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Abstract The canine of saber‐toothed predators represents one of the most specialized dental structures known. Hypotheses about the function of hypertrophied canines range from display and conspecific interaction, soft food processing, to active prey acquisition. Recent research on the ontogenetic timing of skull traits indicates the adult canine can take years to fully erupt, but the consequences of prolonged eruption on inferences of canine functional morphology are missing from current discourse and have not been quantified. Here I evaluate hypotheses about adult canine bending strength and stiffness, respectively, during eruption in the felidSmilodon fatalis. Simulated eruption sequences of three adult canines were generated from specimen models to assess shifting cross‐sectional geometry properties, and bending strength and stiffness under laterally directed loads were estimated using finite element analysis. Consistent with beam theory expectations,S. fataliscanine cross‐sectional geometry is optimized for increased bending strength with increased erupted height. However, canine cross‐sectional geometry changes through eruption exaggerate rather than minimize lateral deflection. Spatial constraint for maximum root length from adjacent sensory structures in the maxilla and the recently identified universal power law are hypothesized to limit the growth capacity of canine anteroposterior length and, consequently, maintenance of bending stiffness through eruption. Instead, the joint presence of the deciduous and adult canines for >50% of the adult canine eruption period effectively increases canine mediolateral width and brings bending strength and stiffness estimates closer to theoretical optima. Similarly prolonged retention of deciduous canines in other sabertooths suggests dual‐canine buttressing is a convergently evolved strategy to maximize bending strength and stiffness. 

Abstract The evolution of organisms can be studied through the lens of developmental systems, as the timing of development of morphological features is an important aspect to consider when studying a phenotype. Such data can be challenging to obtain in fossil amniotes owing to the scarcity of their fossil record. However, the numerous remains of Rancho La Brea allow a detailed study of the postnatal changes in an extinct sabertoothed felid:Smilodon fatalis. Despite numerous previous studies on the ontogeny ofSmilodon, an important question remained open: how did the cubs ofSmilodonacquire and process food? By applying 3D geometric morphometrics and finite element analyses to 49 mandibles at various developmental stages (22 ofS. fatalis, 23 ofPanthera leo, and 4 of early diverging felids), we assess the changes in mandibular shape and performance during growth. Both lions and sabertooths exhibit a shift in mandibular shape, aligning with eruption of the lower carnassial. This marks the end of weaning in lions and suggests a prolonged weaning period inS. fatalisowing to its delayed eruption sequence. We also highlight distinct ontogenetic trajectories, withS. fatalisundergoing more postnatal mandibular shape changes. Finally, althoughS. fatalisappears more efficient thanP. leoat performing an anchor bite, this efficiency is acquired through ontogeny and at a quite late age. The delayed shape change compared withP. leoand the low biting efficiency during the growth inSmilodoncould indicate an extended duration of the parental care compared withP. leo.