[en] Smilodon fatalis is one of the most extreme sabertoothed felids to have ever existed. Their peculiar phenotype undergoes dramatic transformation through ontogeny: cubs have much shorter fangs than adults and erupt their permanent upper canines at a relatively late age. Therefore, the ontogeny of Smilodon partially recapitulates the evolutionary shift from a more ‘feline-like’ to a ‘sabretoothed’ phenotype. We scanned 24 mandibles of Smilodon from La Brea, representing an ontogenetic sequence, and quantified growth-related morphological changes using geometric and linear morphometrics. Comparisons were made to an ontogenetic sequence of the extant lion (Panthera leo). We used finite element analysis to study the change of mechanical behaviour through ontogeny in both species. Smilodon undergoes much more morphological transformation during growth than P. leo, the former showing a growth in two phases: the mandibular corpus of Smilodon cubs resemble that of lions at early stages and the eruption of permanent m1 (around 10 months of age) marking a clear shift in morphology. Although Smilodon cub mandibles are perfectly shaped to handle stress and deformation, our analyses shown that they are particularly inefficient to convey the muscle force on the incisors and lower canines. These findings suggest that Smilodon cubs did not used their mandible as anchor and were poorly equipped to perform a sabretooth killing bite until they erupt their full adult dentition (past 20 months).
