Thescelosaurus is an oft-forgotten dinosaur. So much so that the critter’s full name is Thescelosaurus neglectus – a nod to the fact that the first known skeleton of the dinosaur was found in 1891, but languished in shipping crates until paleontologist Charles Gilmore named it in 1913. And even since then, the 12-foot-long Thescelosaurus remains a pretty obscure dinosaur. Compared to some of its 68-66 million year old neighbors – like the giant, imposing Tyrannosaurus and Triceratops – Thescelosaurus was small, herbivorous, and lacked any fancy ornamentation that would make it stand out.
The most attention Thescelosaurus ever received was when one specimen, found in 1993 and described in 2000, looked like it had a fossilized heart. Unfortunately, though, it turns out that “Willo” (as the dinosaur was named) really had a mineral concretion develop inside its ribcage after burial and did not have a heart of stone after all. Thescelosaurus just couldn’t catch a break.
But if we’re going to understand dinosaurs and their world, we can’t just look at the sexy species that make headlines. The meek herbivores matter, too, especially since every dinosaur species was part of a greater, ever-evolving ecology in the prehistoric past. That’s why I was glad to see Thescelosaurus get a little more attention last month. In the pages of PeerJ, South Dakota School of Mines and Technology paleontologist Clint Boyd described the skull of the neglected dinosaur.
Even though Thescelosaurus was named over a century ago, our knowledge of this dinosaur has been incomplete. Up until very recently, all that was known of this dinosaur’s skull were three skull bones. That’s it. But drawing from Willo and another well-preserved specimen, Boyd went about providing the first scientific rundown of the Thescelosaurus skull.
So what can we learn from Thescelosaurus? First off, dinosaur skulls can be very informative in figuring out who was related to whom. That’s because skulls are not made up of single bones, but instead are a network of different bones. The size, placement, and anatomy of the skull bones can help paleontologists sort out dinosaur relationships.
For Thescelosaurus, Boyd found that the dinosaur’s skull shares some key characteristics with a similar, slightly-earlier dinosaur named Parksosaurus found in Canada. This questions other studies that proposed a closer relationship between Parksosaurus and a dinosaur from South America named Gasparinisaurua. Sorting this out will help paleontologists better understand how these dinosaurs evolved and spread around the world.
Not that everything about a dinosaur skull is straightforward. For one of the last non-avian dinosaurs, Thescelosaurus had some traits that looked very ancient. The upper and lower jaws of Thescelosaurus, Boyd found, had twenty tooth sockets each. This is more like the very, very ancient forerunners of Thescelosaurus, before its ancestors split from the armored dinosaurs and other lineages on its side of the dinosaur family tree. The more recent relatives of Thescelosaurus had fewer tooth positions in their jaws, following a pattern of reduction. Did Thescelosaurus retain the ancestral trait, or does it represent an evolutionary reversal? Figuring that out might help us understand how this unassuming dinosaur was different from others of its kind.
Boyd, C. 2014. The cranial anatomy of the neornithischian dinosaur Thescelosaurus neglectus. PeerJ. doi: 10.7717/peerj.669