Species abundance, richness and body size evolution of kangaroos (Marsupialia: Macropodiformes) throughout the Oligo-Miocene of Australia

Abstract

The Riversleigh World Heritage Area, northwestern Queensland, Australia, contains numerous Oligo-Miocene and Pleistocene fossil bearing deposits. Species of the suborder Macropodiformes (kangaroos and allies) described from Oligo-Miocene sediments at Riversleigh include representatives of all three macropodiform families: Macropodidae, Hypsiprymnodontidae and Balbaridae, a family of extinct fanged kangaroos. Despite extensive taxonomic study, few studies have focused on the ecology of balbarids that are present in Late Oligocene to Late Miocene faunal assemblages. Recently, several macropodiform species from Riversleigh have been described or revised that significantly alter previous interpretations of species richness and abundance at Riversleigh. In this study, Riversleigh macropodiform species richness and relative abundance is explored against a framework of recently revised taxonomic interpretations and biostratigraphy. With the exception of the Early Miocene, our results suggest that balbarids were less abundant than macropodids at Riversleigh. Balbarid species richness declined by the Early Miocene while macropodid species diversity declined from the Early Miocene to Middle Miocene and again in the Late Miocene. We also estimate body mass for macropodiform taxa throughout the Oligo-Miocene. A statistically significant increase in body mass is evident for most taxa through time. A number of ancestral macropodid genera suffer extinction in the Middle Miocene and are replaced by larger sthenurine macropodids around the time of the Miocene Climatic Optimum. Trends in faunal turnover (extinction and replacement of several macropodiform species) in the Middle Miocene are consistent with trends for other mammalian groups both from Riversleigh and globally.