Andrewsarchus—the World's Largest Predatory Mammal

 Andrewsarchus is one of the world's most tantalizing prehistoric animals: its three-foot-long, toothstudded skull indicates that it was a giant predator, but the fact is that we have no idea what the rest of this mammal's body looked like.

01
of 10

Andrewsarchus Is Known by a Single Skull

Andrewsarchus
Wikimedia Commons

All we know about Andrewsarchus amounts to a single, three-foot-long, vaguely wolf-shaped skull, discovered in Mongolia in 1923. While the skull clearly belongs to some type of mammal—there are obvious diagnostic markers by which paleontologists can distinguish between reptilian and mammalian bones—the lack of an accompanying skeleton has resulted in nearly a century of confusion, and debate, about what type of animal Andrewsarchus really was.

02
of 10

The Fossil of Andrewsarchus Was Discovered by Roy Chapman Andrews

Roy chapman andrews
Wikimedia Commons

During the 1920's, the swashbuckling paleontologist Roy Chapman Andrews, sponsored by the American Museum of Natural History in New York, embarked on a series of well-publicized fossil-hunting expeditions to central Asia (then, as it still is now, one of the most remote regions on earth). After its discovery, Andrewsarchus ("Andrews' ruler") was named in his honor, though it's unclear whether Andrews bestowed this name himself or left the task to other members of his team.

03
of 10

Andrewsarchus Lived During the Eocene Epoch

Andrewsarchus
Wikimedia Commons

One of the amazing things about Andrewsarchus is that it lived at a time when mammals were just beginning to achieve giant sizes—the Eocene epoch, from about 45 to 35 million years ago. The size of this predator indicates that mammals may have grown much bigger, much faster, than had previously been suspected—and if Andrewsarchus had a predatory lifestyle, it would also mean that this area of central Asia was well-stocked with comparably sized plant-eating prey.

04
of 10

Andrewsarchus May Have Weighed As Much as Two Tons

Andrewsarchus
Andrewsarchus (orange) compared to various dinosaurs and a modern bear. Wikimedia Commons

If one naively extrapolates from the size of its skull, it's easy to come to the conclusion that Andrewsarchus was the biggest predatory terrestrial mammal that ever lived. (But not the biggest predatory mammal overall; that honor goes to prehistoric killer whales like Leviathan.) However, that weight estimate drops dramatically if one considers the possibility of other, less bulky Andrewsarchus body plans.

05
of 10

No One Knows if Andrewsarchus Was "Robust" or "Gracile"

Andrewsarchus
Wikimedia Commons

Its enormous head aside, what kind of body did Andrewsarchus possess? While it's easy this megafauna mammal having a robust, muscular build, it's important to keep in mind that a giant skull size does not necessarily entail a giant body size—just look at the comically large-headed modern warthog. It may well be that Andrewsarchus had a relatively "gracile" build, which would knock it off the top of the size charts and back into the middle of the Eocene rankings.

06
of 10

Andrewsarchus May Have Had a Hump on its Back

Andrewsarchus
BBC

Whether or not Andrewsarchus was robust or gracile, its massive head would have had to be securely anchored to its body. In comparably built animals, the musculature attaching the skull to the spine produces a prominent "hump" along the upper back, resulting in a vaguely comical-looking, top-heavy build. Of course, pending further fossil evidence, we may never know for sure what type of body was attached to Andrewsarchus' head!

07
of 10

Andrewsarchus Was Once Thought to Be Related to Mesonyx

Mesonyx
Mesonyx, to which Andrewsarchus was once thought to be related. Charles R. Knight

For decades, paleontologists assumed that Andrewsarchus was a type of prehistoric mammal known as a creodont—a family of meat eaters, typified by Mesonyx, that has left no living descendants. In fact, it was a series of reconstructions patterning its body after the better-known Mesonyx that led some paleontologists to the conclusion that Andrewsarchus was a multi-ton predator. If it wasn't actually a creodont, but some other type of mammal, then all bets would be off!

08
of 10

Today, Paleontologists Believe Andrewsarchus Was an Even-Toed Ungulate

Entelodon
Entelodon, to which Andrewsarchus may have been related. Charles R. Knight

The Andrewsarchus-as-creodont theory was dealt a near-decisive blow by more recent analyses of this mammal's skull. Today, most paleontologists believe that Andrewsarchus was an artiodactyl, or even-toed mammal, which would place it in the same general family as giant prehistoric pigs like Enteledon. However, one dissenting view holds that Andrewsarchus was in fact a "whippomorph," part of the evolutionary clade that includes both modern whales and hippopotami.

09
of 10

The Jaws of Andrewsarchus Were Amazingly Strong

Andrewsarchus
The skull of Andrewsarchus, compared to various other mammals. Wikimedia Commons

You don't need to be a rocket scientist (or an evolutionary biologist) to conclude that the jaws of Andrewsarchus were immensely strong; otherwise, there would have been no reason for it to evolve such an enormous, elongated skull. Unfortunately, given the lack of fossil evidence, paleontologists have yet to determine exactly how strong this mammal's bite was, and how it compared with that of the much bigger Tyrannosaurus Rex, which lived about 20 million years before.

10
of 10

The Diet of Andrewsarchus is Still a Mystery

Andrewsarchus
Dmitry Bogdanov

Given its tooth structure, the musculature of its jaws, and the fact that its single skull was discovered along the shoreline, some scientists speculate that Andrewsarchus fed mostly on hard-shelled mollusks and turtles. We don't, however, know if the "type specimen" wound up on the beach naturally or by accident, and there's no reason to rule out the possibility that Andrewsarchus was omnivorous, perhaps supplementing its diet with seaweed or beached whales.