Andrewsarchus (Andrewsarchus mongoliensis)

Order: Arctocyonia

Family: Mesonychidae

Andrewsarchus was an early giant mammal living during the Eocene of Mongolia 50 million years ago. Estimates based on a massive skull nearly 3 feet long indicate that Andrewsarchus's overall length was between 13 and 15 feet. Larger than a grizzly bear, it is believed that Andrewsarchus weighed close to a ton, making it the largest terrestrial mammalian carnivore ever to exist. An ungulate closely related to today's hoofed animals, Andrewsarchus has been described as a cross between a wolf and a wild boar, but the most popular reconstruction is similar to a dog or wolf.

Andrewsarchus was first discovered in 1923 by Kan Chuen Pao in Irden Mannah [probably Oldziyt,at 48-32-08N,101-22-00E, with variants Erdeni-Mandal and Erdenemandal 'jeweled mandala'], Mongolia, on the third Asiatic expedition sponsored by the American Museum of Natural History. Led by Roy Chapman Andrews, these expeditions yielded spectacular finds. Among them was a 3-foot-long skull of a previously unknown animal. After being examined by Andrews, the skull was first identified as belonging to a carnivore known as Mesonyx. Soon thereafter, Andrews was convinced by paleontologist Walter Granger to reclassify the skull as an artiodactyl Entelodon, describing not a huge carnivore but a hoofed, pig-like animal. Back at the museum, curator W.D. Matthew studied a sketch and concluded that Andrew's initial identification had been far closer to the truth than that of Granger's. Matthew believed the skull clearly belonged to a carnivore that was most likely a member of a primitive group called the "creodonts" within the amily Mesonychidae.

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 1923. Whether Andrewsarchus was an active predator or merely a large scavenger is open to debate. 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.

It is also important to mention that Andrewsarchus is believed to be a land-dwelling ancestor of modern-day whales. It is likely that Andrewsarchus was more of a distant cousin in the whale lineage rather than a direct ancestor. From this related animal developed an aquatic descendant, Packicetus, which hunted the early Eocene oceans. Packicetus maintained many of its predecessors' features, possessing triangular teeth for slicing through prey and ears still adapted for air-borne sound rather than for long-range sound as used by modern whales.