The influence of ecology and phylogeny on the canid frontal sinus

Despite the fact that a well-developed frontal sinus is an apomorphy evolved only in the subfamily Caninae, important ecological factors might have played a role in the development of this paranasal cavity. Here, we present the first analysis of the 3D morphology of three fossil species of the genus Canis using an innovative deformation-based morphometric approach. Our aim was to disentangle the relative contributions of phylogenetic relationships and ecological adaptations. Based on the reconstructed morphology of the fossil species sinuses, we were able to corroborate and to better reconstruct the palaeodiet of the analysed fossil taxa. In particular, the overall structure and morphology of the frontal sinus of Canis etruscus suggests a lower proportion of meat in its diet. This species also displays the most primitive morphology among the three fossil species analysed, indicating an ancestral condition within the Canina lineage. On the other hand, the sinus shape and size of Canis mosbachensis and Canis borjgali suggest a higher proportion of meat consumption. In particular, C. borjgali closely resembles the extant wolf (Canis lupus) condition and suggests a possible hypercarnivorous group-hunting adaptation. Our results thus indicate that ecology is the primary driver of frontal sinuses shape and size, whereas phylogeny accounts for differences at higher taxonomic levels (i.e., subtribe level), highlighting how the analysis of this paranasal cavity can help in the further comprehension of both the paleoecology and phylogeny of fossil canids.