Research press release


Nature Communications

Fossils: Climate change drove dolphin-like reptiles to extinction



今回、Valentin Fischerたちは、系統発生学的方法を用いて、魚竜類の多様性の経時変化を推定し、その推定結果と環境データ(例えば、海洋の化学組成と海水準の変化)を関連づけた。その結果、魚竜類が白亜紀前期を通じて多様性が非常に高く、絶滅寸前の魚竜類には進化速度の低下という特徴があったことが判明した。Fischerたちのデータは、気候変動が海洋生態系の変化の主たる駆動要因だとする考え方を裏づけており、魚竜類が他の海生爬虫類と魚類との競争に敗れたという仮説とは一致しない。


The extinction of the iconic dolphin-like marine reptiles known as ichthyosaurs was driven by climatic instability and reduced evolutionary rates, suggests a new study in Nature Communications. Ichthyosaurs became extinct roughly 90 million years ago, in the Late Cretaceous period, about 28 million years before the end Cretaceous mass extinction which wiped out the dinosaurs and made way for mammals to dominate food webs.

Although increased competition with other marine reptiles or a drop in food resources have been proposed as possible causes of this early demise, recent studies have suggested that ichthyosaurs were diverse up to a few million years before their extinction, and the overall cause of their disappearance has therefore remained unclear up to now.

Valentin Fischer and colleagues use phylogenetic-based methods to estimate ichthyosaur diversity over time and correlate their results with environmental data, such as ocean chemistry and sea level change. They find that ichthyosaurs were highly diverse throughout the Early Cretaceous and that the last ichthyosaurs are characterized by reduced evolutionary rates. The authors’ data support climate changes as a main driver of marine ecosystem changes and are not consistent with the hypothesis that ichthyosaurs were outcompeted by other marine reptiles and fishes.

In addition, the study identifies an earlier extinction event (about 100 million years ago) as having reduced ichthyosaur diversity. The authors therefore propose that ichthyosaurs suffered from a two-phase demise.

doi: 10.1038/ncomms10825

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