Dire wolf

The dire wolf (Canis dirus "fearsome dog") is an extinct carnivorous mammal of the genus Canis, roughly the size of the extant gray wolf, but with a heavier build. 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 to 10,000 years ago, persisting for approximately 1.79 million years.

Morphology
The dire wolf averaged about 1.5 m (5 ft) in length and weighed between 50 and 79 kg (110 and 174 lb),[1] which made it the largest species in the genus Canis.[2] Limb elements are rarely found outside the La Brea Tar Pits, which makes it hard to compare the size of average individuals between populations. The dire wolf is estimated to have been 8% shorter at the shoulder than the modern Northwestern wolf, and of equal height to the typical gray wolf, but more heavily built.[3] With the exception of the canine teeth in some populations, male and female body and teeth sizes evidence no major sexual dimorphism, similar to most canines. In some populations, males’ canine teeth were considerably larger, implying male competition for breeding access. In other populations, lack of dimorphism in the canine teeth implies little competition.[4]

Despite superficial similarities to the gray wolf, the two species differed significantly. Wolves of the Late Pleistocene are genetically unique and morphologically distinct. None of the 16 mtDNA haplotypes recovered from a sample of 20 Pleistocene Eastern-Beringian wolves was shared with any modern wolf. Instead, they appear most closely related to Late Pleistocene wolves found in Eurasia.[5] 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 have weighed 25% more than living gray wolves.[3]

Many of these characteristics were needed to fight off and prey on larger megafauna.[6] 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.

Dentition
The dire wolf's teeth were similar to the gray wolf's, only slightly larger, pointing to a hypercarnivorous to mesocarnivorous activity. The dietary characteristics were primarily carnivorous, as well as partially omnivorous.[8] Other than size, there is no significant special adaptations in the mandibular corpus of the dire wolf to set it apart from the gray wolf.[9]

Between C. lupus and C. dirus, C. lupus had a significantly greater mechanical advantage of the temporalis muscle over C. dirus at the lower carnassial and P4 (MATM1, MATP4).[10]

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.[11]

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.[12] 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.[13]

Dire wolf teeth lacked the craniodental adaptations of habitual bonecrushers such as hyenas and borophagines.[12] The dire wolf's robust skull and susceptibility to tooth breakage suggests that it hunted for large prey or scavenged the carcasses of large prey.[14] 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.

Behavior and ecology
Dire wolves are part of the same carnivorous guild as the smaller gray wolves and coyotes.[15] 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.[16]

Compared to modern species, a remarkable number of dire wolf specimens from the La Brea pits showed evidence of having broken their teeth in life. Specimens in the older part of the pit exhibited more tooth wear than those in the younger pit, which could be a result of either the older part of the pit containing more senior dire wolf specimens or a diet that included harder foods such as carcasses and bones.[17][18] Another explanation for increased tooth wear and breakage could be intense competition among carnivores forcing C. dirus to eat as much of the carcass as quickly as possible.[18]

The dire wolf has an extremely extensive fossil range. It is known to be located as far north as Canada and south into southern Bolivia. Ten localities in 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. The majority of these localities occur in the central and southeast-central portions of Mexico with few occurrences in the north or west. 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 are known by only a few specimens.[19]

Due to the large amount of remains at the Rancho La Brea tar pits it is possible dire wolves used animals trapped here as a food source and some end up being trapped and preserved themselves. It can also be concluded that they were social predators as they are most successful in defending carcasses.