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Dire Wolf

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The dire wolf (Canis dirus) 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 1.79 million years.

 Discovery

A display of some of the thousands of Dire Wolf skulls found in La Brea tar pitsThe 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 that 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, as well as the type specimen itself, are preserved at the Academy of Natural Sciences although one of the letters indicates that the specimen was to be returned to Linck's family, as Linck himself 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 3,600 dire wolves have been recovered from the tar pits, more than any other mammal species. This large number suggests that the Dire Wolf, like modern wolves and dogs, probably hunted in packs. It also gives some insight into the pressures placed on the species near the end of its existence.

 Taxonomic history

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.

 Evolution and extinction

Timeline of canids including Canis dirus in red. (Tedford & Wang)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.

 From C. armbrusteri

Over the next nine million years, extensive development and diversification of the North American wolves took place by the Middle Pleistocene. Canis armbrusteri appeared, and there is good evidence that 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 move into Central America and South America, appearing in the Late Pleistocene fossil record in northwestern South America.

 Relationship to gray wolf

Artistic rendition of two possible appearances of the dire wolf, one based on a North American origin and the other on a possible South American originAlthough it was closely related to the gray wolf and other sister species, Canis dirus is not the direct ancestor of any species known today. 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.

 Prevalence

The dire wolf was one of the abundant Pleistocene megafauna—a wide variety of very large mammals that lived during the Pleistocene. Approximately 10,000 years ago the dire wolf became extinct along with most other North American megafauna. During the Late Pleistocene (300,000 years ago) the gray wolf (Canis 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, it could not hunt the swifter species that remained and was forced to subsist by scavenging. By 10,000 years ago, the large mammals and the Dire Wolf were extinct.

 Morphology

 Body mass and dimensions

Restoration by Charles R. KnightThe dire wolf was larger than the gray wolf, averaging about 1.5 metres (5 ft) in length and weighing between 50 kg (110 lb) and 79 kg (174 lb). Despite superficial similarities to the Gray Wolf, there were significant differences between the two species. 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. Paleontologist R.M. Nowak states the dietary characteristics are primarily carnivorous as well as partially omnivorous.

Many paleontologists have proposed that the dire wolf may have used its relatively large teeth to crush bone, an idea that is supported by the frequency of large amounts of wear on the crowns of their fossilized teeth. The upper carnassials had a 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 that 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 post-carnassial molars is much higher than in fossil gray wolves, indicating that the species was probably less adapted to bone crushing than the gray wolf.


Video

Prehistoric Predators Dire Wolf46:41

Prehistoric Predators Dire Wolf

Prehistoric Predators: Dire Wolves

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