Rare fossil of an adolescent tyrannosaur – 'Teen Rex' – discovered by American children

Rare fossil of an adolescent tyrannosaurus – 'Teen Rex' – discovered by American children

By Will Dunham

(Reuters) – A rare fossil of an adolescent Tyrannosaurus rex has been discovered in the badlands of North Dakota – a remarkable discovery for the scientific insight it can offer into the life history of this famous dinosaur and for the story of the children who found it.

The discovery of the fossil, nicknamed “Teen Rex,” was announced Tuesday by the Denver Museum of Nature & Science, where it will be studied and exhibited.

In July 2022, brothers Liam and Jessin Fisher, then aged 7 and 10, and their cousin, Kaiden Madsen, aged 9, were hiking and looking for fossils with Sam Fisher, father of Liam and Jessin, on lands managed by the United States. Bureau of Land Management, approximately 10 miles from the town of Marmarth in southwestern North Dakota. Liam and his father noticed a large leg bone sticking out of the ground.

“My dad yelled for Jessin and Kaiden to come, and they came running,” said Liam, now 9. “And dad said, 'What is that?' And Jessin said, 'It's a dinosaur.'

“I didn’t know what type,” said Jessin, now 12.

Sam Fisher texted a photo to paleontologist Tyler Lyson, a Marmarth native and his former high school classmate who is now curator of vertebrate paleontology at the Denver Museum of Nature & Science. Lyson obtained excavation permits, and in July 2023 everyone returned to the site.

Initially, it appeared that the paw belonged to a herbivorous duck-billed dinosaur.

“However, on the first day of excavation, Jessin and I discovered the lower jaw with several large T. rex teeth protruding from it,” Lyson said.

“It always gives me goosebumps,” Lyson added.

“I was completely speechless,” said Kaiden, now 11.

Tyrannosaurus Rex, which roamed western North America, was one of the largest carnivorous dinosaurs.

It appears that this tyrannosaurus was approximately 13 to 15 years old, two-thirds the size of an adult, measured 7.6 meters long, and weighed 1,600 kg (3,500 pounds). T. rex had reached full growth around 18-21 years old. The largest known tyrannosaur, a specimen named Sue kept at the Field Museum in Chicago, was perhaps 40 feet long.

This individual lived around 67 million years ago, towards the end of the Cretaceous. Tyrannosaurus Rex and the rest of the dinosaurs, except for their bird descendants, were wiped out 66 million years ago after an asteroid hit Earth.

The fossil comes from the Hell Creek Formation region that “preserves Earth's last dinosaur ecosystem” just before the mass extinction, Lyson said. Based on the soft sandstone in which it was found, the animal's body apparently ended up on a sandbar in an ancient river system.

The completeness of the skeleton remains uncertain because many bones remain embedded in a three-ton piece of rock, currently being studied at the museum. There appears to be a large portion of the skull, hip bone and some vertebrae in addition to the leg, Lyson said.

Tyrannosaurus Rex had a massive head and enormous bite force, walked on two legs, and had spindly arms with only two fingers. A younger tyrannosaurus had a different body type than an adult – more graceful and faster, and with a more streamlined skull – and might have hunted different prey, reducing competition with its elders.

“Juvenile T. rexes were much lighter, with long, lanky legs, but without the large mass of adult T. rexes,” Lyson said.

Having juvenile specimens helps reveal Tyrannosaurus growth rate and body changes during maturation, Lyson said. Only a handful of these fossils are available for study. This one appears to be slightly larger than another juvenile Tyrannosaurus fossil called “Jane” housed at the Burpee Museum of Natural History in Rockford, Illinois, Lyson said.

A minority of paleontologists believe that Tyrannosaurus lived alongside a smaller cousin called Nanotyrannus, based on fossils that most paleontologists believe represent juvenile Tyrannosaurus. Lyson said the new fossil could shed light on this question.

A documentary crew was present during the excavation, with the film “T. REX” scheduled for release on June 21.

(Reporting by Will Dunham in Washington, Editing by Rosalba O'Brien)