Elpistostege and the origin of the vertebrate hand

Richard Cloutier (), Alice M. Clement, Michael S. Y. Lee, Roxanne Noël, Isabelle Béchard, Vincent Roy and John A. Long
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Richard Cloutier: Université du Québec à Rimouski, Rimouski
Alice M. Clement: Flinders University
Michael S. Y. Lee: Flinders University
Roxanne Noël: Université du Québec à Rimouski, Rimouski
Isabelle Béchard: Université du Québec à Rimouski, Rimouski
Vincent Roy: Université du Québec à Rimouski, Rimouski
John A. Long: Flinders University

Nature, 2020, vol. 579, issue 7800, 549-554

Abstract: Abstract The evolution of fishes to tetrapods (four-limbed vertebrates) was one of the most important transformations in vertebrate evolution. Hypotheses of tetrapod origins rely heavily on the anatomy of a few tetrapod-like fish fossils from the Middle and Late Devonian period (393–359 million years ago)1. These taxa—known as elpistostegalians—include Panderichthys2, Elpistostege3,4 and Tiktaalik1,5, none of which has yet revealed the complete skeletal anatomy of the pectoral fin. Here we report a 1.57-metre-long articulated specimen of Elpistostege watsoni from the Upper Devonian period of Canada, which represents—to our knowledge—the most complete elpistostegalian yet found. High-energy computed tomography reveals that the skeleton of the pectoral fin has four proximodistal rows of radials (two of which include branched carpals) as well as two distal rows that are organized as digits and putative digits. Despite this skeletal pattern (which represents the most tetrapod-like arrangement of bones found in a pectoral fin to date), the fin retains lepidotrichia (fin rays) distal to the radials. We suggest that the vertebrate hand arose primarily from a skeletal pattern buried within the fairly typical aquatic pectoral fin of elpistostegalians. Elpistostege is potentially the sister taxon of all other tetrapods, and its appendages further blur the line between fish and land vertebrates.

Date: 2020
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DOI: 10.1038/s41586-020-2100-8

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