THE ORAL APPARATUS OF MARSUPIALS IS MORE INTEGRATED BUT NOT LESS MORPHOLOGICALLY DIVERSE THAN THAT OF PLACENTAL CARNIVORES

Different clades can display different levels of morphological, taxonomical and ecological variability. Understanding the factors promoting or decreasing organismal variability is a central question for paleobiologists. To answer this question researchers have focused on identifying the key innovations that determined the patterns of radiation in specific clades. In this context developmental constraints can have a major impact on the evolution of morphological variability (e.g. disparity). Phenotypic integration, or covariation among traits, has been shown to play an important role in shaping organismal disparity at macro-evolutionary scale. A longstanding proposition about mammalian evolution has been that morphological variability among marsupials was limited by developmental constraints, in particular, constraints on the marsupial oral apparatus linked to the need for the embryo to access the mother’s teat early in its ontogeny. In this study we apply a recently proposed Geometric morphometric approach, i.e., Global Integration, to investigate integration intrinsic to a particular structure to compare the degree of oral apparatus morphological disparity between marsupial and placental carnivores. Our results show that marsupial oral apparatus is significantly more integrated than that of placentals, however, at least when fossil specimens are included, morphological disparity among marsupials was not significantly different to that found in placentals.