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澳大利亚弗林德斯大学Richard Cloutier研究组在2020年3月18日出版的《自然》杂志发表论文，揭秘Elpistostege和脊椎动物手的起源。

他们报告了一个来自加拿大上泥盆纪时期的1.57米长的Elpistostege watsoni的关节标本，据了解，这是迄今为止发现的最完整的腕骨类目。高能计算机断层扫描显示，胸鳍的骨架上有四行放射状近端行（其中两行包括分支的腕骨），以及两行按数字和推定数字排列的远端行。除了这种骨骼模式（代表了迄今为止在胸鳍中发现的最类似四脚架的骨骼排列），鳍也保留了放射状的鳞翅目（鳍射线）远端。他们建议，脊椎动物的手主要是由掩埋在典型的腕骨类目水生胸鳍内的骨骼模式引起的。Elpistostege可能是所有其他四足动物的姊妹类群，其附属物进一步模糊了鱼类和陆地脊椎动物之间的界线。

据介绍，鱼向四足动物（四足脊椎动物）的进化是脊椎动物进化中最重要的转变之一。四足动物起源的假说在很大程度上是在泥盆纪中晚期（393-359百万年前）的一些四足动物鱼类化石的解剖结构。这些类群-被称为腕骨类目-包括Panderichthys，Elpistostege和Tiktaalik，这些都没有揭示胸鳍的完整骨骼解剖结构。

附：英文原文

Title: Elpistostege and the origin of the vertebrate hand

Author: Richard Cloutier, Alice M. Clement, Michael S. Y. Lee, Roxanne Nol, Isabelle Bchard, Vincent Roy, John A. Long

Issue&Volume: 2020-03-18

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.

DOI: 10.1038/s41586-020-2100-8

Source: https://www.nature.com/articles/s41586-020-2100-8

Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
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