Stable isotopic signatures of fossilised rodent teeth: climate change in south-eastern Australia during the late Quaternary and faunal response

Abstract

The stable carbon (ẟ13C) and oxygen (ẟ18O) isotopic composition of bioapatite from fossilised mammalian tooth material is a well-established proxy for the reconstruction of palaeovegetation and palaeoclimate. The use of small mammals, in particular rodents, has been overlooked in the past for such studies. High abundances of fossilised rodent remains deposited by avian predators in cave deposits, such as Blanche Cave in the Naracoorte Caves World Heritage Area (NCWHA), gives researchers easy access to fossil materials, to which a temporal scale of climate and vegetation change can be reconstructed.

ẟ18O and ẟ13C analyses were performed on crushed incisors of three species of Pseudomys (P. auritus, P. australis and P. shortridgei) over the upper 27 layers from Blanche Cave, NCWHA. The relative abundances of the three species were collected from each layer and compiled into climatic-stratigraphic units: pre-glaciation (layers 27-25), early-glaciation (layers 24-20), Last Glacial Maximum (layers 19-15) and deglaciation (layers 13-1). The carbonate-bound component of the bioapatite was analysed for ẟ13C and ẟ18OCO3, as well as the additional analysis of phosphate bound oxygen (ẟ18OPO4) using isotope ratio mass spectrometry. Isotopic signatures from ẟ13C and ẟ18O were used to reconstruct palaeoclimate and palaeovegetation over the four climatic-stratigraphic units, which were compared to existing palaeoclimate studies. As rodents are commonly abundant in fossil deposits, they have the potential of being used to determine climatic and vegetation change associated with extinction events, such as the megafauna extinction in Australia.