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MORPHOLOGICAL DISPARITY OF LARGE CARNIVOROUS MAMMALS THROUGH TIME: EVIDENCE FROM MANDIBULAR GEOMETRY
The most commonly known examples of flesh-eating mammals are within the placental order Carnivora. However, highly specialized forms of predators emerged several times during mammalian evolutionary history. In South America, the carnivorous Sparassodonta (Metatheria) represented the dominant carnivores from the Paleocene until the Pliocene, while marsupials of the order Dasyuromorphia diversified much later in Australia, from the Oligocene until the present day. Similarly, creodonts and mesonychids evolved predatory forms in the Old and New World from the Paleocene until the Miocene. In this study, we aimed to investigate the morphological disparity of these multiple lineages of carnivorous mammals, how they emerged, and why. Using eleven homologous landmarks, we applied geometric morphometrics to quantify mandibular size and shape for 155 extant and fossil species belonging to the orders Carnivora, Creodonta, Mesonychia, Sparassodonta, and Dasyuromorphia, and built a phylogenetic relationship for comparative analyses. Patterns of disparity through time (phylogenetically corrected) were then explored in relation to prey diversity and climate proxies (i.e. Zachos isotopic curves for oxygen and carbon). Both mandible size and shape data showed a significant phylogenetic signal although only small differences in morphological disparity could be identified. Carnivora showed the highest disparity in mandible shape followed by Mesonychia and Creodonta. Peaks in disparity in the latter two clades occurred during the early and late Eocene, while metatherian and carnivoran peaks occurred much later, in the Neogene and Quaternary. Overall, we found that morphological disparity of carnivorous mammals is positively associated with oxygen-18 isotopic values through time (that is, peaks in disparity coincide with the coldest periods) but that prey diversity has no detectable impact when climate is controlled for. These preliminary results support previous observations about the rise and fall of different carnivorous clades through the Cenozoic and the predominant effect of climate. By increasing the fossil sample, we will explore this pattern in greater detail at the continental scale to potentially control for phylogeographic history.
comparative methods; ecomorphology; isotopes; macroevolution; paleoclimate; paleontology.
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES), Finance Code 001 for JB. JB is currently supported by the CAPES sandwich PhD program/Process number 88881.189949/2018-01. NC has a research fellowship in Ecology (Process number 313.191/2018-2), granted by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).
Jamile Bubadué, Nilton Cáceres, Darin Croft, Tamagnini Davide, Carlo Meloro