Wiley, Edward O., III Natural History Museum, University of Kansas, Lawrence, Kansas.
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- Lampreys and fossil jawless fishes
- Jawed vertebrates
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The major subphylum of the phylum Chordata, including all animals with backbones, from fish to humans. The subphylum Vertebrata constitutes the largest natural group (clade, monophyletic group) of chordate animals (phylum Chordata). As is observed in all chordates, vertebrates have a notochord, but it is largely replaced by vertebrae (initially neural arches that surround the nerve cord) during development. Together with the living hagfishes (order Myxiniformes) and many fossil groups, vertebrates are members of the Craniata. One major theme of craniate evolution is the increasing elaboration of the brain, its cranial nerves, and many sensory organs, such as the organs of smell (olfactory), hearing (inner ear), and feel (sensory organs of the lateral line system). A unique innovation is the evolution of neural crest cells, that is, cells that begin development along the neural crest of the embryo and that then migrate to many parts of the body, giving rise to or contributing to the formation of such structures as the cranium and the branchial arches (a remnant of which remains in humans as parts of the larynx). Vertebrates have a long fossil history. Earliest fossils of jawless vertebrates are known from the late Cambrian (490 million years before the present). Jawed vertebrate fossils are known from the Ordovician (450 million years before the present), and this group began to predominate in the Devonian (about 360 million years before the present). See also: Animal evolution; Chordata; Fossil; Myxiniformes; Nervous system (vertebrate); Neural crest; Vertebra; Vertebrate brain (evolution)
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