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Temporal range: Early Pleistocene–Late Pleistocene
Temporal range: Early Pleistocene–Late Pleistocene
The dire wolf (Canis dirus "fearsome dog") is an extinct carnivorous mammal of the genus Canis related to the smaller extant gray wolf. It was most common in North America and South America from the Irvingtonian stage to the Rancholabrean stage of the Pleistocene epoch, living 1.80 Ma—10,000 years ago, persisting for approximately .
The dire wolf averaged about 1.5 m (4.9 ft) in length and weighed between 50 kg (110 lb) and 79 kg (174 lb). With the exception of the canine teeth in some populations, male and female body and teeth sizes evidence no major differences. In some populations, males’ canines were considerably larger, implying male competition for breeding access. In other populations, lack of sexual dimorphism in the canine teeth implies little competition.
Despite superficial similarities to the gray wolf, the two species differed significantly. Today’s largest gray wolves would have been of similar size to an average dire wolf; the largest dire wolves would have been considerably larger than any modern gray wolf. The dire wolf is calculated to weigh 25% more than living gray wolves.
Many of these characteristics were needed to fight off and prey on larger megafauna. The legs of the dire wolf were proportionally shorter and sturdier than those of the gray wolf, and its brain case was smaller than that of a similarly sized gray wolf.
The dire wolf's teeth were similar to the gray wolf's, only slightly larger, pointing to a hypercarnivorous to mesocarnivorous activity. Paleontologist R.M. Nowak states the dietary characteristics are primarily carnivorous, as well as partially omnivorous.
The slicing teeth (P4, the carnassial) on the upper jaw of C. dirus are larger than those of the gray wolf, but those on the lower jaw are similar. The temporalis of the dire wolf could generate more force than seen in modern gray wolves, suggesting stronger killing bites.
Many paleontologists have proposed that the dire wolf may have used its relatively large teeth to crush bone, an idea supported by the frequency of large amounts of wear on the crowns of their fossilized teeth. The upper carnassial had much larger blade than that of the gray wolf, indicating greater slicing ability. It had a longer temporal fossa and broader zygomatic arches, indicating the presence of a large temporalis muscle capable of generating slightly more force than a gray wolf's. However, other scientists have noted the dorsoventral and labiolingual force profiles are indistinguishable from those of other canids, such as coyotes and African wild dogs, indicating a similar diet.
Dire wolf teeth lacked the craniodental adaptations of habitual bonecrushers such as hyenas and borophagines. The dorsoventrally weak symphyseal region indicates it killed in a manner similar to its modern relatives, by delivering a series of shallow bites, strongly indicating pack hunting behaviour. However, the incidence of broken postcarnassial molars is much higher than in fossil gray wolves, indicating the species was probably less adapted to bone crushing than the gray wolf.
Dire wolves' overpowering bite, 129% of the force of the modern gray wolf, could hold and subdue their prey. As inferred from their large bodies and carnivorous teeth, they often took on large prey or megafauna, made possible by traveling in packs. Dire wolves were not specialized hunters—they fed on whatever megafauna was abundant.
The recovery of material belonging to over 4,000 individuals at the La Brea Tar Pits suggests that dire wolves were social animals living in large groups.
The habitat of C. dirus varied considerably. The dire wolf preferred elevations from sea level up to 2,255 m.
Canis dirus was named by Joseph Leidy in 1858 and recombined as Aenocyon dirus by Merriam (1918), Hibbard (1949) and Hibbard and Taylor in 1960. In 1916, Canis ayersi was named by Sellards. It was recombined as Aenocyon ayersi by Merriam in 1918 and was synonymized subjectively with C. dirus by Lundelius in 1972, Martin (1974), Nowak (1979), Kurten and Anderson (1980) and Kurten in 1984. Leidy also named the dire wolf as Canis indianensis in 1869 which was synonymized subjectively with C. dirus by Troxell in 1915. Canis mississippiensis was named by Allen in 1876 and synonymized subjectively with Canis dirus by Nowak (1979), Kurten and Anderson (1980) and again by Kurten in 1984.
The type specimen of the dire wolf was found in Evansville, Indiana, in the summer of 1854, when 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. Norwood, who at that time was the first state geologist of Illinois, sent the specimen to Joseph Leidy at the Academy of Natural Sciences in Philadelphia. Leidy determined the specimen represented an extinct species of wolf and published a note to that effect in November 1854. In a publication dated 1858, Leidy assigned the name Canis dirus.
Norwood's letters to Leidy are preserved along with the type specimen at the Academy of Natural Sciences, although one of the letters indicates the specimen was to be returned to Linck's family, as Linck died in August 1854.
The dire wolf is best known for its unusually high representation in La Brea Tar Pits in California. Fossils from more than 4,000 dire wolves have been recovered from the tar pits, more than any other mammal species. This large number suggests the dire wolf, like modern wolves and dogs, hunted in packs. The abundance of remains of the gray wolf (C. lupus, also known as C. furlongi) in the tar pits is about one per cent that of the dire wolf.
Whether the dire wolf originated in North America versus South America is the subject of controversy. Most paleontologists lean toward a North American origin for three reasons: first, more potential progenitors are present in the middle Pleistocene of North America; second, distribution of C. dirus is much better represented in North America, with 136 sites versus only three localities in South America; and last, C. dirus appears earlier in the fossil record in North America than South America. A North American origin implies that C. dirus migrated into South America from North and Central America.
The fossil record suggests that the genus Canis diverged from the small, foxlike Leptocyon in North America sometime in the Late Miocene epoch 9 to 10 million years (Ma) ago, along with two other genera, Urocyon, and Vulpes. Canids soon spread to Asia and Europe (8 Ma BP) and became the ancestors of modern wolves, jackals, foxes, and the raccoon dog.
By 3–5 Ma BP, canids had spread to Africa (Early Pliocene) and South America (Late Pliocene). Their invasion of South America as part of the Great American Interchange was enabled by the formation of the Isthmus of Panama 3 Ma ago.
Over the next nine million years, extensive development and diversification of the North American wolves took place by the Middle Pleistocene. Canis armbrusteri appeared, possibly from C. chihliensis in Asia. There is good evidence that the dire wolf evolved from C. armbrusteri, with the two taxa sharing in the open plains and grasslands of what is now the central United States.
C. dirus eventually displaced C. armbrusteri, with the latter's final range shrinking to what is now the southeastern U.S., more specifically Florida. While this occurred, C. dirus expanded its range to include that of C. armbrusteri and moved into Central America and South America, appearing in the Late Pleistocene fossil record in northwestern South America.
Two subspecies of the dire wolf are known to have inhabited what is now the United States. C. dirus guildayi was smaller and ranged west of the Rocky Mountains. C. dirus dirus was larger and ranged east of the Rockies.
Although it was closely related to the gray wolf and other sister species, C. dirus is not the direct ancestor of any modern species. Unlike the gray wolf, which is of Eurasian origin, the dire wolf evolved on the North American continent, along with the coyote. The dire wolf co-existed with the gray wolf in North America for about 100,000 years.
The dire wolf was one of the abundant Pleistocene megafauna—a wide variety of large mammals that lived during the Pleistocene. Approximately 10,000 years ago the dire wolf became extinct along with most other North American megafauna. This timing can only be approximated because very few radiocarbon dates are directly associated with the dire wolf.
During the Late Pleistocene (300,000 years ago) the gray wolf (C. lupus) crossed into North America on the Bering Strait land bridge and competed with the dire wolf. Starting about 16,000 years ago, coinciding with the end of the last glacial period and the arrival of humans in North America, most of the large mammals upon which the dire wolf depended for prey began to die out (possibly as a result of climate and/or human-induced changes as suggested in a 2008 National Geographic Channel documentary).
Slower than the other wolf species on the continent at the time, primarily the gray wolf and red wolf, the dire wolf could not hunt the swifter species that remained and was forced to subsist by scavenging. By approximately 10,000 years ago, the large mammals and the dire wolf were extinct. In order to fully understand the extinction of C. dirus, many more dire wolf specimens must be directly dated. In addition to this, more information must be gathered on the factors that affected its biogeographical range and population size, including competition, interactions with predators and prey, its physical environment, as well as how all of its competitors and prey responded to the event of time; thus, the timing of extinction of megafauna that closely interacted with C. dirus must be determined.
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