Abstract
Mammals exhibit vast ecological diversity, including a panoply of locomotor behaviours. The foundations of this diversity were established in the Mesozoic, but it was only after the end-Cretaceous mass extinction that mammals began to increase in body size, diversify into many new species and establish the extant orders. Little is known about the palaeobiology of the mammals that diversified immediately after the extinction during the Palaeocene, which are often perceived as ‘archaic’ precursors to extant orders. Here, we investigate the locomotor ecology of Palaeocene mammals using multivariate and disparity analyses. We show that tarsal measurements can be used to infer locomotor mode in extant mammals, and then demonstrate that Palaeocene mammals occupy distinctive regions of tarsal morphospace relative to Cretaceous and extant therian mammals, that is distinguished by their morphological robustness. We find that many Palaeocene species exhibit tarsal morphologies most comparable with morphologies of extant ground-dwelling mammals. Disparity analyses indicate that Palaeocene mammals attained similar morphospace diversity to the extant sample. Our results show that mammals underwent a post-extinction adaptive radiation in tarsal morphology relating to locomotor behaviour by combining a basic eutherian bauplan with anatomical specializations to attain considerable ecomorphological diversity.
Highlights
Mammals have evolved an array of locomotor behaviours, from cursoriality in ungulates and branch-swinging in primates, to deep-diving in cetaceans and powered flight in bats [1]
The principal component analysis (PCA) demonstrates that Cretaceous, Palaeocene and extant mammals all have distinctive tarsal morphologies. Despite their distinctiveness in principal component (PC) morphospace, the Linear discriminants analysis (LDA) visualization and regularized discriminant analysis (RDA) classification show that the fossil species share similar tarsal functions to extant mammals in terms of stance and movement and loading through the tarsus but are often exploiting locomotor strategies using different combinations of morphologies distinguished by their underlying robustness
The Palaeocene followed a catastrophic mass extinction and the abolition of complex and highly structured ecosystems dominated by dinosaurs, and heralded the beginning of the Age of Mammals
Summary
Mammals have evolved an array of locomotor behaviours, from cursoriality in ungulates and branch-swinging in primates, to deep-diving in cetaceans and powered flight in bats [1] The foundations of this ecomorphological diversity were established in the Mesozoic, in a miscellany of species distantly related to extant crown mammal groups [2]. Anatomical and functional insights on Palaeocene mammals have previously either been limited to qualitative inferences [12,13,14,15], or focused on a specific extinct taxon [16,17,18], or a small and/or closely related sample of extinct taxa [19,20]. We investigate the locomotor ecology of Palaeocene eutherians, in comparison to a sample of Cretaceous cladotherians and extant therian mammals
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