The Bony Labyrinth in Diprotodontian Marsupial Mammals: Diversity in Extant and Extinct Forms and Relationships with Size and Phylogeny

The shape of the bony labyrinth of the inner ear was quantified using geometric morphometrics in a sample of 16 species of living marsupial diprotodontians, the extinct Diprotodon and Thylacoleo, and four outgroups. X-ray micro-computed tomography (μCT) and conventional computed tomography (CT) were used to acquire 3D data. The analyses of 22 landmarks revealed a strong body-mass related allometric pattern. A discriminant analysis on allometry-free labyrinthine shape served to evaluate the phylogenetic signal portion of the labyrinth for Macropodiformes, Phalangeroidea, Petauroidea, and Vombatiformes. The inner shape of Thylacoleo is consistent with its phylogenetic placement as a vombatiform.