Each kingdoms is divided into Phyllums Chordata, Arthropoda, Mollusca, etc. Cephalopoda, Gasteropoda Gasteropoda, as Pelecypoda and Cephalopoda, is a class of the phyllum Mollusca. Gasteropods are characterized by a spiral shell that does not contain internal chambers.
Brachiopods are marine animals that, upon first glance, look like clams, but unlike bivalve brachiopods shell is made of two inequal halves. They are also quite different from clams in their anatomy, and they are not closely related to the molluscs. As the phyllum Mollusca, Brachiopods is a phyllum of Lophotrochozoa, therefore Brachiopods are lophophorates, and so are related to the Bryozoa and Phoronida.
Although they seem rare in today's seas, they are actually fairly common. However, they often make their homes in very cold water, either in polar regions or at great depths in the ocean, and thus are not often encountered. There are about living species of brachiopods.
Despite their relative obscurity today, brachiopods have a long and rich paleontological history. During the Paleozoic era, they were extremely abundant.
They diversified into a number of different morphologies and even participated in the build-up of ancient reefs. At the end of the Paleozoic, they were decimated in the worst mass extinction of all time, the Permo-Triassic event. Their numbers have never been as great since that time.
Cephalopod Cambrian to present , a member of the Cephalopoda, a class of higly organized marine molluscs of which squid, octopus, cuttlefish and nautilus are living representatives. Their squeleton, when there is one, is made of chambered univalve shell, composed mainly of aragonite. The shell can be internal or external. Secondary deposits in the shell are well developed.
They entered the fossil record in the Ordovician and left in the Carboniferous. They are the probable ancestor to other cephalopoda. At their surface the ammonite shells display complex sutures that varies from species to species. Like the bactritoids, they have have a bulbous protoconch and a marginal siphuncle. They appeared in the Late Cambrian and quickly expanded. The only surviving Nautiloidea are members of the genus Nautilus picture in heading of page.
The members of the subclass Nautiloidea have orthoconic or coiled shells. Many of the straight Nautiloidea secreted deposits in their older chambers to make their shells neutrally buoyant. Corals belong to class Anthozoa. Rugose Corals - Middle Ordovician to Upper Permian The outer skin of the corallum, the epitheca, may be transversely wrinkled, hence the name "rugose". They range from simple solitary to complex colonial types. Unlike tabulata, rugose coral were not reef builders. Tabulate corals - Extinct group Lower Ordovician to Permian of colonial corals characterized by slender corallites with prominent tabulae and reduced or absent septa dividing-walls.
Tabulate corals were reef builders. Thamnopora the one on the top left is adjacent to a brachiopod. The bottom two pictures shows Thamnopora from the Yassensis limestone. Stromatopora characterized by prominent mamelons with opening of astrorhizal canals at their summits. The main victims were marine creatures, with up to 70 percent of species wiped out.
Reef-building communities almost completely disappeared. Theories put forward to explain this extinction include global cooling due to the re-glaciation of Gondwana, or reduced atmospheric levels of the greenhouse gas carbon dioxide because of the foresting of the continents. A major asteroid impact has also been suggested. All rights reserved. Shark Ancestors Despite their heavy protection, these primitive fishes weren't built to last.
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The supercontinent Gondwana occupied most of the Southern Hemisphere, although it began significant northerly drift during the Devonian Period. Eventually, by the later Permian Period, this drift would lead to collision with the equatorial continent known as Euramerica, forming Pangaea.
The mountain building of the Caledonian Orogeny, a collision between Euramerica and the smaller northern continent of Siberia, continued in what would later be Great Britain, the northern Appalachians and the Nordic mountains.
Rapid erosion of these mountains contributed large amounts of sediment to lowlands and shallow ocean basins. Sea levels were high with much of western North America under water. Climate of the continental interior regions was very warm during the Devonian Period and generally quite dry.
The Devonian Period was a time of extensive reef building in the shallow water that surrounded each continent and separated Gondwana from Euramerica. Reef ecosystems contained numerous brachiopods, still numerous trilobites, tabulate and horn corals.
Placoderms the armored fishes underwent wide diversification and became the dominant marine predators. Placoderms had simple jaws but not true teeth. Instead, their mouths contained bony structures used to crush or shear prey. Some Placoderms were up to 33 feet 10 meters in length.
Cartilaginous fish such as sharks and rays were common by the late Devonian. Devonian strata also contain the first fossil ammonites. By the mid-Devonian, the fossil record shows evidence that there were two new groups of fish that had true bones, teeth, swim bladders and gills.
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