Jawless
| Jawless | ||||||||
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Obsolete systematic group The taxon dealt with here is not part of the systematics presented in the German-language Wikipedia. More information can be found in the article text. |
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| Systematics | ||||||||
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| Scientific name | ||||||||
| Agnatha | ||||||||
| Cope , 1889 | ||||||||
The jawless (Agnatha) were formerly considered an original group of vertebrates , which today are completely extinct except for the lampreys and the hagfish . The hallmark was that they did not have a jaw , but, unlike the skullless, had a skull.
It was assumed that the heyday of the pineless with several hundred species was in the Cambrian , in which they developed and spread. The extinct groups were grouped together as the Ostracodermi . It was assumed that many species developed either free-sitting teeth or tooth-like outgrowths on the head armor (ostracodermi) that were common at the time as a replacement for a real jaw. Their time ended with the appearance of the first fish with jaws, which in these animals had developed from the foremost gill arches .
In modern taxonomy , the jawless taxon is no longer used because it is paraphyletic . The absence of pines is just an original feature. The only recent Agnathen class, the round-mouthed (Cyclostomata), is the sister group of the jaw-mouthed (Gnathostomata), and both together are the only recent representatives of the vertebrates . Cyclo- and gnathostomes together form the taxon myopterygia , because skeletal muscles gain access to their fin rays, which is not the case with the hagfish.
