A Diprotodon's last supper

Abstract

Among the extinct marsupial megafauna bones recovered in 1893 from Lake Callabonna, Pilatapa Country, South Australia, were remnants of dried plant remains, which were deduced to be the gut contents of a Diprotodon optatum. These plant remains, now located in the South Australian Museum, have been used for both beta-counting and AMS radiocarbon (14C) dating at four different laboratories, all of which yielded non-finite ages approaching the upper age limits of the 14C method. We used delta13C analysis on the gut contents for comparison with modern plants collected near the lake to assess the animal's diet. We also analysed an M2 molar tooth from the Diprotodon skeletal remains, which contained the gut contents for delta13C and delta18O ratios, and used combined U-series/Electron Spin Resonance dating to obtain a finite age for the tooth. Considering the uncertainties associated with environmental dose rate estimation, we argue that our us-ESR age of 55 +- 5/4 ka (1σ) is the most secure estimate for the true age of this Diprotodon, which overlaps with published ages on sediments containing extinct avian megafauna at the same lake. Our delta13C measurements show that the most likely fodder being consumed by this particular now-extinct Diprotodon just before it died on the lake floor was Atriplex spp. saltbushes, which are still present around the lake today and follow the C4 photosynthetic pathway.