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.The presence of blubber and distribution of melanophores in a countershading pattern in an Early Jurassic ichthyosaur demonstrate that the evolutionary convergence of these reptiles with extant marine amniotes extends to the cellular and molecular levels.

中文翻译：

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侏罗纪鱼龙恒温和隐匿的软组织证据

鱼龙是已灭绝的海洋爬行动物，与现代齿鲸有着显着的外部相似性。在这里，我们表明这种相似性不仅仅是肤浅的。我们应用多学科实验方法来表征保存完好的早期侏罗纪鱼龙 Stenopterygius 标本中外皮组织的细胞和分子组成。我们的分析恢复了原始无鳞皮肤的仍然灵活的残余物，其中包括形态上不同的表皮和真皮层。这些被绝缘的鲸脂所覆盖，可以增强流线型、浮力和恒温。此外，我们还鉴定了内源性蛋白质和脂质成分，以及含有真黑色素色素的角质形成细胞和分支黑素细胞。全身黑色素细胞的分布变化表明反阴影，可能通过颜色的生理调整来增强光保护、隐藏和/或温度调节。因此，鱼龙与现存海洋羊膜动物的融合延伸到超微结构和分子水平，反映了它们共同适应远洋生活的无处不在的限制。早侏罗世鱼龙中鲸脂的存在和黑色素细胞的分布呈反阴影模式，表明进化趋同这些具有现存海洋羊膜的爬行动物延伸到细胞和分子水平。