Distinct predatory behaviors in scimitar- and dirk-toothed sabertooth cats

Over the Cenozoic, large cat-like forms have convergently evolved into
specialized killers of ‘megaherbivores’ that relied on their large, and
laterally-compressed (saber-like) canines to rapidly subdue their prey
[1-5]. Scimitar- and dirk-toothed sabertooths are distinct ecomorphs that
differ in canine tooth length, degree of serration, and postcranial
features indicative of dissimilar predatory behavior [6-13]. Despite these
differences, it is assumed that they used a similar ‘canine-shear’ bite to
kill their prey [14,15]. We investigated the killing behavior of the
scimitar-toothed Homotherium serum and the dirk-toothed Smilodon fatalis
using a comparative sample of living carnivores and a new quantitative
approach to the analysis of skull function. For the first time, we
quantified differences in the relative amount and distribution of cortical
and trabecular bone in coronal sections of skulls to assess relative skull
stiffness and flexibility [16-19]. We also use finite element analysis to
simulate various killing scenarios that load skulls in ways that likely
favor distinct proportions of cortical versus trabecular bone across the
skull. Our data reveal that S. fatalis had an extremely thick skull and
relatively little trabecular bone, consistent with a large investment in
cranial strength for a stabbing canine-shear-bite. However, H. serum had
more trabecular bone, and likely deployed an unusual predatory behavior
more similar to the clamp-and-hold technique of the lion than S. fatalis.
These data broaden the killing repertoire of sabertooths and highlight the
degree of ecological specialization among members of the large carnivore
guild during the Late Pleistocene of North America.