Developmental constraints do not influence long-term phenotypic evolution of marsupial forelimbs as revealed by interspecific disparity and integration patterns

Marsupials show a smaller range of forelimb ecomorphologies than placental mammals, and it is hypothesized that this results from macroevolutionary constraints imposed by the specialised reproductive biology of marsupials. Specifically, the accelerated development of the marsupial forelimb allows neonates to crawl to the mother’s pouch, but may constrain adult morphology. This hypothesis makes three main predictions: (i) that marsupial forelimbs should show less interspecific disparity than their hindlimbs; (ii) that morphological integration within the marsupial forelimb is stronger than integration between limbs; and (iii) that these patterns should be strongest in diprotodontians, which undergo the most rigorous crawls as neonates. We use a three-dimensional geometric morphometric dataset of limb bones for 51 marsupial species to tests these predictions. We find that (i) marsupial forelimbs and hindlimbs show similar disparities, (ii) no clear differences in integration
exist either...