Mandibular disparity of early sabertoothed felids from the Late Miocene of Spain

Machairodontinae is a subfamily of extinct felids that gathered much attention thanks to their iconic saber-teeth. Unfortunately, how this morphology evolved is unclear because of the patchy fossil record of early machairodontines. The Batallones localities (Madrid, Spain) have the potential to shed light on this issue, as two cavities (Batallones-1 and Batallones-3) contain hundreds of fossils of the early machairodontines Machairodus aphanistus and Promegantereon ogygia from the late Miocene (MN10). Previous analyses suggested that these two cavities are not contemporaneous and that a morphological drift could be observed between the different sites; characterizing this intraspecific variability is thus important to better understand the evolution early machairodontines. To tackle this issue, we modelled 45 mandibles of Machairodus aphanistus and Promegantereon ogygia, 6 mandibles of more derived machairodontines, and 11 mandibles of extant felines in 3D using a laser surface scanner. We applied linear morphometry and 3DGM on these models to test for differences in populations and to better characterize the morphology of early machairodontines. All our analyses (PCA, PCoA, clustering, Procrustes ANOVA an PERMANOVA) converge in finding no morphological change in the mandibular shape between Batallones-1 and Batallones-3 questioning the the hypothesis of a morphological drift between the cavities. The morphospaces derived from 3DGM were compared to those obtained via linear morphometry and a Mantel test confirmed that the position of each individual was not significantly different between the two morphospaces. The morphospace occupation of Batallones species is closer to extant felines than to other machairodontines, suggesting the existence of a morphological gap between primitive and derived machairodontines. Also, we reveal that the peculiar orientation and large size of the mandibular condyle is a unique feature of Machairodontinae among Felidae.