Arctodus, or the North American short-faced bear, is an extinct bear genus that inhabited North America from the latest Pliocene to the Holocene epoch, from ~2.5 Mya until 10,000 years ago. Today considered to be an enormous omnivore, Arctodus was the most common short-faced bear in North America. There are two recognized species: the lesser short-faced bear (Arctodus pristinus) and the giant short-faced bear (Arctodus simus), with the latter considered to be one of the largest known terrestrial mammalian carnivorans that has ever existed.
Arctodus was first described by Joseph Leidy in 1854, with finds of A. pristinus from the Ashley Phosphate Beds, South Carolina.[1][2][3] The scientific name of the genus, Arctodus, derives from Greek, and means "bear tooth". The first fossils of A. simus were found in the Potter Creek Cave, Shasta County, California, by J. A. Richardson in 1878, and were described by Edward Drinker Cope in 1879.[4][5][6] The most nearly complete skeleton of A. simus found in the US was unearthed in Indiana; the original bones are in the Field Museum of Natural History, Chicago.[7][8]
In the 19th and early 20th centuries, specimens of Arctodus were occasionally referred to Arctotherium, and visa versa.[9] However, today neither genera are considered to have overlapped, with the closest point of contact being the giant Arctodus simus in central Mexico, and the smaller Arctotherium wingei in the Yucatán Peninsula.[10] Conversely, fossils of Arctodus pristinus are often confused with the similarly sized, partially contemporaneous short-faced bear, Tremarctos floridanus.[1]
Arctodus belongs to a group of bears known as the short-faced bears (Tremarctinae), which appeared in North America during the earliest parts of the late Miocene epoch in the form of Plionarctos, a genus considered ancestral to Tremarctinae. Plionarctos gave way to the medium sized Arctodus pristinus, Tremarctos floridanus and Arctotherium sp. in the Late Pliocene of North America.[2][11][12] Both Arctodus and Tremarctos were largely restricted to the more forested eastern part of the continent, as Boropahgus and Agriotherium are thought to have limited tremarctine presence in the more open Western North America. Tremarctos floridanus established a range mostly hugging the Gulf Coast (but also extending to California and Idaho),[12] whereas Arctodus pristinus ranged from Aguascalientes, Mexico,[13] to New Jersey in the US.[14] Perhaps due to their evolutionary history, both Tremarctos floridanus and Arctodus pristinus have the greatest concentration of fossils in Florida- in particular, the Santa Fe River 1 site of Gilchrist County. However, in the early Quaternary, when both Borophagus and Agriotherium went extinct, Arctodus would take advantage and spread into the rest of the continent, primarily in the form of A. simus. Concurrently, during the Great American Interchange that followed the joining of North and South America, the Central American based Arctotherium invaded South America,[11] leading to the diversification of the genus, including the colossal Arctotherium angustidens.