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In 1987, a new hypothesis proposed that a mammal population could give rise to a larger form called a hypermorph during times when food was abundant, but when food later became scarce the hypermorph would either adapt to a smaller form or go extinct.This hypothesis might explain the large body sizes found in many Late Pleistocene mammals compared to their modern counterparts.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 controversial.Dire wolves lived as recently as 9,440 years ago, according to dated remains.The largest collection of its fossils has been obtained from the Rancho La Brea Tar Pits in Los Angeles.Dire wolf 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 fossilized jawbone with cheek-teeth was obtained by the geologist Joseph Granville Norwood from an Evansville collector, Francis A. The paleontologist Joseph Leidy determined that the specimen represented an extinct species of wolf and reported it under the name of Canis primaevus.
The first specimen of what would later become associated with Canis dirus was found in mid-1854 in the bed of the Ohio River near Evansville, Indiana.
In 1984 a study by Björn Kurten recognized a geographic variation within the dire wolf populations and proposed two subspecies: Canis dirus guildayi (named by Kurten in honor of the paleontologist John E.
Guilday) for specimens from California and Mexico that exhibited shorter limbs and longer teeth, and Canis dirus dirus for specimens east of the North American Continental Divide that exhibited longer limbs and shorter teeth.
The dire wolf (Canis dirus, "fearsome dog") is an extinct species of the genus Canis.
It is one of the most famous prehistoric carnivores in North America, along with its extinct competitor, the sabre-toothed cat Smilodon fatalis.