The early evolution of the sabre-toothed felid killing bite: the significance of the cervical morphology of Machairodus aphanistus (Carnivora: Felidae: Machairodontinae)

Abstract The study of cervical anatomy in the Miocene machairodontine felid Machairodus aphanistus reveals the early stages of evolution of the sabre-toothed adaptations in the homotherin lineage. The cervical vertebrae of M. aphanistus show a surprising mosaic of features, combining a more primitive atlas than its derived relative Homotherium, with a set of elongated, caudal cervical vertebrae that display well-developed transverse processes with complex and strong muscle insertion areas. In spite of its primitive morphology, the atlas of M. aphanistus does show a slight caudal projection of the atlas wings, indicating an emphasis on vertical motions of the cranial portion of the neck and skull. The rest of the cervical vertebrae of M. aphanistus show clear adaptations for strength, flexibility and precise control of neck motions compatible with the canine shear-bite model and comparable to those of Homotherium. Such a powerful and flexible neck could provide additional stability to partly compensate for the risk of canine breakage created by the less specialized adaptations of the skull and cranial cervical vertebrae for the machairodontine bite.