Data from: Ancient mitochondrial DNA reveals convergent evolution of giant short-faced bears (Tremarctinae) in North and South America

The Tremarctinae are a subfamily of bears endemic to the New World, including two of the largest terrestrial mammalian carnivores that have ever lived: the giant, short-faced bears Arctodus simus from North America and Arctotherium angustidens from South America (greater than or equal to 1000 kg). Arctotherium angustidens became extinct during the Early Pleistocene, whereas Arctodus simus went extinct at the very end of the Pleistocene. The only living tremarctine is the spectacled bear (Tremarctos ornatus), a largely herbivorous bear that is today only found in South America. The relationships among the spectacled bears (Tremarctos), South American short-faced bears (Arctotherium) and North American short-faced bears (Arctodus) remain uncertain. In this study, we sequenced a mitochondrial genome from an Arctotherium femur preserved in a Chilean cave. Our molecular phylogenetic analyses revealed that the South American short-faced bears were more closely related to the extant South American spectacled bear than to the North American short-faced bears. This result suggests striking convergent evolution of giant forms in the two groups of short-faced bears (Arctodus and Arctotherium), potentially as an adaptation to dominate competition for megafaunal carcasses.

短面熊亚科（Tremarctinae）是新大陆特有的熊类亚科，包含曾生存过的体型最大的陆生食肉哺乳动物中的两类：来自北美洲的巨型短面熊Arctodus simus，以及体重≥1000千克的南美洲短面熊Arctotherium angustidens。Arctotherium angustidens于更新世早期灭绝，而Arctodus simus则在更新世末期彻底灭绝。现存唯一的短面熊亚科物种为眼镜熊（Tremarctos ornatus），该物种以植食性为主，目前仅分布于南美洲。眼镜熊属（Tremarctos）、南美短面熊属（Arctotherium）与北美短面熊属（Arctodus）三者之间的系统发育关系至今仍未明确。本研究对保存在智利一处洞穴中的Arctotherium股骨样本进行了线粒体基因组测序。分子系统发育分析结果显示，南美短面熊与现存的南美眼镜熊的亲缘关系，要近于其与北美短面熊的亲缘关系。该结果表明，北美短面熊与南美短面熊这两类短面熊的巨型体型演化属于显著的趋同演化，这一现象可能是为了适应在巨型动物尸体的资源竞争中占据优势。