Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles
Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles
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DOI：
10.1038/nature12899
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发表时间：
2014-02-27
期刊：
影响因子：
64.8
通讯作者：
Polcyn, Michael J.
中科院分区：
文献类型：
--
作者：
Lindgren, Johan;Sjovall, Peter;Polcyn, Michael J.
在整个动物界，适应性着色具有从不显眼的伪装到炫耀的性展示等关键功能，并可以提供关于特定有机体的环境和生物学的重要信息(1，2)。最普遍和最丰富的色素，黑色素，也有各种各样的非视觉作用，包括体温外调节体温(3，4)。然而，由于我们在化石记录中明确识别其痕迹的能力有限，人们对这种重要的生物色素在很长时间内的功能进化知之甚少。在这里，我们提出了三种远亲海洋爬行动物的皮肤化石中色素沉积的直接化学证据：棱皮龟(5)，马赛龙(6)和鱼龙(7)。我们证明，这些化石中的黑色软组织痕迹主要由分子保存的真黑蛋白主导，与化石的黑素小体密切相关。此外，我们认为，与许多远洋动物(8，9)相反，至少有一些鱼龙在生活中是均匀的深色。我们的分析扩展了目前关于化石被片中的色素作用的知识，超越了羽毛(2，10)，允许在更大范围的已灭绝的分类群和解剖学上重建颜色。反过来，我们的结果提供了在三个不同的次生水生四足动物谱系中融合的黑化现象的证据。基于现有的海洋类似物，我们提出，温度调节和/或隐蔽的好处可能是导致这种黑化的原因，前者对每一组利用寒冷环境的能力有影响。
Throughout the animal kingdom, adaptive colouration serves critical functions ranging from inconspicuous camouflage to ostentatious sexual display, and can provide important information about the environment and biology of a particular organism(1,2). The most ubiquitous and abundant pigment, melanin, also has a diverse range of non-visual roles, including thermoregulation in ectotherms(3,4). However, little is known about the functional evolution of this important biochrome through deep time, owing to our limited ability to unambiguously identify traces of it in the fossil record(2). Here we present direct chemical evidence of pigmentation in fossilized skin, from three distantly related marine reptiles: a leatherback turtle(5), a mosasaur(6) and an ichthyosaur(7). We demonstrate that dark traces of soft tissue in these fossils are dominated by molecularly preserved eumelanin, in intimate association with fossilized melanosomes. In addition, we suggest that contrary to the countershading of many pelagic animals(8,9), at least some ichthyosaurs were uniformly dark-coloured in life. Our analyses expand current knowledge of pigmentation in fossil integument beyond that of feathers(2,10), allowing for the reconstruction of colour over much greater ranges of extinct taxa and anatomy. In turn, our results provide evidence of convergent melanism in three disparate lineages of secondarily aquatic tetrapods. Based on extant marine analogues, we propose that the benefits of thermoregulation and/or crypsis are likely to have contributed to this melanisation, with the former having implications for the ability of each group to exploit cold environments.