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Middle to Late Pleistocene
Dire Wolf fossils at theNational Museum of Natural History, Washington, DC
Species: C. dirus
The Dire Wolf (Canis dirus) is an extinct carnivorous mammal of the genus Canis, and was most common in North America during the Pleistocene. Although it was closely related to the Gray Wolf, it was not the direct ancestor of any species known today. The Dire Wolf co-existed with the Gray Wolf in North America for about 100,000 years. They were 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.
The first specimen of a Dire Wolf was found by Francis A. Linck at the mouth of Pigeon Creek along the Ohio River near Evansville, Indiana in 1854, but the vast majority of fossils recovered have been from the La Brea Tar Pits in California.
The Dire Wolf was slightly larger than the Gray Wolf. It averaged about 1.5 metres (5 feet) in length and weighed about 50 kilograms (110 pounds) Though large specimens may have weighed as much as 80kg (175 pounds).1
Despite superficial similarities in appearance between the Grey Wolf and the Dire 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, which suggests that the Dire Wolf was a poorer runner, and may have scavenged for food or hunted large, slower-moving prey.
The dire wolf's dentition was similar to the grey wolf's, only slightly larger. The upper carnassials had a much larger blade than that of a grey 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 grey wolf's. Dire wolf teeth lack the craniodental adaptations of habitual bonecrushers such as hyenas. Molars from the skulls of dire wolves found in the La Brea tar pits show wear, indicating possible bone gnawing, though the wear is not to the same extent as that found in Borophaginae teeth. 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. However, others have noted that the dorsoventral and labiolingual force profiles are indistinguishable from those of other canids, indicating a similair diet. Its dorsoventrally weak symphyseal region indicates it killed in a manner similair to it's modern relatives, by delivering a series of shallow bites, strongly indicating pack hunting behaviour. The greater incidence of broken post-carnassial molars than in fossil grey wolves indicates that it probably was less adapted to bone crushing than the grey wolf.
Evolution and Extinction
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 ago (Ma), along with two other genera, Urocyon, and Vulpes. Canids soon spread to Asia and Europe (8 Ma) and became the ancestors of modern wolves, jackals, foxes, and the Raccoon Dog. By 3-5 Ma, 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, and by the Mid-Pleistocene (800,000 years ago) Canis ambrusteri appeared and spread across North and South America. It soon disappeared from North America, but probably continued to survive in South America to become the ancestor of the Dire Wolf. (However there is some evidence to suggest that the Dire Wolf may have arisen from other small South American wolves.)
During the Late Pleistocene (300,000 years ago) the Gray Wolf (Canis lupus) crossed into North America on the Bering Strait land bridge. By 100,000 years ago the Dire Wolf also appeared in North America (probably from South America).
Starting about 16,000 years ago, coinciding with the end of the most recent Ice Age 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). 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 on scavenging. By 10,000 years ago, the large mammals and the Dire Wolf were extinct, although some fossils found in Arkansas suggest that they may have lived as a relict population in the Ozark mountains as recently as 4,000 years ago.
A display of some of the thousands of Dire Wolf skulls found in the La Brea tar pits
The Dire Wolf is best known for its unusually high representation in the La Brea Tar Pits in California. In total, fossils from more than 3,600 individual 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.
Evansville Dire Wolf
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 Dr. Joseph Granville Norwood from an Evansville collector named Francis A. Linck. Dr. Norwood, who at that time was the first state geologist of Illinois, sent the specimen to Joseph Leidy at the Academy of Natural Sciences of Philadelphia. Dr. 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.
Dr. Norwood's letters to Dr. Leidy, as well as the type specimen itself, are preserved at the Academy of Natural Sciences in Philadelphia, although one of the letters indicates that the specimen was to be returned to Linck's family, as Linck himself died in August 1854.