Jawless vertebrates agnathans

The lamprey is a primitive jawless (agnathan) vertebrate fish and recently it has been shown that HoxL6 gene is expressed in the mandibular arch of developing embryos and that it co-localizes with Dlx, a marker of lamprey neural crest cells... 

Concerning broader hypotheses of early vertebrate diversity, the view that diversity patterns and the extinction of most clades of jawless fish reflect competition between agnathans and gnathostomes or between specific clades of jawless and jawed fish, although widely held, must be regarded as untested, and at present untestable, speculation. The available data for feeding habits, palaeogeographic distribution, and habitats are inadequate for this purpose, and the possibility that members of two contemporary clades were potential competitors can be neither confirmed nor refuted. Competitive interactions are just one of a number of possible explanations of the pattern of early vertebrate diversity. 

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