A molecular and morphometric assessment of the systematics of the Macropus complex clarifies the tempo and mode of kangaroo evolution

Abstract

Kangaroos and wallabies of the Macropus complex include the largest extant marsupials and hopping mammals. They have traditionally been divided among the genus Macropus (with three subgenera: Macropus, Osphranter and Notamacropus) and the monotypic swamp wallaby, Wallabia bicolor. Recent retrotransposon and genome-scale phylogenetic analyses clarify the placement of Wallabia as sister to Notamacropus, with Osphranter and Macropus branching successively deeper. In view of the traditional Macropus concept being paraphyletic, we undertake to resolve the species-level phylogeny and genus-level taxonomy of the Macropus complex. For the first time, we include nuclear and mitochondrial DNA covering all extant species, and the first DNA sequences from the extinct Toolache wallaby (Notamacropus greyi), which we find groups with the black-gloved wallaby (Notamacropus irma). Morphological variation was examined using geometric morphometric methods on three-dimensional surface-scanned skulls. Wallabia skull shape fell close to Notamacropus (or Thylogale when controlling for allometry). We recommend the subgenera Macropus, Osphranter and Notamacropus be elevated to genera, alongside Wallabia, based on comparisons with other established macropodine genera for cranial disparity, ecology and molecular divergence. Our time tree estimates that all four ‘Macropus’ genera diverged close to the Miocene–Pliocene boundary (~6–5 Mya), then diversified coincident with Pliocene expansion of grasslands in Australia.