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Image-1463320438

An artistic rendition of two possible appearances of the dire wolf, one based on a North American origin (left) and the other on a South American origin (right)

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Two dire wolves mired in the La Brea tar pits, while fighting Smilodon over a Columbian mammoth carcass by R. Bruce Horsfall

The dire wolf (Canis dirus, "terrible dog") is an extinct carnivorous mammal of the genus Canis, roughly the size of the extant gray wolf, but with a heavier build. It evolved in the New World and was its most evolutionary derived species of Canis. Canis dirus lived during the Rancholabrean land mammal age of North America (240,000–10,000 years BP) and was among the many large carnivores and megaherbivores that became extinct in North and South America near the end of the Pleistocene epoch. Its ending is associated with the Quaternary extinction event.

Taxonomy[]

Canis dirus was named by Joseph Leidy in 1858. In 1984, a study recognized a geographic variation within the North American dire wolf populations and proposed two subspecies: Canis dirus guildayi for specimens from California and Mexico with shorter limbs and longer teeth, and Canis dirus dirus for specimens east of the North American Continental Divide with longer limbs and shorter teeth. The study also proposed that C.l. guildayi might be a more derived form because it has a more recent origin.

The first type specimen was originally found in the summer of 1854 at Evansville, Indianawhen the Ohio River was quite low. The specimen, a fossilized jawbone, was obtained by Joseph Granville Norwood from an Evansville collector named Francis A. Linck. Leidy determined 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 at the Academy of Natural Sciences. Canis primaevus(Leidy 1854) was later renamed Canis indianensis (Leidy 1869) when Leidy discovered that the name Canis primaevus had previously been used overseas.

Canis indianensis (Leidy 1869) was first associated with Canis dirus (Leidy 1858) by Allen in 1876 along with his discovery of Canis mississippiensis. As there were so few pieces of these 3 specimens, it was thought best to leave each specimen listed under these 3 provisional names until more material could be provided to show their relationship. Canis indianensis (Leidy 1869) was declared a subjective synonym with Canis dirus according to a taxonomic opinion of Troxell in 1915. In 1918, Merriam studied these fossils and proposed consolidating their names under the separate genus Aenocyon (from Aenos:terrible and cyon:wolf) to become Aenocyon dirus, however not everyone agreed with moving away from genus Canis. Canis ayersi (Sellards 1916) and Aenocyon dirus (Merriam 1918) were subjective synonyms with Canis dirusaccording to a taxonomic opinion of Lundelius in 1972. All of the named taxa were subjective synonyms with Canis dirus according to a taxonomic opinion by Nowak in 1979, except for Aenocyon dirus nebrascensis.

Evolution[]

The fossil record suggests that Feliforms and caniforms emerged within the super-family Carnivoramorpha 43 million years before present (YBP). The caniforms included the fox-like Leptocyon genus whose various species existed from 34 million YBP before branching 11.9 million YBP into vulpes(foxes) and canini (canines). The Eucyon genus diverged 6.2 million YBP towards Canis ferox, which diverged 5 million YBP towards Canis lepophagus, which diverged 3.5 million YBP towards the wolf-like canids.

North America[]

The sudden appearance in North America during the early Pleistocene of the large Canis armbrusteri (Armbruster's wolf) suggests that this was an immigrant from Asia, as was Canis lupus (Gray wolf) later in the Pleistocene. In China, the Pliocene wolf Canis chihliensis was a sister taxon of the lupus clade and may have been the ancestor for both Canis armbrusteri and Canis lupus.

The late Irvingtonian wolf Aenocyon dirus nebrascensis (Frick 1930 undescribed) from the Hay Springs area in Sheridan County, Nebraska, may represent the earliest record of the largely Rancholabrean Canis dirus, according to both Frick and Tedford. Nowak referred to the material as Canis armbrusteri, however Tedford described the material and noted that although these exhibited some morphological characteristics of both, he referred to the material as Canis dirus. There is good evidence of the evolution of Canis dirus from Canis armbrusteri. These taxa share a number of characteristics (synapomorphy), which suggests an origin of Canis dirus in the late Irvingtonian, probably in more open terrain in the midcontinent, and later extending its way to the east and displacing Canis armbrusteri. The timing of Canis dirus would therefore be the Late Irvingtonian of California and Nebraska, and the Rancholabrean of Canada, the United States, Mexico, Venezuela, Ecuador, Bolivia and Peru.

The discovery of a fossil in the Horse Room of the Salamander Cave in the Black Hills of South Dakota may possibly be that of a dire wolf, and if so then it is also one of the earliest records. The specimen was catalogued as Canis cf. C. dirus (where cf. in Latin means confer, uncertain). A horse fossil found in the room gave a uranium-series dating of 252,000 years before present (YBP) and the Canis cf. dirus specimen was assumed to be from the same period. If the material actually represents Canis dirus, it would be a late Irvingtonian record of the species.

South America[]

In South America, dirus remains have been dated to the late Pleistocene and seems to have been restricted to the north and west coasts. Its remains have not been found in Argentina that produced Canis gezi and Canis nehringi, and their remains have not been found elsewhere in South America. Some researchers have proposed that Canis dirus may have originated in South America. In 1988 a study of these two large South American wolves described them, with Canis gezi found in South American Ensenadan deposits that relate to the North American late Blancan and Irvingtonian, and Canis nehringi found in South American Lujanian deposits that relate to the Late Pleistocene. Given their similarities and timeframes, it was proposed that Canis gezi was the ancestor of Canis nehringi. The study indicated that Canis gezi was most similar to the late Irvingtonian Aenocyon dirus nebrascensis and was its sister taxa, but Canis nehringi had a closer relationship to Rancholabrean Canis dirus. The study found that Canis diruswas the most derived genus Canis species in the New World, and compared to Canis nehringi was larger in size and construction of its lower molars that were increased for more efficient predation. In 2009, Tedford proposed that because there was now seen a link between Canis armbrusteri and the Rancholabrean Canis dirus, that a case could be argued for a collateral South American lineage linking Canis gezi with Canis nehringi. These two clades share dental and cranial similarities developed for hypercarnivory, suggesting a common ancestor for both clades.

In 2010, a study found that DNA analysis and the dental characteristics of South America hypercanivorous canids showed a "South American clade" and the Canis clade. Canis gezi was a member of the "South American clade" of carnivores, but Canis dirus and Canis nehringi were included as derived species in the Canis clade. Canis dirus was the sister taxon of Canis lupus, but the scientific scoring used in this study for Canis nehringi was identical to those observed in Canis dirus, which supports the proposal that both could have been the same species.

Description[]

Size[]

A study using the length and circumference of femur bones from dire wolves estimated their body mass, with specimens of Canis dirus guildayi giving a mean body mass of 60 kg (130 lb) and Canis dirus dirus giving a mean body mass of 68 kg (150 lb). Another study proposes that the increased stress caused in the humerus when running at maximum speed may have imposed a biomechanical upper limit on body mass, and for Canis dirus dirus this upper limit was 110 kg (240 lb). In comparison, the mean body mass of the extant gray wolf was 40 kg (88 lb) (with the smallest specimen recorded at 12 kg (26 lb) and the largest at 80 kg (176 lb)). The figures indicate that on average dire wolves were the same size as the largest gray wolves, with the largest individuals possibly exceeding this size. Extant wolves that are approximately the average size of dirus are the Yukon wolf (Canis lupus pambasileus) and the Northwestern wolf (Canis lupus occidentalis).

Skull and dentition[]

A study of Canis dentition found that dirus was the most evolutionary derived: "Canis dirus is regarded here as the most derived species of the genus Canis in the New World. The following combination of derived characters separates C. dirus from all other species of Canis: P2 with a posterior cusplet; P3 with two posterior cusplets; M1 with a mestascylid, entocristed, entoconulid, and a transverse crest extending from the metaconid to the hyperconular shelf; M2 with entocristed and entoconulid."

A study of the estimated bite force at the canine teeth of a large sample of living and fossil mammalian predators when adjusted for the body mass found that for placental mammals, the bite force at the canines (in Newtons/kilogram of body weight) was greatest in the dire wolf (163), then followed among the extant canids by the four hypercarnivores that often prey on animals larger than themselves: the African hunting dog (142), the gray wolf (136), the dhole (112), and the dingo (108). The bite force at the carnassials showed a similar trend. A predator’s largest prey size is strongly influenced by its biomechanical limits. The morphology of dirus was similar to that of its living relatives, and assuming that dirus was a social hunter, then its high bite force relative to extant canids suggests that it preyed on relatively large animals. The bite force rating of the bone-consuming feliform, the spotted hyena (117), challenged the common assumption that high bite force in the canines and the carnassials was necessary in order to consume bone.

A study of the cranial measurements and jaw musculature of dirus found no significant differences with extant lupus in all but 4 of 15 measures. Upper dentition was the same except that dirus had larger dimensions and the P4 had a relatively larger, more massive blade which indicates enhanced slicing ability at the carnassial. The jaw indicated that dirus had a relatively broader and more massive temporalis muscle, indicating that it could generate slightly more bite-force than lupus. However, due to the jaw arrangement dirus had lower temporalis leverage than lupus at the lower carnassial and lower P4, and the functional significance of this is not known. The lower premolars were relatively slightly larger than lupus, and the dirus M1 was much larger and had more shearing ability. The dire wolf canines had greater bending strength than those of extant canids of equivalent size. These differences indicate that dirus was able to deliver stronger bites, and together with flexible and more rounded canines indicates that it had struggled with its prey.

Tooth breakage[]

A study of nine modern carnivores found that one in four adults had suffered tooth breakage, of which half were the canine teeth. The study proposed that this breakage was related to behavior, with the most breakage appearing in the spotted hyena that consumes all of its prey including the bone. A later study of the fossil remains dated 36,000-10,000 YBP from the Rancho La Brea Tar Pits indicated tooth breakage rates of 5-17% for the dire wolf, coyote, American lion and saber-tooth cat, compared to 0.5-2.7% for 10 modern predators. These higher fracture rates were across all teeth and not more often the canine teeth as when compared to the modern carnivores. The dire wolf broke its incisors more often when compared to the extant gray wolf, therefore it was proposed that dirusused its incisors more closely to the bone when feeding. Data from dirus fossils from Mexico and Peru show a similar pattern of breakage. The study proposed that the higher frequency of tooth breakage compared with extant carnivores was not the result of hunting larger game because the Pleistocene carnivores were larger than their modern counterparts. Carnivores feed more rapidly when food is scarce and competition is high, often consuming bone. The study proposed that the breakage was due to increased carcass consumption including bone due to low or seasonal prey availability, or greater competition, or both. As their prey became extinct around 10,000 years ago so too did these competing carnivores except for the omnivorous coyote.

A later study compared Rancho La Brea tar pits tooth breakage of dirus between two time periods. One pit contained fossil dirus dated 15,000 YBP and another dated 13,000 YBP. The results showed that the 15,000 YBP dirus had three times more tooth breakage than the 13,000 YBP dirus whose breakage matched those of nine modern carnivores. The study concluded that between 15,000-14,000 YBP prey availability was less or that competition was higher for dirus, and by 13,000 YBP as the prey species and dirus moved towards extinction that predator competition had declined and therefore the frequency of tooth breakage had also declined.

In carnivores, the solitary hunters depend on a powerful canine bite to subdue their prey and these also have a strong mandibular symphysis, while the pack hunters that deliver many shallow bites have a relatively weaker one. The mandibles of canids are buttressed behind the carnassial teeth in order to crack bones with their post-carnassial teeth (molars M2 and M3). A study found that the mandible buttress profile of dirus was lower than that of the gray wolf and the red wolf, but very similar to the coyote and the African hunting dog. The dorsoventrally weak symphyseal region (in comparison to premolars P3 and P4) of dirus indicates that it delivered shallow bites similar to its modern relatives and therefore was a packhunter. This suggests that dirus may have processed bone but was not as well adapted at this as lupus. The fact that the fracture incidence of dirus reduced in frequency in the late Pleistocene to that of its extant relatives indicates that reduced competition allowed dirus to return to a feeding behaviour with a lower amount of bone consumption for which it was best suited for.

In 2015, a study looked at specimens of all of the carnivore species from Rancho La Brea, California, including remains of the large wolf Canis dirus that was also a megafaunal hypercarnivore. The evidence suggests that these carnivores were not food-stressed just before extinction and that carcass utilization was less than among large carnivores today. The high incidence of tooth breakage likely resulted from the acquisition and consumption of larger prey.

Behavior[]

The Rancho La Brea tar pits located near Los Angeles, California are a collection of sticky asphalt deposits made up of pits which differ in deposition time from 40,000-12,000 YBP. Predatory birds and mammals were attracted to dead or dying herbivores that had become mired, and then these predators became trapped themselves. The remains range from saber-toothed cats to squirrels, invertebrates and plants. The time period includes the Last Glacial Maximum when global temperatures were eight degrees lower than today, the Pleistocene–Holocene transition, the Younger Dryas cooling 12,800–11,500 YBP, and the American megafaunal extinction event 12,700 YBP when 33 genera of large mammals disappeared.

The estimated herbivore entrapment was estimated to have occurred once every fifty years, and for every herbivore remains that was found in the pits there were ten carnivores. Canis dirus guildayi and Smilodon fatalis are the two most common carnivorans from Rancho La Brea. Assuming that only a small number of the carnivores that were feeding became trapped, it is likely that fairly sizeable groups of Canis dirus guildayi fed together on these occasions. Sexual dimorphism is the difference between the male and female of a species apart from their sex organs and there is little variance among canids regardless of their group size. A study of the skull length, canine tooth size, and lower molar length of dirus remains, dated between 15,360–14,310 YBP and taken from one pit, showed little dimorphism and therefore indicated that dirus lived in monogamous pairs. The level of dimorphism is similar to that of the gray wolf. Their large size and highly carnivorous dentition indicates a predator that feeds on large prey. In order to kill ungulates larger than themselves the African wild dog, the dhole, and the gray wolf depend on their jaws because they cannot use their forelimbs to grapple with prey, and they work together as a pack that consist of an alpha pair and their offspring from the current and previous years. It can be assumed that dirus lived in packs of relatives that were led by an alpha pair. Large and social carnivores would have been successful at defending carcasses of trapped prey from smaller solitary predators, and the most likely to become trapped themselves, which indicates that both Canis dirus guildayi and Smilodon fatalis were social predators.

All social terrestrial mammalian predators feed mostly on terrestrial herbivorous mammals with a body mass similar to the combined mass of the social group members attacking the prey animal. The large size of dirus provides an estimated prey size in the 300-600kg range. Stable isotope analysis of dirus bones indicate that they had a preference for consuming ruminants such as bison rather than other herbivores but moved to other prey when food became scarce, occasionally scavenged on beached whales along the Pacific coast when available. A pack of timber wolves can bring down a 500kg moose as their preferred prey, and a pack of dire wolves bringing down a bison is conceivable. Although some studies have suggested that because of tooth breakage that dirus gnawed bones and may have been a scavenger, its widespread occurrence and the more gracile limbs of Canis dirus dirus indicate a predator. The dire wolf probably used its molars to crack bones similar to the gray wolf, however due to their larger size it could crack larger bones to give access to bone marrow.

A study of carbon and nitrogen isotope data of Rancho La Brea dirus fossils dated 10,000 YBP indicated that the horse was at that time the important prey species, and that sloth, mastodon, bison and camel were less common. This indicates that dirus was not a prey specialist and at the close of the Late Pleistocene in the La Brea area it was hunting or scavenging off the most available herbivores. The extinction of the large Pleistocene carnivores and scavengers is thought to be caused by the extinction of their megafaunal herbivore prey.

Habitat and distribution[]

During the Last Glacial Maximum, coastal California is thought to have been a refuge with the climate slightly cooler and wetter than today. The major fossil-producing site for C.d. guildayi is located at the Rancho La Brea tar pits in Los Angeles, California and some of the major fossil-producing sites for C.d. dirus located east of the Rocky Mountains include Friesenhahn Cave, Texas, Carroll Cave, Missouri, and Reddick, Florida. Over 200,000 specimens (fragments) have been recovered from the tar pits. Remains of C. dirus outnumber remains of gray wolves in the tar pits by a ratio of five to one. A comparison of the frequency of "dirus" and other predator remains at La Brea to other parts of California and North America indicated significantly greater relative abundances, and that dirus numbers in the La Brea region did not reflect the wider area.

Dire wolf remains have been found across a broad range of habitats: South America in arid savannah conditions; and North America on the plains and grasslands, and in some forested mountain areas. The sites range in elevation from sea level to 2,255 m (7400 feet). Canis dirus does not occur at high latitudes, unlike its close relative, Canis lupus. Its remains have been found in 136 places, from Alberta, Canada, to Tarija, Bolivia. The dire wolf was recorded as far north as Alberta, Canada and may have migrated to northern Canada during interglacial periods, however its remains would likely have been obliterated by later glacial activity. In South America, dirus has been dated younger than 17,000 YBP and reported from only three localities: Muaco, Venezuela; Talara, Peru; and Tarija, Bolivia.

Ten localities in the central and southeast-central areas of Mexico are known to contain Canis dirus: Cedazo, Aguascalientes; Comondu, Baja California; El Cedral, San Luis Potosí; El Tajo Quarry, Tequixquiac, and Valsequillo, all in Distrito Federal, Mexico; Lago de Chapala, Jalisco; Loltun Cave, Yucatán; Potrecito, Sinaloa; and San Josecito Cave, Nuevo León. Of the central localities, San Josecito Cave and Cedazo have the greatest number of individuals of Canis dirus collected from a single locality. Other localities in Mexico have only a few specimens. A study of specimens from Sonora were confirmed as belonging to Canis dirus guildayi.

If Canis dirus originated in North America, the species likely dispersed into South America via the Andean corridor, a proposed pathway for temperate mammals to migrate from Central to South America because of the favorable cool, dry and open habitats that characterized the region at times. This most likely happened during a glacial period, however, as the pathway then consisted of open, arid regions and savanna whereas during inter-glacial periods, it would have been characterized by tropical rain forest habitat.

Competitors[]

During the Late Pleistocene (125,000 years ago) the gray wolf (C. lupus) crossed into North America on the Bering land bridge and competed with the dire wolf. Specimens that have been identified by morphology to be Beringian wolves and radiocarbon dated between 25,800-14,300 YBP have been found in the Natural Trap Cave at the base of the Bighorn Mountains in Wyoming, USA. The location is directly south of what would at that time have been the division between the Laurentide Ice Sheet and the Cordilleran Ice Sheet. A temporary channel between the glaciers may have existed that allowed these megafaunally-adapted direct competitors of the dire wolf south of the ice sheets. How widely they were distributed is unknown. Overlapping fossil findings of the extinct saber tooth cat, the Smilodon, shows that the dire wolf had these as competition in North America. Both species were social animals that hunt in packs and preyed on the same animals.

Extinction[]

The American megafaunal extinction event occurred 12,700 YBP when 33 genera of large mammals disappeared. It has been proposed that the extinction of large carnivores was the result of the extinction of their mega herbivore prey. A study concluded that the loss of prey species remains the prime hypothesis for the extinction of the dirus and not competition with other large carnivores. The dire wolf is inferred to have become extinct near the end of the Pleistocene in both North and South America.

Approximately 10,000 years ago the dire wolf became extinct along with most other American megafauna. However, in 2015 a study looked at specimens of all of the carnivore species from Rancho La Brea, California, including remains of the large wolf Canis dirus that was also a megafaunal hypercarnivore . The evidence suggests that these carnivores were not food-stressed just before extinction and that carcass utilization was less than among large carnivores today.

Gallery[]

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