Clack J A
University Museum of Zoology, Cambridge, Downing St., Cambridge CB2 3EJ, UK.
Nature. 2002 Jul 4;418(6893):72-6. doi: 10.1038/nature00824.
The fossil record of early tetrapods has been increased recently by new finds from the Devonian period and mid-late Early Carboniferous period. Despite this, understanding of tetrapod evolution has been hampered by a 20-million-year gap ('Romer's Gap') that covers the crucial, early period when many key features of terrestrial tetrapods were acquired. Here I describe the only articulated skeleton of a tetrapod, Pederpes, yet found from the Tournaisian epoch (354-344 million years ago (Myr)). The new taxon includes a pes with five robust digits, but a very small, possibly supernumerary digit preserved on the manus suggests the presence of polydactyly. Polydactylous early tetrapods may have survived beyond the end of the Devonian and pentadactyly cannot be assumed for the pes. However, the pes has characteristics that distinguish it from the paddle-like feet of the Devonian forms and resembles the feet of later, more terrestrially adapted Carboniferous forms. Pederpes is the earliest-known tetrapod to show the beginnings of terrestrial locomotion and was at least functionally pentadactyl. With its later American sister-genus, Whatcheeria, it represents the next most primitive tetrapod clade after those of the Late Devonian, bridging the temporal, morphological and phylogenetic gaps that have hitherto separated Late Devonian and mid-Carboniferous tetrapod faunas.
最近，泥盆纪时期以及石炭纪早期中晚期的新发现增加了早期四足动物的化石记录。尽管如此，由于存在一个长达2000万年的间隔（“罗默空缺”），四足动物进化的研究受到了阻碍，这个间隔涵盖了陆地四足动物许多关键特征形成的关键早期阶段。在此，我描述了唯一一具已发现的来自杜内期（3.54亿至3.44亿年前）的四足动物——佩德普斯的关节相连的骨骼。这个新分类单元包括一只具有五个粗壮脚趾的足部，但在手部保存下来的一个非常小、可能是多余的脚趾表明存在多指畸形。多指的早期四足动物可能在泥盆纪末期之后仍然存活，并且不能假定足部为五趾。然而，该足部具有一些特征，使其有别于泥盆纪形态的桨状足，并且类似于后来更适应陆地生活的石炭纪形态的足部。佩德普斯是已知最早显示出陆地运动开端的四足动物，并且至少在功能上是五趾的。它与其后来在美洲的姐妹属瓦奇特里亚一起，代表了晚泥盆世之后的下一个最原始的四足动物分支，弥合了迄今将晚泥盆世和石炭纪中期四足动物群分隔开来的时间、形态和系统发育上的差距。
