Postweaning Skull Growth in Living American and Australasian Marsupials: Allometry and Evolution

Abstract

Previous reports have shown an effect of historical legacy on patterns of growthof the mammal skull. The knowledge of developmental patterns of the marsupialskull are fundamental to understanding the evolution of skull form function in thisclade. The allometric patterns of skull growth are described and discussed,experienced on functional parts of the skull in representatives of all major livingmarsupial groups. The hypothesis that ontogenetic similarity is correlated withphylogeny in New and OldWorld marsupials, in a data set of 61 species, is tested.Ontogenetic trajectories onto the marsupial phylogeny are mapped, treating thetrajectories as composite, continuously varying characters. Didelphids, dasyurids,and diprotodontians differed widely in the magnitude of skull allometry acrossspecies. Splanchnocranial components exhibited all possible patterns of interspecificvariation, whereas mandibular variables were predominantly allometricallypositive or isometric, and neurocranial components were predominantly allometricallynegative. The ontogenetic trajectories deviated with respect to that ofreconstructed common ancestors in varying degree. Didelphids inherited anancestral constellation of allometry coefficients without change and retainedmuch of it throughout their lineage history, but Dasyuromorphia andDiprotodontia exhibited many changes from the ancestral allometric plan oneach group, evolving in highly modified patterns with respect to theirancestral plan.