CNRS, UMR 5276 LGL-TPE, Univ Lyon, Université Lyon 1, Ens de Lyon, Villeurbanne, France.
CNRS, UMR 5199 PACEA, Université de Bordeaux, Bordeaux, France.
Nature. 2018 Jun;558(7708):68-72. doi: 10.1038/s41586-018-0159-2. Epub 2018 May 30.
The fish-to-tetrapod transition-followed later by terrestrialization-represented a major step in vertebrate evolution that gave rise to a successful clade that today contains more than 30,000 tetrapod species. The early tetrapod Ichthyostega was discovered in 1929 in the Devonian Old Red Sandstone sediments of East Greenland (dated to approximately 365 million years ago). Since then, our understanding of the fish-to-tetrapod transition has increased considerably, owing to the discovery of additional Devonian taxa that represent early tetrapods or groups evolutionarily close to them. However, the aquatic environment of early tetrapods and the vertebrate fauna associated with them has remained elusive and highly debated. Here we use a multi-stable isotope approach (δC, δO and δS) to show that some Devonian vertebrates, including early tetrapods, were euryhaline and inhabited transitional aquatic environments subject to high-magnitude, rapid changes in salinity, such as estuaries or deltas. Euryhalinity may have predisposed the early tetrapod clade to be able to survive Late Devonian biotic crises and then successfully colonize terrestrial environments.
从鱼类到四足动物的过渡——随后是陆地化——代表了脊椎动物进化中的一个重大步骤，由此产生了一个成功的分支，其中包含了超过 30,000 种四足动物。早期的四足动物鱼石螈于 1929 年在东格陵兰的泥盆纪老红砂岩沉积物中被发现（距今约 3.65 亿年）。从那时起，由于发现了其他代表早期四足动物或与其进化密切相关的群体的泥盆纪分类群，我们对鱼类到四足动物的过渡的理解有了相当大的提高。然而，早期四足动物的水生环境和与之相关的脊椎动物群仍然难以捉摸，并且存在高度争议。在这里，我们使用多稳定同位素方法（δC、δO 和 δS）表明，一些泥盆纪脊椎动物，包括早期四足动物，是广盐性的，栖息在受高幅度、快速盐度变化影响的过渡性水生环境中，如河口或三角洲。广盐性可能使早期四足动物的分支能够在晚泥盆世生物危机中幸存下来，然后成功地殖民到陆地环境中。
