Using 3D geometric morphometrics to aid taxonomic and ecological understanding of a recent speciation event within a small Australian marsupial (genus Antechinus)

Taxonomic distinction of species forms the foundation of biodiversity assessments and conservation priorities. However, traditional morphological and/or genetics-based taxonomic assessments frequently miss the opportunity of elaborating on the ecological and functional context of species diversification. Here, we used 3D geometric morphometrics of the cranium to improve taxonomic differentiation and add eco-morphological characterisation of a young cryptic divergence within the marsupial carnivorous genus Antechinus. Specifically, we used 168 museum specimens to characterise the recently proposed clades A. stuartii “south”, A. stuartii “north” and A. subtropicus. Beyond slight differences attributable to overall size (and therefore not necessarily diagnostic), we also found clear allometry-independent shape variation. This allowed us to define new, easily measured diagnostic traits in the palate, which differentiate the three clades. Contrary to previous suggestions, we found no support for a latitudinal gradient as causing the differentiation between the clades. However, skull shape co-varied with temperature and precipitation seasonality, suggesting that the clades may be adapted to environmental variables that are likely to be impacted by climate change. Our study demonstrates the use of 3D geometric morphometrics to improve taxonomic diagnosis of cryptic mammalian species, while providing perspectives on the adaptive origins and potential future threats of mammalian diversity.