor belonged to a major group of dinosaurs called saurischians, or lizard-hipped dinosaurs. Their hip structures are similar to that of the modern lizard.

The fact that it possessed some herbivore teeth and five fully developed 'fingers' has led scientists to place Eoraptor at more ancient than even Herrerasaurus. Only some prosauropods, recently discovered in Madagascar, are thought to be older. There is a possibility that Staurikosaurus may be older, but it is rather large. Staurikosaurus seems to have features in common with both prosauropods and theropods, which has led scientists to question how primitive Eoraptor was in relation to other dinosaurs.

Herrerasaurus (meaning "Herrera's lizard," after the name of the rancher who discovered the first fossil of the animal) was one of the earliest dinosaurs.

All known specimens of this carnivore have been discovered in northwest Patagonia, Argentina, in late Triassic Period rocks (early Carnian stage, around 228 million years ago). The type species, Herrerasaurus ischigualastensis, was described by Osvaldo Reig in 1963 and is the only species assigned to the genus.

For many years, the classification of Herrerasaurus was unclear, as the animal was initially known from very fragmentary remains; it has been hypothesized to be a basal theropod, a basal sauropodomorph, a basal saurischian, or not a dinosaur at all.

However, with the discovery of a mostly-complete skeleton and skull in 1988, Herrerasaurus has been classified as either an early theropod or an early saurischian in at least five recent surveys of theropod evolution. This medium-sized bipedal reptile is a member of the Herrerasauridae, a group of similar animals which were among the earliest of the dinosaurian radiation.

Herrerasaurus was a lightly-built bipedal carnivore with a long tail and a relatively small head. Its length is estimated at 3 to 6 meters (10 to 20 ft),and its hip height at more than 1.1 meters (3.3 ft). It may have weighed around 210–350 kilograms (463–772 lb).In a large specimen at first thought to belong to a separate genus, Frenguellisaurus, the skull measured 56 centimeters (1.8 ft) in length.

Skull
Herrerasaurus had a long, narrow skull that lacked nearly all the specializations that characterized later dinosaurs, being not that different from those of more primitive archosaurs such as Euparkeria.

It had five pairs of fenestrae (skull openings) in its skull, two of which were for ocular and nasal openings. Between the eyes and the nostrils were two antorbital fenestrae and a pair of tiny, 1-centimeter-long (0.4 in) slit-like holes called promaxillary fenestrae. Behind the eyes were large infratemporal fenestrae. These holes helped reduce the weight of the skull.

Herrerasaurus had a flexible joint in the lower jaw; this allowed the animal to slide its lower jaw back and forth and deliver a grasping bite. This cranial specialization is unusual among the dinosaurs but has evolved independently in some lizards. The rear of the lower jaw also had fenestrae. The jaws were equipped with large serrated teeth for biting and eating flesh, and the neck was slender and flexible.

Herrerasaurus had relatively short forelimbs, which were less than half the length of its hind limbs. The upper arm and forearm were rather short, while the manus was elongated. The first two fingers and the thumb bore curved, sharp claws for grasping prey.

Its fourth and fifth digits were small stubs without claws. Herrerasaurus was bipedal. It had strong hind limbs with short thighs and rather long feet, indicating this animal was most likely a swift runner. The balancing tail, partially stiffened by overlapping vertebral processes, also indicates an adaptation for speed.

Derived and basal characteristics
This dinosaur is an enigmatic creature, showing traits that are found in different groups of dinosaurs. Although it shared most of the characteristics of dinosaurs, there were a few differences, particularly in regard to the shape of its hip and leg bones.

Its pelvis was similar to that of saurischian dinosaurs, but it had a bony acetabulum (where the femur meets the pelvis) that was only partially open. The ilium, the main hip bone, was supported only by two sacrals, a basal trait, but the pubis pointed backwards, a derived trait that parallels what is seen in dromaeosaurids and birds.

Additionally, the end of the pubis had a booted shape, similar to what is present in avetheropods, and the vertebral centra had an Allosaurus-like hourglass shape.

Classification
Herrerasaurus gives its name to its family, Herrerasauridae, of the mid- to late Triassic, though where it and its close relatives lie on the early dinosaur evolutionary tree is unclear. They are possibly basal theropods or basal saurischians but may in fact predate the saurischian-ornithischian split.

Other members of the clade may include Eoraptor from the same Ischigualasto Formation of Argentina as Herrerasaurus, Staurikosaurus from the Santa Maria Formation of southern Brazil, Chindesaurus from the Upper Petrified Forest (Chinle Formation) of Arizona, and possibly Caseosaurus from the Dockum Formation of Texas, although the relationships of these animals are not fully understood, and not all paleontologists agree.

Other possible basal theropods, Alwalkeria from the Late Triassic Maleri Formation of India, and Teyuwasu, known from very fragmentary remains from the Late Triassic of Brazil, might be related. Novas (1992) defined the group as Herrerasaurus, Staurikosaurus, and their most common ancestor. Sereno (1998) defined the group as the most inclusive clade including H. ischigualastensis but not Passer domesticus. Langer (2004) created a higher level taxon, infraorder Herrerasauria.

History
Herrerasaurus was named by paleontologist Osvaldo Reig after Victorino Herrera, an Andean goatherd who first noticed its fossils in outcrops near the city of San Juan in 1959. These rocks, which later yielded Eoraptor, are part of the Ischigualasto Formation and date from the late Ladinian - early Carnian stages of the Late Triassic period.

Reig named a second dinosaur from these rocks in the same publication as Herrerasaurus; this dinosaur, Ischisaurus cattoi, is now considered a junior synonym and a juvenile of Herrerasaurus. Two other partial skeletons, with skull material, were named Frenguellisaurus ischigualastensis by Fernando Novas in 1986, but this species too is now thought to be a synonym.

Reig believed Herrerasaurus was an early example of a carnosaur, but this was the subject of much debate over the next 30 years, and the genus was variously classified during that time. In 1970, Steel classified Herrerasaurus as a prosauropod. In 1972, Peter M. Galton classified the genus as not diagnosable beyond Saurischia.

Later, using cladistic analysis, some researchers put Herrerasaurus and Staurikosaurus at the base of the dinosaur tree before the separation between ornithischians and saurischians. Several researchers classified the remains as non-dinosaurian.

A complete Herrerasaurus skull was not found until 1988, by a team of paleontologists led by Paul Sereno. Based on the new fossils, authors such as Thomas Holtz and Jose Bonaparte classified Herrerasaurus at the base of the saurischian tree before the divergence between prosauropods and theropods.

However, Sereno favored classifying Herrerasaurus (and the Herrerasauridae) as primitive theropods. These two classifications have become the most persistent, with Rauhut (2003) and Bittencourt and Kellner (2004) favoring the early theropod hypothesis, and Max Langer (2004), Langer and Benton (2006), and Randall Irmis and his coauthors (2007) favoring the basal saurischian hypothesis.

If Herrerasaurus was indeed a theropod, it would indicate that theropods, sauropodomorphs, and ornithischians diverged even earlier than herrerasaurids, before the middle Carnian (age of the Ischigualasto Formation), and that "all three lineages independently evolved several dinosaurian features, such as a more advanced ankle joint or an open acetabulum".

This view is further supported by ichnological records showing large tridactyl footprints that can be attributed only to a theropod dinosaur, dating from the Ladinian (Middle Triassic) of the Los Rastros Formation in Argentina and predating Herrerasaurus by 3 to 5 million years.

The importance of Herrerasaurus and Eoraptor lies in the fact that their remains allow for directly testing the idea of dinosaurs being a monophyletic group, i.e. all dinosaurs have a common ancestor. The monophyly of dinosaurs was explicitly proposed in the 1970s by Bakker, and nine cranial and about fifty postcranial synapomorphies (common anatomical traits derived from the common ancestor) have been listed.

However, an extensive study of Herrerasaurus by Sereno indicates that only one cranial and seven postcranial synapomorphies in Bakker's original list are actually supported while additional synapomorphies were discovered.

Paleoecology
Although Herrerasaurus shared the body shape of the large carnivorous dinosaurs, it lived about 230 million years ago, a time when dinosaurs were small and insignificant. It was the time of non-dinosaurian reptiles, not dinosaurs, and a major turning point in the Earth's ecology. The vertebrate fauna of the Ischigualasto Formation and the slightly later Los Colorados Formation consisted mainly of a variety of crurotarsal archosaurs and synapsids.

For instance, in the Ischigualasto Formation, dinosaurs constituted only about 6% of the total number of fossils. By the end of the Triassic Period, dinosaurs were becoming the dominant large land animals, and the other archosaurs and synapsids lost diversity.

Studies suggest that the paleoenvironment of the Ischigualasto Formation was a volcanically active floodplain covered by forests and subject to strong seasonal rainfalls. Vegetation consisted of ferns (Cladophlebis), sphenopsids (horsetails), and giant conifers (Protojuniperoxylon). The plants formed an upland riparian forest.

Herrerasaurus remains appear to have been the most common among the carnivores of the Ischigualasto Formation. It lived in the jungles of Late Triassic South America alongside another early dinosaur, Eoraptor, as well as Saurosuchus, a giant land-living meat-eating rauisuchian; Venaticosuchus, an ornithosuchid; and the predatory chiniquodontid cynodonts.

Herbivores were much more abundant than carnivores and were represented by rhynchosaurs such as Hyperodapedon (formerly Scaphonyx); aetosaurs; kannemeyeriid dicynodonts such as Ischigualastia, and traversodontids such as Exaeretodon. These non-dinosaurian herbivores were much more abundant than early ornithischian dinosaurs like Pisanosaurus [44] and therefore more likely prey for Herrerasaurus than were the early dinosaurs.

The teeth of Herrerasaurus indicate it was a carnivore; its size indicates it would have preyed upon small and medium-sized animals. It may have fed on other dinosaurs, such as the herbivorous Pisanosaurus. However, since Herrerasaurus lived during an era when other dinosaurs were uncommon, more plentiful prey would have included rhynchosaurs and aetosaurs.

Herrerasaurus itself may have been preyed upon by giant rauisuchids like Saurosuchus, as puncture wounds were found in one skull.

Coprolites (fossilized dung) containing small bones but no trace of plant fragments, discovered in the Ischigualasto Formation, have been assigned to Herrerasaurus based on fossil abundance. The mineralogical and chemical analysis of these coprolites indicate that the carnivorous animal had the ability to digest bones.

Liliensternus was a genus of coelophysoid dinosaur from the Late Triassic period, between about 215-200 mya. Liliensternus was originally found in 1934 in Germany and was named after the German scientist, Dr. Hugo Rühle von Lilienstern. Liliensternus was around 6 meters long and may have preyed on herbivores like Plateosaurus. It

probably weighed around 400 kilograms.

The type species is Liliensternus liliensterni. A second species, Liliensternus airelensis, which had an extra pair of cervical pleurocoels, is now considered a separate genus, Lophostropheus.

Lystrosaurus (meaning 'shovel lizard', pronunciation in IPA: /?l?str?'s?r?s/) was a genus of Late Permian and Early Triassic Period dicynodont therapsids, which lived around 250 million years ago in what is now Antarctica, India and South Africa. At present 4 to 6 species are recognized, although from the 1930s to 1970s the number of species was thought to be much higher.

Being a dicynodont, Lystrosaurus had only two teeth, a pair of tusk-like canines, and is thought to have had a horny beak that was used for biting off pieces of vegetation. Lystrosaurus was a heavily-built, herbivorous animal, approximately the size of a pig. The structure of its shoulders and hip joints suggest that Lystrosaurus moved with a semi-sprawling gait. The forelimbs were even more robust than the hindlimbs, and the animal is thought to have been a powerful digger that nested in burrows.

Lystrosaurus was by far the most common terrestrial vertebrate of the Early Triassic, accounting for as many as 95% of the total individuals in some fossil beds. It has often been suggested that it had anatomical features that enabled it to adapt better than most animals to the atmospheric conditions that were created by the Permian–Triassic extinction event and which persisted through the Early Triassic — low concentrations of oxygen and high concentrations of carbon dioxide. However recent research suggests that these features were no more pronounced in Lystrosaurus than in genera that perished in the extinction or genera that survived but were much less abundant than Lystrosaurus.

Lystrosaurus was a pig-sized dicynodont therapsid, typically about 3 feet (0.91 m) long and weighing about 200 pounds (91 kg). Unlike other therapsids, dicynodonts had very short snouts and no teeth except for the tusk-like upper canines. It is generally assumed that dicynodonts had horny beaks like those of turtles, for shearing off pieces of vegetation which were then ground on a horny secondary palate when the mouth was closed.

The jaw joint was weak and moved backwards and forwards with a shearing action, instead of sideways or up and down. It is thought that the jaw muscles were attached unusually far forward on the skull and took up a lot of space on the top and back of the skull. As a result the eyes were set high and well forward on the skull, and the face was shortFeatures of the skeleton indicate that Lystrosaurus moved with a semi-sprawling gait:

The lower rear corner of the scapula (shoulder blade) was strongly ossified (built of strong bone), which suggests that movement of the scapula contributed to the stride length of the forelimbs and reduced sideways flexing of the body.
The 5 sacral vertebrae were massive but not fused to each other and to the pelvis, making the back more rigid and reducing sideways flexing while the animal was walking. Therapsids with fewer than 5 sacral vertebrae are thought to have had sprawling limbs, like those of modern lizards.

In dinosaurs and mammals, which have erect limbs, the sacral vertebrae are fused to each other and to the pelvis.
A buttress above each acetabulum (hip socket) is thought to have prevented dislocation of the femur (thigh bone) while Lystrosaurus was walking with a semi-sprawling gait.
The forelimbs were massive. Lystrosaurus is thought to have been a powerful burrower.

Placerias was a dicynodont (a group of mammal-like reptiles) that lived during the late Carnian age of the Triassic Period (221-210 million years ago). It was a member of the family Kannemeyeridae, the last known representative of the group at this time: the dicynodonts went extinct shortly afterwards.

This animal was the biggest herbivore of its home, measuring up to 3.5 metres long and weighing one to two

tonnes with a powerful neck, strong legs, and a barrel-shaped body. There are possible ecological and evolutionary parallels with the modern hippopotamus, spending much of its time during the wet season wallowing in the water, chewing at bankside vegetation.

Remaining in the water would also have given Placerias some protection against land-based predators such as Postosuchus. Placerias used its beak to slice through thick branches and roots with two short tusks that could be used for defence and for intra-specific display.

Fossils of forty Placerias were found near St. Johns, southeast of the Petrified Forest in Arizona. This site has become known as the 'Placerias Quarry' and was discovered in 1930, by Charles Camp and Samuel Welles, of the University of California, Berkeley. Sedimentological features of the site indicate a low-energy depositional environment, possibly flood-plain or overbank. Bones are associated mostly with mudstones and a layer that contains numerous carbonate nodules.

the past.

Discovered in 1834 and described three years later, Plateosaurus was one of the first dinosaurs formally named, although not one of the three genera originally used to define Dinosauria, because at the time it was poorly known and impossible to identify as a dinosaur. Plateosaurus were bulky bipedal herbivores which had small skulls on long necks, sharp plant-crushing teeth, powerful limbs, and large thumb claw on each 'hand' probably used for defense and feeding.

Plateosaurus was the largest known dinosaur of its time, reaching 6 to 10 meters in length and up to an estimated 700 kg in mass. A member of the group of early herbivores known as prosauropods, it was more powerfully built than that of similar animals such as Anchisaurus. Plateosaurus had a long neck, composed of around nine cervical vertebrae, a stocky body and a pear-shaped torso. It had a long tail composed of at least forty caudal vertebrae which served to counterbalance the front-heavy body and long neck.

The skull of Plateosaurus was deeper than that of most prosauropods, although still small and narrow compared to the size of its body. It had four sets of fenestrae (skull openings); these openings were for the naris and orbit as well as an infratemporal fenestra at the back of the skull and an antorbital fenestra between the eye and nose. It had a long snout and many small, leaf-shaped, socketed teeth and the low-slung hinge of its lower jaw, which give the muscles greater leverage.

These features suggest that it fed exclusively on plants. Its eyes were directed to the sides, rather than the front, providing all-round vision to watch for predators. Some fossil skeletons have preserved sclerotic rings.

Plateosaurus had numerous small teeth in both the upper and lower jaw, five to six on the premaxilla, twenty four to thirty on the maxilla, and twenty one to twenty eight on the dentary. These teeth had serrated, leaf-shaped crowns suitable for digestion of plant material. It is thought Plateosaurus had narrow cheek pouches which kept food from spilling out when it ate.

In 1834, physician Johann Friedrich Engelhardt discovered some vertebrae and leg bones at Heroldsberg near Nuremberg, Germany. Three years later German palaeontologist Hermann von Meyer designated them as the type specimen of his new genus, Plateosaurus.

This name is derived from the Greek words p?at??/platys ('broad' or 'flat') which is derived as well from p?at?/platé ('flat surface'), and sa???? ('lizard'), which refers to the animal's flat bones and reptilian nature. The type species was named in honor to its discoverer.

Between the 1910s and 1930s, excavations in a clay pit at Saxony-Anhalt dug up between 39 and 50 skeletons that belonged to Plateosaurus, Liliensternus and Halticosaurus. Some of this material was assigned to P. longiceps, which was described by paleontologist Otto Jaekel in 1914. At the same time, bonebeds at Trossingen revealed several remains of Plateosaurus, most of which were designated to species now dubious or invalid.

In 1997, workers of an oil platform of the Snorre oilfield located at the northern end of the North Sea, were drilling through sandstone for oil exploration when they stumbled upon a long cylinder of rock, drilled out at 2,256 meters below the seafloor. This cylinder contained a fossil which they believed was plant material. In 2003, the specimen was sent to Jørn Harald Hurum, paleontologist at the University of Oslo for study.

After consulting paleontologists of the University of Bonn, they, with microscopic examination, concluded that the rock preserved fibrous bone tissue located within a crushed knucklebone which they identified as belonging to Plateosaurus, making it the first dinosaur found in Norway and the deepest in the world.

In August 2007, an amateur paleontologist unearthed a mass grave of dinosaurs near Frick, Switzerland, comprised of around 300 bones, in which two Plateosaurus individuals were discovered. Martin Sander, paleontologist at the University of Bonn, indicated the area could extend for 1.5 kilometers, making it the biggest fossil site in Europe.

There is an estimate of one dinosaur per 100 square meters.
Plateosaurus was the first prosauropod to be described, and is the type genus of the family Plateosauridae, to which gives its name. At the beginning, when the genus was poorly known, it was only included in Sauria, with the possibility of being any kind of reptile.

In 1845, Von Meyer created the group Pachypodes (now unused) to include Plateosaurus, Iguanodon, Megalosaurus and Hylaeosaurus, however, Dinosauria (technically the same as Pachypodes) already existed. Plateosauridae was proposed by Othniel Charles Marsh in 1895 within Theropoda. Years later, it was moved to Prosauropoda by Huene, and was accepted by most authors. For many years the clade only included Plateosaurus, but recently two more genera, Sellosaurus and possibly Unaysaurus, have been recognized.

The small leaf-shaped teeth of Plateosaurus indicate it was an herbivore, one of the first large dinosaurs that browsed in tall vegetation like conifers and cycads, supported by its long neck.

Like all prosauropods, Plateosaurus had forelimbs which were much shorter than the hindlimbs and they had distinct digits ('fingers') and a spiked 'thumb'. Plateosaurus has been traditionally depicted as quadrupedal, but a 2007 anatomical study of the forelimbs demonstrated that their range of motion precluded effective habitual quadrupedal gait.

Like theropods, Plateosaurus and other related prosauropods could not rotate the hand so that their palms faced downward, and so would have been unable to use the front limbs for standing or walking. The study also ruled out the possibility of "knuckle-walking" and other forms of locomotion that would avoid the issue of the limited ability of Plateosaurus to pronate its hands. Thus, although its mass suggests a quadrupedal nature, it would have been restricted to its hind legs for locomotion. The forelimbs may have been used to rake trees for food, for grasping or for defense.

The hand bones of Plateosaurus were large, and bore five digits. The last two digits on each hand were very small.

A recent analysis of fossil deposits reveals there was considerable variation in size in individuals. Furthermore, growth rings in bone suggests periods of varying growth which may relate to the surrounding environment. Some plateosaurs reached their maximum size at twelve years old, while others were still growing after more than two decades. The size of adult specimens varies too; there are smaller specimens which when fully grown were four to six meters long, and others that measured up to ten meters long.

Bone histology of Plateosaurus is well-preserved and studied. However, due to the absence of individuals smaller than 4.8 meters long, it is not possible to deduce an ontogenetic series for Plateosaurus. Like many other dinosaurs, Plateosaurus exhibits high growth rates, suggesting an advanced dinosaurian physiology. The paper's authors propose that the metabolism of Plateosaurus may have been intermediate between a reptilian and a warm-blooded one.

poorly-preserved skeleton found in Württemberg, Germany.

The name is derived from Compsognathus meaning 'elegant jaw' (Greek kompsos/??µ??? meaning 'elegant', 'refined' or 'dainty' and gnathos/??a??? meaning 'jaw'), which was a later (Jurassic) dinosaur. The prefix p??/pro implies 'before' or 'ancestor of', although this direct lineage is not supported by subsequent research.

Procompsognathus may have been about 1.2 meters long (4 ft). A biped, it had long hind legs, short arms, large clawed hands, a long slender snout with many small teeth, and a stiff tail. It lived in a relatively dry, inland environment and may have eaten insects, lizards, and other small prey.

While it is undoubtedly a small, bipedal carnivore, the extremely poor preservation of the only known Procompsognathus fossil makes its exact identity difficult to determine. It has historically been considered a theropod dinosaur, though some, such as Allen (2004), have found Procompsognathus to be a primitive, non-dinosaurian ornithodiran.

However, Rauhut and Hungerbuhler (2000) noted features of the vertebrae that suggest it may be a coelophysid or ceratosaur, and Carrano et al. (2005), in their re-study of the related genus Segisaurus, found both Segisaurus and Procompsognathus to belong to the Coelophysidae within Dinosauria.

fossils of the species were found. It was one of the top predators of its area during the Triassic, larger than the small dinosaur predators of its time (such as Megapnosaurus and Coelophysis). It was a hunter which probably preyed on dicynodonts and many other creatures smaller than itself.

Postosuchus was a quadrupedal reptile with a wide skull and a long tail. It was about 6 meters long, 2 meters tall, and was held up by columnar legs (a quite uncommon feature in reptiles). A crocodile-like snout, filled with many large-sized dagger-like teeth, was used to kill its prey. Rows of protective plates covering its back formed a defensive shield.

In popular culture
Postosuchus appears in the first program of the BBC's series Walking with Dinosaurs, where CG animation was used to recreate extinct creatures of the Mesozoic era. In this episode, it appears as the top predator, preying on Placerias, large dicynodonts. In one segment a female Postosuchus sustains a fatal injury when hunting, loses her territory to another Postosuchus, and is finally killed by a swarm of Coelophysis, too weak to defend herself.

Staurikosaurus is a genus of early dinosaur.
Discovery

There exists only a single specimen of Staurikosaurus ("Lizard of the Southern Cross"), recovered from the Santa Maria formation in Rio Grande do Sul, southern Brazil. The name refers to the star constellation "The Southern Cross",

only visible in the southern hemisphere - when Staurikosaurus was found in 1970, it was unusual to find dinosaurs in the southern hemisphere. It was first described by Edwin H. Colbert, working at the American Museum of Natural History.

Description
Staurikosaurus was a small theropod from the late Triassic Period, 225 million years ago - specifically the Carnian age. It is one of the earliest dinosaurs that is known. At just two metres in length, 80 cm tall and weighing just thirty kilograms, Staurikosaurus was tiny in comparison to later theropods like Megalosaurus. Although its teeth and posture suggest it was an omnivore, some paleontologists prefer to classify Staurikosaurus as a sauropod like the later Diplodocus due to its prosauropod-like skeleton.

It seems to represent a transition period as one of these sub-orders evolved from the other. However, another fossil (as yet unnamed) was found in 1984 in Arizona's Painted Desert that was such a typical prosauropod that it seems that the group evolved before Staurikosaurus. Newer research seems to confirm that Staurikosaurus and the related Eoraptor and Herrerasaurus are definite theropods and evolved after the sauropod line had split from theropoda.

There exists very incomplete fossil record of Staurikosaurus, consisting most of the spine, the legs and the large lower jaw. However, dating from such an early period in the dinosaurs' history and being otherwise so primitive, most of Staurikosaurus' other features as being primitive also can be reconstructed. For example, Staurikosaurus is usually depicted with five toes and five fingers - very simple features of an unspecialised dinosaur.

However, since the skeletal structure of the legs is known, it can be seen that Staurikosaurus was a quick runner for its size. It also had just two vertebrae joining the pelvis to the spine, a distinctly primitive arrangement. The tail would have been long and thin to balance the border - later sauropods had larger, shorter tails relative to their weight.

The recovered mandible suggests that sliding joint of the jaw allowed it to move backwards and forwards, as well as up and down. Thus smaller prey could be worked backwards towards Staurikosaurus' throat, along its small and backwards-curving teeth. This feature is common in theropods of the time, but disappears in later theropods who presumably had no need for efficiency in eating smaller prey.

Classification

Order - Saurischia

Sub-order - Theropoda (Subject to some debate - see above)

Family - Staurikosauridae

Since one specimen of Staurikosaurus exists, evidently only one species is known. That is Colbert's original S. pricei. This is named for Colbert's fellow paleontologist Llewellyn Ivor Price. However, there are some related staurikosaurids, such as Chindesaurus bryansmalli, named by Murray & Long in 1985. This was from a similar time period and has been found in Arizona and New Mexico. This suggests that staurikosaurids spread widely across Central Pangaea.

kilograms).

Although not actually the earliest member of the group (that honour belongs to as yet unnamed sauropodomorphs from Madagascar (Flynn and Wyss 2002)), Thecodontosaurus is the most primitive well-known representative of the sauropodomorph dinosaurs.

Originally it was included under the Prosauropoda (Upchurch 1998) but more recently it has been suggested that Thecodontosaurus and its relatives were prior to the Prosauropod-Sauropod split (Yates & Kitching 2003). New reconstructions show that its neck is proportionally shorter than in more advanced early sauropodomorphs.

The original type specimen of Thecodontosaurus was a victim of World War II bombings by the Germans. The remains of this dinosaur and other material related to it were destroyed in 1940. However, more remains have been found at a number of localities, including Bristol. Some of this new material pertains to a juvenile specimen that may belong to a distinct species, Thecodontosaurus caducus Yates, 2003. The Australian dinosaur Agrosaurus macgillivrayi (Seeley, 1891) is probably synonymous with Thecodontosaurus antiquus.

In 2007, a paper by Yates, Galton, and Kermack put forth the claim that Thecodontosaurus caducus belongs to a different genus, which they have named Pantydraco.

Species
A single species of Venaticosuchus has been described, the type species, V. rusconii from the Late Triassic of Argentina, around 210 million years ago.

Closely related species
Venaticosuchus is a member of Ornithosuchidae, a family of faculatively biped carnivores that were geographicaly widespread during the Late Triassic. Two other genera are currently known, Ornithosuchus and Riojasuchus.

Cynodonts, or 'dog teeth', are a taxon of Therapsids, traditionally called mammal-like reptiles. They were one of the most diverse groups of therapsids. They are named after their dog-like teeth.

Characteristics
Cynodonts have nearly all the characteristics of mammals. Their teeth were fully differentiated, the braincase bulged

at the back of the head, and many of them walked in an upright manner. Cynodonts still laid eggs, as all Mesozoic proto-mammals probably did. Their temporal fenestrae was much larger than its ancestors, and the widening of the zygomatic arch allowed for more robust jaw musculature supporting the evidence of a more mammal-like skull.

They also have the secondary palate that other primitive therapsids lacked, except the therocephalians, who were the closest relatives of cynodonts. Their dentary was the largest bone in their lower jaw, as other smaller bones moved into the ears. They were probably warm-blooded, and covered in hair.

Evolutionary history
The cynodonts themselves are part of a group of therapsids called theriodonts, together with the extinct gorgonopsians and the therocephalians. Cynodonts' evolutionary track began late in the Permian, as a small, Gorgonopsid-like theriodont. The oldest and the most basal cynodont yet found is Charassognathus. Other basal cynodonts were the Procynosuchids, a family that includes Procynosuchus and Dvinia. Cynodonts were among the groups which survived the Permian-Triassic extinction event and had a slow recovery after the extinction.

The most derived cynodonts are found within Eucynodontia clade, which also contains the members of Mammalia. Representative genera include the large carnivorous cynognathids, equally large herbivorous traversodonts, and small and mammal-like tritylodontids and ictidosaurs. It is likely that Cynodonts were at least partially if not completely warm-blooded, covered with hair, which would have insulated them and helped to maintain a high body temperature.

The mammal-like structure of Cynodonts hints that all mammals have descended from a single group of eucynodonts.
During their evolution, cynodonts changed their teeth from being designed for catching and holding prey and then swallowing whole, to adding specialized teeth, including molars, designed for better mastication of food allowing for quicker digestion. Additionally, the jaw of the cynodonts reduced the number of jaw bones. This freed up the superfluous bones to evolve into an entirely new function, becoming parts of the mammal's inner ear.

Improved hearing gave these creatures a better awareness of their environment and, in turn, this increasing sensitivity called for a greater capacity for processing the auditory information in the brain. Cynodonts also developed a secondary palate in the roof of the mouth. This allowed air to flow to the lungs through the back of the mouth, allowing cynodonts to chew and breathe at the same time. This characteristic is present in all mammals.

Hypuronector limnaios

Hypuronector is a genus of extinct reptile from the Triassic Period that lived in what is now New Jersey. The etymology of the name translates as "deep-tailed swimmer from the lake." A member of the Simiosauria, Hypuronector is related to the arboreal Megalancosaurus.

It was a small animal, estimated to be only 12 cm long in life. So far dozens of specimens of Hypuronector are known, but despite this, scientists have not found any complete skeletons. This makes attempts to reconstruct Hypuronector's body or life-style highly speculative and controversial.

Lifestyle Controversy
Despite their evolutionary relationship, it has been suggested that Hypuronector had a different ecological niche than other Simiosaurs. It has long been accepted that Megalancosaurus was an arboreal chameleon-like animal. However, Hypuronector has been suggested to be aquatic due to its deep, paddle-like tail and the fact that its remains were found in an ancient lake bottom.

Experts holding the contrary position, that Hypuronector was also arboreal note that other Simiosaurs that are believed to be arboreal even though all have been found preserved. The only current remains of Hypuronector are too scanty to reach a certain conclusion about the lifestyle practiced by members of the genus.

The discovery of the animals hands and feet might demonstrate adaptations present in its relatives for an arboreal lifestyle, which would help settle the debate. Unfortunately, paleontologists have no remains from Hypuronector's head, neck, feet or hands and thus must await future discoveries.

Prolacertiformes (sometimes called Protorosaurs) were an order of archosauromorph reptiles that lived during the Permian and Triassic Periods.

Many species seem to have been adapted for an arboreal lifestyle, including the "delta-winged glider" Sharovipteryx, while others, such as Tanystropheus, had extremely long, stiffened necks (possibly used to catch fish), and may have been at least partly aquatic.
Other enigmatic reptile groups have sometimes been

assigned by some resarches to the Prolacertiformes, including the drepanosaurids, Longisquama, and the Pterosaurs. Senter (2004) re-assigned the bizarre, arboreal drepanosaurids and Longisquama to a group of more primitive diapsids called Avicephala, though some researchers still place these forms among the prolacertiformes.

Classification

Order Prolacertiformes

Family Protorosauridae

Protorosaurus

Family Prolacertidae

Kadimakara

Pamelaria

Prolacerta

Jesairosaurus

Malerisaurus

Macrocnemus

Langobardisaurus

Boreopricea

Cosesaurus

Family Sharovipterygidae

Sharovipteryx

Family Tanystrophidae

Tanytrachelos

Tanystropheus

Dinocephalosaurus

Sphenodontia is an order of lizard-like reptiles that includes only one living genus, the tuatara (Sphenodon). Despite its current lack of diversity, the Sphenodontia at one time included a wide array of genera in several families, and represents a lineage stretching back to the Mesozoic Era.

Classification
Classification follows Wu (1994), Evans et al. (2001), and

Apesteguia & Novas (2003) [1]. super

Order RHYNCHOCEPHALIA / SPHENODONTIA

Family Gephyrosauridae

Gephyrosaurus

Diphydontosaurus

Family Pleurosauridae

Palaeopleurosaurus

Pleurosaurus

Family Sphenodontidae

Colognathus

Godavarisaurus

Kawasphenodon

Lamarquesaurus

Leptosaurus

Pelecymela

Piocormus

Sigmala

Theretairus

Tingitana

Rebbanasaurus

Planocephalosaurus

Polysphenodon

Brachyrhinodon

Clevosaurus

Subfamily Sphenodontinae

Homeosaurus

Kallimodon

Sapheosaurus

Ankylosphenodon

Pamizinsaurus

Zapatadon

Tribe Sphenodontini

Cynosphenodon

Sphenodon (tuatara)

(unranked) Opisthodontia

Opisthias

Tribe Eilenodontini

Toxolophosaurus

Priosphenodon

Eilenodon

Arecaceae or Palmae (also known by the name Palmaceae, which is taxonomically invalid.), the Palm Family, is a family of flowering plants belonging to the monocot order, Arecales. There are roughly 202 currently known genera with around 2600 species, most of which are restricted to tropical, subtropical, and possibly warm temperate climates.

Most palms are distinguished by their large, compound, evergreen leaves arranged at the top of an unbranched stem. However, many palms are exceptions to this statement, and palms in fact exhibit an enormous diversity in physical characteristics.

As well as being morphologically diverse, palms also

inhabit nearly every type of habitat within their range, from rainforests to deserts.
Palms are one of the most well-known and extensively cultivated plant families. They have had an important role to humans throughout much of history.

Many common products and foods are derived from palms, and palms are also widely used in landscaping for their exotic appearance making them one of the most economically important plants. In many historical cultures, palms were symbols for such ideas as victory, peace, and fertility. Today, palms remain a popular symbol for the tropics and vacations .

Characteristics and evolution
Range

The vast majority of palms live in the tropics. Palms are abundant throughout the tropical regions around the world, and are present in almost every type of habitat in the tropics. Diversity is highest in wet, lowland tropical forests, especially in ecological "hotspots" such as Madagascar, which has more endemic palms than the entire continental Africa. Colombia may have the highest number of palm species in one country.

It is estimated that only 130 palm species grow naturally beyond the tropics, most of which grow in the subtropics. The northernmost palm is Chamaerops humilis, which reaches 44°N latitude in southern France, where the local Mediterranean climate is milder than other places as far north. The southernmost palm is the Rhopalostylis sapida, which reaches 44°S on the Chatham Islands where an oceanic climate has a similar warming effect.

Morphology and habitat
The growth habit of palms is usually a straight, unbranched stem, and rarely a dichotomous branching stem or a creeping vine-like habit (liana). They have large evergreen leaves that are either palmately ('fan-leaved') or pinnately ('feather-leaved') compound and spirally arranged at the top of the stem. The leaves have a tubular sheath at the base that usually splits open on one side at maturity.

The inflorescence is a panicle or spike surrounded by one or more bracts or spathes that become woody at maturity. The flowers are generally small and white, radially symmetric, and can be either uni- or bisexual. The sepals and petals usually number three each and may be distinct or joined at the base. The stamens generally number six, with filaments that may be separate, attached to each other, or attached to the pistil at the base. The fruit is usually a single-seeded drupe, but some genera (e.g. Salacca) may contain two or more seeds in each fruit.

Palms inhabit a variety of habitats. Over two-thirds of palms live in tropical forests, where some species grow tall enough to form part of the canopy and other shorter palms adapted to shade form part of the understory. Some species form pure stands in areas with poor drainage or regular flooding, including Raphia hookeri which is common in coastal freshwater swamps in West Africa.

Other palms live in tropical mountain habitats above 1000 meters, such as those in the genus Ceroxylon native to the Andes. Palms may also live in grasslands and scrublands, usually associated with a water source, and in desert oases such as the Date Palm. A few palms are adapted to extremely basic lime soils, while others are similarly adapted to very acidic serpentine soils.

Arecaceae is notable for having the individual trees with the largest seed, largest leaf, largest inflorescence, as well as the tallest individual monocot. The Coco de mer (Lodoicea maldivica) has the largest seeds of any plant, 40-50 centimeters in diameter and weighing 15-30 kilograms each. Raffia palms (Raphia spp.), with leaves up to 25 meters long and 3 meters wide, have the largest leaves of any plant.

The Corypha species have the largest inflorescence of any plant, up to 7.5 meters tall and containing millions of small flowers. Ceroxylon quindiuense, Colombia's national tree, is the tallest monocot in the world, reaching heights of 60 meters.

Taxonomy
Palms are a monophyletic group of plants, meaning that the group consists of a common ancestor and all its descendants. Extensive taxonomic research on palms began with botanist H.E. Moore, who organized palms into fifteen major groups based mostly on general morphological characteristics. The following classification, proposed by N.W. Uhl and J. Dransfield in 1987, is a revision of Moore's classification that organizes palms into six subfamilies.

A few general traits of each subfamily are listed.
Coryphoideae is the most diverse subfamily and is a paraphyletic group, meaning that all members of the group share a common ancestor but the group does not include all the ancestor's descendants. Most palms in this subfamily have palmately lobed leaves and solitary flowers with three, sometimes four carpels.

The fruit normally develops from only one carpel. Subfamily Calamoideae includes the climbing palms such as rattans. The leaves are usually pinnate; derived characters (synapomorphies) include spines on various organs, organs specialized for climbing, an extension of the main stem of the leaf bearing reflexed spines, and overlapping scales covering the fruit and ovary. Subfamily Nypoideae contains only one genus and one species, Nypa fruticans, which has large pinnate leaves.

The fruit is unusual in that it floats, and the stem is dichotomously branched, also unusual in palms. Subfamily Ceroxyloideae has small to medium-sized flowers that spirally arranged, with a gynoecium of three joined carpels. Arecoideae is the largest subfamily with six diverse tribes containing over 100 genera. All tribes have pinnate or bipinnate leaves and flowers arranged in groups of three, with a central pistillate and two staminate flowers. Phytelephantoideae is a monoecious subfamily.

Members of this group have distinct monopodial flower clusters. Other distinct features include a gynoecium with five to ten joined carpels, and flowers with more than three parts per whorl. Fruits are multiseeded and have multiple parts.

Currently, few extensive phylogenetic studies of Arecaceae exist. In 1997, Baker et al. explored subfamily and tribe relationships using chloroplast DNA from 60 genera from all subfamilies and tribes. The results strongly showed that Calamoideae is monophyletic, and that Ceroxyloideae and Coryphoideae are paraphyletic.

The relationships of Arecoideae are uncertain but it is possibly related to Ceroxyloideae and Phytelephantoideae. However, hybridization has been observed among Orbignya and Phoenix species, and using chloroplast DNA in cladistic studies may produce inaccurate results due to maternal inheritance of the chloroplast DNA. Chemical and molecular data from non-organelle DNA, for example, could be more effective for studying palm phylogeny.

Selected genera
Areca – Betel palm

Bactris – Pupunha

Borassus – Palmyra palm

Calamus – Rattan palm

Cocos – Coconut

Copernicia – Carnauba wax palm

Elaeis – Oil palm

Euterpe – Cabbage Heart palm, Açaí palm

Jubaea – Chilean Wine palm, Coquito palm

Metroxylon – Sago palm

Phoenix – Date palm

Raphia – Raffia palm

Roystonea – Royal palm

Sabal – Palmettos

Salacca – Salak

Trachycarpus – Windmill palm, Kumaon palm

Washingtonia

See list of Arecaceae genera arranged by taxonomic groups or by alphabetical order for a complete listing of genera.

Evolution
Arecaceae is the first modern family of monocots that is clearly represented in the fossil record. Palms first appear in the fossil record around 80 million years ago, during the late Cretaceous Period. The first modern species, such as Nypa fruticans and Acrocomia aculeata, appeared 69-70 million years ago, confirmed by fossil Nypa pollen dated to 70 million years ago. Palms appear to have undergone an early period of adaptive radiation.

By 60 million years ago, many of the modern, specialized genera of palms appeared and became widespread and common, much more widespread than their range today. Because palms separated from the monocots earlier than other families, they developed more intrafamilial specialization and diversity. By tracing back these diverse characteristics of palms to the basic structures of monocots, palms may be valuable in studying monocot evolution.

Conservation
Like many other plants, palms have been threatened by human intervention and exploitation. The greatest risk to palms is destruction of habitat, especially in the tropical forests, due to urbanization, wood-chipping, mining, and conversion to farmland. Palms rarely reproduce after such great changes in the habitat, and palms with a small habitat range are most vulnerable to them.

The harvesting of heart of palm, a delicacy in salads, also poses a threat because it is derived from the inner core of the tree and thus harvesting kills the tree. The use of rattan palms in furniture has caused a major population decrease in these species that has negatively affected local and international markets as well as biodiversity in the area. The sale of seeds to nurseries and collectors is another threat, as the seeds of popular palms are sometimes harvested directly from the wild.

At least 100 palm species are currently endangered, and nine species have reportedly recently become extinct .
However, several factors make palm conservation more difficult. Palms live in almost every type of habitat and have tremendous morphological diversity.

Most palm seeds lose viability quickly, and they cannot be preserved in low temperatures because the cold kills the embryo. Using botanical gardens for conservation also presents problems, since they can only house a few plants of any species and cannot truly imitate the natural setting .

The Palm Specialist Group of the World Conservation Union (IUCN) began in 1984 and has performed a series of three studies in order to find basic information on the status of palms in the wild, utilization of wild palms, and palms under cultivation. Two projects on palm conservation and utilization supported by the World Wildlife Fund took place from 1985-1990 and 1986-1991, in the American tropics and southeast Asia respectively.

Both studies produced a large amount of new data and publications on palms. Preparation of a global action plan for palm conservation began in 1991, supported by the IUCN, and was published in 1996 .
The rarest palm known is the Hyophorbe amaricaulis. The only living individual that remains is at the Botanic Gardens of Curepipe in Mauritius.

The Ginkgo (Ginkgo biloba; '??' in Chinese), frequently misspelled as "Gingko", and also known as the Maidenhair Tree, is a unique tree with no close living relatives. It is classified in its own division, the Ginkgophyta, comprising the single class Ginkgoopsida, order Ginkgoales, family Ginkgoaceae, genus Ginkgo and is the only extant species within this group.

It is one of the best known examples of a living fossil. Ginkgoales are not known in the fossil record after the Pliocene, making Ginkgo biloba a living fossil.
For centuries it was thought to be extinct in the wild, but is now known to grow in at least two small areas in Zhejiang province in Eastern China, in the Tian Mu Shan Reserve.

Ginkgo trees in these areas may have been tended and preserved by Chinese monks for over 1000 years. Therefore, whether native ginkgo populations still exist is uncertain.
The relationship of Ginkgo to other plant groups remains uncertain. It has been placed loosely in the divisions Spermatophyta and Pinophyta, but no consensus has been reached.

Since Ginkgo seeds are not protected by an ovary wall, it can morphologically be considered a gymnosperm. The apricot-like structures produced by female ginkgo trees are technically not fruits, but are the seeds having a shell that consists of a soft and fleshy section (the sarcotesta), and a hard section (the sclerotesta).

Characteristics: General Morphology
Ginkgos are very large deciduous trees, normally reaching a height of 20–35 m (66-115 feet), with some specimens in China being over 50 m (164 feet). The tree has an often angular crown and long, somewhat erratic branches, and is usually deep rooted and resistant to wind and snow damage. Young trees are often tall and slender, and sparsely branched; the crown becomes broader as the tree ages.

During autumn, the leaves turn a bright yellow, then fall, sometimes within a short space of time (1–15 days). A combination of resistance to disease, insect-resistant wood and the ability to form aerial roots and sprouts makes ginkgos very long-lived, with some specimens claimed to be more than 2,500 years old: A 3,000 year-old ginkgo has been reported in Shandong province in China.

Some old Ginkgos produce aerial roots, known as chichi (Japanese; "nipples") or zhong-ru (Mandarin Chinese), which form on the undersides of large branches and grow downwards. Chichi growth is very slow, and may take hundreds of years to occur. The function, if any, of these thick aerial roots is unknown.

Stem
Ginkgo branches grow in length by growth of shoots with regularly spaced leaves, as seen on most trees. From the axils of these leaves, "spur shoots" (also known as short shoots) develop on second-year growth. Short shoots have very short internodes (so that several years' growth may only extend them by a centimeter or two) and their leaves are ordinarily unlobed.

They are short and knobby, and are arranged regularly on the branches except on first-year growth. Because of the short internodes, leaves appear to be clustered at the tips of short shoots, and reproductive structures are formed only on them (see picture to above left— seeds and leaves are visible on short shoots).

In Ginkgos, as in other plants that possess them, short shoots allow the formation of new leaves in the older parts of the crown. After a number of years, a short shoot may change into a long (ordinary) shoot, or vice versa.

Leaves
The leaves are unique among seed plants, being fan-shaped with veins radiating out into the leaf blade, sometimes bifurcating (splitting) but never anastomosing to form a network. Two veins enter the leaf blade at the base and fork repeatedly in two; this is known as dichotomous venation.

The leaves are usually 5-10 cm (2-4 inches), but sometimes up to 15 cm (6 inches) long. The old popular name "Maidenhair tree" is because the leaves resemble some of the pinnae of the Maidenhair fern Adiantum capillus-veneris.
Leaves of long shoots are usually notched or lobed, but only from the outer surface, between the veins.

They are borne both on the more rapidly-growing branch tips, where they are alternate and spaced out, and also on the short, stubby spur shoots, where they are clustered at the tips.

Reproduction
Ginkgos are dioecious, with separate sexes, some trees being female and others being male. Male plants produce small pollen cones with sporophylls each bearing two microsporangia spirally arranged around a central axis.

Female plants do not produce cones. Two ovules are formed at the end of a stalk, and after pollination, one or both develop into seeds. The seed is 1.5-2 cm long. Its fleshy outer layer (the sarcotesta) is light yellow-brown, soft, and fruit-like. It is attractive in appearance, but contains butanoic acid and smells like rancid butter (which contains the same chemical) when fallen.

Beneath the sarcotesta is the hard sclerotesta (what is normally known as the "shell" of the seed) and a papery endotesta, with the nucellus surrounding the female gametophyte at the center.
The fertilization of ginkgo seeds occurs via motile sperm, as in cycads, ferns, mosses and algae. The sperm are large (about 250-300 micrometres) and are similar to the sperm of cycads, which are slightly larger. Ginkgo sperm were first discovered by the Japanese botanist Sakugoro Hirase in 1896.

The sperm have a complex multi-layered structure, which is a continuous belt of basal bodies that form the base of several thousand flagella which actually have a cilia-like motion. The flagella/cilia apparatus pulls the body of the sperm forwards. The sperm have only a tiny distance to travel to the archegonia, of which there are usually two or three. Two sperm are produced, one of which successfully fertilizes the ovule. Although it is widely held that fertilization of ginkgo seeds occurs just before or after they fall in early autumn, embryos ordinarily occur in seeds just before and after they drop from the tree.

Etymology
The (older) Chinese name for this plant is ?? yínguo ('silver fruit'). The most usual names today are ?? bái guo ('white fruit') and ?? yínxìng ('silver apricot'). The latter name was borrowed in Japanese (as icho) and Korean (as eunhaeng), when the tree itself was introduced from China.

The scientific name Ginkgo appears to be due to a process akin to folk etymology. Chinese characters typically have multiple pronunciations in Japanese, and the characters ?? used for icho can also be mistakenly pronounced ginkyo. Engelbert Kaempfer, the first Westerner to see the species in 1690, wrote down this incorrect pronunciation in his Amoenitates Exoticae (1712); his y was misread as a g, and the misspelling stuck.

Prehistory
The Ginkgo is a living fossil, with fossils recognisably related to modern Ginkgo from the Permian, dating back 270 million years. They diversified and spread throughout Laurasia during the middle Jurassic and Cretaceous, but became much rarer thereafter. By the Paleocene, Ginkgo adiantoides was the only Ginkgo species left in the Northern Hemisphere (but see below) with a markedly different (but not well-documented) form persisting in the Southern Hemisphere, and at the end of the Pliocene Ginkgo fossils disappeared from the fossil record everywhere apart from a small area of central China where the modern species survived.

It is in fact doubtful whether the Northern Hemisphere fossil species of Ginkgo can be reliably distinguished; given the slow pace of evolution in the genus, there may have been only 2 in total; what is today called G. biloba (including G. adiantoides), and G. gardneri from the Paleocene of Scotland.
At least morphologically, G. gardneri and the Southern Hemisphere species are the only known post-Jurassic taxa that can be unequivocally recognised, the remainder may just as well have simply been ecotypes or subspecies.

The implications would be that G. biloba had occurred over an extremely wide range, had remarkable genetic flexibility and though evolving genetically never showed much speciation. The occurrence of G. gardneri, it seems a Caledonian mountain endemic, and the somewhat greater diversity on the Southern Hemisphere, suggests that old mountain ranges on the Northern Hemisphere could hold other, presently undiscovered, fossil Ginkgo species.

Since the distribution of Ginkgo was already relictual in late prehistoric times, the chances that ancient DNA from subfossils can shed any light on this problem seem remote. While it may seem improbable that a species may exist as a contiguous entity for many millions of years, many of the Ginkgo's life-history parameters fit.

These are extreme longevity, slow reproduction rate, (in Cenozoic and later times) a wide, apparently contiguous, but steadily contracting distribution coupled with, as far as can be demonstrated from the fossil record, extreme ecological conservatism (being restricted to light soils around rivers), and a low population density.
Ginkgophyta fossils have been classified in the following families and genera:

Ginkgoaceae

Arctobaiera

Baiera

Eretmophyllum

Ginkgo

Ginkgoites

Sphenobaiera

Windwardia

Trichopityaceae

Trichopitys

Ginkgo has been used for classifying plants with leaves that have more than four veins per segment, while Baiera for those with less than four veins per segment. Sphenobaiera has been used to classify plants with a broadly wedge-shaped leaf that lacks a distinct leaf stem. Trichopitys is distinguished by having multiple-forked leaves with cylindrical (not flattened) thread-like ultimate divisions; it is one of the earliest fossils ascribed to the Ginkgophyta.

Cycads are an ancient group of seed plants characterized by a large crown of compound leaves and a stout trunk. They are evergreen, gymnospermous, dioecious plants having large pinnately compound leaves.

They are frequently confused with and mistaken for palms or ferns, but are related to neither, belonging to the division Cycadophyta.
Cycads are found across much of the subtropical and

tropical parts of the world. They are found in South and Central America (where the greatest diversity occurs), Australia, the Pacific Islands, Japan, China, India, Madagascar, and southern and tropical Africa, where at least 65 species occur. Some are renowned for survival in harsh semi-desert climates, and can grow in sand or even on rock.

They are able to grow in full sun or shade, and some are salt tolerant. Though they are a minor component of the plant kingdom today, during the Jurassic period they were extremely common. Sago flour is generally made from true palms - not from the cycad popularly known as "Sago Palm" (Cycas revoluta).

They have very specialized pollinators and have been reported to fix nitrogen in association with a cyanobacterium living in the roots. This blue-green algae produces a neurotoxin called BMAA that is found in the seeds of cycads.

Origins
The cycad fossil record dates to the Early Permian, 280 mya. There is controversy over older cycad fossils that date to the late Carboniferous period, 300 -325 mya. One of the first colonizers of terrestrial habitats, this clade probably diversified extensively within its first few million years, although the extent to which it radiated is unknown as relatively few fossil specimens have been found. The regions to which cycads are restricted probably indicate their former distribution on the supercontinents Laurasia and Gondwana.

The family Stangeriaceae (named for Dr. William Stanger, 1812(?)-1854), consisting of only three extant species, is thought to be of Gondwanan origin as fossils have been found in Lower Cretaceous deposits in Argentina, dating to 70 – 135 mya.

Zamiaceae is more diverse, with a fossil record extending from the Middle Triassic to the Eocene (54 – 200 mya) in North and South America, Europe, Australia, and Antarctica, implying that the family was present before the break-up of Pangea. Cycadaceae is thought to be an early offshoot from other cycads, with fossils from Eocene deposits (38 – 54 mya) in Japan and China, indicating that this family originated in Laurasia.

Cycas is the only genus in the family and contains 99 species, the most of any cycad genus. Molecular data has recently shown that Cycas species in Australasia and the east coast of Africa are recent arrivals, suggesting that adaptive radiation may have occurred.

The current distribution of cycads may be due to radiations from a few ancestral types sequestered on Laurasia and Gondwana, or could be explained by genetic drift following the separation of already evolved genera. Both explanations account for the strict endemism across present continental lines.

Taxonomy
There are currently 305 described species, in 10-12 genera and 2-3 families of cycads (depending on taxonomic viewpoint). The classification below, proposed by Dennis Stevenson in 1990, is based upon a hierarchical structure based on cladistic analyses of morphological, anatomical, karyological, physiological and phytochemical data.

The number of species in the clade is low compared to the number of species in most other plant phyla. However, paleobotanical and molecular research indicates that diversity was higher in the history of the phylum. Fossil evidence shows that structural diversity in Mesozoic cycad pollen "considerably exceeds that seen in surviving genera today". The impacts of extinction on diversity are highlighted below.

The disparity in molecular sequences is very high between the three main lineages of cycads, implying that genetic diversity in the clade was once high, but this fact has led to major disagreements about the divisions within the Cycadales.

The number of described cycad species has doubled in the past 25 years, mostly due to improved sampling and further exploration. Experts assume there may still be about 100 undescribed species, based on the rate of discovery. These are likely to be in Asia and South America where areas of endemism are currently highest.

Diversity hotspots also occur in Australia, South Africa, Mexico, China and Vietnam, which together account for more than 70% of the world’s cycad species. The taxonomy of the Cycadophyta is, however, now stabilizing.

Cycad systematists reject the biological species concept, as clearly defined cycad species can interbreed and produce fertile offspring; this character is thus not disproportionately weighted when determining species barriers. The phenetic species concept, which states that a species is defined based on overall similarities with other individuals of the same species combined with a significant gap in variation with other species, is also rejected.

Most cycad taxonomists agree on a modified version of the evolutionary species concept, termed the ‘morphogeographic’ species concept, which recognises the combined effects of geographical isolation and morphological disparity. Thus the presence of large geographical gaps in cycad distribution has greatly affected the way cycads are classified.

Suborder Cycadineae

Family Cycadaceae

Subfamily Cycadoideae

Cycas. About 90 species in the Old World from Africa east to southern Japan, Australia and the western Pacific Ocean islands; type: C. circinalis L.; see also C. pruinosa and C. revoluta

Suborder Zamiineae

Family Stangeriaceae

Subfamily Stangerioideae

Stangeria. One species in southern Africa; type: S. eriopus (Kunze) Baillon

Subfamily Bowenioideae

Bowenia. Two species in Queensland, Australia; type: B. spectabilis Hook. ex Hook. f.

Family Zamiaceae

Subfamily Encephalartoideae

Tribe Diooeae

Dioon. Ten species in Mexico and Central America; type: D. edule Lindley

Tribe Encephalarteae

Subtribe Encephalartinae

Encephalartos. About 60 species in southeast Africa; type: E. friderici-guilielmi Lehmann, E. transvenosus (Modjadji cycad)

Subtribe Macrozamiinae

Macrozamia. About 30 species in Australia; type: M. riedlei (Fischer ex Gaudichaud) C.A. Gardner

Lepidozamia. Two species in eastern Australia; type: L. peroffskyana Regel

Subfamily Zamioideae

Tribe Ceratozamieae

Ceratozamia. 16 species in southern Mexico and Central America; type: C. mexicana Brongn.

Tribe Zamieae

Subtribe Microcycadinae

Microcycas. One species in Cuba; type: M. calocoma (Miquel) A. DC.

Subtribe Zamiinae

Chigua. Two species in Colombia; type: C. restrepoi E. Stevenson

Zamia. About 60 species in the New World from Georgia, USA south to Bolivia; type: Z. pumila L.; see also Z. furfuracea

History
Modern knowledge about Cycads began in the 9th century with the recording by two Arab naturalists that the genus Cycas was used as a source of flour in India. Later, in the 16th century, Antonio Pigafetta, Fernao Lopez de Castanheda and Francis Drake found Cycas plants in the Moluccas, where the seeds were eaten. The first report of cycads in the New World was by Giovanni Lerio in his 1576 trip to Brazil, where he observed a plant named ayrius by the indigenous people; this species is now classified in the genus Zamia.

Cycads belonging to the genus Encephalartos were first described by Johann Georg Christian Lehmann in 1834. The name is derived from the Greek articles "en", meaning "in", "cephale", meaning "head", and "artos", meaning "bread".

Throughout the 18th-19th centuries, discoveries of several species were reported by numerous naturalist researchers and discoverers traveling throughout the world. One of the most notable researchers of cycads was American botanist C.J.

Chamberlain whose work is noteworthy for the quantity of data and the novelty of his approach to studying cycads. His 15 years of travel throughout Africa, the Americas and Australia to observe cycads in their natural habitat resulted in his 1919 publication of The Living Cycads which remains a flowing and data-rich volume, and which remains current in its synthesis of taxonomy, morphology and reproductive biology of cycads, most of which was obtained from his original research.

His 1940's monograph on the Cycadales, though never published (most likely because of his death) was never used by botanists. There are no other complete works on the cycads.

Distribution
Overall species diversity peaks at 17°N and 28°S, with a minor peak at the equator. There is therefore not a latitudinal diversity gradient towards the equator but towards the tropics. However, the peak in the northern tropics is largely due to Cycas in Asia and Zamia in the New World, whereas the peak in the southern tropics is due to Cycas again, and also to the diverse genus Encephalartos in southern and central Africa and Macrozamia in Australia.

Thus the distribution pattern of cycad species with latitude appears to be an artifact of the geographical isolation of cycad genera, and is dependent on the remaining species in each genus that did not follow the extinction pattern of their ancestors. Cycas is the only genus that has a broad geographical range and can thus be used to infer that cycads tend to live in the upper and lower tropics.

This is probably because these areas have a drier climate with relatively cool winters; while cycads require some rainfall, they appear to be partly xerophytic. Potted specimens are found and thrive in global locations such as, Canada, Russia,Finland, chile.

Speciation
There are no documented cases of sympatric speciation in cycads and allopatry appears to be the most common form of speciation in the group. This is difficult to study as they are long-lived plants, and so natural experiments have been investigated. One example is Cycas seemannii, which occurs only in Fiji, New Caledonia, Tonga and Vanuatu.

Genetic diversity within populations was found to be significantly lower than between islands, suggesting that genetic drift is a likely mechanism for speciation, and is probably currently occurring between the isolated populations.

Allopatry has also been proposed as the mechanism of speciation in Dioon, which predominantly occurs in Mexico. The many rivers that have shaped the region, and repeated glaciation and consequent disjunction, are thought to have been important in reproductive isolation not only in Dioon but in many other plant and animal taxa. Parapatric speciation may also have occurred, especially as cycads are pollinated by insects rather than by wind.

As the range of the species grows, the individuals furthest apart are prevented from interbreeding as insects have relatively small ranges and will not pollinate between these plants. If sympatric speciation has occurred in cycads this would most likely be because of a host shift in pollinators, due to the very fact that cycads are uniformly dioecious.

Extinction
The probable former range of cycads can be inferred from their current global distribution. For example, the family Stangeriaceae only contains three extant species, in Africa. Diverse fossils of this family have been dated to 135 mya, indicating that diversity may have been much greater before the Jurassic and late Triassic mass extinction events.

However, the cycad fossil record is generally poor and little can be deduced about the effects of each mass extinction event on their diversity.
Instead, correlations can be made between the number of extant gymnosperms and angiosperms. It is likely that cycad diversity was affected more by the great angiosperm radiation in the mid-Cretaceous than by extinctions.

Very slow cambial growth was first used to define cycads, and because of this characteristic the group could not compete with the rapidly growing, relatively short-lived angiosperms, which now number over 250,000 species, compared to the 947 remaining gymnosperms . It is surprising that the cycads are still extant, having been faced with extreme competition and five major extinctions. The ability of cycads to survive in relatively dry environments where plant diversity is generally lower, and their great longevity may explain their long persistence.