Was the Giant Short-Faced Bear a Hyper-Scavenger? A New Approach to the Dietary Study of Ursids Using Dental Microwear Textures

Shelly L Donohue,Peter S Ungar,Blaine W Schubert,Larisa R G Desantis,Laurent Viriot

doi:10.1371/journal.pone.0077531

Shelly L Donohue, Peter S Ungar + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0077531

Copy DOI

Abstract

Dramatic environmental changes associated with global cooling since 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, we assess correspondence of dental microwear textures of first and second lower molars with diet in extant ursids. We use the resulting baseline data to evaluate the hypothesis that the Pleistocene giant short-faced bear, Arctodus simus, was a bone consumer and hyper-scavenger at Rancho La Brea, California, USA. 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 (Ursus maritimus, U. americanus) have significantly higher and more variable complexity (Asfc) than more herbivorous ones (Ailuropoda melanoleuca, Tremarctos ornatus, U. malayanus), and A. melanoleuca is differentiated from U. maritimus and U. americanus by significantly higher and more variable anisotropy (epLsar) values. Arctodus simus from Rancho La Brea exhibits wear attributes most comparable to its closest living relative (T. ornatus), which is inconsistent with hard-object (e.g., bone) consumption, and the hypothesis that short-faced bears were bone consuming hyper-scavengers across their range.

Highlights

The Pleistocene short-faced bear, Arctodus simus was the largest member of the order Carnivora to traverse North America, yet whether this giant was primarily an active predator, opportunistic omnivore, or bone-crushing hyper-scavenger remains unknown
We analyze five extant species to construct a modern baseline: the specialist bamboo-consuming giant panda (Ailuropoda melanoleuca) [8], [40], [41], herbivorous/ omnivorous spectacled bear (Tremarctos ornatus) [5], frugivorous/ insectivorous/omnivorous sun bear (Ursus malayanus) [7], [42], omnivorous American black bear (U. americanus) [6], [43], [44], and carnivorous polar bear (U. maritimus) [9], [45], [46], [47]. We develop this modern baseline to address the following questions: (i) do modern bears with disparate diets have distinct dental microwear textures, and (ii) does dental microwear vary significantly between lower first and second molars given functional differentiation of teeth? We examine Ar. simus microwear and compare results to our baseline to evaluate the hypothesis that the Pleistocene short-faced bear at Rancho La Brea, California (USA) was a bone-crushing hyper-scavenger
Specimens were sampled from publicly accessible collections in the United States, including the following: the American Museum of Natural History (AMNH) in New York, NY, the Florida Museum of Natural History (FLMNH) in Gainesville, FL, and the Smithsonian Institute National Museum of Natural History (NMNH) in Washington DC

Summary

Introduction

The Pleistocene short-faced bear, Arctodus simus was the largest member of the order Carnivora to traverse North America, yet whether this giant was primarily an active predator, opportunistic omnivore, or bone-crushing hyper-scavenger remains unknown. Could the dietary adaptability exhibited in past and present ursids have been an important driving force throughout their evolutionary history?. Given that most modern bears are adaptable opportunists in the face of changing seasons and environments (e.g., [5], [6], [7], [8], [9]), dietary versatility may have allowed ursids to persist during the dramatic habitat fluctuations of the Pleistocene. Clarifying the diets of past ursids, such as Ar. simus, is key to understanding the evolutionary history of the family and predicting responses to current and future climate change

Methods

Results

Conclusion