More than one way to eat a mouse: Skull shape variation within a monophyletic group of mammals (Marsupialia; Dasyurinae)

Functional requirements for different diets have a strong selective pressure leading to convergent adaptations across different groups of mammals. As body size has an influence on many biomechanical and physiological characteristics, it is logical that dietary adaptations often have a strong link to body size resulting in observed ‘size guilds’ in many diverse phylogenetic lineages. However, non-allometric variation in skull shape may provide an alternative pathway for species to adapt to diets or prey handling by breaking the mould away from the line of least evolutionary resistance, increased body size. We investigated the relationships between cranial shape and body size in the evolutionary context of the shift from insectivory to hypercarnivory in a monophyletic group of 16 dasyurine marsupial species. Analysis of 35 Procrustes-corrected 3D skull landmarks revealed that overall, there was a correlation between mean skull shape and size that correlated with diet. However, the dominant shape variation (almost 80% irrespective of phylogeny, and more than 90% when constrained by phylogeny) was not size-related. This non-allometric pattern of skull shape reveals adaptation for different feeding strategies that is independent of absolute size. This highlights the potential for specific ‘thresholds’ in size and shape to exist that have the potential to mark shifts from one dietary niche to the next, that might be applied to the evolution of carnivorous taxa from other lineages.