A Muscular Perspective on Vertebrate Evolution

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Science  12 Jul 2013:
Vol. 341, Issue 6142, pp. 139-140
DOI: 10.1126/science.1241451

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Most living vertebrates, from sharks to shrews and from hummingbirds to humans, are “jawed vertebrates,” distinguished by their possession of a jaw. These animals share other traits as well, such as two sets of paired appendages, shoulder girdles, and dual nostrils, revealing the basic anatomical architecture inherited from a common ancestor. Another group of vertebrates, the cyclostomes, comprises the two modern jawless vertebrates, lampreys and hagfish. These animals lack not only a jaw but also paired fins and shoulder girdles, showing that an even more ancient ancestor of vertebrates that gave rise to both the cyclostomes and jawed vertebrates also lacked these features. On page 160 this issue, Trinajstic et al. (1) systematically describe the muscle anatomy of three fossil animals from the earliest jawed vertebrate group, the placoderms, which evolved soon after the acquisition of the jaw.