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The three species of bears in North America, polar bears (Ursus maritimus Phipps, 1774), brown bears (Ursus arctos L., 1758), and black bears (Ursus americanus Pallas, 1780), have differentiated morphologies and nuclear and mitochondrial genomes. An exception is a paraphyletic mitochondrial DNA relationship and some nuclear gene lineages common to polar bears and a population of brown bears from islands in southeast Alaska. In this study, we quantified the genetic relationships of extant brown bears and black bears from Alaska and Montana, and polar bears from Alaska, with amplified fragment length polymorphisms (AFLP) and mtDNA cytochrome-b sequences. Bayesian cluster analyses of the AFLP data show each species is distinct. All brown bears, including those from the islands in southeast Alaska, cluster separately from polar bears, and black bears cluster separately from brown bears and polar bears. The mtDNA of polar bears and southeast Alaska island brown bears is paraphyletic as reported previously, but the species have different haplotypes. These data indicate that extant populations of brown bears and polar bears have separate nuclear and mitochondrial gene pools and are supported as species under the genetic species concept.

DNA sequence and morphometric data were used to re-evaluate the taxonomy and systematics of . Phylogenetic analyses (maximum likelihood and Bayesian inference) of DNA sequences from the mitochondrial cytochrome- gene in 44 samples of indicated 2 well-supported monophyletic clades. The 1st clade contained specimens from Texas historically assigned to; the 2nd was comprised of specimens previously referable to ,, and obtained from northern and eastern Mexico. Levels of genetic variation (~7%) between these 2 clades indicated that the genetic divergence typically exceeded that reported for other species of. Samples of north and south of the Río Grande were not monophyletic. In addition, samples representing and formed 2 clades that differed genetically by 7.14%. Multivariate analyses of external and cranial measurements from 63 populations of revealed 4 morpho-groups consistent with clades in the DNA sequence analysis: 1 from Texas and New Mexico assignable to ; a 2nd from western and southern Mexico assignable to; a 3rd from northern and central Mexico previously assigned to but herein shown to represent an undescribed taxon; and a4th from southeastern Mexico assignable to . Based on the concordance of these results, populations from the United States are referred to as, whereas populations from Mexico are referred to as (including some samples historically assigned to, , and). A new subspecies is described to represent populations south of the Río Grande in northern and central Mexico. Additional research is needed to discern if warrants species recognition.

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