When I visit New York City, one of my favorite places is, unsurprisingly, the American Museum of Natural History.
And my favorite spot in that museum is the Hall of Mammals in the paleontology section. I've always had a fascination for prehistoric mammals, especially those lineages that are extinct -- strange animals like the gargantuan brontotheres, the oddly rodent-like multituberculates, and the diverse South American hoofed litopterns.
Seeing all the dioramas of what these creatures may have looked like always highlights two things, which I was chatting about with a paleontologically-inclined friend a couple of days ago. The first is that even though we know a great deal about Earth's biological history, there's a ton that we don't know and will probably never know. Fossilization requires a very specific (and rare) set of conditions -- most organisms that die are never fossilized in the first place. Then, those few fossils that form have to survive all of the geological processes that happen afterward, and not get eroded, melted, or crushed. And last, a paleontologist (or interested amateur) has to find it. So chances are, for every one species we know about, there are likely to be hundreds of others that we don't -- because the remains from those species haven't been found, or perhaps never were preserved in the first place.
Second, the natural world has often been a very, very dangerous place, with large quantities of animals with Big Nasty Pointy Teeth roaming around. My friend and I both agreed that as fascinating as they are, neither of us would be keen on hopping into a time machine and visiting the Cretaceous-age Western Interior Seaway or the shallow sea that led to the Kem Kem Formation in what is now Morocco. Both were chock-full of enormous BNPT-owners who would have been thrilled to turn any human-sized animal into a light snack.
Well, a recent discovery has added another place and time to the "Fascinating Spot, But Let's Not Visit, Mmmkay?" list: Oligocene-age Egypt. It was the home of an extinct lineage of carnivorous mammals called hyaenodonts -- named after, but only distantly related to, modern hyenas -- in particular one spectacularly scary beast called Bastetodon, a complete skull of which was the subject of a paper last week in The Journal of Vertebrate Paleontology.
The skull was found in a fossil-rich stratum in the Faiyum Depression, a green oasis in central Egypt surrounded by trackless desert. During the Oligocene, Faiyum (and the rest of northern Africa) was a lush jungle, and Bastetodon and the other hyaenodonts were apex predators, preying not only on the hippos and elephants of the time, but on primates like Aegyptopithecus -- a close cousin of our own ancestors, who evolved farther south in what is now Kenya and Tanzania.
Bastetodon was brilliantly equipped to fill its niche. "I think of them as like really beefy wolverines or basically like pitbulls," said Matthew Borths, of Duke University, who co-authored the paper. "They have really big heads that were just covered in muscle."
That, combined with an impressive set of BNPTs, made it a fearsome animal, but it bears mention that it wasn't the largest of the hyaenodonts. That honor goes to Megistotherium osteothlastes -- the name is Greek for "giant bone-crushing beast" -- which is estimated to have weighed five hundred kilograms, with a sixty-centimeter-long skull.
Yeah, fascinated as I am with prehistoric mammals, I think Oligocene-age north Africa is a place I'd just as soon not visit.
Interestingly, though, not long after Bastetodon and Megistotherium reached their apogee, the entire group went into steep decline. No one is quite sure why, but it's probably that climate change had a lot to do with it. The region was getting hotter and drier, reducing the amount of vegetation and ultimately producing the desert we have now. These sorts of changes percolate their way up the food chain, ultimately hitting carnivores the hardest; the last of the hyaenodonts went extinct during the Miocene Epoch. (Even bigger changes were on the way, however -- during the Pliocene Epoch, the Straits of Gibraltar closed for a time, the Mediterranean Sea dried up almost completely, and the entire region became so hot it was uninhabitable -- then when the Straits reopened, it created a flood the likes of which is nearly impossible to imagine.)
But for a while, when northern Africa was lush jungle, the hyaenodonts were on the top of the heap. There was nothing that could come close to matching their strength and fierceness, until the climate and the passage of time ended their hegemony. Just showing that no species is immortal -- and that today's powerful are tomorrow's (pre)historical footnote.
