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The Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon and ended about 490 million years BP with the beginning of the Ordovician period.

It is the first period of the Paleozoic era of the Phanerozoic eon. The Cambrian is the earliest period in whose rocks are found numerous large, distinctly-fossilizable multicellular organisms that are more complex than sponges or

medusoids. During this time, roughly fifty separate major groups of organisms or "phyla", including almost all the basic body plans of modern animals, emerged suddenly, in most cases without evident precursors. This radiation of animal phyla is referred to as the Cambrian explosion.

By nearly any measure, the most successful animals on the planet are the arthropods. They have conquered land, sea and air, and make up over three-fourths of all currently known living and fossil organisms, or over one million species in all.

Since many arthropod species remain undocumented or undiscovered, especially in tropical rain forests, the true number of living arthropod species is probably in the tens of millions. One recent conservative estimate puts the number of arthropod species in tropical forests at 6 to 9 million species (Thomas, 1990).

Arthropods range in distribution from the deep sea to mountain peaks, in size from the king crab with its 12-foot armspan to microscopic insects and crustaceans, and in taste from chocolate covered ants to crawfish jambalaya and lobster Newburg. Despite this unbelievable diversity, the basic body plan of arthropods is fairly constant. Arthropods have a stiff cuticle made largely of chitin and proteins, forming an exoskeleton that may or may not be further stiffened with calcium carbonate.

They have segmented bodies and show various patterns of segment fusion (tagmosis) to form integrated units (heads, abdomens, and so on). The phylum takes its name from its distinctive jointed appendages, which may be modified in a number of ways to form antennae, mouthparts, and reproductive organs.

Soft-bodied relatives of the arthropods, as well as trace fossils that were made by some arthropod-like organisms, appear in the Vendian.

However, arthropods underwent rapid evolution in the Cambrian Period; Cambrian localities like the world-famous Burgess Shale in British Columbia are rich in unusual athropods, many of which are not obviously related to the traditional classes of living arthropods. Trilobites were a dominant marine group in the early Paleozoic. The earliest arachnids turn up in the Silurian, and move onto land shortly before the insects appeared in the middle Devonian Period, about 385 million years ago; over the next hundred or so million years both groups radiated into several diverse lineages.

The annelid fossil record is sparse, but a few definite forms are known as early as the Cambrian, and there are some signs they were around in the later Precambrian.

A few small groups have been treated as separate phyla: the Pogonophora and Vestimentifera, now included in the family Siboglinidae, and the Echiura.

The annelids, collectively called Annelida (from Latin annellus "little ring), are a large phylum of animals, comprising the segmented worms, with about 15 000 modern species including the well-known earthworms and leeches.

They are found in most wet environments, and include many terrestrial, freshwater, and especially marine species, as well as some which are parasitic or mutualistic.

They range in length from under a millimetre to over 3 metres.

Anatomy

Annelids are triploblastic protostomes.

The body cavity is a coelom, a fluid-filled cavity in which the gut and other organs are suspended. Oligochaetes and polychaetes typically have spacious coeloms; in leeches, the coelom is largely filled in with tissue and reduced to a system of narrow canals; archiannelids may lack the coelom entirely.

The coleom is divided into a sequence of compartments by walls called septa. In the most general forms each compartment corresponds to a single segment of the body, which also includes a portion of the nervous and (closed) circulatory systems, allowing it to function relatively independently. Each segment is marked externally by one or more rings, called annuli. Each segment also has an outer layer of circular muscle underneath a thin cuticle and epidermis, and a

system of longitudinal muscles. In earthworms, the longitudinal muscles are strengthened by collagenous lamellae; the leeches have a double layer of muscles between the outer circulars and inner longitudinals. In most forms they also carry a varying number of bristles, called setae, and among the polychaetes a pair of appendages, called parapodia.

Anterior to the true segments lies the prostomium and peristomium, which carries the mouth, and posterior to them lies the pygidium, where the anus is located. The digestive tract is usually specialized. Different species of annelids have a wide variety of diets, including active and passive hunters, scavengers, filter feeders, direct deposit feeders which simply ingest the sediments, and blood-suckers.

The vascular system and the nervous system are separate from the digestive tract. The vascular system includes a dorsal vessel conveying the blood toward the front of the worm, and a ventral longitudinal vessel which conveys the blood in the opposite direction. The two systems are connected by a vascular sinus and by lateral vessels of various kinds, including in the true earthworms, capillaries on the body wall.

The nervous system has a solid, ventral nerve cord from which lateral nerves arise in each segment. Every segment has an autonomy; however, they unite to perform as a single body for functions such as locomotion. Growth in many groups occurs by replication of individual segmental units, in others the number of segments is fixed in early development.

Reproduction

Depending upon species, annelids can reproduce both sexually and asexually.

Asexual reproduction

Asexual reproduction by fission is a method used by some annelids and allows them to reproduce quickly. The posterior part of the body breaks off and forms a new individual. The position of the break is usually determined by an epidermal growth. Lumbriculus and Aulophorus, for example, are known to reproduce by the body breaking into such fragments. Many other taxa (such as most earthworms) cannot

reproduce this way, though they can regrow the posteriormost segments in most instances.

Sexual reproduction

Sexual reproduction allows a species to better adapt to its environment. Some annelid species are hermaphroditic, while others have distinct genders.

Hermaphrodite annelids like earthworms mate periodically throughout the year in favored environmental conditions. Earthworms mate by copulation. Two worms which are attracted by each other's secretions lay their bodies together with their heads pointing opposite directions. The fluid is transferred from the male pore to the other worm. Different methods of sperm tranference have been observed in different genera, and may involve internal spermathecae (sperm storing chambers) or spermatophores that are attached to the outside of the other worm's body.

Most polychaete worms have separate males and females and external fertilization. The earliest larval stage, which is lost in some groups, is a ciliated trocophore, similar to those found in other phyla. The animal then begins to develop its segments, one after another, until it reaches its adult size. The oligochaetes and leeches tend to be hermaphroditic and lack free-living larvae of this sort. While annelids have some regenerative abilities, sometimes to the point where each half of an adult divided cross-wise will survive, this is not universal, and especially does not occur among the earthworms as folklore would suggest.

Relationships

The arthropods and their kin have long been considered the closest relatives of the annelids, on account of their common segmented structure, but a number of differences between the two groups suggest this may be convergent evolution. The other major phylum which is of definite relation to the annelids are the molluscs, which share with them the presence of trochophore larvae. These groups are united as the Trochozoa, and when the arthropods are included, they and the annelids are treated in a subgroup called the Articulata.

Classes and subclasses of Annelida

Clitellata

Oligochaeta - The class Oligochaeta includes the megadriles (earthworms), which are both aquatic and terrestrial, and the microdrile families such as tubificids, which include many marine members as well.

Leeches (Hirudinea) - These include both bloodsucking external parasites and predators of small invertebrates.

Polychaeta - This is the largest group of the Annelids and majority are marine. All segments are identical each consisting a parapodia. The parapodia are used for swimming, burrowing and feeding current.

Most trilobites lived in fairly shallow water and were benthic; they walked on the bottom, and probably fed on detritus.

A few, like the agnostids, may have been pelagic, floating in the water column. Cambrian and Ordovician trilobites generally lived in shallow water.

After the Ordovician, when many trilobite groups declined or went extinct, the survivors tended to be restricted to deeper water.

Food particles were stirred up by the legs and passed forward to the mouth.

Since the mouth had no large mandibles, we infer that trilobites were not usually predatory and were restricted to soft food. Some trilobites had long spines on the first leg segment, the gnathobase; these may have been able to tear up larger pieces of food, and probably scavenged for a living.

Fossil burrows and tracks have been found that match trilobite bodies very precisely; these show that trilobites could burrow into sediment to feed or to avoid predators.

Many trilobites living after the Cambrian developed the ability to roll up, also probably as a defense against predators.

This specimen of Pliomera fischeri, from the Ordovician of the St. Petersburg region of Russia, is doing just that.

Notice the notches in the pygidium just where it contacts the glabella.

In the living trilobite, these would have allowed water to enter and flow over the gills, so that the trilobite could breathe while enrolled.

The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. The Ordovician follows the Cambrian period and is followed by the Silurian period.

The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a situation where followers of Adam Sedgwick and Roderick Murchison were placing the same rock beds in the Cambrian and Silurian periods respectively. Charles Lapworth simply took all the conflicting strata and placed them in the new Ordovician period.

Brachiopod

The earliest known brachiopods are found in the late Neoproterozoic. The first brachiopods were inarticulate (hingeless), but articulate (hinged) brachiopods appeared soon thereafter, in the Lower Cambrian. Brachiopods are extremely common fossils throughout the Paleozoic.

The major shift came with the Permian extinction. Before this extinction event, brachiopods were more numerous and diverse than bivalve mollusks.

Afterwards, in the Mesozoic, their diversity and numbers were drastically reduced, and they were largely replaced by bivalve mollusks. Mollusks continue to dominate today, and the remaining orders of brachiopods survive in fringe environments of more extreme cold and depth. Brachiopods - both articulate and inarticulate - are still present in modern oceans. The most abundant are the terebratulids (class Terebratulida).

The perceived resemblance of terebratulid shells to ancient oil lamps gave the brachiopods their common name "lamp shell". The phylum most closely related to Brachiopoda is probably the small phylum Phoronida (known as "horseshoe worms").

The inarticulate brachiopod genus Lingula has the distinction of being the oldest, relatively evolutionarily unchanged animal known. The oldest Lingula occur in the very early Cambrian, roughly 550 million years ago. The origin of brachiopods is unknown.

A possible ancestor is a sort of ancient "armored slug" known as Halkeria that was recently been found to have had small brachiopod-like shields on its head and tail.

During the Ordovician and Silurian periods brachiopods became adapted to life in most marine environments and became particularly numerous in shallow water habitats, in some cases forming whole banks in much the same way as bivalves (such as mussels) do today. In some places, large sections of limestone strata and reef deposits are composed largely of their shells.

Throughout their long geological history the brachiopods have gone through several major proliferations and diversifications, and have also suffered from major extinctions as well.

It has been suggested that the slow decline of the brachiopods over the last 100 million years or so is a direct result or the rise in diversity of filter feeding bivalves, which have ousted the brachiopods from their former habitats. However, it should be noted that the greatest successes for the bivalves have been in habitats which have never been adopted by the brachiopods, such as burrowing and free swimming.

The abundance, diversity, and rapid evolution of brachiopods during the Paleozoic make them useful as index fossils when correlating strata across large areas.

Jellyfish or Medusa (also known as a hydromedusa) is a form of cnidarian in which the body is shortened on its principal axis and broadened, sometimes greatly, in contrast with the hydroid or polyp.

Medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below.The upper or aboral surface is called the exumbrella and the lower surface is called the subumbrella; the mouth is located on the lower surface, which may be partially closed

The margin of the disk bears sensory organs and tentacles. In the class Hydrozoa medusae are the sexual individuals of many species, alternating in the life cycle with asexual polyps, but in Scyphozoa (or jellyfishes proper) and Cubozoa the medusa alone is well developed. Except the freshwater jellyfish, these are the only classes in which medusae appear.

collectively called Annelida (from Latin annellus "little ring"), are a large phylum of animals, comprising the segmented worms, with about 15,000 modern species including the well-known earthworms and leeches. They are found in most wet environments, and include many terrestrial, freshwater, and especially marine species (such

as the polychaetes), as well as some which are parasitic or mutualistic. They range in length from under a millimeter to over 3 meters (the seep tube worm Lamellibrachia luymesi).

Anatomy

Annelids are triploblastic protostomes with a coelom, closed circulatory system and true segmentation. Oligochaetes and polychaetes typically have spacious coeloms; in leeches, the coelom is largely filled in with tissue and reduced to a system of narrow canals; archiannelids may lack the coelom entirely. The coleom is divided into a sequence of compartments by walls called septa. In the most general forms each compartment corresponds to a single segment of the body, which also includes a portion of the nervous and (closed) circulatory systems, allowing it to function relatively independently.

Each segment is marked externally by one or more rings, called annuli. Each segment also has an outer layer of circular muscle underneath a thin cuticle and epidermis, and a system of longitudinal muscles. In earthworms, the longitudinal muscles are strengthened by collagenous lamellae; the leeches have a double layer of muscles between the outer circulars and inner longitudinals. In most forms they also carry a varying number of bristles, called setae, and among the polychaetes a pair of appendages, called parapodia.

Anterior to the true segments lies the prostomium and peristomium, which carries the mouth, and posterior to them lies the pygidium, where the anus is located. The digestive tract is quite variable but is usually specialized. For example, in some groups (notably most earthworms) it has a typhlosole (to increase surface area) along much of its length. Different species of annelids have a wide variety of diets, including active and passive hunters, scavengers, filter feeders, direct deposit feeders which simply ingest the sediments, and blood-suckers.

The vascular system and the nervous system are separate from the digestive tract. The vascular system includes a dorsal vessel conveying the blood toward the front of the worm, and a ventral longitudinal vessel which conveys the blood in the opposite direction. The two systems are connected by a vascular sinus and by lateral vessels of various kinds, including in the true earthworms, capillaries on the body wall.

The nervous system has a solid, ventral nerve cord from which lateral nerves arise in each segment. Every segment has an autonomy; however, they unite to perform as a single body for functions such as locomotion. Growth in many groups occurs by replication of individual segmental units, in others the number of segments is fixed in early development.

Reproduction

Depending upon the species, annelids can reproduce both sexually and asexually.

Asexual reproduction

Asexual reproduction by fission is a method used by some annelids and allows them to reproduce quickly. The posterior part of the body breaks off and forms a new individual. The position of the break is usually determined by an epidermal growth. Lumbriculus and Aulophorus, for example, are known to reproduce by the body breaking into such fragments. Many other taxa (such as most earthworms) cannot reproduce this way, though they have varying abilities to regrow amputated segments.

Sexual reproduction

Sexual reproduction allows a species to better adapt to its environment. Some annelida species are hermaphroditic, while others have distinct sexes.

Most polychaete worms have separate males and females and external fertilization. The earliest larval stage, which is lost in some groups, is a ciliated trochophore, similar to those found in other phyla. The animal then begins to develop its segments, one after another, until it reaches its adult size.

Earthworms and other oligochaetes, as well as the leeches, are hermaphroditic and mate periodically throughout the year in favored environmental conditions. They mate by copulation. Two worms which are attracted by each other's secretions lay their bodies together with their heads pointing opposite directions. The fluid is transferred from the male pore to the other worm.

Different methods of sperm transference have been observed in different genera, and may involve internal spermathecae (sperm storing chambers) or spermatophores that are attached to the outside of the other worm's body. The clitellata lack the free-living ciliated trochophore larvae present in the polychaetes, the embryonic worms developing in a fluid-filled "cocoon" secreted by the clitellum.

Fossil record

The annelid fossil record is sparse, but a few definite forms are known as early as the Cambrian, and there are some signs they were around in the later Precambrian, but the earliest unequivocal annelid fossils are only known from the Cambrian. Because the creatures have soft bodies, fossilization is an especially rare event.

The best-preserved and oldest annelid fossils come from Cambrian Lagerstätten such as the Burgess Shale of Canada, and the Middle Cambrian strata of the House Range in Utah. The Annelids are also diversely represented in the Pennsylvanian-age Mazon Creek fauna of Illinois. A few small groups have been treated as separate phyla: the Pogonophora and Vestimentifera, now included in the family Siboglinidae, and the Echiura.

Their skeletons tend to have arm-like extensions that resemble spikes, which are used both to increase surface area for buoyancy and to capture prey. Most radiolarians are planktonic, and get around by coasting along ocean currents.

Most are somewhat spherical, but there exist a wide variety of shapes, including cone-like and tetrahedral forms (see the image above). Besides their diversity of form, radiolarians also exhibit a wide variety of behaviors.

They can reproduce sexually or asexually; they may be filter feders or predators; and may even participate in symbiotic relations with unicellular algae.

Though their silica skeletons have allowed us to find numerous fossils, scientists still have not been able to successfully develop a complete classification scheme for them. The evolution of the Radiolaria can be easily traced on the broad scale, with major transitions in the global fauna, but a concise taxomony reflecting the evolutionary relationships of major groups is still elusive.

Until comparatively recently, radiolarians were primarily studied by micropaleontologists, and only at the end of the 20th century have scientists from other fields begun to study these fascinating protists as well.

The largest, such as Pterygotus, reached 2 meters or more in length, but most species were less than 20 cm. They were formidable predators among the coral reefs that thrived in the warm, shallow seas of the Silurian period,

around 410 million years ago. Eurypterids were the most fearsome swimming predators of the Palaeozoic. Although called "sea scorpions", only the earliest ones were marine. While the earliest eurypterids may have lived in the sea, it is thought that most swam in small pools of fresh water. The move from the sea to fresh water probably occurred by the Pennsylvanian period. Eurypterus is perhaps the most well-known genus of eurypterid, of which 200 fossil species are known.

The genus Eurypterus was created in 1825 by James E. DeKay, a zoologist. He recognized the arthropod nature of the first ever described eurypterid specimen found by Dr. S. L. Mitchell. In 1984, Eurypterus remipes was named the State Fossil of New York.Body Structure

Though fossils are a bit unclear, the typical eurypterid had a large, flat, semicircular carapace, followed by a jointed section, and finally a tapering, flexible tail, with a long spine at the end. Under the head of the eurypterids were twelve body segments known as tergites. The tail, which is spiked and may have been poisonous, is known as the telson.

Some eurypterids have paddles, which were used to propel themselves through water. Some argue that the paddles were also used for digging. Underneath, the creature had 8 pairs of jointed legs for walking, two small scorpion-like claws at the front (pedipalps). Other features, common to ancient and modern arthropods of this type, include ocelli, compound eyes, and chelicerae

Although many eurypterids had legs too tiny to do more than allow them to crawl over the sea bottom, a number of forms had large stout legs, and were clearly capable of terrestrial locomotion (like land crabs today).

While functional studies suggest that eurypterids used out-of-phase walking techniques, their trackways indicate that they used in-phase, hexapodous (six-legged) and octopodous (eight-legged) gaits. Some species may have been amphibious, emerging onto land for at least part of their life cycle. They may have been capable of breathing both in water and in air.

Eurypterid Fossils

Eurypterid fossils have been found on nearly every continent. Locations currently producing excellent fossils include western New York State and southern Ontario, Canada in Silurian rock. Although relatively rare, the fossils are famous for excellent preservation. People seeking eurypterid fossils commonly search at Ridgemount Quarry, in Fort Erie, Ontario Canada.

Eurypterids are related to the modern horseshoe crab and sea scorpion. About two dozen families of eurypterids are known. They went extinct in the Permian-Triassic extinction event.

During the later Ordovician, the continents were in very different positions than you find them today. The continents have only assumed their present locations on the globe in the last few ten's of million years. The process

which moves the continents around the surface of the Earth is called "Plate Tectonics," and is a refinement of the earlier ideas of continental drift. North America roughly straddled the equator. It was rotated about 45 degrees clockwise from its presentorientation.

Much, if not all, was covered by ocean. The map shows North America separated from other continents; an alternative theory places it very near the west coast of South America.

(The positions of the plates during the Ordovician has been determined by the remnant paleomagnetism in the rocks deposited at the time. Paleomagnetism can only determine the paleolatitude, and paleolongitude must be determined from other, indirect evidence.)

Southern Europe, Africa, South America, Antarctica and Australia were bonded together into a supercontinent of Gondwana, and was in position over the South Pole. Western and Central Europe were separate from the rest of Eurasia, and were rotated about 90 degrees counterclockwise from their present orientation, and was in the southern tropics.

Ordovican communities typically displayed a higher ecological complexity than Cambrian communities due to

the greater diversity of organisms.

However, as in the Cambrian, life in the Ordovician continued to be restricted to the seas. Species Affected: The Ordovician extinction occurred at the end of the Ordovician period, about 440-450 million years ago.

This extinction, cited as the second most devastating extinction to marine communities in earth history, caused the disappearance of one third of all brachiopod and bryozoan families, as well as numerous groups of conodonts, trilobites, and graptolites. Much of the reef- building fauna was also decimated. In total, more than one hundred families of marine invertebrates perished in this extinction.

The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 439 million years ago (mega years ago, mya), to the beginning of the Devonian period, about 408.5 mya. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by 5-10 million years. The base of the

Silurian is set at a major extinction event where 60% of marine species were wiped out. See Ordovician-Silurian extinction events.

Superfamily Eurypteracea

Ordovician to Permian

This superfamily includes the "typical" (unmodified) Eurypterids, in which the last prosomal appendages developed as swimming legs that carry paddles formed by expansion of the two penultimate joints. They can be considered the ancestral lineage from which the other groups evolved.

Eurypterus remipes Dekay

length about 20 cm

Ludlow of Western Euramerica (New York)

illustration from Moore, Lalicker and Fischer, Invertebrate Fossils family Eurypteridae

time range: Llandeilo to Frasnian

known distribution: Euramerica , Asia habitat: Marginal marine and fresh water representative taxa:

Baltoeurypterus tetragonophthalmus (= Eurypterus fischeri), Eurypterus lacustris, Eurypterus remipes

notes: typical Eurypterids. The body is fairly elongate; the largest species attaining a length of about a meter but most much smaller (average about 20 cm). The prosoma is squared off, the compound eyes kidney-shaped and placed towards the middle of the head, so they look upwards. Between them are two ocelli or simple eyes.

Lepidoderma mansfieldi

Late Carboniferous - length about 12 cm

illustration from Treatise on Invertebrate Paleontology

family Adelophthalmidae

time range: Llandovery to Artinskian

known distribution: Euramerica , Asia

habitat: Marginal marine, brackish and fresh water; amphibious representative taxa: Lepidoderma mansfieldi, Lepidoderma mazonense (both late Carboniferous), Adelophthalmus sellardsi (early Permian), notes: Mostly small forms, similar to Eurypterus but spiny, the outer surfaces with pointed scales and striae; the elongate body equipped with spurs.

The postabdomen is narrow and the telson very long

(styliform). The compound eyes are located somewhat towards the center of the head. The walking legs are mostly devoid of spines. In Adelophthalmus the genital appendage of the male is long, of the type "B" form short, with spatulate lateral lobes. These creatures seem to have been semi-aquatic swamp dwellers. They were among the last of the Eurypterids.

The ancient (cohort Belemnoidea) and modern Coleoidea (cohort Neocoleoidea) diverged from the external shelled Nautiloidea around 425 million years ago. Unlike most modern cephalopods, 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.

The Baragwanathia plant formed scrubby cover over tidal flats in the latter part of the Silurian Period, a time of earth history almost inconceivably long ago (400 million years).

At the time Central Victoria was part of a submarine trench bounding the east of the continent.

According to the plate tectonics theory this was itself part of an enormous land mass called Pangaea, comprised of the continental masses prior to separation into their present day entities.

The rocks at the Yea site are sandstone and shale, alternating in very clearly defined beds that have been deformed and significantly tilted from their original horizontal aspect.

The Baragwanathian fossils are present only in some of the beds, generally as pieces of stem 10 to 50cm in length with attached long narrow leaves.

Deep burial for millions of years has resulted in drastic alteration of the stem, which is now evident as impressions, often made clearly visible by iron staining on the more weathered surfaces.

As mentioned above, the rocks in the Yea area were deposited under an ancient sea now long departed. This means of course that the Baragwanathia plant must have either grown on the shore line or has been washed out to sea by stream or other action, to ultimately attain the fossil condition.

Large vascular land plants (plants with woody tissue) like Baragwanathia have not been found elsewhere in rocks of Silurian age.

The vegetation at this time principally existed in the sea as algae like the kelp

and seaweed common in the oceans of today.

Land plants are known from overseas beds of similar age to those of this Yea site, but they were small erect naked stems a few centimetres in height (often with a fertile extremity), quite unlike the large vegetative body of Baragwanathia.

Baragwanathia is not the only fossil plant found at Limestone Road, about a dozen others have been recognised, but less than half of these have so far been described and named.

One or two are possibly relatives of Baragwanathia but most are not vascular land plants.

There are also animal fossils at the site. A mollusc fossil, called Orthoceras is even more common than Baragwanathia, and divalve shells are occasionally found. At least one fish, affiliation not yet determined, has also been collected.

More important from the point of view of establishing the age of the beds are members of an extinct Order, the Graptoelites. These are important because the species present are used as the criterion for the confirmation of the Silurian age. Baragwanathia is found at several other parts of Central Victoria but these localities are all in younger ( Devonian ) rocks.

Registration in the National Estate (after application by interested parties) is approved only after close scrutiny into the merit of the application. This Yea locality is one of only two fossil localities so far accorded this status in Victoria.

The other fossil locality is the Koonwarra Fish Bed locality in South Gippsland, of Cretaceous age. It contains a renowned fish, insect, crustacean, bird feather, and plan fossil assemblage.-W Baragwanath was Director of the Geological Survey of Victoria from 1920 to 1943.

Sea stars do not have movable skeletons, but instead possess a hydraulic water vascular system. The water

vascular system has many projections called tube feet, on the ventral face of the sea star's arms, which function in locomotion and feeding.

Digestion

Sea star digestion is carried out in two separate stomachs, the cardiac stomach and the pyloric stomach. The cardiac stomach, which is a sacklike stomach located at the center of the body may be everted - pushed out of the organism's

body and used to engulf and digest food. Some species take advantage of the great endurance of their water vascular systems to open the shells of molluscs (clams, mussels and the like), and inject their stomachs into the shells. Once the stomach is inserted inside the shell it digests the mollusk in place. Because of this ability to digest food outside of its body, the sea star is able to hunt prey that are much larger than its mouth would otherwise allow (including mollusks, arthropods, and even small fish). Partially-digested food is passed to the inside of the sea star where digestion continues in the pyloric stomach. Due to all of this digestive demand, the sea star's arms are filled with digestive glands called pyloric caeca or hepatic caeca.

External Anatomy

The tube feet can be clearly seen on this sea starSea stars are composed of a central disc with five arms exhibiting pentaradial symmetry. The mouth is located underneath (oral or ventral) the sea star, and the spiney surface covering the species is called the aboral or dorsal surface. On the aboral surface there is a structure called the madreporite which acts as a water filter and supplies their water vascular system with water to move (Gilbertson, 1999). Sea stars have a simple eye at the end of each arm. The eye is able to "see" only differences of light and dark; useful in detecting movement.

A sea star on the sea floor.On the surface of the sea star surrounding the spines are small white objects known as pedicellariae. There consists thousands and thousands of these pedicellariae on the external body. Inside the sea star underneath all the hepatic caeca consist the gonads which are involved in reproduction. The radial canal which is across each arm of the sea star has what are called ampullae which surround the radial canal.

The ampullae are teeth-like structures.

Sea stars are developmentally (embryologically) known as deuterostomes. Since echinoderms and chordates share this same embryological pattern, they are thought to be closely related. Nevertheless, as these creatures are invertebrates and not actually fish, most marine biologists are pushing to completely replace the term starfish with sea star.

Regeneration

Some species of sea stars have the ability to regenerate lost arms. When some sea stars are cut into pieces, each part that includes a portion of the central disk may grow into a whole other organism.

One genus particularly noted for its regeneration ability is Linckia, named for naturalist J.H. Linck. These sea stars can cast off an arm that regrows into an entire organism, as a means of asexual reproduction.

Geological history

Fossil sea stars (Asteroidea) have been found in rocks as old as the middle Ordovician period. Brittle stars (Ophiuroidea) are first recorded as fossils in rocks from the Carboniferous period. Complete fossil sea stars are very rare, but where they do occur they may be abundant. Most fossil sea stars consist of scattered individual plates or segments of arms.

This is because the skeleton is not rigid, as in the case of echinoids (sea urchins), but is composed of many small plates (or ossicles) which quickly fall apart and are scattered after death and the decay of the soft parts of the creature. Scattered sea star ossicles are reasonably common in the Cretaceous Chalk Formation of England.

Three famous localities where complete fossil sea stars are found are the Devonian Bundenbach slates of Bundenbach in Germany, the Jurassic lithographic Solnhofen limestone of Solnhofen in Germany, and the Jurassic 'Sea star bed' of the Middle Lias formation near Bridport, Dorset in England.

Although the basic echinoderm pattern of five-fold symmetry can be recognized, most crinoids have many more than five arms.

Crinoids usually have a stem used to attach themselves to a substrate, but many live attached only as juveniles and become free-swimming as adults.

There are only a few hundred known modern forms, but crinoids were much more numerous both in species and numbers in the past. Some thick limestone beds dating to

the mid- to late-Paleozoic are entirely made up of disarticulated crinoid fragments. Button-like, fossilized pieces of crinoid stem from Ordovician limestone of Batavia, Ohio (USA)The earliest known crinoids come from the Ordovician. They are thought to have evolved from primitive echinoderms known as Eocystoids.

Confusingly, another early group of echinoderms were also the Eocrinoids, but that group is currently thought to be an ancestor of blastoids rather than of crinoids.

Some fossil crinoids, such as Pentacrinites, seem to have lived attached to floating driftwood and complete colonies are often found. Sometimes this driftwood would become waterlogged and sink to the bottom, taking the attached crinoids with it.

The stem of Pentacrinites can be several metres long. Modern relatives of Pentacrinites live in gentle currents attached to rocks by the end of their stem, which is fairly short.

Drawing of the calyx of the crinoid PentacrinitesMost modern crinoids are free-swimming and lack a stem. Examples of free-swimming crinoid fossils include Marsupitsa, Saccocoma and Uintacrinus.

Many fossils of free-swimming crinoids (such as Pterocoma) are found in the Jurassic-dated Solnhofen limestone of Solnhofen in Germany, and the Cretaceous-dated Niobrara chalk of Kansas contains large numbers of Uintacrinus.

The crinoids have had an eventful geologic history. Once evolved, they soon spread to a variety of marine habitats. The group as a whole suffered a major crisis during the Permian period when most of the crinoid forms of the Palaeozoic era died out, with a few surviving into the Triassic period. During the Mesozoic era there was another great radiation of the crinoids with more modern forms possessing flexible arms becoming widespread.

Fossil crinoid stems from Arkansas.The long and varied geological history of the crinoids demonstrates how well the echinoderms have adapted to filter-feeding. The fossils of other stalked filter-feeding echinoderms, such as blastoids, are also found in the rocks of the Palaeozoic era. These extinct groups can exceed the crinoids in both numbers and variety in certain horizons. They were evidently competing with the crinoids on an equal basis. However, none of these others survived the crisis at the end of the Permian period.

An abundance of (stemmed) crinoids occurs in the rocks of the Silurian period in the United Kingdom and the eastern United States, the Devonian period of Kentucky, Michigan, New York state and the Eifel region of Germany, the Carboniferous period of the United Kingdom, Belgium and Russia, the Mississippian period of Iowa and Indiana, the Pennsylvanian period of the mid-continental United States, the Permian period of the island of Timor, and the Triassic period of Germany.

Their closest living relative is probably the modern nautilus, whom they resemble. Their fossil shells have the form of flat spirals (though there are some rarer non-spiraled forms, called heteromorphs) and are responsible for the animals' name as they somewhat resemble a tightly coiled ram's horn (the god Ammon was commonly depicted as a

man with ram's horns).

Plinius the Elder (died 79 AD near Pompeii) called fossils of these animals ammonis cornua, "horn of Ammon." Often the name of ammonite species ends in ceras, Greek (???a?) for "horn" (e.g. Pleuroceras).

Jeletzkytes, a Cretaceous ammonite from the USA. Because ammonites and their close relatives are extinct, little is known about their way of life. Their soft body parts are practically never preserved in any detail. Nonetheless, a lot has been worked out by examining ammonite shells and by using models of these shells in water tanks.

Most ammonites probably lived at the surface of ancient seas; this is suggested by the fact that their fossils are often found in rocks that were laid down under conditions where no benthic (bottom-dwelling) life is found. Many of them are

thought to have been good swimmers with flattened, discus-shaped, streamlined shells (such as Oxynoticeras), although some were less effective swimmers and were likely to have been bottom dwellers. Ammonites probably preyed on fishes and crustaceans and were themselves preyed upon by marine reptiles (such as Mosasaurs). Fossilized shells are sometimes found showing teeth marks from such attacks.

Basic shell anatomy

The chambered part of the ammonite shell is called a phragmocone. The phragmocone contains a series of progressively larger chambers, called camerae (sing. camera) that are divided by thin walls called septa (sing. septum). Only the last and largest chamber, the body chamber, was occupied by the living animal. 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 an osmotic process, the ammonite emptied water out of and secreted gas into these shell chambers. This enabled it to control the buoyancy of the shell.

A primary difference between ammonites and nautiloids is that the siphuncle of ammonites runs along the inside of the outer axis of the shell, while the siphuncle of nautiloids runs through the center of the septa and camerae.

Sexual dimorphism

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

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

Variations in shape

The majority of ammonites have a shell that is a planispiral flat coil, but some have a shell that is partially uncoiled, partially coiled and partially straight (as in Australiceras), nearly straight (as in baculites and belemnites), or coiled helically - superficially like that of a large gastropod (as in Turrilites and Bostrychoceras).

These partially uncoiled and totally uncoiled forms began to appear during the early part of the Cretaceous and are known as heteromorphs.

Perhaps the most extreme and bizarre looking example of a heteromorph is Nipponites, which appears to be a tangle of irregular whorls lacking any obvious symmetrical coiling.

However, upon closer inspection the shell proves to be a three-dimensional network of connected "U" shapes. Nipponites occurs in rocks of the upper part of the Cretaceous in Japan and the USA.

Ammonites vary greatly in the ornamentation of their shells. Some may be smooth and relatively featureless, except for growth lines, and resemble that of the modern nautilus. In others various patterns of spiral ridges and ribs or even spines are shown.

This type of ornamentation of the shell is especially evident in the later ammonites of the Cretaceous.

The aptychus

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

Asteroceras, a Jurassic ammonite from EnglandAnaptychi are rare as fossils. They are found in ammonites from the Devonian period through those of the Cretaceous period.

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

Large numbers of detached aptychi occur in certain beds of rock (such as those from the Mesozoic in the Alps). These rocks are usually accumulated at great depths. The modern nautilus lacks any calcitic plate for closing its shell, and none has been found in any of the extinct nautiloids. It does, however, have a leathery head shield 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 unclear as to which species of ammonite many aptychi belong.

Size

Few of the ammonites occurring in the lower and middle part of the Jurassic period reach a size exceeding 23 centimetres (9 inches) in diameter. Much larger forms are found in the later rocks of the upper part of the Jurassic and the lower part of the Cretaceous, such as Titanites from the Portland Stone of Jurassic of southern England, which is often 53 centimetres (2 feet) in diameter, and Pachydiscus seppenradensis of the Cretaceous period of Germany, which is the largest known ammonite sometimes reaching 2 metres (6.5 feet) in diameter. The largest known North American ammonite is Parapuzosia bradyi from the Cretaceous with specimens measuring 137 centimetres (4.5 feet) in diameter.

Ammonite distribution

A specimen of Hoploscaphites from the Pierre Shale of South Dakota. Much of the original shell has survived.Starting from the late Silurian, ammonites were extremely abundant, especially in the Mesozoic seas. Many genera evolved and ran their course quickly, becoming extinct in a few million years. Due to their rapid evolution and widespread distribution, ammonites are useful for geologists and paleontologists for biostratigraphy. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods.

An iridescent ammonite from Madagascar.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 still intact.

Other fossils, such as many found in Madagascar, display iridescence. These iridescent ammonites are often of gem quality when polished.

The ammonites survived several major extinction events, with often only a few species surviving. But each time, this handful would diversify into a multitude of forms. Ammonites fossils become less abundant during the upper part of the Cretaceous, and none survive into the Cenozoic era. The last surviving lines died out about 65 million years ago along with the dinosaurs in the Cretaceous-Tertiary extinction event.

During the Devonian Period the first fish evolved legs and started to walk on land as amphibians, and the first arthropods like insects and spiders also started to colonize terrestrial habitats. The first seed-bearing plants spread across dry land, forming huge forests. In the oceans, fish diversified into the first sharks, and the first lobe-finned and bony fish. The first ammonite mollusks appeared, and trilobites, the mollusk-like brachiopods, as well as great coral reefs were still common. The Late Devonian extinction severely impacted marine life. The paleogeography was

dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, and the early formation of the small supercontinent of Euramerica in the middle.

Corals

Although corals first appeared in the Cambrian period, some 570 million years ago, they are extremely rare as fossils until the Ordovician period, when Rugose and Tabulate corals became widespread.

Fossil coral Heliophyllum halli from the Devonian of Canada.Tabulate corals occur in the limestones and calcareous shales of the Ordovician and Silurian periods, and often form low cushions or branching masses alongside Rugose corals. Their numbers began to decline during the middle of the Silurian period and they finally became extinct at the end of the Permian period. The skeletons of Tabulate corals are composed of a form of calcium carbonate known as calcite. Rugose corals became dominant by the middle of the Silurian period, and became extinct early in the Triassic period. The Rugose corals may be either solitary or colonial, and like the Tabulate corals their skeletons are also composed of calcite. The finest details of their skeletal structures are often well preserved, and such fossils may be cut and polished.

Scleractinian corals diversified during the Mesozoic and Cenozoic eras and are at the height of their development today. Their fossils may be found in small numbers in rocks from the Triassic period, and they are relatively common fossils in rocks from the Jurassic and Cretaceous periods as well as the Caenozoic era. The skeletons of Scleractinian corals are composed of a form of calcium carbonate known as aragonite. Although they are geologically younger than the Tabulate and Rugose corals, the aragonite skeleton Scleractinian corals does not tend to preserve well, so it is often easier to find fossils of the more ancient Tabulate and Rugose corals.

At certain times in the geological past corals were very abundant, just as modern corals are in the warm clear tropical waters of certain parts of the world today. And like modern corals their fossil ancestors built reefs beneath the ancient seas. Some of these reefs now lie as great structures in the midst of sedimentary rocks.

Such reefs can be found in the rocks of many parts of the world including those of the Ordovician period of Vermont, the Silurian period

of the Michigan Basin and in many parts of Europe, the Devonian period of Canada and the Ardennes in Belgium, and the Cretaceous period of South America and Denmark. Reefs from both the Silurian and Carboniferous periods have been recorded as far north as Siberia, and as far south as Australia.

However, these ancient reefs are not composed entirely of corals. Algae and sponges, as well as the fossilized remains of many echinoids, brachiopods, bivalves, gastropods, and trilobites that lived on the reefs help to build them.

These fossil reefs are prime locations to look for fossils of many different types, besides the corals themselves.

Corals are not restricted to just reefs, many solitary corals may be found in rocks where reefs are not present (such as Cyclocyathus which occurs in the Cretaceous period Gault clay formation of England).

As well as being important rock builders, some corals are useful as zone (or index) fossils, enabling geologists to date the age the rocks in which they are found, particularly those found in the limestones of the Carboniferous period.

Corals and past climate

Some coral species exhibit banding in their skeletons resulting from annual variations in their growth rate.

In fossil and modern corals these bands allow geologists to construct year-by-year chronologies, a kind of incremental dating, which combined with geochemical analysis of each band, can provide high-resolution records of paleoclimatic and paleoenvironamental change.

The tusk shells are a class Scaphopoda of marine mollusks distinguished by curved tubular shells open at both ends, resembling a elephant's tusk (thus the name). They are mostly small, with some species reaching 15 centimeters long, and live in the bottom sediment where they feed on microscopic detritus and organisms such as foraminifera.

The several hundred known species are found worldwide. The mantle is entirely within the shell. The foot extends from the larger end of the shell, and is used to burrow

through the substrate. A number of minute tentacles around the foot, called captacula, sift through the sediment and latch onto bits of food which they then convey to the mouth. The mouth has grinding teeth that break the bit into smaller pieces for digestion.

The scaphopid vascular system is rudimentary, lacking both heart and blood vessels; the blood is held in sinuses throughout the body cavity, and pumped by the rhythmic action of the foot. Tusk shells are well-known in the fossil record, first appearing in the Ordovician (last of all molluscan groups). The shells were used by the natives of the Pacific Northwest as wampum.

So pronounced is this evolutionary radiation that the Devonian has been called "the age of Fish".

The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 340 million years ago (mya), to the beginning of the Permian period, about 280 mya.

As with most older geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by 5–10 million years. The Carboniferous is named for the extensive coal beds of that age found in England and Western Europe. In North

America, the first third of the Carboniferous is called the Mississippian period, and the remainder is called the Pennsylvanian.

Eogyrinus

Eogyrinus was a long-bodied (15 foot) aquatic predator. It lived much like a an alligator in the swamps and deltas. The dorsal along the back would have stabilized it while swimming after prey. During the Carboniferous period (which began 360 million years ago), vast extensions of land were covered by dense forests of plants representing groups that are minoritary today, like the already mentioned ferns. Some land vertebrates began reproducing themselves through amniotic eggs, which prevented that the animals became dry in their interiors. These animals, the reptiles, started to put eggs on land, overcoming the amphibians in what concerns to their capability for adapting to a non-aquatic environment and, therefore, they achieved to expand into the interior of the continents

Hylominus: The most ancient reptile known, which lived during the Carboniferous period.

While everybody thought it was extincted since 65 millions of years, in december 22th 1938, Hendrick Goosen, captain of the Nerine took found in his net a strange fish, from a 70 meters depth.

There was an upwelling that day (cold water that going up)

and some other abyssal sharks were caught that day. The fish in question was from an electric blue, and had a 1,50 meters lenght. Since 1952, up to 200 specimens were caught, from a 100 to 300 meters depth. Even if it was a big discovery for the Occidental world, the Comores' fishers knows this fish since a long time.

They call it Kombessa and sometime eat it, and they also use it's rough skin to put on their bicycle's tire when they have a flat before to put something more appropriated! The scientifical name of the animal is Lattimeria chalumnae, in honor to Marjorie Courtenay-Latimer and in reference to the place where it was found (Chalumna river).The fish is caracterised by its pawlike fins. Its tail's also caracteristic to the specie. Africa is full of mysteries, and this one is about to be solved. But is there are other prehistoric animals living in Africa? Perhaps yes...

The Permian is a geologic period that extends from about 280 to 248 million years before the present (mya). As with most older geologic periods, the strata that define the Permian are well identified, but the exact date of the period's start is uncertain by a few million years.

The Permian follows the Carboniferous (Pennsylvanian in North America) and is followed by the Triassic. The end of the period is marked by a major extinction event, called the Permian-Triassic extinction event, that is more tightly dated. The Permian is named from the extensive exposures

in the region around the city of Perm in Russia. Permian exposures consist largely of continental redbeds and shallow water marine exposures.

Plesiosaurs

Were large, carnivorous aquatic reptiles. They are somewhat fancifully said to look like "a turtle with a string running through it", though they lacked a shell.

They first appeared in the late Triassic period and thrived until the K-T extinction at the end of the Cretaceous. Despite being large Mesozoic reptiles, they were not a type of dinosaur. Modern reports of plesiosaurs are usually explained as basking shark carcasses or hoaxes.

Description