Timothy H. Heaton
Dept. of Earth Sciences
Univ. of South Dakota
Vermillion, SD 57069
Fossil Ursus arctos skeletons have recently been found in three caves (one coastal, two alpine) on Prince of Wales Island, Alaska, dating back to 12,295+/-120 yr. B.P. This species does not currently inhabit the island, though two modern specimens at the U.S. National Museum and University of Utah were reportedly collected there. The late Pleistocene/early Holocene bears of Prince of Wales Island are much larger than their modern counterparts of the southern Alaska coast, and some are as large as or larger than any living U. arctos.
A study of modern bear skulls is being conducted in order to assess individual variation. Ursus arctos is an unusually variable species, even within local populations, in terms of overall size, zygomatic width relative to skull length, and tooth morphology. The second upper molar, traditionally considered the most diagnostic tooth, is extremely variable in size and shape with some mimicking U. americanus exactly. Since late Pleistocene U. americanus can be as large as U. arctos, this is a source of potential confusion.
Occasionally skulls of U. arctos contain one or both third upper molars as an atavism. When present these teeth are triangular in shape and much smaller than the second molars.