Meeting Abstract
Hypercarnivory and bone-crushing are metabolically costly specializations, and their appearance in a lineage is invariably irreversible: an example of an evolutionary “ratchet”. While modern ecosystems are relatively depauperate of hypercarnivores and bone-crushers, these specializations have repeatedly arisen in the fossil record, permitting exploration of a) how hypercarnivory may affect extinction rate and b) how quickly an empty hypercarnivore niche is filled. North American fossil dogs (Mammalia: Carnivora: Canidae) comprise over 100 species spanning a wide range of ecomorphologies, including iterative occurrences of hypercarnivory. Here, we reconstruct the initial rise of hypercarnivory in canids, examining a morphospace of 10 ecomorphological indices over nine time slices from the origin of Canidae (40 million years ago) to the height of canid species richness (25 species at its peak; 15 million years ago). Hotspots of elevated extinction rate correspond to areas of the canid morphospace occupied by large – but not small – hypercarnivores, matching the prediction of hypercarnivory representing an evolutionary “dead end”. However, hypercarnivory is slow to arise in canids. With non-canid carnivorans occupying the carnivore and large-hypercarnivore space, canids first saturate the omnivore and small-carnivore space. Even as large hypercarnivorous non-canids become extinct, canids remain in the omnivore and small-hypercarnivore space, becoming large hypercarnivores only after several million years. This significant lag in the movement of canids into the large-hypercarnivore space suggests that the turnover resulted from passive replacement and ecological release rather than active displacement. Strikingly, little ecomorphological overlap occurs among canids and non-canids, confounding hypotheses that canids declined taxonomically from competition with other carnivoran clades.
