Research press release





今回、Johan Lindgrenたちの研究グループは、約1億8000万年前のものとされる保存状態の良好な魚竜類ステノプテリギウス(Stenopterygius)属の化石標本に含まれる皮膚組織の組成を調べた。その結果、ステノプテリギウスのもともとの滑らかな皮膚の遺残物が、いまだ柔軟性を保っており、明確な内層(真皮層)と外層(表皮層)から構成され、その下に脂肪層があることが明らかになった。脂肪層は、現生海洋哺乳類の特徴であり、断熱性によって低温から身を守り、浮力を増し、脂肪を貯蔵する作用がある。魚竜類の化石で脂肪層が同定されたのは今回が初めてで、魚竜類が温血動物だったことが確認された。


The skin of a fossil ichthyosaur with preserved inner and outer layers, underlying blubber, and pigmentation is described in a paper published online this week in Nature. These findings, which represent the first reported fossilized ichthyosaur blubber, suggest that the creatures were warm-blooded reptiles.

Ichthyosaurs are extinct marine reptiles that resemble modern toothed whales, such as dolphins. Their similar appearance suggests that ichthyosaurs and whales evolved similar strategies to adapt to marine life - an example of convergent evolution. Ichthyosaurs have long been suspected to be warm-blooded, but the limited preservation of their fossils has made this and other similarities difficult to confirm.

Johan Lindgren and colleagues studied the composition of skin tissues from a well-preserved ichthyosaur specimen, of the genus Stenopterygius, dating from around 180 million years ago. They found remnants of the animal’s original, smooth skin that was still flexible and comprised of distinct inner (dermal) and outer (epidermal) layers, with blubber underneath. The latter is characteristic of present-day marine mammals and insulates against the cold, aids buoyancy, and acts as a fat store. This is the first time fossil ichthyosaur blubber has been identified, and confirms that ichthyosaurs were warm-blooded.

In addition, the authors find that the ichthyosaur skin is pigmented in a pattern that suggests the reptiles were ‘countershaded’ - having a light underbelly and a darker upper surface. This colouration is seen in many modern marine mammals and can act as camouflage, protect against UV light, and aid heat regulation.

doi: 10.1038/s41586-018-0775-x

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