Evolutionary rates, disparity, and ecomorphology of the mandible in American marsupials

The American marsupials have been consistently reported to present a highly integrated and conserved morphology. This has been repeatedly argued as one of the main reasons why marsupial morphology is not as diverse as other mammals. Here we explore if these animals present specific mandibular ecomorphs, while also comparing the tempo of evolution and the amount of morphological disparity between clades. We found that marsupial mandibular size variation is partially explained by their feeding ecology. Insectivores are the smallest species, carnivores and frugivores present intermediate values, and omnivores are the largest. Because large marsupials have a more diversified diet, it is possible that they are able to optimize nutritional value of food contents throughout the seasons, which can be key to support their large sizes. While no specific ecomorphs were found for mandible shape, allometry, the correlation of size and shape, is one of the leading pathways to increase marsupial morphological diversity. According to our results, it has been previously argued that the marsupial generalized morphology is functionally sufficient to perform their feeding behaviours while varying in size. Furthermore, Didelphini and Thylamyini tend to evolve at faster rates than others clades. We discuss these results further in light of their ecology and evolutionary history and encourage future studies to investigate different models of evolution while studying American marsupials, especially those focusing on varying rates and strength of selection among selective regimes.