2025-11-20 イェール大学
The new method uses machine-learning models, trained on modern species, to predict the aquatic habits and associated soft-tissue adaptations of ancient extinct species.
<関連情報>
- https://news.yale.edu/2025/11/20/back-beach-why-did-evolution-return-some-animals-water
- https://www.cell.com/current-biology/abstract/S0960-9822(25)01449-6
四肢の比率は絶滅した有羊膜類の水生習性と軟組織ヒレを予測する Limb proportions predict aquatic habits and soft-tissue flippers in extinct amniotes
Caleb M. Gordon ∙ Lisa S. Freisem ∙ Christopher T. Griffin ∙ Jacques A. Gauthier ∙ Bhart-Anjan S. Bhullar
Current Biology Published:November 20, 2025
DOI:https://doi.org/10.1016/j.cub.2025.10.068
Highlights
- Amniote limb proportions predict flippers and aquatic habits with >90% accuracy
- Mesosaurs and other Paleozoic reptiles did not evolve highly/fully aquatic habits
- Mesozoic marine reptiles show lineage-specific patterns of aquatic adaptation
- Phylogenetic ROC analysis reconstructs cryptic phenotypes in extinct species
Summary
Among mammals and reptiles, the recurring evolution of fully aquatic forms from land-dwelling ancestors highlights the remarkable powers and implications of natural selection. The most aquatically specialized of these groups have limb morphologies that betray a fully marine lifestyle, but the transitional forms near the base of each lineage have more ambiguous features, making it difficult to determine which fossil species were aquatic. Here, we use a scalable phylogenetic machine-learning pipeline to test previously proposed osteological correlates of interdigital webbing, soft-tissue flippers, and aquatic habits in amniotes. We collect >11,000 original measurements from amniote limbs and use these measurements to train and test phylogenetic logistic regression models that can predict aquatic affinities in extinct species. We then interpret and select among competing predictor models with receiver-operating characteristic analysis. Ultimately, relative hand length makes the best predictions, reconstructing soft-tissue flippers and aquatic habits with >90% accuracy across amniotes and clarifying the aquatic habits of fossil species with historically ambiguous ecologies. Placing these predictions on the phylogenetic tree of amniotes reveals semi-terrestrial habits in mesosaurs and all other sampled stem reptiles, highly/fully aquatic habits in all known ichthyosauromorphs, and multiple independent origins of highly/fully aquatic habits among sauropterygians, mosasaurs, and theropod dinosaurs. Taken more broadly, these results enable a broader comparative assessment of amniote limb proportions that reveals distinct evolutionary landscapes in limb morphometry for highly/fully aquatic vs. semi-terrestrial amniotes, as well as between total-group mammals and reptiles.
