Friday, January 1, 2021

Getty Images/Stocktrek Images

Allosaurus was one of the top predators of the Jurassic, which makes it one of the scariest animals of all time. Anything that could plausibly eat a full-grown Stegosaurus is the stuff of actual, primal nightmares. But unfortunately for Allosaurus, it’s overshadowed by its later brethren. The oversized therapods of the Cretaceous — T. rex, Giganotosaurus, Carcharodontosaurus, etc. — rather put it to shame in both mass and raw power, relegating their elder to something like little-brother status.

There’s a tendency to look at Allosaurus as akin to a slightly-miniaturized and therefore less-interesting tyrannosaur. This is not fair to Allosaurus, but it’s also unfair to the dinosaur-interested public. Because when modern paleontologists looked at Allosaurus in detail, they start noticing strange things. Wonderful things. They noticed, for instance, that the damn thing might have killed its prey by using its head as a huge spiky axe.

If the head-axe theory sounds vanishingly implausible to you, fair enough. But this is a legitimate, if disputed, line of scientific inquiry, supported by some eminent paleontologists, and there are a number of good reasons to think that it is not as absurd as it might sound. With that caveat in mind — we’ll come back to the evidence in a little bit — let’s go back to the intense horrocomedy of ALLOSAURUS: AXE DINO.

Allosaurus was something like 10′ tall at the shoulder and 30′ long. (For context, that’s about the height of an African elephant and more than twice as long.) Its skull was about four feet long, and, as you can see in the photograph above, was occupied in large part by a row of fiendishly serrated teeth. It could, apparently, open its jaws to ridiculous angles, perhaps as much as 90 degrees. To accommodate this gape, its jaws were relatively weak, able to apply far less force than comparable top predators. Its neck, on the other hand, was fantastically strong.

So let’s envision this thing using the hunting technique outlined earlier. Perhaps it’s hunting a sauropod — let’s say a juvenile Diplodocus, which would have been about half the length of a basketball court, mostly in neck and tail. The Allosaurus would have approached from the side, avoiding the tail. It wasn’t a particularly fast predator, but it didn’t need to be. Apart from that tail, which it used as a whip in order to defend itself (it had spikes on it, because, duh), Diplodocus was basically the dictionary definition of ‘lumbering’.

Once within striking distance, Allosaurus would have opened its horrible jaws, exposing rows of glistening teeth. Presumably there’d have been some slavering involved, and perhaps a bit of tongue-lolling. It’d have been gross, and about to get way more gross. Allosaurus would have lifted its head way back, and then, using its oversized neck muscles, slammed its upper jaw down onto its prey. Its saw-like teeth would have ripped through the Diplodocus’s skin, tearing open a huge wound and weakening the big sauropod. Then Axe-Dino would have reared back and struck again.

An Allosaurus skullTHOMAS COEX/AFP via Getty Images

This would be an absolutely horrific way to die, especially if Allosaurus hunted in packs, as is sometimes suspected. Imagine getting sent into the next life by something that doesn’t even have the wherewithal to eat you normally. Being headbutted to death sounds bad enough, but being toothbutted into oblivion? That’d be embarrassing. The other dinosaurs would probably snicker, and you’d have to haunt them from beyond your Allosaurus-poop grave.

So far we’ve been imagining an axe-style attack from Allosaurus. What makes paleontologists think such a thing would be plausible, or even possible? How can we work this stuff out when all we have to go off is bones and teeth?

Turns out you can do a lot with those things. Comparative anatomy between reptiles and birds gives us a solid idea as to the musculature which must have been present in dinosaurs, and skeletons also have to accommodate that musculature, which gives us even more clues. In Allosaurus, Stephan Lautenschlager notes that:

[T]he comparably weak muscle-driven bite in Allo. fragilis was used in combination with the neck musculature in a strike-and-tear mode to attack prey. In order to be able to hunt prey in such a manner, Allo. fragilis possessed a jaw joint configuration which allowed wide gapes without the risk of dislocation, but would also require a muscle arrangement to permit large gape angles

We’re also able to do some heavy biomechanics work with the skeleton. Finite-element modeling of Allosaurus skulls show that they could withstand a baffling amount of vertical force, which is even more surprising since those same studies also show a low bite force. Later therapods don’t possess these adaptations: the likes of Tyrannosaurus were hard-chomping biters, who could much more straightforwardly take chunks out of their prey.

With these pieces (plus a few more), the likes of Robert Bakker and Emily Rayfield came up with the axe-style attack. It explains Allosaurus’s low bite force, the absurd neck strength, the reinforced jaw, and the hyper-articulated mouth. It’s also incredibly fun. Bakker envisions “a long, jagged wound with concomitant trauma and blood loss, especially if the mega-serrated blade is pulled backward as it strikes its target”. This is not to say that the Dino Axe idea is true. Truth in paleontology, especially when we’re speculating about hunting behavior or other aspects of paleoecology, is difficult to come by. What matters is coming up with parsimonious explanations of the evidence to hand, which is what’s been done here.

Do I believe it? To be clear, I’m in no way qualified to seriously comment on anything but the purely biomechanical aspects of the studies, and since it’s been more than a decade since I was even adjacent to academia, I’m probably not even qualified to comment on those either.

That said, there are a couple of issues with the Axe-Dino hypothesis, fascinating though it is. First of all — and this probably says more about me than it does anything else — I have a very hard time squaring this potential hunting method with the fact it’s not used by any modern animal*. Perhaps, at a push, you could claim, like Bakker does, that the recently-extinct saber-toothed cats deployed a similar style, but I think that comparison is a little superficial.

*A fair rebuttal to this point would be that no modern animal hunts things as large as Stegosaurus or Diplodocus.

I also have a really hard time seeing Allosaurus’s teeth surviving this sort of assault for long. They’d be shedding them left and right if their dentistry was being deployed as a saw. Lone Allosaurus teeth are common fossils, but they’re not that common, and, as Antón, Sanchéz et al. point out, replacing lost teeth would have been very, very difficult at the rates required. I’m also deeply concerned about the role of the lower jaw here, which seems just ... implausible. Does it hang out by itself while the upper jaw is being used as a weapon? The risk of injury seems high enough with the current configuration that one would expect an Axe-Dino to have some more specific anatomical modifications to accommodate it.

But these quibbles are part of the joy of paleontology. It’s a domain of science where imagination is given room to play within the constraints of the evidence. The Allosaurus hypothesis is interesting and worth considering (and also extremely funny), and if there are issues with it, hey, that’s all right. We just need to keep pushing ahead on the science and work it out.

And besides, it’s never a good idea to underestimate the sort of things evolution can throw at you. Why not an Axe-Dino?