Using tooth wear as a window into past community dynamics is a novel approach to the fossil record that I pioneered. I first explored the implications of unusually heavy tooth wear in Pleistocene carnivores in a 1993 Science paper on Rancho La Brea carnivores. More recently I compared dental fracture frequencies between several Pleistocene predator populations (Alaska, California, Texas, Mexico, Venezuela) and those of 35 species of extant carnivores, ranging from skunks to lions. The mean frequency of tooth fracture in all the Pleistocene species was four times that of modern species, and the trend was even apparent when comparing Pleistocene and living populations of the same species such as coyotes and wolves. This suggests that selection pressures on large carnivore in the pre-human dominated world may have been just as severe, although different in kind from what they experience at present and historically, and should alter our view of how pristine mammal communities functioned.
Seeking yet another novel approach to interpreting the lives of extinct species, I turned to predator playback experiments in Africa used to census lion and hyenas. In these experiments, the sounds of dying wildebeest are used to attract carnivores and the individuals are counted. I was struck by the similarity between the playbacks and the situation at Rancho La Brea in which numerous carnivores were lured to their death by a dying herbivore in the tar seeps. In the African experiments, large and small social species (lions, hyenas, jackals) actively moved towards the playbacks while large and small solitary species rarely did so. This suggested a strong advantage for sociality (safety in numbers) when approaching a carcass, given the potential danger for battle with similarly motivated individuals. Working with C. Carbone and others, we showed that the parallels between La Brea and Africa were remarkable, assuming that the sabertooth cat (Smilodon) was social. Instead of hyenas, lions, and jackals, it was dire wolves, Smilodon, and coyotes. It is very difficult to infer social behavior in extinct species, and our paper provides the strongest inferential evidence for sociality in a sabertooth cat thus far.