Nanotyrannus Isn’t a Juvenile T-Rex—It’s a Separate Dinosaur

‘Dueling Dinosaurs’ Fossil Solves the Mystery of a ‘Mini T. rex’

By Anirban Mukhopadhyay edited by Sarah Lewin Frasier

For greater than three many years, paleontologists have argued over whether or not a lithe predatory dinosaur referred to as Nanotyrannus ever actually prowled Cretaceous North America—or whether or not the bones that some researchers attributed to the creature as a substitute belonged to teenage examples of Tyrannosaurus rex that have been nonetheless rising into their monstrous body. A brand new research in Nature might have lastly settled the rating in favor of Nanotyrannus based mostly on an evaluation of Montana’s hanging “Dueling Dinosaurs” fossil, found in 2006. The fossil exhibits a triceratops entwined with a small tyrannosaurlike dinosaur, each with vital accidents.

“Simply put, the Dueling Dinosaur Nanotyrannus is fully grown at half the length and one tenth the body mass of a mature T. rex,” says research co-author Lindsay Zanno, a paleontologist at North Carolina State University. “There is no scenario in which this animal morphs into a T. rex.” She explains that Nanotyrannus should have been a smaller, sleeker predator that hunted alongside Tyrannosaurus.

---

On supporting science journalism

If you are having fun with this text, take into account supporting our award-winning journalism by subscribing. By buying a subscription you’re serving to to make sure the way forward for impactful tales in regards to the discoveries and concepts shaping our world immediately.

---

The most definitive proof comes from a microscopic function referred to as an exterior elementary system—a sequence of tightly packed development rings in bone—that implies the fossilized animal had completed rising, explains research co-author James G. Napoli, a paleontologist at Stony Brook University. Zanno and Napoli argue this confirms Nanotyrannus as a definite genus alongside T. rex within the ecosystem of the fossil-rich Hell Creek Formation web site in Montana, which spanned the final million years of the Cretaceous.

Using high-resolution scans, the crew additionally discovered the Nanotyrannus cranium contained extra tooth sockets than a T. rex of any age and totally different routes for cranial nerves and sinuses than T. rex displays. These options would have been established early in embryonic growth and stay mounted for all times.

The researchers performed a computer-based evolutionary evaluation, which positioned Nanotyrannus in a brand new clade simply exterior the T. rex line. This clade, referred to as Nanotyrannidae, might have originated in japanese North America.

Additionally, the crew in contrast the Dueling Dinosaurs specimen with two earlier finds that have been additionally made in Montana’s Hell Creek Formation—a skull unearthed by a team from the Cleveland Museum of Natural History (CMNH) that first outlined Nanotyrannus and a fossil referred to as “Jane” that was found by a crew from the Burpee Museum of Natural History. In doing so, Zanno and Napoli formalized the names of those specimens: They confirmed the Dueling Dinosaurs fossil represented the identical species because the CMNH cranium, which was named Nanotyrannus lancensis in 1988. And they described Jane as a brand new species, Nanotyrannus lethaeus.

That image builds on hints famous many years in the past by paleontologist Philip J. Currie, who co-authored the 1988 paper that first named Nanotyrannus. Currie says he nonetheless factors to Nanotyrannus’s increased tooth counts as a definitive distinction from T. rex. Thomas R. Holtz, Jr., a paleontologist on the University of Maryland, who was not a part of the brand new paper, observes that such pairing isn’t unprecedented—Asia’s tyrannosaur Tarbosaurus lived beside the smaller tyrannosaur Alioramus, with the 2 splitting the menu between large and fleet-footed prey.

Long-time advocates of the juvenile T. rex speculation, although acknowledging the robust proof within the new paper, aren’t but able to rewrite the household tree of T. Rex and its kin. Stephen Brusatte, an evolutionary biologist on the University of Edinburgh, who was not concerned within the research, asks, “If every small skeleton is Nanotyrannus, where are the juvenile T. rexes?” Paleontologist Thomas Carr of Carthage College, who was additionally not a part of the analysis, argues that skeletal maturity alone doesn’t outline a species. Without extra small T. rex fossils, he says, distinguishing development from evolution stays troublesome.

Nevertheless, Nanotyrannus provides a contemporary dimension to the ultimate days of the dinosaurs. Rather than a one-species monopoly below T. rex, the Hell Creek panorama might have hosted a tiered guild of hunters. Zanno calls the subsequent problem “a completely new question” for analysis on tyrannosaurs and their kin: understanding how Nanotyrannus and Tyrannosaurus coexisted, averted competitors and formed the evolution of their prey. Napoli says the findings problem many years of deciphering these littler dinosaurs as juvenile T. rexes. “Now that we’ve corrected the record on Nanotyrannus, we think it’s possible that other smaller tyrannosaur fossils are misidentified and that there may be many more species awaiting recognition.”

It’s Time to Stand Up for Science

If you loved this text, I’d prefer to ask to your assist. Scientific American has served as an advocate for science and business for 180 years, and proper now stands out as the most crucial second in that two-century historical past.

I’ve been a Scientific American subscriber since I used to be 12 years outdated, and it helped form the way in which I take a look at the world. SciAm at all times educates and delights me, and evokes a way of awe for our huge, stunning universe. I hope it does that for you, too.

If you subscribe to Scientific American, you assist be certain that our protection is centered on significant analysis and discovery; that we now have the sources to report on the choices that threaten labs throughout the U.S.; and that we assist each budding and dealing scientists at a time when the worth of science itself too typically goes unrecognized.

In return, you get important information, fascinating podcasts, good infographics, can’t-miss newsletters, must-watch movies, difficult video games, and the science world’s greatest writing and reporting. You may even present somebody a subscription.

There has by no means been a extra necessary time for us to face up and present why science issues. I hope you’ll assist us in that mission.