Using dental microwear textures to assess feeding ecology of extinct and extant bears

Abstract

Dramatic environmental changes associated with a global cooling trend beginning in the late Miocene, and the onset of glacial-interglacial cycles in the Pleistocene served as a backdrop to the evolutionary radiation of modern bears (family Ursidae). These environmental changes likely prompted changes in food availability, and triggered dietary adaptations that served as motive forces in ursid evolution. Here, I assess correspondence of dental microwear textures of first and second lower molars with diet in extant ursids. I use the resulting baseline data to evaluate the hypothesis that the giant short-faced bear, <i>Arctodus simus</i>, was a bone consumer and hyper-scavenger at Rancho La Brea, California. Significant variation along the tooth row is consistent with functional differentiation, with the second molar serving as a better dietary recorder than the first. Results evince significant variation among species: carnivorous and omnivorous ursids (<i>Ursus maritimus, U. americanus</i>) have significantly higher and more variable complexity (<i>Asfc</i>) than more herbivorous bears (<i>Ailuropoda melanoleuca, Tremarctos ornatus, U. malayanus</i>), and <i>A. melanolueca</i> is differentiated from <i>U. maritimus</i> and <i>U. americanus</i> by significantly higher and more variable anisotropy (<i>epLsar</i>) values. <i>Arctodus simus</i> exhibits wear attributes most comparable to its closest modern relative (<i>T. ornatus</i>) and inconsistent with hard object (e.g., bone) consumption, and the hypothesis that short-faced bears were bone consuming hyper-scavengers across their range. Rather, plant matter was likely an important component of the diet of <i>Ar. simus</i> at Rancho La Brea.