Fossil evidence may help resolve a longstanding debate on hagfish evolution, according to a study. Biologists have yet to resolve where hagfish, a jawless, marine-dwelling slime "eel," fits in the tree of life. Whereas the morphology-based view of hagfish evolution places hagfish as an outgroup of vertebrates, molecular studies suggest that hagfish and lampreys should be grouped together as a distinct clade known as cyclostomes. Tetsuto Miyashita and colleagues report a hagfish fossil from the Late Cretaceous of Lebanon that reduces the gap in the fossil record by 100 million years. Using the fossil's well-preserved soft tissue anatomy, the authors demonstrate that many of the defining characteristics of extant hagfish appeared well before the Cretaceous period. Based on the fossil, the authors re-evaluated morphological features among jawless vertebrates and performed phylogenetic analyses. The analyses suggest that hagfish and lampreys form a clade of cyclostomes, and the convergence between morphological and molecular phylogenies potentially resolves the longstanding debate about early vertebrate evolution. These insights into hagfish evolution imply that living jawless vertebrates may not be as primitive as their anatomy suggests, according to the authors.
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Article #18-14794: "Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological-molecular conflict in early vertebrate phylogeny," by Tetsuto Miyashita et al.
MEDIA CONTACT: Tetsuto Miyashita, Department of Organismal Biology and Anatomy, University of Chicago, IL; tel: 773-834-8417; e-mail: tetsuto@ualberta.ca
Proceedings of the National Academy of Sciences