UCLA

Competition likely shaped the evolution of the mammalian family Canidae (dogs and their ancestors; order Carnivora). From their origin 40 million years ago (Ma), early canids lived alongside potential competitors that may have monopolized the large-carnivore niche—such as bears, bear-dogs, and nimravid saber-toothed cats—before becoming large and hypercarnivorous (diet of >70% meat) later in their history. This ecomorphological context, along with high phylogenetic resolution and an outstanding fossil record, makes North American fossil canids an ideal system for investigating how biotic interactions (e.g. competition) and ecological specialization (e.g. hypercarnivory) might influence clade evolution.

Chapter 1 investigates whether ecological generalization enables species to have longer durations and broader geographic range. I developed and applied a carnivory index to 100+ species, processing 3708 occurrences through a new duration-estimation method accounting for varying fossil preservation. A non-linear relationship between duration and carnivory emerged: both hyper- and hypocarnivores have shorter durations than mesocarnivores.

Chapter 2 tests the cost of hypercarnivory, quantified as elevated extinction risk. Large hypercarnivorous canids experienced extinction rates on par with other canids. However, in each canid subfamily, extinction rates rose after the first occurrence of large hypercarnivores, supporting the idea of hypercarnivory as a “macroevolutionary ratchet” for individual clades. Large hypercarnivores originated just over 10 Ma after the origin of Canidae, exhibiting constant diversification rates and peaking in richness around 12 Ma. Relationships emerge between diversification rates of canid subfamilies and temperature, suggesting future hypotheses to be investigated.

Chapter 3 quantifies functional morphology in 114 fossil canids and non-canid competitors from 40 to 15 Ma, testing for ecological congruence between continental and regional scales and whether ecomorphological disparity reflects taxonomic diversity. Disparity appears inversely related to diversity. All four geographic regions examined preserved a narrower range of ecomorphology than at the continental scale. These results suggest that partitioning dietary as well as geographic resources, despite constraints to size, permitted canids to minimize competition and diversify.

These macroecological and macroevolutionary studies of early canids and their potential competitors improve understanding of the resilience of the carnivore niche over long timescales, including periods of accelerated global change.