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- Ostracoderm abstract "Ostracoderms ("shell-skinned") refers to the armored jawless fishes of the Paleozoic. The term does not often appear in classifications today because it is paraphyletic or polyphyletic, and has no phylogenetic meaning. However, the term is still used as an informal way of loosely grouping together the armored jawless fishes.An innovation of ostracoderms was the use of gills not for feeding, but exclusively for respiration. Earlier chordates with gills used them for both respiration and feeding. Ostracoderms had separate pharyngeal gill pouches along the side of the head, which were permanently open with no protective operculum. Unlike invertebrates that use ciliated motion to move food, ostracoderms used their muscular pharynx to create a suction that pulled small and slow moving prey into their mouths.The first fossil fishes that were discovered were ostracoderms. The Swiss anatomist Louis Agassiz received some fossils of bony armored fish from Scotland in the 1830s. He had a hard time classifying them as they did not resemble any living creature. He compared them at first with extant armored fish such as catfish and sturgeons but later realizing that they had no movable jaws, classified them in 1844 into a new group "ostracoderms" which means "shell-skinned".Ostracoderms have heads covered with a bony shield. They are among the earliest creatures with bony heads. The microscopic layers of that shield appear to evolutionary biologists, "like they are composed of little tooth-like structures." Neil Shubin writes: "Cut the bone of the [ostracoderm] skull open…pop it under a microscope and…you find virtually the same structure as in our teeth. There is a layer of enamel and even a layer of pulp. The whole shield is made up of thousands of small teeth fused together. This bony skull--one of the earliest in the fossil record--is made entirely of little teeth. Teeth originally arose to bite creatures (see Conodonts); later a version of teeth was used in a new way to protect them."Ostracoderms existed in two major groups, the more primitive heterostracans and the cephalaspids. The cephalaspids were more advanced than the heterostracans in that they had lateral stabilizers for more control of their swimming.It was long assumed that pteraspidomorphs and thelodonts were the only ostracoderms with paired nostrils, while the other groups have just a single median nostril. But it has since been revealed that even if galeaspidans have just one external opening, it has two internal nasal organs.After the appearance of jawed fish (placoderms, acanthodians, sharks, etc.) about 420 million years ago, most ostracoderm species underwent a decline, and the last ostracoderms became extinct at the end of the Devonian period. More recent research indicates, however, that fish with jaws had far less to do with the extinction of the ostracoderms than previously assumed, as they coexisted without noticeable decline for about 30 million years.The Subclass Ostracodermi has been placed in the division Agnatha along with the extant Subclass Cyclostomata, which includes lampreys and hagfishes.".
- Ostracoderm thumbnail Osteostraci_Janvier.gif?width=300.
- Ostracoderm wikiPageID "1086573".
- Ostracoderm wikiPageLength "14784".
- Ostracoderm wikiPageOutDegree "96".
- Ostracoderm wikiPageRevisionID "678348112".
- Ostracoderm wikiPageWikiLink Acanthodii.
- Ostracoderm wikiPageWikiLink Agnatha.
- Ostracoderm wikiPageWikiLink Anaspida.
- Ostracoderm wikiPageWikiLink Arandaspida.
- Ostracoderm wikiPageWikiLink Armour_(anatomy).
- Ostracoderm wikiPageWikiLink Armour_(zoology).
- Ostracoderm wikiPageWikiLink Astraspida.
- Ostracoderm wikiPageWikiLink Australia.
- Ostracoderm wikiPageWikiLink Braincase.
- Ostracoderm wikiPageWikiLink Category:Agnatha.
- Ostracoderm wikiPageWikiLink Category:Devonian_fish.
- Ostracoderm wikiPageWikiLink Category:Ordovician_fish.
- Ostracoderm wikiPageWikiLink Category:Silurian_fish.
- Ostracoderm wikiPageWikiLink Catfish.
- Ostracoderm wikiPageWikiLink Cephalaspidomorphi.
- Ostracoderm wikiPageWikiLink Chordate.
- Ostracoderm wikiPageWikiLink Chordates.
- Ostracoderm wikiPageWikiLink Cilium.
- Ostracoderm wikiPageWikiLink Conodont.
- Ostracoderm wikiPageWikiLink Conodonts.
- Ostracoderm wikiPageWikiLink Convergent_evolution.
- Ostracoderm wikiPageWikiLink Cyclostomata.
- Ostracoderm wikiPageWikiLink Devonian.
- Ostracoderm wikiPageWikiLink Devonian_period.
- Ostracoderm wikiPageWikiLink Duboisia.
- Ostracoderm wikiPageWikiLink Extinction.
- Ostracoderm wikiPageWikiLink Galeaspida.
- Ostracoderm wikiPageWikiLink Georgina_Basin.
- Ostracoderm wikiPageWikiLink Gill.
- Ostracoderm wikiPageWikiLink Gnathostomata.
- Ostracoderm wikiPageWikiLink Gnathostome.
- Ostracoderm wikiPageWikiLink Hagfish.
- Ostracoderm wikiPageWikiLink Heterostraci.
- Ostracoderm wikiPageWikiLink Hypocercal.
- Ostracoderm wikiPageWikiLink Invertebrate.
- Ostracoderm wikiPageWikiLink Jaw.
- Ostracoderm wikiPageWikiLink Lamprey.
- Ostracoderm wikiPageWikiLink Late_Devonian.
- Ostracoderm wikiPageWikiLink Late_Devonian_extinction.
- Ostracoderm wikiPageWikiLink Lateral_line.
- Ostracoderm wikiPageWikiLink Louis_Agassiz.
- Ostracoderm wikiPageWikiLink Middle_Devonian.
- Ostracoderm wikiPageWikiLink Monophyly.
- Ostracoderm wikiPageWikiLink Morphology_(biology).
- Ostracoderm wikiPageWikiLink Neeyambaspis.
- Ostracoderm wikiPageWikiLink Neeyambaspis_enigmatica.
- Ostracoderm wikiPageWikiLink Neil_Shubin.
- Ostracoderm wikiPageWikiLink Neurocranium.
- Ostracoderm wikiPageWikiLink Operculum_(fish).
- Ostracoderm wikiPageWikiLink Ordovician.
- Ostracoderm wikiPageWikiLink Osteostraci.
- Ostracoderm wikiPageWikiLink Paleozoic.
- Ostracoderm wikiPageWikiLink Paraphyletic.
- Ostracoderm wikiPageWikiLink Paraphyly.
- Ostracoderm wikiPageWikiLink Pituriaspida.
- Ostracoderm wikiPageWikiLink Pituriaspis.
- Ostracoderm wikiPageWikiLink Pituriaspis_doylei.
- Ostracoderm wikiPageWikiLink Placoderm.
- Ostracoderm wikiPageWikiLink Placodermi.
- Ostracoderm wikiPageWikiLink Polyphyletic.
- Ostracoderm wikiPageWikiLink Polyphyly.
- Ostracoderm wikiPageWikiLink Predation.
- Ostracoderm wikiPageWikiLink Prey.
- Ostracoderm wikiPageWikiLink Pteraspidomorphi.
- Ostracoderm wikiPageWikiLink Queensland.
- Ostracoderm wikiPageWikiLink Respiration_(physiology).
- Ostracoderm wikiPageWikiLink Rostrum_(anatomy).
- Ostracoderm wikiPageWikiLink Scotland.
- Ostracoderm wikiPageWikiLink Silurian.
- Ostracoderm wikiPageWikiLink Sturgeon.
- Ostracoderm wikiPageWikiLink Swiss.
- Ostracoderm wikiPageWikiLink Switzerland.
- Ostracoderm wikiPageWikiLink Taxon.
- Ostracoderm wikiPageWikiLink Thelodont_scales.
- Ostracoderm wikiPageWikiLink Thelodonti.
- Ostracoderm wikiPageWikiLink Wenlock_(Silurian).
- Ostracoderm wikiPageWikiLink Wenlock_epoch.
- Ostracoderm wikiPageWikiLink File:Anaspida.png.
- Ostracoderm wikiPageWikiLink File:Cardipeltis_bryanti_fossil_fish,_Bighorn_Mountains_WY.jpg.
- Ostracoderm wikiPageWikiLink File:Galeaspida_1.JPG.
- Ostracoderm wikiPageWikiLink File:Osteostraci_Janvier.gif.
- Ostracoderm wikiPageWikiLink File:Pituriaspida.jpg.
- Ostracoderm wikiPageWikiLink File:Pteraspis_NT.jpg.
- Ostracoderm wikiPageWikiLink File:Thelodonti.gif.
- Ostracoderm wikiPageWikiLinkText "Ostracoderm".
- Ostracoderm wikiPageWikiLinkText "armoured fish".
- Ostracoderm wikiPageWikiLinkText "armoured".
- Ostracoderm wikiPageWikiLinkText "ostracoderm".
- Ostracoderm hasPhotoCollection Ostracoderm.
- Ostracoderm wikiPageUsesTemplate Template:Citation_needed.
- Ostracoderm wikiPageUsesTemplate Template:Evolution_of_fish.
- Ostracoderm wikiPageUsesTemplate Template:Portal.
- Ostracoderm wikiPageUsesTemplate Template:Reflist.
- Ostracoderm wikiPageUsesTemplate Template:Rp.