New postcranial elements of mesonychid mammals from the Ypresian of France: New hypotheses for the radiation and evolution of the mesonychids in Europe

New postcranial elements of two mesonychids that lived during the Ypresian (early Eocene) in Europe are here described. The postcranial bones found at La Borie (France; ≈MP8 + 9) can be confidently ascribed to Hyaenodictis raslanloubatieri, while the astragalus found at Palette (France; ≈MP7) probably represents H. rougierae. Our study demonstrates that H. raslanloubatieri and H. rougierae were digitigrade in posture and relatively cursorial in locomotion. A single lumbar vertebra was recovered at La Borie and referred to H. raslanloubatieri; this element suggests this species was a moderately dorsostable predator. In addition, we illustrate the first maxillary fragment referable to H. raslanloubatieri, also discovered at La Borie. In comparison, we describe the postcranial elements of Pachyaena gigantea partially published in the early twentieth century, probably a plantigrade predator species. Morphological data derived from the La Borie specimens were included in phylogenetic analyses and support the reinstatement and monophyly of Hyaenodictis. Hyaenodictis was considered to be a junior synonym of Dissacus, but here we find that the Hyaenodictis clade includes almost all European mesonychids formerly referred to Dissacus along with the North American Wasatchian species H. willwoodensis.

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