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"Triassic:
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More Important Topics of Cylinder |
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| Triassic | |
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The Triassic is a geologic period that extends from about 251 ± 0.4 to 199.6 ± 0.6 Ma (million years ago). As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events. The extinction event that closed the Triassic period has recently been more accurately dated, but as with most |
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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
faunal stages from the youngest to oldest are: Paleogeography 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. 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. |
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| Mapa de la Tierra en el Triásico | |
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| Climate | |
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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. |
| Life | |
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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. |
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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 Lepidosauromorphaspecifically
the Sphenodontiaare 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
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 In
the oceans, 22% of marine families and possibly about half of marine
genera went missing, according to University of Chicago paleontologist
Jack Sepkoski. 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. |
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| Anthozoa | |
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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. |
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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) Subclass
Zoantharia (= Hexacorallia (6-way symmetry) |
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| Ammonites | |
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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 |
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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 Suture
patterns 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 Life 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 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 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 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 Anaptychi
are relatively rare as fossils. They are found representing ammonites
from the Devonian period through those of the Cretaceous period. 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 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 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. |
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| Cephalopods | |
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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. |
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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 Nervous
system and behaviour 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 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 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. 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 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 Class
Cephalopoda (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). |
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| Queensland lungfish | |
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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. |
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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. |
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| Ichthyosaurs | |
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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 |
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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 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 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. |
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| Ichthyosaurs: Evolutionary history | |
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The earliest ichthyosaurs, looking more like finned lizards than the familiar fish or dolphin forms, are known from the Early and Early-Middle (Olenekian and Anisian) Triassic strata of Canada, China, Japan, and Spitsbergen in Norway. These primitive forms included the genera Chaohusaurus, Grippia, and Utatsusaurus. These very early proto-ichthyosaurs, which are now classified as Ichthyopterygia |
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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). |
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| Gerrothorax | |
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Gerrothorax
("Wicker Chest") is an extinct genus of temnospondyl amphibian
from the Triassic period. It was about 1 m (3 ft 4 in) long. Gerrothorax was an extremely flattened creature that probably hid under sand or mud on river and lake bottoms, scanning for prey with its large, upward-facing eyes. Gerrothorax had an unusually shaped skull with angular protrusions on the sides. This looked vaguely similar to the skull of the earlier Diplocaulus, but less developed. Fossils have shown that Gerrothorax was pedomorphic, retaining its larva gills as an adult. This is also seen in some modern-day salamanders, such as the mudpuppy, the axolotl, and |
| the olm. Gerrothorax had three pairs of external gills allowing it to breathe under water. | |
| Cymbospondylus | |
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Cymbospondylus was a primitive early Ichthyosaur that lived in the middle of the Triassic period (220 million years ago). Despite its primitive nature, it was also one of the largest Ichthyosaurs, and fossils range from 18 ft (6 meters) up to 30 ft long (10 meters). It was one of the |
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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 |
|
| Endennasaurus | |
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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. |
|
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. |
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| Nothosaurus Mirabilis | |
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Nothosaurs (order Nothosauria) were Triassic marine sauropterygian reptiles that may have lived like seals of today, catching food in water but coming ashore on rocks and beaches. They averaged about three meters in length, with a long body and tail. The feet had become paddle-like, and were most certainly webbed in life, to help power the animal when swimming. The neck was quite long, and the head was elongate and flattened, and relatively small in |
| relation
to the body. The margins of the long jaws were equipped with numerous
sharp outward-pointing teeth, indicating a diet of fish. The nothosaurs consist of two suborders--the Pachypleurosaurs, tiny, primitive forms, and the true Nothosaurs, which evolved from pachypleurosaurs. Nothosaur-like reptiles were in turn ancestral to the more completely marine plesiosaurs, which replaced them at the end of the Triassic period. |
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| Shonisaurus popularis | |
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Shonisaurus was the largest genus of Icthyosaur that has yet been found; fossils of Shonisaurus were first found in a large deposit in Nevada, 1920. Thirty years later, they were excavated and it was found that the deposit contained the remains of 37 very large icthyosaurs which were named |
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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. |
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| Mastodonsaurus | |
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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: Henodus | |
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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. |
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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 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. |
|
| Placodonto-Proganochelys | |
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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. |
| a
club, its head could not be retracted under the shell, and its neck
was protected by small spines. While it lacked teeth, it did have "small
denticles that formed a pavement over some of the bones of the palate". Because of its generally advanced characteristics however, most biologists feel that Proganochelys, while the oldest known turtle found thus far, cannot be the oldest turtle species and thus it is quite possible even older fossils may one day be found. |
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| Tanystropheus | |
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Tanystropheus, or Long Necked One, was a 6 metre (20 ft) long reptile that dated from the Middle Triassic period. The main feature that stands out about this animal is its extremely elongated neck, which measured 3 meters (10 ft) long, longer than its body and tail combined. Despite this length, it had only ten neck vertebrae, but they were |
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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 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. |
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| Triadobatrachus | |
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Triadobatrachus
is an extinct genus of frog, including only one known species, Triadobatrachus
massinoti. It is about 10 cm (4 in) long and the oldest frog known to
science. Triadobatrachus still retained many primitive characteristics, such as more vertebrae (24) than modern frogs (5-9), including six tail vertebrae in adults. It probably swam with kicking movements of its hind legs, |
| which
would further develop into the powerful jumping legs seen in modern
frogs. Triadobatrachus's skull resembled that of modern frogs, consisting
of a latticework of thin bones separated by large openings. As evidenced
by its large ear openings, Triadobatrachus possessed good hearing. This creature, or a cousin, evolved eventually into modern frogs, the earliest example of which is Sanyanlichan, millions of years later in the late Jurassic. |
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| Triadobatrachus | |
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| Protoavis | |
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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 Chatterjees
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) |
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| Eudimorphodon | |
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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. |
| Eudimorphodon ranzii | |
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Eudimorphodon ranzii is a small pterosaur, one of the first of this breed. |
| Kuehneosaurus | |
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Kuehneosaurus was a late Triassic reptile -- of the order Squamata, not a dinosaur -- which was about two feet long, and had ribs which jutted out from its body as much as one foot (30 cm), which were connected by a membrane which allowed it to fly like the present dayflying dragon. |
| Peteinosaurus | |
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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. 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. |
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| Sharovipteryx | |
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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. |
|
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. |
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| Longisquama | |
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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. |
|
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's
'long scales' 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. Relationships
of Longisquama 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 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. |
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| Coelophysis | |
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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. |
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Description 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 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. History
of discovery 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 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 |
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| Cynognathus | |
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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. |
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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 Age 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. |
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| Eoraptor | |
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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 |
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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. |
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| Eoraptor | |
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| Herrerasaurus | |
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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. |
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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 210350 kilograms (463772 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 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 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 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 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 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. |
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| Liliensternus | |
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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 |
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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. |
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| Lystrosaurus | |
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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. |
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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 PermianTriassic 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. In
dinosaurs and mammals, which have erect limbs, the sacral vertebrae
are fused to each other and to the pelvis. |
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| Placerias | |
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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 |
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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. |
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| Plateossauro | |
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Plateosaurus (meaning 'flat lizard') is a genus of plateosaurid prosauropod dinosaur that lived during the Norian and Rhaetian stages of the Late Triassic period, around 216 to 199 million years ago in what is now Europe. There are two currently recognized species, P. engelhardti and P. longiceps, although others have been assigned in |
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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. 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. |
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| Procompsognathus | |
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Procompsognathus (pronounced /?pro?k?mp's?gn???s/) is a genus of small theropod dinosaur that lived during the Late Triassic Period, about 222 to 219 million years ago. Procompsognathus was named by Eberhard Fraas in 1913. He named the type species, P. triassicus, on the basis of a |
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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. |
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| Postosuchus | |
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Postosuchus was a basal archosaur which lived in what is now North America during the middle through to the late Triassic period (228-202 million years ago). It was a rauisuchian, a cousin of crocodiles and came from the same ancestry as dinosaurs. Its name means "crocodile from Post", named after the Post Quarry in Texas, where many |
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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 |
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| Staurikosaurus pricei | |
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Staurikosaurus
is a genus of early dinosaur. 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", |
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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 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. |
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| Thecodontosaurus | |
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Thecodontosaurus ("socket-tooth lizard") was a herbivorous dinosaur which lived during the late Triassic period Period (Norian and/or Rhaetian age). Its remains are known mostly from Triassic "fissure fillings" in South England and Wales. On average, it was 4 feet (1.20 metres) long, 1 foot tall (0.3 metres), and weighed 25 pounds (11 |
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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. |
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| Venaticosuchus | |
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Venaticosuchus
was a Late Triassic quadrupedal crurotarsan archosaur. Originally it
was thought to be the ancestor to the carnosaur dinosaurs (which then
included Tyrannosaurus); however, now it is known to be more closely
related to crocodilians than dinosaurs. It was a carnivore. |
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Species Closely
related species |
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| Cinodonts | |
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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 |
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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 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. 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. |
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| Eozostrodon | |
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Eozostrodon
was one of the earliest mammals. It lived during the late Triassic and
the early Jurassic,about 210 million years ago. Eozostrodon was one
of the largest early mammals, measuring more than a meter long. As with most early mammals, the classification of Eozostrodon is uncertain. |
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the modern platypus, this mammal laid eggs, but these eggs' hatchlings
were then fed with milk from their mother's mammary glands. Its teeth
were typically mammalian, being differentiated into molars and premolars
with triangular cusps. With its long snout, four legs, five toes, clawed paws and a long hairy tail, Eozostrodon resembled a shrew. |
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Hypuronector limnaios |
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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. |
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Lifestyle
Controversy 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. |
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| Prolacertiformes: Langobardisaurus | |
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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. |
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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 |
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| Sphenodontia: Diphydontosaurus | |
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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 |
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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 |
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| Macrocnemus | |
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Macrocnemus is a small to medium sized prolacertiform reptile with a moderately elongate neck and a great length disparity between anterior and posterior limbs. |
| Palm | |
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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 |
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inhabit
nearly every type of habitat within their range, from rainforests
to deserts. 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 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
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 A
few general traits of each subfamily are listed. 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 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 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 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 . 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 . |
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| Ginkgo biloba | |
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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. |
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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. 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 During
autumn, the leaves turn a bright yellow, then fall, sometimes within
a short space of time (115 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 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 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. 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 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
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
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 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. 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. 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. |
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| Cycads | |
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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. |
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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 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 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 worlds
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 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 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 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 However,
the cycad fossil record is generally poor and little can be deduced
about the effects of each mass extinction event on their diversity. 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. |
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