Andrewsarchus mongoliensis was a giant mammalian predator of Central Asia and the largest member of the mesonychids, a group of extinct prehistoric mammals. The mesonychids were the only known group of ungulates to become carnivorous, and looked rather like wolves. Andrewsarchus ("Andrews's ruler") was named for the famous explorer and fossil hunter Roy Chapman Andrews, who led the expedition on which it was discovered.

Description

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Andrewsarchus is known only from an enormous skull 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. The skull, the only fossil bone known, was itself over a meter long. Extrapolating from the body proportions of similar mesonychids, Andrewsarchus was most likely about 4-6 metres (13-18 feet) long, standing nearly 2 metres (6 feet) at the shoulder, making it the largest terrestrial carnivorous mammal that has ever existed. It probably averaged over 1500 kilograms in weight with some exceptional animals over 2000 kilograms, making it usually about twice as heavy as the most obese modern brown bears.

Prehistory

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Andrewsarchus lived 60-32 million years ago, in the Eocene era. Since Andrewsarchus evolved not long after the Cretaceous-Tertiary extinction event, it is somewhat of a mystery as to what Andrewsarchus ate. It obviously ate large land animals, though the fossil record of such prey from the Paleocene and early Eocene has not been conclusively determined.

Just after the dinosaurs went extinct there were at first no large land mammals, no whales, and no dedicated dry-land predators of any size. But the extinction opened up ecological niches and caused a burst of evolution to occur. Very soon large land mammals evolved, carnivorous birds such as Gastornis/Diatryma, and even crocodiles adapted for a running existence evolved. These all may have been potential prey.

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 had evolved in the region of Central Asia. Andrewsarchus possessed some of the strongest jaws ever evolved in a land mammal, able to bite through large bones if needed.

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 fed on large animals such as the extinct brontotheres, and possibly even the enormous Indricotherium - another prehistoric inhabitant of Central Asia and the largest land mammal ever to exist. Simply scavenging smaller animals would not have required a body and jaws of the size that Andrewsarchus posessed.

Andrewsarchus apparently had a successful run as a species, lasting for some 25-30 million years, but eventually became extinct around 32 million years ago. It and related predatory mammals lived in the Northern Hemisphere alongside with most of the creodonts and earliest modern carnivores, also with giant terrestrial predatory birds such as Diatryma. Isolated Southern Hemisphere areas such as Australia and South America evolved their own totally separate lines of predatory land animals, including lines of flightless giant birds and marsupials such as the Australian Thylacoleo, a "marsupial lion," by the process of convergent evolution.

Eventually the Carnivora replaced the Creodonts, Mesonychids, and giant flightless predatory birds entirely. The order Carnivora includes such animals as the dogs, cats, and bears. Various species of Carnivora have now spread (partly assisted by humans) to every continent, as well as most islands, and have replaced most other large non-avian terrestrial predators worldwide.

External links

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• Artistic reconstruction Andrewsarchus is shown feeding while Sarkastodon waits its turn. The dead Brontothere easily would have been the size of a large modern rhinoceros.

Eocene extinctions | Eocene mammals | Mesonychids | Paleocene mammals

Andrewsarchus mongoliensis | Andrewsarchus | Andrewsarchus | Ендрюзарх