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 [Kenny.Travouillon@museum.wa.gov.au], Western Australian Museum, Locked Bag 49, Welshpool DC, WA, 6986 Australia; Kaylene Butler [kaylene.butler@uqconnect.edu.au ], School of Earth and Environmental Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia; Michael Archer [m.archer@unsw.edu.au ], 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 [s.hand@unsw.edu.au ], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, New South Wales 2052, Australia.