Two new species of the genus Gumardee (Marsupialia, Macropodiformes) reveal the repeated evolution of bilophodonty in kangaroos

Abstract

Two new species of the fossil macropodiform genus Gumardee are described that provide insights into the evolution of early kangaroos. Gumardee has a continuous record from the late Oligocene to the early Miocene and is likely to have become extinct before the middle Miocene. The two new species are the most derived members of the genus. They exhibit some dental size variation, especially in P3/p3, which we interpret as evidence for sexual dimorphism. From the stratigraphically oldest species of Gumardee to the youngest, the dental morphology also shows a progression from bunolophodont to increasingly bilophodont. This trend appears to have occurred in at least four different lineages of macropodoids; however, a fully bilophodont condition was achieved only twice, once in the ancestral lineage of balbarids, and again in ancestral radiation of modern macropodids as implied by the species of Gumardee.

Kenny. J. Travouillon [[email protected]], Western Australian Museum, Locked Bag 49, Welshpool DC, WA, 6986 Australia; Kaylene Butler [[email protected]], School of Earth and Environmental Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia; Michael Archer [[email protected]], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, New South Wales 2052, Australia; Suzanne J. Hand [[email protected]], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, New South Wales 2052, Australia.

Keywords:

• Macropodidae; Miocene; kangaroo; evolution; phylogeny; bilophodonty

Acknowledgements

Research facilities were provided by the University of Queensland, QM, Western Australian Museum, and University of New South Wales. Assistance in the field has come from hundreds of volunteers, staff and postgraduate students of the University of New South Wales. We thank Kirsten Spring, Andrew Rozefelds and Scott Hocknull (QM) for access and loan of specimens. The late Robert Day (University of Queensland) facilitated postdoctoral funding for KJT. The UNSW Palaeosciences Lab and the UQ Palaeo Hub contributed support. The Alcheringa Editorial Board and anonymous reviewers provided helpful comments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

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Additional information

Funding

This study was funded by a Robert Day Postdoctoral Fellowship to KJT from the University of Queensland. Research in the Riversleigh WHA was supported by an Australian Research Council grant [DP170101420] to MA and SJH. Other financial sponsors include the University of New South Wales, Phil Creaser and the CREATE Fund, Queensland Parks and Wildlife Service, Environment Australia, QM, the Riversleigh Society Inc., Outback at Isa, Mount Isa City Council, and private supporters including Ken and Margaret Pettit, Elaine Clark, Margaret Beavis, and Martin Dickson.