Nanotyrannus or baby T. Rex? $20 million fossil divides scientists

When fossil hunters unearthed the remains of a dinosaur in the hills of eastern Montana five years ago, the bones had several key features of a Tyrannosaurus rex: a giant pair of legs for walking, a much smaller pair of arms for tearing prey and a long tail. But unlike an adult T. rex, which would be about the size of a city bus, it was more the size of a pickup truck.

The specimen, now on sale for $20 million at a London art gallery, became the latest find to raise a question that has come to obsess paleontologists: Is it a young T. rex or could it be a different, but related, dinosaur species?

The dispute over the existence of Nanotyrannus, as the possible relative of T. rex has been called, has produced a great deal of scientific research and decades of debate. With dinosaur fossils fetching increasingly impressive prices, the debate has begun to spread through auction houses and galleries, where some see the T. rex name as a valuable trademark.

“The debate always gets a little fiercer when the king of the dinosaurs is involved,” said Steve Brusatte, a paleontologist at the University of Edinburgh, Scotland.

The David Aaron gallery, which sells the specimen discovered in Montana, known as Chomper, faced a choice. Call it a juvenile T. rex? Label it Nanotyrannus? Or embrace ambiguity? He chose to call it “rare juvenile Tyrannosaurus rex skeleton.” He cited an influential 2020 study led by Holly N. Woodward, which used an analysis of growth rings in bone samples from two disputed specimens — estimated to have been similar in size to Chomper — to argue that they were juveniles. that were approaching a growth spurt.

But Pete Larson, a fossil expert known for his involvement in the excavation of two of the world's most famous T. rex, said he believed Chomper was a Nanotyrannus. The specimen was featured in a 2020 episode of the Discovery Channel documentary series “Dino Hunters,” in which Larson pointed to the apparent fusion of its nasal bones as evidence that it was not a juvenile T. rex.

Another specimen sure to shape the debate is a marvel known as the Dueling Dinosaurs, a well-preserved fossil of a Tyrannosaurus that was discovered next to the remains of a Triceratops, giving the impression that the animals died while fighting.

The dueling dinosaur specimen—discovered by a team led by Clayton Phipps, the same fossil hunter who excavated Chomper—was acquired by the North Carolina Museum of Natural Sciences in 2020. This spring, it plans to open an exhibit in where the public will be able to visit the dueling dinosaurs while paleontologists actively study them.

“We need to elucidate what, in my career, has been one of the most complex questions to address, because you have to distinguish many variables,” said Lindsay Zanno, director of paleontology at the museum, listing growth, sex and the fossilization process. as examples. “That's why it's had the scientific community stumped for years.”

The origin of the paleontological debate dates back to 1942, when an expedition from the Cleveland Museum of Natural History, Ohio, unearthed a 56-centimeter dinosaur skull in Montana. It was originally identified as a Gorgosaurus, but in the 1960s new analysis argued that it belonged to a juvenile T. rex.

The debate has continued since then. Even to non-scientists, there are clear differences between that specimen's skull and that of adult T. rex: the smaller skull has a thinner snout and thinner, blade-like teeth. In the late 1980s, research led by Robert T. Bakker argued that these differences, and others, indicated that this was a new species. He named it Nanotyrannus lancensis.

Many paleontologists believe that to really put an end to this dispute, more evidence is needed. Some see the rise in dinosaur prices as a crisis, fearing that important specimens will end up out of reach of researchers.

Salomon Aaron, director of the London gallery, said he hoped Chomper would go to a museum where scientists could study it.

“We need more specimens to solve the mystery,” said David Evans, a paleontologist at the Royal Ontario Museum. “And this is precisely the type of specimen scientists need.”

By: JULIA JACOBS and ZACHARY SMALL