Department of Geology, Lund University, Lund, Sweden.
RISE Research Institutes of Sweden, Chemistry and Materials, Borås, Sweden.
Nature. 2018 Dec;564(7736):359-365. doi: 10.1038/s41586-018-0775-x. Epub 2018 Dec 5.
Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.
鱼龙是已经灭绝的海洋爬行动物，它们的外部形态与现代有齿鲸有显著的相似之处。在这里，我们表明这种相似性不仅仅是表面上的。我们采用多学科的实验方法来描述早侏罗世鱼龙 Stenopterygius 保存异常完好的标本的表皮组织的细胞和分子组成。我们的分析发现了原始无鳞皮肤仍然具有弹性的残余物，该皮肤由形态上不同的表皮和真皮层组成。这些结构下面是隔热的鲸脂，可以增强流线型、浮力和恒温性。此外，我们还鉴定出了内源性蛋白质和脂质成分，以及含有真黑素色素的角蛋白细胞和分支黑素细胞。黑素细胞在身体上的分布变化表明存在对比色，这可能通过生理上调整颜色来增强，以实现光保护、隐藏和/或体温调节。因此，鱼龙与现生海洋羊膜动物的趋同进化扩展到了超微结构和分子水平，反映了它们共同适应海洋生活的普遍限制。
