The craniodental anatomy of Machairodus catocopis is assessed through the study of a well-preserved specimen from the early Hemphillian site of Sebastin Place (Kansas) and through comparisons with other Miocene American and Eurasiatic machairodonts, in order to resolve its affinities and to gain a clearer understanding of the evolution of machairodontine felids in the Holarctic. In view of the similarities with the Old World species Machairodus aphanistus, the original generic assignment seems correct, and later attribution of this species to the genus Nimravides appears unjustified. Similarities with Old World Miocene homotherins are too extensive to be the result of convergent evolution, especially considering the mosaic evolution of different machairodont adaptations. Hypotheses suggesting that M. catocopis is a part of a native American lineage originating from a feline, rather than machairodontine, immigrant are unjustified on anatomical or evolutionary grounds. The succession of sabertoothed felid species in the American Miocene is best explained as the result of three immigration events. A first immigration of a felid of Pseudaelurus grade led to the evolution of primitive species such as Pseudaelurus intrepidus and Nimravides pedionomus. A second immigration of a species of Machairodus aphanistus grade around the time of the ‘Hipparion event’ would result in the evolution of M. catocopis. The late Hemphillian species ‘Machairodus’ coloradensis is clearly a member of the Old World Turolian Amphimachairodus lineage, and would be the result of a third immigration event.
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