Dire wolf

The dire wolf (Canis dirus, 'fearsome dog') is an extinct species of the genus Canis. It is one of the most famous prehistoric carnivores in North America, along with its extinct competitor, the sabre-toothed cat Smilodon fatalis. The dire wolf lived in the Americas during the Late Pleistocene and Early Holocene epochs (125,000–9,500 years ago). The species was named in 1858, four years after the first specimen had been found. Two subspecies are recognized: Canis dirus guildayi and Canis dirus dirus. The dire wolf probably evolved from Armbruster's wolf (Canis armbrusteri) in North America. The largest collection of its fossils has been obtained from the Rancho La Brea Tar Pits in Los Angeles. Dire wolf remains have been found across a broad range of habitats including the plains, grasslands, and some forested mountain areas of North America, and in the arid savannah of South America. The sites range in elevation from sea level to 2,255 meters (7,400 ft). Dire wolf fossils have rarely been found north of 42°N latitude; there have been only five unconfirmed reports above this latitude. This range restriction is thought to be due to temperature, prey, or habitat limitations imposed by proximity to the Laurentide and Cordilleran ice sheets that existed at the time. The dire wolf was about the same size as the largest modern gray wolves (Canis lupus): the Yukon wolf and the northwestern wolf. C. d. guildayi weighed on average 60 kilograms (132 lb) and C. d. dirus was on average 68 kg (150 lb). Its skull and dentition matched those of C. lupus, but its teeth were larger with greater shearing ability, and its bite force at the canine tooth was the strongest of any known Canis species. These characteristics are thought to be adaptations for preying on Late Pleistocene megaherbivores, and in North America its prey are known to have included horses, ground sloths, mastodons, bison, and camels. As with other large Canis hypercarnivores today, the dire wolf is thought to have been a pack hunter. Its extinction occurred during the Quaternary extinction event along with most of the American megafauna of the time, including a number of other carnivores, that occurred soon after the appearance of humans in the New World. Its reliance on megaherbivores has been proposed as the cause of its extinction, along with climate change and competition with other species, but the cause remains controversial. Dire wolves lived as recently as 9,500 years ago, according to dated remains. From the 1850s, the fossil remains of extinct large wolves were being found in the United States, and it was not immediately clear that these all belonged to one species. The first specimen of what would later become associated with Canis dirus was found in mid-1854 in the bed of the Ohio River near Evansville, Indiana. The fossilized jawbone with cheek-teeth was obtained by the geologist Joseph Granville Norwood from an Evansville collector, Francis A. Linck. The paleontologist Joseph Leidy determined that the specimen represented an extinct species of wolf and reported it under the name of Canis primaevus. Norwood's letters to Leidy are preserved along with the type specimen (the first of a species that has a written description) at the Academy of Natural Sciences of Philadelphia. In 1857, while exploring the Niobrara River valley in Nebraska, Leidy found the vertebrae of an extinct Canis species that he reported the following year under the name C. dirus. The name C. primaevus (Leidy 1854) was later renamed Canis indianensis (Leidy 1869) when Leidy found out that the name C. primaevus had previously been used by the British naturalist Brian Houghton Hodgson for the dhole. In 1876 the zoologist Joel Asaph Allen discovered the remains of Canis mississippiensis (Allen 1876) and associated these with C. dirus (Leidy 1858) and Canis indianensis (Leidy 1869). As so little was found of these three specimens, Allen thought it best to leave each specimen listed under its provisional name until more material could be found to reveal their relationship. In 1908 the paleontologist John Campbell Merriam began retrieving numerous fossilized bone fragments of a large wolf from the Rancho La Brea tar pits. By 1912 he had found a skeleton sufficiently complete to be able to formally recognize these and the previously found specimens under the name C. dirus (Leidy 1858). Because the rules of nomenclature stipulated that the name of a species should be the oldest name ever applied to it, Merriam therefore selected the name of Leidy's 1858 specimen, C. dirus. In 1915 the paleontologist Edward Troxell indicated his agreement with Merriam when he declared C. indianensis a synonym of C. dirus. In 1918, after studying these fossils, Merriam proposed consolidating their names under the separate genus Aenocyon (from Aenos, terrible and cyon, wolf) to become Aenocyon dirus, but not everyone agreed with this extinct wolf being placed in a new genus separate from the genus Canis. Canis ayersi (Sellards 1916) and Aenocyon dirus (Merriam 1918) were recognized as synonyms of C. dirus by the paleontologist Ernest Lundelius in 1972. All of the above taxa were declared synonyms of C. dirus in 1979, according to the paleontologist Ronald M. Nowak. In 1984 a study by Björn Kurten recognized a geographic variation within the dire wolf populations and proposed two subspecies: Canis dirus guildayi (named by Kurten in honor of the paleontologist John E. Guilday) for specimens from California and Mexico that exhibited shorter limbs and longer teeth, and Canis dirus dirus for specimens east of the North American Continental Divide that exhibited longer limbs and shorter teeth. Kurten designated a maxilla found in Hermit's Cave, New Mexico as representing the nominate subspecies C. d. dirus. Both the canid family and its genus Canis are thought to have originated in North America, roughly 40 and 6 million years ago, respectively. Members of both radiations subsequently emigrated to the Old World. Wolf-like species of Canis apparently originated there, and then returned to North America.:p148