Andrewsarchus mongoliensis

Cladus: Eukaryota
Supergroup: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Classis: Mammalia
Subclassis: Theria
Infraclassis: Eutheria
Superordo: Laurasiatheria
Ordo: †Mesonychia
Familia: Triisodontidae
Genus: Andrewsarchus
Species: Andrewsarchus mongoliensis

Name

†Andrewsarchus mongoliensis Osborn, 1924

References

cited sources

* Osborn, H.F. 1924: Andrewsarchus, giant mesonychid of Mongolia. American Museum novitates, (146)

Vernacular names
Català: Andrewsarchus mongoliensis
Deutsch: Andrewsarchus mongoliensis
English: Andrewsarchus
Español: Andrewsarchus
Français: Andrewsarchus
Italiano: Andrewsarchus mongoliensis
Magyar: Andrewsarchus mongoliensis
Nederlands: Andrewsarchus
日本語: アンドリューサルクス
Polski: Andrewsarchus
Português: Andrewsarchus
Русский: Эндрюсарх
Suomi: Andrewsarchus
Svenska: Andrewsarchus mongoliensis
Українська: Ендрюзарх
中文: 安氏中獸

links

* ION
* Nomenclator Zoologicus

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Andrewsarchus mongoliensis (pronounced /ˌændruːˈsɑrkəs/ AN-drew-SAR-kəs; Andrews + Greek ἀρχός, "ruler"), was a mammal that lived during the Eocene epoch, roughly between 45 and 36 million years ago. It had a long snout with large, sharp teeth and flat cheek teeth that may have been used to crush bones. Because Andrewsarchus is only known from a single skull, 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 1923 by Kan Chuen Pao, a member of Andrews' 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 was classified in the clade Mesonychia due to the similarity in structure between its teeth and skull with those of other mesonychid species known from complete skeleton, however, much of this was based only on Osborn's original publication, and more recent studies have found it to have no special mesonychid affinities, instead grouping with various artiodactyl clades. Indeed one study (Spaulding et. al.) has not only found them to be closer to entelodonts, but also are also a kin to Cetancodonta in their Cetacodontamorpha[1].

Description
Size comparison of Andrewsarchus against other carnivores. Andrewsarchus itself is shown in orange.
Reconstruction of A. mongoliensis

Andrewsarchus is known only from an enormous skull (32.8 in/83 cm long and 22/56 cm wide)[2] and pieces of bone. 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 11 feet (3.4 m) and a height from the ground to the shoulder or middle of the back of about 6 feet (1.8 m). Thus in round numbers it is possible that it may have been three times the size of Synoplotherium (Dromocyon) vorax or of Mesonyx obtusidens and possibly the largest land-dwelling carnivorous mammal known.[3] The cranium is about twice the length of that of a modern Alaskan brown bear (Ursus arctos middendorffi), but with a lower length-to-width ratio, and about triple the length of an American wolf's (Canis occidentalis). With modern brown bears or polar bears weighing between 450 kg (~1000 lb) and 675 kg (~1500 lb) and only an extreme specimen of a wolf weighs up to 77 kg (170 lb), this plausibly puts Andrewsarchus in the 1000 kg size range. This weight appears close to the practical size limit of carnivorous land mammals, possibly relating to available food as well as metabolic requirements.[4]

There is as yet no complete skeleton found. As it is not known if Andrewsarchus had a robust or gracile build, the weight of the average animal is in dispute. If the build was robust, some specimens of the animal might have weighed up to 4000 pounds. However, if future fossils show that the animal was that large, this will point more to a partly herbivorous, partly scavenging lifestyle.

Further fossil finds should shed light on the size of the animal, as it is not known if the present specimen represents an average, or exceptional animal of the species. Nor does it specify its age. In the BBC mini-series Walking with Beasts, it was reported that Andrewsarchus is the largest mammalian land predator of all time. The professional paleontologists that were brought in to research Andrewsarchus for this series state as a "Key Fact" that it weighed "one quarter of a metric ton (550 lb)." [5][6] Other authorities, however, have claimed the title for the extinct Giant Short-faced bear, fossils of which suggest an animal that could stand 13 ft/4m on the hind legs and weight up to 1 ton.[7]. The extinct creodont, Sarkastodon was slightly smaller, while Megistotherium was much smaller[8]. If omnivores are also included as apex predators then Daeodon is another contender, as is the Kodiak Bear, a race of North American brown bear, which can reach 10 ft/3m and weigh over 1700 lbs/770 kg as well as some examples of the Cave Bear.[9]

It is noted that some of the above mentioned animals mentioned could, or did, consume plants as part of their diet (e.g. Daedon, Kodiak Bear, Cave bear) and thus secured more caloric intake. In addition, isolated individuals of any of these animals could have been much heavier (e.g. obese captive brown bears can weigh well over a ton). Some hoofed mammals, such as swine or hippopotami will consume meat at least on occasion.

Paleobiology
The skull of Andrewsarchus, compared to other carnivore skulls. Note the front teeth useful for piercing but the teeth further back in the jaw are large and blunted and probably not very useful in tearing flesh from bone or crushing.

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. If plant material was also eaten, Andrewsarchus would have had a lifestyle similar to entelodonts.

Due to the food requirements of Andrewsarchus, 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 to dry out, ultimately resulting in a dramatic faunal turnover. It is suggested that Andrewsarchus became extinct due to this orogeny.

References

1. ^ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2740860/
2. ^ Benton, M.J. (2005). Vertebrate Palaeontology. Oxford, 333.
3. ^ Osborn, Henry Fairfield (November 11, 1924). "Andrewsarchus, giant mesonychid of Mongolia" (PDF). American Museum Novitates (The American Museum of Natural History) (146). http://digitallibrary.amnh.org/dspace/bitstream/2246/3226/1/N0146.pdf. Retrieved 2007-08-05.
4. ^ Carbone, Chris; Teacher, Amber; Rowcliffe, J (2007). "The Costs of Carnivory". PLoS Biology 5 (2): e22. doi:10.1371/journal.pbio.0050022. PMID 17227145. PMC 1769424. http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0050022. Retrieved 2009-12-28.
5. ^ http://www.abc.net.au/cgi- If this was the correct quote, there was a clear typographical error as there is no way an animal of the size of Andrewsarchus could weigh so little. bin/common/printfriendly.pl?/beasts/factfiles/factfiles/andrewsarchus.htm
6. ^ BBC (2001). Walking with Prehistoric Beasts (DVD). British Broadcasting Corporation. ISBN 0-7907-6195-5.
7. ^ Prehistoric America BBC mini-series, 2002
8. ^ SORKIN, B. (2008), A biomechanical constraint on body mass in terrestrial mammalian predators. Lethaia, 41: 333–347
9. ^ grizzly bear. (2008). It is noted that all of these animals could, or did, consume plants as part of their diet, and thus secured more caloric intake. In addition, isolated individuals of any of these animals could have been much heavier (e.g. obese captive brown bears can weigh well over a ton), In Encyclopædia Britannica. Retrieved December 06, 2008, from Encyclopædia Britannica Online: [1]