Feeding Biomechanics Influences Craniofacial Morphology at the Subspecies Scale among Australian Pademelons (Macropodidae: Thylogale)

Interspecific variation in the craniofacial morphology of kangaroos and wallabies is associated with diet and feeding behaviors. Yet, to how fine a taxonomic scale this relationship might exist is unknown. Using a combination of established morphometric analyses and novel finite element approaches, we test the limits of these associations by examining three closely-related pademelon taxa: the red-necked pademelon (Thylogale thetis), and two subspecies of the red-legged pademelon (Thylogale stigmatica stigmatica and Thylogale stigmatica wilcoxi). All three taxa have distinct proportions of graze (grasses) and browse (leaves, stems, and branches of trees and shrubs) in their diets. We identified clear morphological differences in the crania between all three taxa and significant influences of geography and climate on cranial shape. We found significant differences in shape and strain magnitudes along the muzzle and cheek bones of each group that are consistent with the properties of their respective diets. These results suggest that feeding ecology influences craniofacial morphology down to the subspecies scale for at least some kangaroos and wallabies, which mirrors what is known at the macroevolutionary level for these species. This lends further weight to the predictive value of cranial morphology in determining feeding ecology among the Macropodiformes and may be of use in inferring feeding ecology of less accessible species for conservation and management.