Andrewsarchus

Surfing the internet this morning, I accidentally stumbled upon the largest carnivorous mammal to have ever existed: the andrewsarchus mongliensis. The andrewsarchus was the largest of a wholly extinct genus of carnivorous ungulates (hoofed animals).

More from Wikipedia:

Andrewsarchus is known only from an enormous, meter-long 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. 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 about 1500 kilograms in weight with some exceptional animals over 2000 kilograms, making it over twice as heavy as most Kodiak brown bears, and rather heavier than a Percheron horse.

The skull of Andrewsarchus was found in Late Eocene sediments in what is now Mongolia. As there has only been a skull and a few bones found, it is still too premature to speculate on its time range, beyond being a Late Eocene apex predator.

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. 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, which were among the largest herbivorous mammals at the time. 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). It was not adapted to eating plants or digging, and hence could not enjoy an omnivorous lifestyle as do pigs and bears today. Most likely, it fed off of brontotheres, possibly both hunting them, and scavenging already dead carcasses.

By the mid Oligocene, the Creodonts supplanted both the Mesonychids, and giant flightless predatory birds entirely in North America, Eurasia and Africa, and in turn, competed with their relatives, the true carnivores until the last creodont genus, Dissopsalis, went extinct about 8 million years ago. 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.