Andrewsarchus mongoliensus, nebulous nightmare:
One of the more interesting and yet tantalizingly enigmatic creatures from the Eocene epoch, a time that abounded with interesting fauna of all kinds, Andrewsarchus is difficult to describe with authority. This is so because so little in the fossil record has been discovered to date to aid in definitive reconstruction.
The type fossil for Andrewsarchus is presently the only fossil, and consists of one large and rather well preserved skull, and a very few smaller bone fragments. And what a skull it is!
About 33 inches long and more than 22 inches wide, the Andrewsarchus skull dwarfs that of any modern day land mammal. It is equipped with a formidable array of teeth, and presumed muscle attachments give it what is estimated to be the most powerful bite force of any animal thus far recorded.
This in and of itself is fascinating, the devil, as they say is in the details.
What we know about Andrewsarchus:
One item that is known for certain is that it lived in the Eocene epoch, in which deposits the third American Museum of Natural History to Asia, led by Roy Chapman Andrews discovered it in 1923 in strata approximately 62 million years old.
Andrews himself is almost as fascinating as Andrewsarchus; he was at times an adventurer, explorer, anthropologist, paleontologist, bandit in some peoples eyes, possible inspiration for Indiana Jones and eventually Director of New York City’s famous American Museum of Natural History. It was perhaps a case of one rarity discovering another.
We also know that Andrewsarchus lived in what is now Mongolia, because that is where the skull was found.
We are reasonably certain that, based on skull morphology Andrewsarchus belonged to the mesonychids, an extinct order of hoofed predatory mammals. Wolf like in form, mesonychids are more closely related to pigs, deer and rhinos than to modern wolves.
What we do not know about Andrewsarchus:
Is nearly everything else that is either interesting or important. The fact that there is only one type specimen means we cannot possibly, at this time, make a definitive statement about the creature’s geographical distribution, nor about the species lifespan on earth. We are not even certain about the creatures’ appearance.
Various sources will chronologically place Andrewsarchus from 60 million years ago to 32 million years ago, from 45 million years ago to 32 million years ago, and varying points between. There is not a scrap of evidence to support any of these guesstimates.
Andrewsarchus was huge, of this there is little doubt. The skull we have dwarfs that of the modern wolf, big cat or largest bear - see the comparison here -.
If the body was robust and rhinoceros like in shape, as has been suggested, then Andrewsarchus may in the opinion of some have stood 6 feet tall at the shoulder, weighing possibly as much as 4000 pounds.
If the form however resembles those of other known mesonychids and is leaner and more wolf like in structure, then Andrewsarchus might have been several feet taller and longer, while slightly lighter and presumably faster, with a head more in proportion to its body size than would be the case in the robust model.
A minority opinion holds that Andrewsarchus was in fact a triisodontine arctocyonid, or intermediary form between land dwelling mesonychids and the cetaceans, or whales. This would have given Andrewsarchus a squat, elongated form superficially crocodilian in appearance.
More skeletal remains are required before we can hope to resolve this issue to anyone’s satisfaction.
Equally contentious are opinions on what Andrewsarchus may have eaten, and how this food source might have been acquired. As previously mentioned Andrewsarchus is credited with the most powerful bite force of any land animal yet discovered; this would seem to indicate that anything could have been fair game.
If the gracile form of relatively light, fleet footed but enormous body type is accepted, then Andrewsarchus was certainly an apex predator, capable of taking down and consuming even the massive gigantic relatives of the modern day rhino that shared its time and space.
If these creatures hunted in packs - and no one has a clue about this - they would have overwhelmed any and all potential prey.
If the proto-whale theory is correct, and Andrewsarchus was caught between land and water in an evolutionary sense, then a diet of crushed shellfish, turtles, marine life and opportunistic hunting and scavenging of land mammals seems more probable.
The robust, rhinoceros like specimen? Considered by many to be too slow and clumsy to be purely an apex predator, this version of Andrewsarchus is supposed to have used its vast bulk and formidable jaws to chase other predators from their kills.
A partially vegetarian diet is also proposed and of course there is no doubt that such a formidable beast could have hunted opportunistically on prey that was young, weak, sick, injured or old.
There are so many questions surrounding this fascinating beast that we can only hope that several reasonably intact skeletons come to light soon, to help resolve them. Until then, speculation and a single skull is almost all that anyone has to go on.