The Making of a Monster: Postnatal Ontogenetic Changes in Craniomandibular Shape in the Great Sabercat Smilodon

Abstract

Derived sabercats had craniomandibular morphologies that in many respects were highly different from those of extant felids, and this has often been interpreted functionally as adaptations for predation at extreme gape angles with hypertrophied upper canines. It is unknown how much of this was a result of intraspecific postnatal ontogeny, since juveniles of sabercats are rare and no quantitative study has been made of craniomandibular ontogeny. Postnatal ontogenetic craniomandibular shape changes in two morphologically derived sabercats, Smilodon fatalis and S. populator, were analysed using geometric morphometrics and compared to three species of extant pantherines, the jaguar, tiger, and Sunda clouded leopard. Ontogenetic shape changes in Smilodon usually involved the same areas of the cranium and mandible as in extant pantherines, and large-scale modularization was similar, suggesting that such may have been the case for all felids, since it followed the same trends previously observed in other mammals. However, in other respects Smilodon differed from extant pantherines. Their crania underwent much greater and more localised ontogenetic shape changes than did the mandibles, whereas crania and mandibles of extant pantherines underwent smaller, fewer and less localised shape changes. Ontogenetic shape changes in the two species of Smilodon are largely similar, but differences are also present, notably those which may be tied to the presence of larger upper canines in S. populator. Several of the specialized cranial characters differentiating adult Smilodon from extant felids in a functional context, which are usually regarded as evolutionary adaptations for achieving high gape angles, are ontogenetic, and in several instances ontogeny appears to recapitulate phylogeny to some extent. No such ontogenetic evolutionary adaptive changes were found in the extant pantherines. Evolution in morphologically derived sabercats involved greater cranial ontogenetic changes than among extant felids, resulting in greatly modified adult craniomandibular morphologies.

Growth trajectories in the cave bear and its extant relatives: an examination of ontogenetic patterns in phylogeny

“…This is a reasonable approach, but it is clear that both parts document different degrees of complexity and can reveal different patterns, even if correlated [ 11 , 53 ]. Differences in the growth trajectories of the mandible and the cranium were found in this work, as had also been found in sabercats [ 54 ]. Independent inheritance of upper and lower jaw features have been reported in hybrids of different dog breeds [ 55 ].…”

Quaternary mammals from central Brazil (Serra da Bodoquena, Mato Grosso do Sul) and comments on paleobiogeography and paleoenvironments

“…The classification of the genus Smilodon is controversial. Some authors claim there was a single species in the Americas (Paula Couto, 1979;Berta, 1987;Lessa et al, 1998;Cartelle & De Iuliis, 2006), whereas others recognize two species (Kurtén & Werdelin, 1990;Christiansen, 2012). Bocherens et al (2016) suggested that S. populator predominantly hunted prey in open environments, behaving as a social predator.…”

On the growth of the largest living rodent: Postnatal skull and dental shape changes in capybara species (Hydrochoerus spp.)

“…7C). In other studies that investigated both crania and mandibles this difference was also reported (Cardini and O'Higgins, 2004;Christiansen, 2012;Fuchs et al 2015;Segura and Prevosti, 2012). The mandible has been shown to follow a complex ontogenetic trajectory associated with tooth development (Swiderski and Zelditch, 2013).…”