Genetic diversity, phylogeography, and sexual dimorphism in the extinct giant short-faced bear (Arctodus simus).

This article focuses on the genetic analysis of the giant short-faced bear (Arctodus simus), an extinct Pleistocene North American carnivoran, to investigate its size variation, phylogeography, and population diversity. By sequencing 31 mitochondrial genomes from specimens across North America, the study found low genetic diversity and no clear phylogeographic structure, contradicting previous subspecies designations (A. s. simus and A. s. yukonensis). Genetic sex determination revealed that all large specimens were male and all small specimens female, supporting the hypothesis that size differences in A. simus are due to sexual dimorphism rather than distinct subspecies. The findings also suggest that females may have used caves for denning, and that the species maintained a wide-ranging, low-density population with limited genetic differentiation despite Pleistocene ice sheet barriers.