Staatliches Museum für Naturkunde in Stuttgart, D-70191 Stuttgart, Germany;
Naturhistorisches Museum Schloss Bertholdsburg, D-98553 Schleusingen, Germany.
Proc Natl Acad Sci U S A. 2020 May 26;117(21):11584-11588. doi: 10.1073/pnas.2001424117. Epub 2020 May 11.
The origin of extant amphibians remains largely obscure, with only a few early Mesozoic stem taxa known, as opposed to a much better fossil record from the mid-Jurassic on. In recent time, anurans have been traced back to Early Triassic forms and caecilians have been traced back to the Late Jurassic , both of which exemplify the stepwise acquisition of apomorphies. Yet the most ancient stem-salamanders, known from mid-Jurassic rocks, shed little light on the origin of the clade. The gap between salamanders and other lissamphibians, as well as Paleozoic tetrapods, remains considerable. Here we report a new specimen of , a hitherto enigmatic tetrapod from the Middle/Late Triassic of Kyrgyzstan, which we identify as the geologically oldest stem-group salamander. This sheds light not only on the early evolution of the salamander body plan, but also on the origin of the group as a whole. The new, second specimen is derived from the same beds as the holotype, the Madygen Formation of southwestern Kyrgyzstan. It reveals a range of salamander characters in this taxon, pushing back the rock record of urodeles by at least 60 to 74 Ma (Carnian-Bathonian). In addition, this stem-salamander shares plesiomorphic characters with temnospondyls, especially branchiosaurids and amphibamiforms.
现存两栖动物的起源在很大程度上仍然不清楚，只有少数早期中生代的主干类群为人所知，而从中侏罗世开始，化石记录要好得多。最近，无尾两栖类可以追溯到早三叠世的形态，蚓螈可以追溯到晚侏罗世，这两者都体现了逐步获得的特征。然而，从中侏罗世岩石中得知的最古老的主干蝾螈，对该类群的起源几乎没有提供任何线索。蝾螈和其他滑体两栖动物以及古生代四足动物之间的差距仍然相当大。在这里，我们报告了一种新的标本，这是一种来自吉尔吉斯斯坦中/晚三叠世的神秘四足动物，我们将其鉴定为地质上最古老的主干蝾螈。这不仅揭示了蝾螈身体结构的早期进化，也揭示了整个蝾螈类群的起源。这个新的第二标本与正模标本来自同一地层，即吉尔吉斯斯坦西南部的马迪根组。它揭示了该类群中一系列蝾螈特征，将有尾目两栖动物的岩石记录至少向前推进了 60 到 74 百万年（卡尼阶-巴通阶）。此外，这种主干蝾螈与迷齿两栖动物，特别是枝角龙类和两栖螈类共享祖征。
