Dire wolf

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Dire wolf
Temporal range: Rancholabrean, 0.25–0.010 Ma
Canis dirus Skeleton 2.jpg
Mounted skeleton
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Class: Mammalia
Order: Carnivora
Suborder: Caniformia
Family: Canidae
Genus: Canis
Species: C. dirus
Binomial name
Canis dirus
Leidy, 1858.[1]
Subspecies
  • Canis dirus dirus Kurten 1984[2]
  • Canis dirus guildayi Kurten 1984[2]
Synonyms

The dire wolf (Canis dirus, "fearsome dog") is an extinct species of the genus Canis. It is perhaps one of the most famous prehistoric carnivores in North America along with its extinct competitor Smilodon, the "sabre-toothed cat". Canis dirus lived in the Americas during the Late Pleistocene epoch (125,000–10,000 years ago). The species was named in 1858 but the first specimen had been found in 1854 in Ohio, USA. Two subspecies are recognized: Canis dirus guildayi and Canis dirus dirus. The species probably descended from Canis ambrusteri and evolved from it in North America. The largest collection of dirus fossils has been obtained from the Rancho La Brea Tar Pits in Los Angeles, California.

Canis dirus 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 m (7,400 feet). Dire wolf fossils have rarely been found north of 42°N latitude, with five unconfirmed reports above it. This range restriction is thought to be due to temperature, prey, or habitat imposed by proximity to the Laurentide Ice Sheet and the Cordilleran Ice Sheet that existed at that time.

Canis dirus was about the same size as the largest extant gray wolves (Canis lupus): the Yukon wolf and the Northwestern wolf. C.d. guildayi weighed on average 60 kg (130 lb) and C.d. dirus on average 68 kg (150 lb). Its skull and dentition matched those of lupus; however, its teeth were larger with greater shearing ability, and its biteforce at the canine tooth was the strongest of any known Canis species. These characteristics are thought to be adaptions for preying on Late Pleistocene megaherbivores, and in North America its prey is known to have included horse, sloth, mastodon, bison and camels. As with other large Canis hypercarnivores today, dirus was thought to have been a pack-hunter. Its extinction occurred during the Quaternary extinction event along with its main prey species. 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 unknown. The latest dire wolf remains were dated to 9,440 years ago.

Taxonomy[edit]

Display at the Page Museum of 404 dire wolf skulls found in the La Brea Tar Pits[9]

Canis dirus[10] was named by Joseph Leidy in 1858.[1] The first specimen of what would become later associated with dirus was found in the summer of 1854 at Evansville, Indiana when the Ohio River was 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.[3] Norwood's letters to Leidy are preserved along with the type specimen at the Academy of Natural Sciences. In 1857, while exploring the Niobrara River valley in Nebraska, Leidy found the vertebrae of an extinct canis which he reported the following year under the name Canis dirus. Canis primaevus (Leidy 1854) was later renamed Canis indianensis (Leidy 1869) when Leidy discovered that the name Canis primaevus had previously been used overseas.[4]

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 listed under these 3 provisional names until more material could be provided to show their relationship.[5] Canis indianensis (Leidy 1869) was declared a subjective synonym with Canis dirus by Troxell in 1915.[11] 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,[7] however not everyone agreed with leaving genus Canis.[12] Canis ayersi (Sellards 1916) and Aenocyon dirus (Merriam 1918) were subjective synonyms with Canis dirus by Lundelius in 1972.[13][14] All of the above taxa were declared as subjective synonyms with Canis dirus according to Nowak in 1979,[15] except for Aenocyon dirus nebrascensis.

In 1984, a study recognized a geographic variation within the 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.[2][16][17][18]

Evolution[edit]

Dire wolf divergence
Canis chihliensis
Canis lupus

Dogs, jackals, wolves, and foxes (Plate V).jpg



Canis armbrusteri
Canis dirus dirus

Canis dirus reconstruction.jpg


Canis dirus guildayi


Canis dirus reconstruction.jpg






Probable phylogeny for Canis dirus based on morphology[19]

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.[19]:146 The sudden appearance in North America during the Early Pleistocene of the large wolf Canis armbrusteri (Armbruster's wolf) suggests that this was an immigrant from Asia, as was Canis lupus (Gray wolf) later in the Pleistocene.[19]:144

The late Irvingtonian wolf Aenocyon dirus nebrascensis (Frick 1930 undescribed) fossil specimens from four sites in the Hay Springs area in Sheridan County, Nebraska, may represent the earliest record of the largely Rancholabrean Canis dirus, according to both Frick[8] and Tedford.[19]:146 Nowak referred to the material as Canis armbrusteri,[15]:93 however Tedford formally recorded a description of the material and noted that although these specimens exhibited some morphological characteristics of both ambrusteri and dirus, he referred to the material as Canis dirus.[19]:146 The three noted paleontologists X. Wang, R. H. Tedford and R. M. Nowak have all proposed that dirus had evolved from armbrusteri,[19]:181[20]:p52 with Nowak stating that there were specimens from Cumberland Cave, Maryland that indicated C. ambrusteri diverging into C. dirus.[21][22]:p243 The two taxa share a number of characteristics (synapomorphy), which suggests an origin of dirus in the late Irvingtonian in the open terrain in the midcontinent, and then later expanding eastward and displacing armbrusteri.[19]:181 The timing of 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,[19]:146 however the identity of the earliest fossils is not confirmed.[23]

The discovery of a fossil in the Horse Room of the Salamander Cave in the Black Hills of South Dakota may possibly be dirus, and if so then it is also one of the earliest records.[17] The specimen was catalogued as Canis cf. C. dirus[24] (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.[17][24] If the material is C. dirus then it would be a late Irvingtonian record of the species,[25] however the identity of the earliest fossils is not confirmed.[23]

Fossils of the eastern Canis dirus dirus have been dated to the Sangamonian era (125,000-75,000 YBP) but the western Canis dirus guildayi fossils are more recent and smaller in size, therefore it has been proposed that C.d. guildayi could be a derived form of the older C.d. dirus.[2][18]

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)[26]

In South America, Late Pleistocene dirus remains have been found along the north and west coasts but nowhere else. Its remains have not been found in Argentina that produced Canis gezi and Canis nehringi.[19]:148 Some researchers have proposed that dirus may have originated in South America.[15]:116[17][27] In 1988, a study formally described these two large South American wolves, with C. gezi found in Ensenadan era deposits that relate to the North American late Blancan and Irvingtonian, and C. nehringi found in Lujanian deposits that relate to the Late Pleistocene. Given their morphological similarities and timeframes, it was proposed that C. gezi was the ancestor of C. nehringi.[28]:113 The study indicated that C. gezi was most similar to the late Irvingtonian Aenocyon dirus nebrascensis and was its sister taxa,[28]:55 but C. nehringi had a closer relationship to Rancholabrean dirus.[28]:113 The study found that dirus was the most evolutionary derived genus Canis species in the New World, and compared to C. nehringi was larger in size and construction of its lower molars for more efficient predation.[28]:113 In 2009, a proposal was made that because there was believed to be a link between Canis armbrusteri and the Rancholabrean dirus, that a case could also be argued for a collateral South American lineage linking C. gezi with C. nehringi. These two clades share dental and cranial similarities developed for hypercarnivory, suggesting Canis ambrusteri as the common ancestor for both the North and South American clades.[19]:148

In 2010, a study of dental characteristics and DNA analyses of all South American extant canids and fossil hypercanivorous canids found that these could be divided into a Canis clade and a "South American clade". The study found that Canis dirus was a sister taxon of Canis lupus. Canis gezi was classified under the "South American clade" but dirus and C. nehringi were included as derived species in the Canis clade. The study indicated that dirus and C. nehringi were the same species, which supports dirus having migrated from North America into South America.[29]:472

Radiocarbon dating[edit]

The age of most dire wolf localities is determined solely by biostratigraphy. Canis dirus and Smilodon fatalis are the two most common carnivorans from the Rancho La Brea tar pits, but biostratigraphy is an unreliable indicator within asphalt deposits.[30][31] Some sites have been radiocarbon dated, with Canis dirus specimens at La Brea dated in calendar years as follows: 82 specimens dated 13,000-14,000 YBP; 40 specimens dated 14,000-16,000 YBP; 77 specimens dated 14,000-18,000 YBP; 37 specimens dated 17,000-18,000 YBP; 26 specimens dated 21,000-30,000 YBP; 40 specimens dated 25,000-28,000 YBP; and 6 specimens dated 32,000-37,000 YBP.[23]:T1 A specimen from Powder Mill Creek Cave, Missouri was dated at 13,170 YBP.[17]

Description[edit]

Dire wolf skeleton compared with that of the gray wolf (left)

Size[edit]

C. dirus was the largest of all Canis species.[20]:52 A study of the length and circumference of femur bones estimated the mean body mass of Canis dirus guildayi to be 60 kg (130 lb) and Canis dirus dirus to be 68 kg (150 lb).[18] Another study proposed that the increased stress caused in the humerus when running at maximum speed may have imposed a biomechanical upper limit on the body mass for Canis dirus dirus to be 110 kg (240 lb).[32] In comparison, the mean body mass of the extant gray wolf is 40 kg (88 lb) (with the smallest specimen recorded at 12 kg (26 lb) and the largest at 80 kg (176 lb)).[18][33][34][35][36] The figures indicate that on average dire wolves were the same size as the Yukon wolf (Canis lupus pambasileus) and the Northwestern wolf (Canis lupus occidentalis),[19] with the largest individuals possibly exceeding this size.[18]

The remains of a complete dirus are sometimes easy to identify because the baculum of the dire wolf is very different from that of all other living canids.[17]

Skull and dentition[edit]

The skull of the Dire wolf[37]

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."[28]:50

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 to the canines. 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.[38]

A study of the landmark 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,[39] and the dirus M1 was much larger and had more shearing ability.[27][39][40] The dire wolf canines had greater bending strength than those of extant canids of equivalent size.[41] These differences indicate that dirus was able to deliver stronger bites, and together with flexible and more rounded canines indicates that it was adapted for struggling with its prey.[39][42] One study that compared the craniodental morphology of dirus to lupus noted the similarity in skull shape between the two, and the variations found in the skull shape of each, and proposed that dirus evolved in North America from lupus that had originated in Eurasia.[22]:p242[43]

Wolf mandible diagram showing the names and positions of the teeth.
Canis lupus and Canis dirus compared by mean mandible tooth measurements (millimeters)
Tooth variable lupus extant[44] lupus La Brea[44] lupus Beringia[44] dirus dirus Early Wisconsin[2][42] dirus dirus Late Wisconsin[2][42] dirus guildayi[2][42]
m1 length 28.2 28.9 29.6 36.1 35.2 33.3
m1 width 10.7 11.3 11.1 14.1 13.4 13.3
m1 trigonid length 19.6 21.9 20.9 24.5 24.0 24.4
p4 length 15.4 16.6 16.5 16.7 16.0 19.9
p4 width - - - 10.1 9.6 10.3
p2 length - - - 15.7 14.8 15.7
p2 width - - - 7.1 6.7 7.4

Paleobiology[edit]

Natural traps[edit]

Two dire wolves mired in the La Brea tar pits, while fighting Smilodon over a Columbian mammoth carcass by R. Bruce Horsfall[45]

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. Over 200,000 specimens (fragments) have been recovered from the tar pits,[18] where the remains range from saber-toothed cats to squirrels, invertebrates and plants.[30] The time period includes the Last Glacial Maximum when global temperatures were eight degrees lower than today, the Pleistocene–Holocene transition (Bølling-Allerød interval), the Oldest Dryas cooling, the Younger Dryas cooling 12,800–11,500 YBP, and the American megafaunal extinction event 12,700 YBP when 90 genera of mammals weighing over 44 kilograms became extinct.[31][46]

Behavior[edit]

At La Brea, predatory birds and mammals were attracted to dead or dying herbivores that had become mired, and then these predators became trapped themselves.[30][47] The estimated herbivore entrapment was estimated to have occurred once every fifty years,[47] and for every herbivore remains that was found in the pits there were ten carnivores.[30] Canis dirus guildayi and Smilodon fatalis are the two most common carnivorans from Rancho La Brea,[31] with dirus the most common.[46] Remains of dirus outnumber remains of lupus in the tar pits by a ratio of five to one.[23] During the Last Glacial Maximum, coastal California is thought to have been a refuge with the climate slightly cooler and wetter than today,[48] and 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 abundances, therefore the higher dirus numbers in the La Brea region did not reflect the wider area.[49]

Skeleton from the La Brea Tar Pits mounted in running pose

Assuming that only a small number of the carnivores that were feeding became trapped, it is likely that fairly sizeable groups of dirus fed together on these occasions.[50] Sexual dimorphism is the difference between the male and female of a species apart from their sex organs and there is little variance among the 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 was similar to that of the gray wolf.[50] Their large size and highly carnivorous dentition indicates that dirus was a predator that feeds on large prey.[50][51][52] 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.[50] 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.[49][53]

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.[32][54] The large size of dirus provides an estimated prey size in the 300–600 kg range.[18][51][52] 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, and occasionally scavenged on beached whales along the Pacific coast when available.[18][39][55] A pack of timber wolves can bring down a 500 kg moose that is their preferred prey,[56] and a pack of dire wolves bringing down a bison is conceivable.[18] 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.[39]

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 an important prey species, and that sloth, mastodon, bison and camel were less common in the dirus diet.[42][48] This indicates that dirus was not a prey specialist, and at the close of the Late Pleistocene in the La Brea area before extinction it was hunting or scavenging off the most available herbivores.[48]

Tooth breakage[edit]

A study of nine modern carnivores found that one in four adults had suffered tooth breakage, of which half of these breakages were of the canine teeth. The study proposed that this breakage was related to behavior, with the most breakage occurring in the spotted hyena that is known to consume all of its prey, including the bone.[57][58] A later study of the fossil remains of large carnivores from the Rancho La Brea Tar Pits that were dated 36,000-10,000 YBP indicated tooth breakage rates of 5-17% for the dirus, 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 dirus used its incisors more closely to the bone when feeding. Data on 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.[46][58][59] As their prey became extinct around 10,000 years ago so too did these competing carnivores except for the omnivorous coyote.[58][59]

A later Rancho La Brea tar pits study compared 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.[59][60]

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.[61] The fact that the fracture incidence of dirus reduced in frequency in the late Pleistocene to that of its extant relatives[58][60] 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.[59][61] A later study found that just before extinction dirus carcass utilization was less than among large carnivores today.[62][63]

Climate impact[edit]

Past studies have indicated that changes in dirus body size correlates with climate fluctuations.[31][46][64][65][66] A later study compared dirus craniodental morphology from 4 La Brea pits, each representing four different time periods. The results indicated a change in dirus size, dental wear and breakage, skull shape and snout shape across time. Dire wolf body size had decreased between the start of the Last Glacial Maximum and near its ending at the warm Allerød oscillation. Food stress is indicated by a smaller body size, skulls with the larger cranial base and shorter snouts (shape neotony and size neoteny), and more tooth breakage and wear. Canis dirus dated 17,900 YBP showed all of these features, which indicated food stress. Canis dirus dated 28,000 YBP also showed to a degree many of these features but were the largest wolves studied, and it was proposed that these wolves were also suffering from food stress and that wolves earlier to this date were even bigger in size.[46] Nutrient stress is likely to lead to stronger bite forces to more fully consume carcasses and to crack bones,[46][67] and with changes to skull shape to improve mechanical advantage. North American climate records revealed cyclic fluctuations during the glacial period that included rapid warming followed by gradual cooling, called Dansgaard–Oeschger events. These cycles would have caused increased temperature and aridity, and at La Brea would have caused ecological stress and therefore food stress.[46] A similar trend was found with C. lupus, which in the Santa Barbara basin was originally massive, robust and possibly convergent with dirus, but was replaced by more gracile forms by the start of the Holocene.[15][43][46]

Canis dirus information based on skull measurements[46]
Variable 28,000 YBP 26,100 YBP 17,900 YBP 13,800 YBP
Body size largest large smallest medium/small
Tooth breakage high low high low
Tooth wear high low high low
Snout shape shortening, largest cranial base average shortest, largest cranial base average
Tooth row shape robust - - gracile
DO event number 3 or 4 none imprecise data imprecise data

Habitat and distribution[edit]

Restoration of a pack by Charles R. Knight, 1922[68]

Canis dirus 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 m (7400 feet).[17] The location of its fossil remains suggests that it lived predominantly in the open lowlands along with its prey the large herbivores.[15] Canis dirus does not occur at high latitudes, unlike its close relative, Canis lupus.[17]

In the United States, its fossils have been reported in Arizona, California, Florida, Idaho, Indiana, Kansas, Kentucky, Missouri, Nebraska, New Mexico, Oregon, Pennsylvania, South Carolina, South Dakota, Texas, Utah, Virginia, West Virginia, and Wyoming.[10] However, the identity of fossils reported further north than California are not confirmed.[10][23] Dire wolf fossils have rarely been found north of 42°N latitude, with five unconfirmed reports above it: Fossil Lake, Oregon (Late Pleistocene), American Falls Reservoir, Idaho (Sangamonian), Salamander Cave, South Dakota (Irvingtonian), and four closely grouped sites in northern Nebraska (Irvingtonian).[10][23][69] This indicates a range restriction on dirus due to temperature, prey, or habitat.[23] The major fossil-producing sites for C.d. dirus are located east of the Rocky Mountains and include Friesenhahn Cave, Texas, Carroll Cave, Missouri, and Reddick, Florida.[18]

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.[42]

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.[17] If Canis dirus originated in North America, the species likely dispersed into South America via the Andean corridor,[17][28] 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.[17][70]

Competitors[edit]

Just before the appearance of C. dirus, North America was invaded by the genus Xenocyon (ancestor of the Asian dhole and the African hunting dog) that was as large as C. dirus and more hypercarnivorous. The fossil record shows them as rare and it is assumed that they could not compete with the newly derived C. dirus.[20]:p60 Stable isotope analysis indicates that Canis dirus, the saber-toothed cat Smilodon fatalis, and the extinct American lion Panthera atrox competed for the same prey.[62][63][71] Other large carnivores present at that time include the extinct North American giant shortfaced bear Arctodus simus, the extant cougar Puma concolor, the Pleistocene coyote Canis latrans, and the gray wolf Canis lupus.[62][63] These predators may have competed with humans who hunted for similar prey.[62] Specimens that have been identified by morphology to be Beringian wolves (lupus) and radiocarbon dated between 25,800-14,300 YBP have been recently found in the Natural Trap Cave at the base of the Bighorn Mountains in Wyoming, United States. 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 large, Alaskan direct competitors of the dire wolf that were also adapted for predating on megafauna to come south of the ice sheets. Dire wolves were absent north of 42°N latitude in the Late Pleistocene, therefore this region would have been available for Beringian wolves to expand south along the glacier line. How widely they were then distributed is unknown. These also became extinct at the end of the Late Pleistocene as did the dire wolf.[23]

Extinction[edit]

The American megafaunal extinction event occurred 12,700 YBP when 90 genera of mammals weighing over 44 kilograms became extinct.[31][46] The dire wolf is inferred to have become extinct near the end of the Pleistocene in both North and South America.[17] The extinction of the large carnivores and scavengers is thought to be caused by the extinction of their megaherbivore prey.[17][48][58][60][72][73][74][75][76] However, a study of the dental microwear on tooth enamel was undertaken for specimens of all of the carnivore species from Rancho La Brea, California, including dirus. The evidence suggests that these carnivores were not food-stressed just before extinction and that carcass utilization was less than among large carnivores today.[62][63] Its extinction has been proposed to be based on its reliance on megaherbivores, the impact of climate change, and competition with other species including humans[62] but the cause is not known.

The latest Canis dirus remains were dated 9,440 YBP and found in Brynjulfson Cave, Boone County, Missouri.[27]

See also[edit]

References[edit]

  1. ^ a b Leidy, J. 1858: Notice of remains of extinct vertebrata, from the Valley of the Niobrara River, collected during the Exploring Expedition of 1857, in Nebraska, under the command of Lieut. G. K. Warren, U. S. Top. Eng., by Dr. F. V. Hayden, Geologist to the Expedition, Proceedings: Academy of Natural Sciences of Philadelphia, volume 10:1858 p21. LINK:[1]
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