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Andrewsarchus mongoliensis
From Wikipedia, the free encyclopedia
| Andrewsarchus mongoliensis Fossil range: Late Eocene |
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 Reconstruction of A. mongoliensis
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| Andrewsarchus mongoliensis Pao, 1923 |
Andrewsarchus mongoliensis (pronounced and-rooz-ARK-us), (Andrews + Greek ἀρχός, "ruler"), was a primitive, heavily-built, wolf-like, hoofed mammal that lived during the Eocene Epoch, roughly between 45 and 40 million years ago. It walked on four short legs and had a long body, a long tail, and feet with hoofed toes. It had a long snout with large, sharp teeth and flat cheek teeth that may have been used to crush bones; however, since Andrewsarchus is only known from a skull and a few bones found, whether it was an active predator or merely a large scavenger is open to debate, as is its exact time range.
Andrewsarchus is named for the famous explorer and fossil hunter Roy Chapman Andrews. It was discovered in June of 1923 by Kan Chuen Pao, a member of Andrew's expedition, on a site in the Gobi Desert in Mongolia known as Irdin Mahna [variants: Erdeni-Mandal and Erdenemandal ('jeweled mandala')] on the third Asiatic expedition that was led by Andrews and sponsored by the American Museum of Natural History. The American Museum of Natural History is where the skull section of the fossil is now on display: the lower jaw was not found. It is classified in the Order Mesonychia due to the similarity in structure between its teeth and skull with those of other mesonychid species known from complete skeletons. As such, it is assumed that it had hoofed toes similar to those of Mesonyx or Sinonyx, and is regarded as a relative of artiodactyl ungulates.
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Andrewsarchus is known only from an enormous skull (83 cm long and 56 cm wide)[1] and pieces of bone, but the skull's similarity to that of smaller mesonychids suggests that Andrewsarchus had the same wolf-like body on a larger scale.
It is possibly the largest land-dwelling carnivorous mammal known. "If Andrewsarchus was proportioned in the same manner as Mesonyx obtusidens, it had a length from the snout to the back of the pelvis of about 12 feet and a height from the ground to the shoulder or middle of the back of about 6 feet. Thus in round numbers it [may have been] three times the size of Synoplotherium (Dromocyon) vorax or of Mesonyx obtusidens."[2] The cranium is about twice the length of an Alaskan brown bear (Ursus gyas), but much narrower, and about triple the length of an American wolf (Canis occidentalis). Since the average brown bear weighs less than 1,000 pounds, and only an extreme specimen of a wolf weighs up to 77 kg (170 lb), we can only suggest, proportionately extrapolating body sizes, that Andrewsarchus probably weighed somewhere between 400 to 1,000 pounds at the most. But since we have only the skull, and no other fossil evidence, this is pure speculation. Paleontologists that researched Andrewsarchus for the highly acclaimed award-winning BBC video "Walking with Prehistoric Beasts" state as a "Key Fact": "Weight - one quarter of a metric ton," or about 550 pounds.[3]
The cranium of Andrewsarchus (834 mm.) is nearly twice as long as that of Mesonyx (429 mm.), the zygomatic arches are twice as broad and the facial length (500 mm.) is 150% as compared with that of Mesonyx (206 mm.), 92%. The face of Andrewsarchus is 150% of the cranium, whereas the face of Mesonyx is 92% of the cranium, supporting the statement that in Andrewsarchus the face is relatively elongate.[2]
Like many archaic animals, Andrewsarchus and other mesonychids had a superproportionally large head in comparison to their body size.
The appearance and behavioral patterns of Andrewsarchus are virtually unknown and have been topics of debate among paleontologists ever since it was first discovered. All that is known about Andrewsarchus comes chiefly from the single, nearly perfectly, preserved three-foot-long skull found in Late Eocene sediments in what is now Mongolia. New theories indicate that the teeth of Andrewsarchus may have been blunt and uncharacteristic of predators. Its diet could have been more omnivorous than carnivorous, consisting of carrion, bones, rooted plants, or mollusks rather than freshly killed meat. As a scavenger, Andrewsarchus may have gained access to freshly killed carcasses by using its formidable size to scare away other smaller predators and scavengers. Until more fossil evidence that may provide insight into these areas of uncertainty is uncovered any reconstructions remain highly speculative.
Andrewsarchus possessed some of the strongest jaws ever evolved in a land mammal, able to bite through large bones if needed. To judge from its immense jaws, and the coastal location of the fossils, Andrewsarchus may have fed on beached primitive whales, shellfish and hard-shelled turtles, and contemporary large mammals at various periods during its existence. Toward the end of the Eocene very large mammals (such as the brontotheres) had evolved in the region of Central Asia.
Despite the enormous jaws and very sturdy teeth, Andrewsarchus did not have teeth adapted for the carnassial shear, though its immensely powerful jaws rendered such an adaptation unnecessary. Judging by its sheer size, the animal most likely fed on large animals such as the extinct brontotheres, which were among the largest herbivorous mammals at the time, possibly both hunting them, and scavenging already dead carcasses. Simply scavenging smaller animals would not have required a body and jaws of the size that Andrewsarchus possessed (over twice that of a modern brown bear).
Due to the food requirements of Andrewsarchus, abundant sources of large animals are thought to have been present in Central Asia during the Eocene, most likely on a year-round basis. When the Indian subcontinent collided with Asia during the Late Eocene/Early Oligocene, this event caused the formation of the Himalaya mountains while closing off the eastern Tethys Ocean, thus changing weather patterns, and caused Central Asia dry out, ultimately resulting in a dramatic faunal turnover. It is suggested that Andrewsarchus became extinct due to this orogeny.[citation needed]
- ^ Benton, M.J. (2005). Vertebrate Palaeontology. Oxford, 333.
- ^ a b Osborn, Henry Fairfield (November 11, 1924). "Andrewsarchus, giant mesonychid of Mongolia". American Museum Novitates (146). The American Museum of Natural History. Retrieved on 2007-08-05.
- ^ BBC (2001). Walking with Prehistoric Beasts (DVD). British Broadcasting Corporation. ISBN 0-7907-6195-5.
- Artistic reconstruction The artist shows the creodont Sarkastodon in the background, waiting for Andrewsarchus to finish feeding on the carcass of a recently deceased Embolotherium. The dead brontothere shown would have been about the size of a modern rhinoceros. A primate can be seen on a tree branch, and an early member of Carnivora, which eventually became the dominant land predators, is seen in the foreground.
- Lifesized model
