DENTAL MEASUREMENTS IN BLACK BEARS (URSUS AMERICANUS) AND BROWN BEARS (URSUS ARCTOS): DISTINGUISHING THE SPECIES THROUGH TIME AND SPACE

The two most widespread bears across North America are the black bear (Ursus americanus) and brown bear (Ursus arctos). While U. americanus has occurred in North America for at least 240,000 years, the arrival of U. arctos is thought to be much more recent, around 25,000 years ago. These bears are primarily represented in the fossil record by teeth and a number of researchers have noted difficulties in distinguishing large black bears from smaller brown bears based on dental morphology. Thus distinguishing U. arctos and U. americanus remains in the fossil record has led to uncertainty and confusion in the arrival of U. arctos in North America, and past distributions of these species. Further, little research on how sympatry in these species impacts their dentition has been conducted. To investigate these problems, we compiled measurements of modern U. arctos and U. americanus lower crown lengths (p4-m3) from across North America to examine variability. Preliminary results based on analysis of a subset of data (U. americanus, n=149; U. arctos, n=140) from southeast Alaska produced particularly intriguing results. Analysis of variation found significant differences (p<0.001) for p4-m3 crown lengths, suggesting the size of these teeth can be used to differentiate U. americanus from U. arctos in sympatric populations. We hypothesize that this size separation could be a result of competitive pressures on U. americanus. Further analysis of a larger dataset will address dental size variation and species identification through time and space.