Mandible shape in marsupial and placental carnivorous mammals: a morphological comparative study using geometric morphometrics

Abstract

We analysed mandible shape of the orders Dasyuromorpha, Didelphimorphia, and Carnivora using twodimensional geometric morphometrics, in order to explore the relationship between shape, size, and phylogeny. We studied 541 specimens, covering most of the genera of the terrestrial Carnivora (115 species) and a wide sample of marsupials (36 species). The observed shape variation had an ecological component. As an example, omnivorous carnivores have thick mandibles and large talonids in the carnassials, while hypercarnivores possess short mandibles and reduced talonids. There is also a discrimination between different taxonomic groups (i.e. marsupials and Carnivora), indicating some kind of constraint. Size explains a large percentage of total variance (large species had shorter and stronger mandibles, with anteriorly displaced carnassials), was significant when phylogeny was taken into account with a comparative method, but not when size and shape were optimized on the phylogeny. Carnivora presents a larger disparity and variation in body size, which could be related to the difference in teeth replacement. The optimization of mandible shape on the phylogenetic tree indicates that functional aspects, such as diet, are a key factor in the evolution of the carnivore mandible, but also that there is a phylogenetic pattern that cannot be explained by differences in diet alone.

Ecomorphology of Carnivora challenges convergent evolution

“…Meloro et al 2008;Figueirido et al 2011;Meloro & O'Higgins 2011;Prevosti et al 2012). As a generalisation confirmed also by previous studies, interspecific allometry explains only a small portion of mandibular shape changes in Carnivora suggesting that shape change might be related to different ecological factors.…”

“…In relation to this, it is also not surprising to find feliforms generally evolving at much lower rate in mandibular shape than caniforms. The early establishment of some particular morphology was also identified in previous studies on the mandible and it supports the tight link between feeding adaptation and mandible shape in groups with limited dietary variation (e.g., felids, Meloro and O'Higgins 2011;Prevosti et al 2012;perissodactyls, Raia et al 2010). This does not preclude convergence to occur on a broader taxonomic scale, but confirms the importance of attaining certain optimal designs.…”

“…Our interpretation is that mandibular design must be optimized in order to cope with the high functional demands of subduing and killing a prey alone, especially since applying killing bites imposes high biomechanical loading on the canines (cf. Prevosti et al 2012). This killing behaviour occurs consistently in all extant large felids and is present also in the fossa and in two large caniforms: the wolverine and the polar bear.…”

“…bamboo or bones). The mandible is favoured over the cranium here because this anatomical structure is entirely devoted to mastication and intimately linked with feeding habits in Carnivora (Raia 2004;Meloro 2011a;Meloro and O'Higgins 2011;Prevosti et al 2012). Morphospace overlap between distantly related extant and fossil species have already been detected in the carnivoran mandible shape (Figueirido et al 2011(Figueirido et al , 2013), yet no formal test for convergence was presented so far.…”

Genome of the Tasmanian tiger provides insights into the evolution and demography of an extinct marsupial carnivore

“…Here we further expand that 3D cranial dataset 6 by an additional 35 species, including members of Canis and Vulpes (the eutherian genera to which the thylacine is most commonly compared [46][47][48][49][50][51][52][53] ), dasyuromorphs and New World didelphids, 8 families of Diprotodontia (the clade containing carnivorous thylacoleonids but also kangaroos, wallabies, koalas, possums, gliders, and wombats), and other insectivorous australidelphids from the orders Microbiotheria, Notoryctemorphia and Peramelemorphia. The majority of newly added taxa are relatively small (0.1-5 kg body mass), representing the noncarnivorous marsupials to which the thylacine is most closely related (such as the southern marsupial mole Notoryctes typhlops and the eastern barred bandicoot Perameles gunnii).…”