If Tyrannosaurus rex is too mainstream, discerning 10-year-olds may now have a new name to spout when asked their favorite dinosaur – Tyrannosaurus mcraeensis. The newly identified species appears to be more primitive than its famous cousin, but just as big and scary.
It’s not surprising that T. rex has utterly captured the public imagination – there’s just no denying the coolness factor of an ancient superpredator the size of a double-decker bus. Although the new species has a way lamer name – T. mcraeensis, named after the layers of rock it was found in – you wouldn’t say that to its face. It was still a 12-m-long (39-ft), 10-ton tank full of teeth.
The differences are way more subtle, and not something you’d be able to pick out if you were in the unfortunate scenario of having both species bearing down on you at once. Compared to T. rex, T. mcraeensis had a longer but shallower lower jaw full of blunter teeth, and its chin and the bumps above the eyes were less prominent. It might not sound like much, but the consistency of differences is what led the team to declare a new species.
“Every single bone is slightly different from the corresponding element in T. rex,” co-author Nick Longrich wrote in his blog. “Since we have lots of T. rex fossils, we have a reasonable idea of what sort of variation exists in a T. rex, and this animal consistently lies outside of that range of variation, in every single bone of its skeleton.”
But the most striking difference, the team says, is the fossil’s age. T. mcraeensis prowled North America at least 72 million years ago – about 6 million years before T. rex appeared on the scene. That would make it more primitive, and although it doesn’t seem to be a direct ancestor it could help plug some gaps in our understanding of how Tyrannosaurus evolved.
Previously, the closest known relatives, like Tarbosaurus, were only known from Asia, suggesting they originated there and migrated over via what’s now Siberia and Alaska. Instead, the team says the new discovery implies Tyrannosaurus evolved in southern North America and then spread north, in a pattern similar to long-necked, horned and duck-billed dinosaurs.
T. mcraeensis is joining the family during a very turbulent time. Over the last few years some paleontologists have proposed that T. rex actually comprises three separate species, coining the names T. regina and T. imperator, while other scientists argue that the differences aren’t strong enough to support the claim. A parallel debate focuses on whether fossils of smaller tyrannosaurs constitute a separate species, dubbed Nanotyrannus, or if they’re just teenage T. rexes. It feels important to note that Longrich, co-author of this new study, is also on Team Nanotyrannus.
More study will be needed to try to untangle this twisted family tree.
The research was published in the journal Scientific Reports.
Source: University of Bath