Not much is known about Daspletosaurus, a late Cretaceous theropod that thrived in the forests of North America 75 million years ago. Now, paleontologists have shined a literal light on one of the animal’s mysteries, by taking CT scans of two of dinosaur braincases to digitally reconstruct the brains and adjacent structures.
Daspletosaurus was a meat-eating dinosaur first described in 1970; it is a tyrannosaur, meaning it’s part of the family Tyrannosauridae, the group that includes Tarbosaurus, Albertosaurus, and of course Tyrannosaurus rex, among other similarly terrifying predators. The research team looked at two Daspletosaurus skulls — one found near Alberta, Canada’s Red Deer river in 1921 and another dug up near the province’s Milk River at the turn of the millennium.
The two specimens are about 2 million years apart, a blink of the eye in terms of dinosaur evolution. At over 70 million years old, they’re far too ancient for any soft tissue to remain intact. But CT scans aren’t just great for peering non-invasively into complex structures like the brain — they can even be useful when the brain is long gone. In this case, the research team was able to map out some otherwise hidden structures in the two skulls that offer glimpses at how the dinosaurs made sense of their environment. Their work, published today in the Canadian Journal of Earth Sciences, found differences between the animals’ braincases, suggesting that tyrannosaur skulls may have had more variation than previously thought.
Compared to other anatomical structures influenced by natural selection, “the brain is a very conservative organ … the bones surrounding it are also considered to change little,” said Tetsuto Miyashita, a paleontologist at the Canadian Museum of Nature and the study’s lead author, in an email.
“This was thought true to dinosaurs, but because we used to have access to so few braincases, we are only finding out recently in tyrannosaurs that the braincase actually varies a lot from species to species, or even within a species,” Miyashita expalined.
That’s a big takeaway from the recent study: that, based on the shapes of the two skulls and their respective ear structures, braincases, and dimensions, the animals may represent two distinct species, which would be a first for daspletosaurs. (The braincase is the specific part of the skull that holds the brain; it therefore offers unique insights on how dinosaurs’ nerves and senses worked.)
In the paper, the researchers describe Daspletosaurus (specifically Daspletosaurus torosus) as a bit of a fallback classification for tyrannosaurs from western North America that aren’t clearly an animal like Albertosaurus or T. rex. As a result, daspletosaurs crop up over an “unusually broad” swath of the continent, the researchers wrote in the paper, though more recent work has begun to sift through these mislabeled creatures.
The new work follows up on studies clarifying the species of Daspletosaurus; Miyashita and his colleagues spent hundreds of hours scanning the internal spaces within the two fossils, which belonged to animals that lived in the late Cretaceous. With a unique view into their heads, the team found canals that hosted nerve bundles connected to the dinosaurs’ eyes. They also spotted air sacs — a common feature in theropods and modern birds — in many of the braincase bones.
“Cavities within the bones not only make the huge skull lighter but also are related to the middle region of the ear. The cavities probably helped to amplify sound and assist the system that communicates to the left and right ears, allowing the brain to determine where a sound is coming from,” said Ariana Paulina Carabajal, a paleontologist specializing in dinosaur braincases at the National University of Comahue in Argentina and a co-author of the paper, in a press release.
Though both fossils had these features, they varied, with one of the specimens having unique-looking sinuses and some internal characteristics more evocative of other tyrannosaur species, like Gorgosaurus and Bistahieversor. Miyashita said the work was just the first step in teasing apart the specimens long thought to be a single species, Daspletosaurus torosus. Next, the team will check out the rest of the body of the more recently discovered Daspletosaurus. We could have a new meat-eating dinosaur on our hands quite soon.