Research press release



Palaeontology: Spinosaurids may have been aquatic

スピノサウルス科恐竜には水生の生活様式に適応した特徴があったという証拠を示した論文が、Nature に掲載される。今回の知見は、大部分の非鳥類型恐竜の生活が陸上環境に限定されていたとする仮説に疑問を投げ掛けている。


今回、Matteo Fabbriたちは、恐竜の水生適応を調べるため、非鳥類型恐竜を含む絶滅種と非絶滅種のさまざまな有羊膜類(哺乳類、トカゲ類、クロコダイル類、鳥類、海生爬虫類、飛翔爬虫類など)の骨380点の密度を分析し、比較した。その結果、捕食性恐竜であるスピノサウルス科恐竜に高密度の骨があることが明らかになり、水中生活に適応していたことが示唆された。Fabbriたちは、スピノサウルス科恐竜は骨密度が高かったため、水中に入った時の浮力調節がしやすかった可能性があり、このことは、スピノサウルスとバリオニクスが水中で採餌していたことと、スコミムスが陸上環境で多く生息していたことと関連していると示唆している。


Evidence that spinosaurids had adaptations for an aquatic lifestyle is presented in a Nature paper. The findings challenge the hypothesis that most non-avian dinosaurs were restricted to terrestrial environments.

Although it can be difficult to infer anatomical adaptations in extinct species, only a few non-avian dinosaur species are thought to be partly or predominantly aquatic. In the past decade, fossils of spinosaurs characterized by paddle-like feet and fin-like tails have emerged, but whether these dinosaurs lived predominantly on land or in the water remains unknown. Bone density is used as a proxy for aquatic adaptation, as even aquatic animals that are not clearly shaped for an aquatic lifestyle — such as the hippopotamus — have very dense bones. Compact bones are a feature that often precedes the evolution of more clearly visible bodily adaptations for life in the water, such as fins or flippers.

To investigate aquatic adaptations in dinosaurs, Matteo Fabbri and colleagues analysed and compared the densities of 380 bones from a broad range of extinct and non-extinct amniotes (mammals, lizards, crocodiles and birds, including marine reptiles, and flying reptiles), including non-avian dinosaurs. The authors found that spinosaurids — a family of predatory dinosaurs — had dense bones, suggesting they were adapted to life in the water. Their increased bone density may have facilitated buoyancy control when immersed in water, relating to underwater foraging in Spinosaurus and Baryonyx, and to more terrestrial environments in Suchomimus, the authors suggest.

The findings imply that adaptations to aquatic environments appeared in spinosaurids during the Early Cretaceous (around 145 million years ago to 100.5 million years ago), following their divergence from other large carnivorous dinosaurs during the Early Jurassic.

doi: 10.1038/s41586-022-04528-0

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