First bone-cracking dog coprolites provide new insight into bone consumption in and their unique ecological niche.

Borophagine canids have long been hypothesized to be North American ecological 'avatars' of living hyenas in Africa and Asia, but direct fossil evidence of hyena-like bone consumption is hitherto unknown. We report rare coprolites (fossilized feces) of from the late Miocene of California and, for the first time, describe unambiguous evidence that these predatory canids ingested large amounts of bone. Surface morphology, micro-CT analyses, and contextual information reveal (1) droppings in concentrations signifying scent-marking behavior, similar to latrines used by living social carnivorans; (2) routine consumption of skeletons; (3) undissolved bones inside coprolites indicating gastrointestinal similarity to modern striped and brown hyenas; (4) body weight of ~24 kg, reaching sizes of obligatory large-prey hunters; and (5) prey size ranging ~35-100 kg. This combination of traits suggests that bone-crushing potentially hunted in collaborative social groups and occupied a niche no longer present in North American ecosystems.