Morphometric Analysis of the Mandible of Primitive Sabertoothed Felids from the late Miocene of Spain

How sabertoothed felids have evolved their iconic morphology remains unclear because of the patchy fossil record of early machairodontines. Batallones localities in the Madrid region (Spain) have the potential to clarify this as two sites have yielded hundreds of fossils of the early machairodontines Promegantereon ogygia and Machairodus aphanistus. Previous analyses suggested that these two sites are not contemporaneous and a morphological drift between cavities was described for these two species; characterizing intraspecific variability is thus important to better understand the evolution of machairodontines. To tackle this issue, we modelled 62 felid mandibles in 3D using a laser scanner. We applied 3D geometric morphometrics (3D GM) and linear morphometrics on these models to test for differences in populations and to better characterize the morphology of early machairodontines. Both linear measurements and 3D data reveal an absence of morphological changes in mandible shape between the two sites. Batallones machairodontines are closer to felines than to other, more derived machairodontines in mandibular morphology, suggesting the existence of rapid shift in the mandibular shape between primitive and derived members of the clade. Our analysis did not reveal any allometric relationship between the overall shape of the mandible when studied with 3D GM and body size. Finally, we reveal a previously overlooked diversity in felid mandibular condyles, with machairodontines having much larger and medially inclined condyles.