The Earliest Ursine Bear Demonstrates the Origin of Plant-Dominated Omnivory in Carnivora

Abstract

In Carnivora, increases in body size often lead to dietary specialization toward hypercarnivory. Ursine bears (Tremarctos and Ursus), however, are the only omnivorous Carnivora that evolved large body sizes (i.e., >50 kg). Traits contributing to their gigantism, and how those traits evolved, have never been studied. Here we propose that special dental characters of Ursinae (parallel buccal and lingual ridges) permit a sagittally oriented mastication associated with increasing emphasis on plant foods. This pattern can be traced back to a new early diverging bear of plant-dominated omnivorous diet, Aurorarctos tirawa gen. et sp. nov. from the late Middle Miocene of North America, which was supported as the earliest known ursine bear by phylogenetic analysis. The anatomical transition to increased masticatory efficiency, probably together with the ability to hibernate, helped bears break prior ecological limitations on body size and led to the evolution of a distinctive lineage of herbivorous-omnivorous, large-bodied Carnivora.

Duplication, Loss, and Evolutionary Features of Specific UDP-Glucuronosyltransferase Genes in Carnivora (Mammalia, Laurasiatheria)

“…Although these data of UGT2Bs expansions were still preliminary and further research to make sure these expansion and isoform number differences in these bears are needed, these data suggested the possible variation of UGT2Bs within Ursids. These two species have a very generalist diet, including much plant matter, such as green vegetation, fruits, cereals, and hard masts (e.g., nuts and acorns) [ 34 , 35 , 36 , 37 , 38 ]. It is likely that the observed UGT2B duplication is the result of adaptation to plant-based food items in the diet of these species.…”