Jackson’s experiments were done with modern crocodiles feeding on modern organisms, but he saw the same patterns of tooth marks and bone damage on the fossils from Olduvai. Some fossils did look they’d been chewed by mammalian carnivores, but others bore the distinctive marks of crocodiles. For example, the fossil leg bone of an antelope-like animal from Olduvai was whole when the animal died (though it was broken after it was originally deposited), had not been gnawed, bore many bisected pits, and was found near shed crocodile teeth in an area that was a prehistoric wetland. All of those lines of evidence suggest that the marks on the bone can be attributed to a crocodile and not to a lion or hyena.

Such details can be important for understanding ancient hominid behavior and evolution in these dangerous environments. For example, some paleoanthropologists had noticed that the Oldowan fossil assemblage included a number of complete limb bones and had hypothesized that early humans had butchered these animals. According to this hypothesis, the early humans had been in a hurry because of the risk of terrestrial carnivore attacks and so had done a sloppy job, failing to break these long bones to get to the marrow. That’s certainly a possibility, but Jackson points out that there may be a simpler explanation for the presence of these whole, long bones — especially given that we know that crocodiles were present at Olduvai. Intact bones are often left behind by crocodiles, buried in muddy wetlands after frenzied feeding.

Crocodiles seem likely to have played an important role in the Olduvai ecosystem, but Jackson wondered whether they might have attacked hominids there as well…