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The large Ceratosaurus at the Natural History Museum of Utah. Photo by Brian Switek.

Let’s Give Ceratosaurus a Hand

“What’s your favorite dinosaur?” I’ve come to hate this question. Not that it’s an unreasonable one. Much of my career has been built on the skeletal backs of dinosaurs and I really do adore them, but I honestly don’t have a strong favorite. I might as well be asked “What’s your favorite kind of burrito?” Any. All. I can’t pick a favorite.

I used to answer the dinosaur question with “Magpie.” And it’s true that I find the sassy little birds incredibly charming. I’m always happy to see them hopping around like little Velociraptors when I walk up to the Natural History Museum of Utah across town. I also know that this is usually a disappointment to whoever’s asking me, given they’re really talking about non-avian dinosaurs and don’t want me to reiterate the point that, yes, magpies and all other birds are living dinosaurs.

So rather than be a grump about the question, I’ve started to say “Ceratosaurus!” This, in public imagination, is more of a proper dinosaur. The Jurassic carnivore had exceptionally long fangs, a trio of horns on its face, and a row of bony armor along its spine, making it look appropriately fearsome.

Even if I hold back from calling it my all-time favorite, I really do have a soft spot for the pointy carnivore—so much so that I have the skeleton of a particularly-massive individual from Utah tattooed on my right arm and that I’m always excited to learn something new about this rare and still-mysterious carnivore. Case in point, I was genuinely excited to see paleontologists Matthew Carrano and Jonah Choiniere publish a new study on Ceratosaurus had bones that have been hidden for decades.

The skeleton from which Ceratosaurus was named – or most of it, anyway – was on display for over a century in the halls of the Smithsonian National Museum of Natural History. With the museum’s fossil halls undergoing a revamp, though, the old skeletons are being cleaned up and removed from their old constraints, including the Ceratosaurus that has been encased in a  plaster wall mount for so many years. And in doing this overdue cleanup, the Smithsonian’s preparators found bones that have gone unexamined since the dinosaur was put in plaster.

Most of what we know about the stubby arms of Ceratosaurus came from the articulated forearm and hand of the Smithsonian skeleton. They really are teeny compared to the dinosaur’s shoulder girdle and the rest of its body, even if it hasn’t received as much ridicule as T. rex for such proportions. In addition to the well-preserved left arm, though, the Smithsonian scientists found some elements of the right hand that were hidden away in the mount that once encased the body, which Carrano and Choiniere took as a jumping-off point to redescribe the arms of this Jurassic classic.

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The lower left arm of Ceratosaurus as it was originally found. From Carrano and Choiniere, 2016.

While not as ridiculous as in later relatives such as Carnotaurus, the arms of Ceratosaurus were pretty stubby. Each hand had four short fingers with small claws on the tips that were not nearly as nasty-looking as the meathooks borne by its neighbors Allosaurus and Torvosaurus. Instead, the arms of Ceratosaurus were comparable to those of earlier, more distantly-related dinosaurs like Dilophosaurus, Carrano and Choiniere point out, albeit with shorter hands and small claws.

Ceratosaurus probably didn’t have a sharp mitt for catching or holding onto a prey, but an arm that fits with the trend overall trend towards a vestigial state seen in its relatives, the abelisaurs, over the following 84 million years.

This only highlights the fact that we don’t actually have a refined idea of how Ceratosaurus made its living during Morrison Formation time. Ceratosaurus was part of a trio of large Late Jurassic carnivores found in the same floodplain habitats, rarer than Allosaurus but not so rare as Torvosaurus. Is this a reflection of different habitat choices, or even varying feeding preferences?

Beyond that, did Ceratosaurus adopt an all-mouth hunting style like a hyena or wild dog, keeping those little arms tucked back while taking down baby sauropods and other prey with a razor-lined maw? We don’t yet know, but specimens like the one at the Smithsonian may hold additional clues. After all, a Ceratosaurus in the hand is worth two in the rock.