Dire wolf

Extinct species of canine mammal

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The dire wolf (Aenocyon dirus ) is an extinct species of canine which was native to the Americas during the Late Pleistocene and Early Holocene epochs (125,000–10,000 years ago). The species was named in 1858, four years after the first specimen had been found. Two subspecies are proposed, Aenocyon dirus guildayi and Aenocyon dirus dirus, but this assignment has been recently considered questionable. 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 plains, grasslands, and some forested mountain areas of North America and the arid savanna 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 records 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 forms of gray wolf (Canis lupus). A. d. guildayi weighed on average 60 kilograms (132 lb) and A. 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 stronger than any known Canis species. These characteristics are thought to be adaptations for preying on Late Pleistocene megaherbivores; in North America, its prey is suggested to have included western horses, dwarf pronghorn, flat-headed peccary, ground sloths, ancient bison, and camels.

Dire wolves lived as recently as 10,000 years ago, according to dated remains. Its extinction occurred during the Quaternary extinction event, disappearing along with its main prey species; its reliance on megaherbivores has been proposed as the cause of its extinction, along with climatic change and competition with other species, or a combination of those factors.

Taxonomy

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 Aenocyon 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 geologist Joseph Granville Norwood from an Evansville collector, Francis A. Linck. 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, 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 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 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 ainos, 'terrible' and cyon, 'dog') to become Aenocyon dirus, but at that time 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. However, Hill et al. (2025) examined the taxonomic history of C. mississippiensis and directly compared the bones attributed to C. mississippiensis with those of the Pleistocene gray wolf (Canis lupus) and the dire wolf (Aenocyon dirus), reaching a conclusion that C. mississippiensis is most likely synonymous with C. lupus.

In 1984, a study by Finnish paleontologist Björn Kurtén recognized a geographic variation within the dire wolf populations and proposed two subspecies: Canis dirus guildayi (named by Kurtén in honor of American 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. Kurtén designated a maxilla found in Hermit's Cave, New Mexico, as representing the nominate subspecies C. d. dirus. In 2019, this subspecific assignment was questioned by paleontologists Damián Ruiz-Ramoni and Marisol Montellano-Ballesteros at National Autonomous University of Mexico, who were unable to find a significant difference between the specimens assigned to each proposed subspecies.

In 2021, a DNA study found the dire wolf to be a highly divergent lineage when compared with the extant wolf-like canines, and this finding is consistent with the previously proposed taxonomic classification of the dire wolf as genus Aenocyon (Ancient Greek: "terrible wolf") as proposed by Merriam in 1918.

Evolution

The canid family first appears in the North American fossil record around 40 million years ago, and the canine subfamily Caninae about 32 million years ago. From the Caninae, the ancestors of the fox-like Vulpini and the dog-like Canini branched off about 9 million years ago. The Canini are first represented by Eucyon, and mostly by coyote-like Eucyon davisi that was widely spread across North America. From the Canini the Cerdocyonina developed 6–5 million years ago, today represented by their canid descendants distinctly native to South America. Fossils of its sister clade, the wolf-like Canina, first appear 5 million years ago; however, they are believed to have likely originated as far back as 9 million years ago. Around 7 million years ago, the canines expanded into Eurasia and Africa, with Eucyon giving rise to the first members of the Canis genus in Europe. Around 4–3 million years ago C. chihliensis, the first wolf-sized member of Canis, arose in China and radiated into multiple other wolf-like canids across Eurasia and Africa. Members of the genus Canis later expand back into North America.

The dire wolf evolved in North America. However, its ancestral lineage is debated, with two competing theories: The first theory is based on fossil morphology, which indicates that an expansion of the genus Canis out of Eurasia led to the dire wolf. The second theory is based on DNA evidence, which indicates that the dire wolf arose from an ancestral lineage that originated in the Americas and was separate from the genus Canis.