Niche partitioning and limited mobility characterise Middle Pleistocene kangaroos from eastern Australia

Abstract

Australias Quaternary fossil record is characterised by a high diversity of macropodid taxa. Based on fossil faunal assemblages, it has been hypothesised many macropodids lived in sympatry during the Pleistocene, however, local geographic and dietary overlap is equivocal due to taphonomic uncertainty. Modern macropodid species rarely exhibit sympatry, suggesting anthropogenic or environmental changes may have disrupted these communities. Using Sr and C isotopes, we reconstruct foraging ranges and dietary preferences of several fossil macropodid lineages recovered in Middle Pleistocene cave deposits, at Mount Etna Caves, central eastern Queensland, Australia. Our results show that most macropodids, baring a single Petrogale potentially dispersing > 60 km, had limited foraging ranges and remained within 15 km of the fossil site. Moderate to large scale dispersal in individual Petrogale mirrors male-biased dispersal observed in some modern Petrogale populations indicating some individuals have the propensity to move between isolated colonies when corridors for dispersal are present. Smaller macropodids show dietary preferences similar to modern counterparts, while Protemnodon exhibit a division between C3/C4 intake, potentially indicating species-level differences. The analysis of geographic range and diet of this fossil assemblage reveals that macropodids partitioned on the landscape around the cave with a C3-dominant community - comprised of Protemnodon, Petrogale, and Thylogale - to the northwest, and a C4-dominant grassland community - comprised of Notamacropus and isolated members of Protemnodon and Petrogale - to the south. Therefore, we conclude, that although faunal assemblages alone suggest a larger number of macropodids living in sympatry, isotopic proxies uncover complex habitat partitioning between C3 and C4 environments around Mount Etna Caves.