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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.

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Our understanding of the biology of the extinct pig-footed bandicoots (Chaeropus) has been substantially revised over the past two decades by both molecular and morphological research. Resolving the systematic and temporal contexts of Chaeropus evolution has relied heavily on sequencing DNA from century-old specimens. We have used sliding window BLASTs and phylogeny reconstruction, as well as cumulative likelihood and apomorphy distributions, to identify contamination in sequences from both species of pig-footed bandicoot. The sources of non-target DNA that were identified range from other bandicoot species to a bird—emphasizing the importance of sequence authentication for historical museum specimens, as has become standard for ancient DNA studies. Upon excluding the putatively contaminated fragments, Chaeropus was resolved as the sister to all other bandicoots (Peramelidae), to the exclusion of bilbies (Macrotis). The estimated divergence time between the two Chaeropus species also decreases in better agreement with the fossil record. This study provides evolutionary context for testing hypotheses on the ecological transition of pig-footed bandicoots from semi-fossorial omnivores towards cursorial grazers, which in turn may represent the only breach of deeply conserved ecospace partitioning between modern Australo-Papuan marsupial orders.

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