RECENT ECOMORPHOLOGICAL SELECTIVITY OF NORTH AMERICAN CANID EXTINCTION

Large-bodied hypercarnivory and bone-cracking are costly; their appearance in a lineage has been posited as a macroevolutionary “ratchet” that signals the lineage’s march toward extinction. While few extant large hypercarnivores remain, this specialization repeatedly punctuates the fossil record, permitting exploration of how it correlates with extinction risk (probability of extinction per unit time) in a world predating human effects. Here, I track this specialization in North American fossil dogs (Canidae), a family of over 130 species and wide ecomorphological range, including iterative occurrences of large-bodied hypercarnivory. Based on a previously identified negative relationship between species duration and hypercarnivory, large hypercarnivores were expected to experience higher extinction risk than all other canids. However, over 40 million years of canid history, a significant association between extinction rate and diet emerges only at the end-Pleistocene ~10,000 years ago, when all extinct canids were large and hypercarnivorous. Diversification rates corroborate this result. Large hypercarnivorous canids peaked in richness around 12 million years ago, exhibiting constant origination and extinction rates that offset reduced species durations. Hesperocyoninae and Borophaginae, the two extinct canid subfamilies, also display constant origination rates; but extinction surpasses origination after the rise of lineages leading to large hypercarnivores, suggesting that this specialization does precipitate decline at the clade level though not at the species level. Global temperature and continental diversification are associated only in Caninae, the remaining extant subfamily, reinforcing an intrinsically rather than extrinsically driven decline of large hypercarnivorous specialists prior to anthropogenic influence.