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Rare fossil of adolescent ‘Teen Rex’ found by American children

Andrey Atuchin and the Denver Museum of Nature and Science / Handout via Reuters
This illustration shows North Dakota’s 67-million-year-old Cretaceous-era landscape with a young Tyrannosaurus rex.

A rare fossil of an adolescent Tyrannosaurus rex has been unearthed in the badlands of North Dakota – a find notable for the scientific insight it may provide 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 June 4 by the Denver Museum of Nature & Science, where it will be studied and displayed.

In July 2022, brothers Liam and Jessin Fisher, then aged 7 and 10, and their cousin, Kaiden Madsen, who was 9, were hiking and looking for fossils with Sam Fisher, Liam and Jessin’s father, on land managed by the US. Bureau of Land Management approximately 10 miles from the town of Marmarth in southwestern North Dakota. Liam and his father saw a large leg 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 this?’ And Jessin said, “That’s a dinosaur.”

“I didn’t know which type,” says Jessin, now twelve.

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 everyone returned to the site in July 2023.

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

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

“It still gives me goosebumps,” Lyson added.

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

Tyrannosaurus, which roamed western North America, was one of the largest meat-eating dinosaurs.

It appears that this Tyrannosaurus was about 13-15 years old, two-thirds of adult size, 7.6 meters long and 1,600 kilograms. T. rex was fully grown at around 18-21 years of age. Perhaps the largest known Tyrannosaurus, a specimen named Sue in the Field Museum in Chicago, is 40 feet (12.3 meters) long.

This individual lived about 67 million years ago, near the end of the Cretaceous period. Tyrannosaurus and the rest of the dinosaurs, apart from 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 “sustained Earth’s last dinosaur ecosystem” just before the mass extinction, Lyson said. Judging from 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 unclear because many of the bones remain embedded in a three-ton piece of rock, now being studied at the museum. It appears that in addition to the leg, a large portion of the skull, hip bone and some vertebrae are present, Lyson said.

Tyrannosaurus had a huge head and enormous bite force, walked on two legs and had small arms with only two fingers. A younger Tyrannosaurus had a different body type than an adult – graceful and faster, and with a skull that was more streamlined – and may have hunted different prey, reducing competition with its elders.

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

Having young specimens helps reveal Tyrannosaurus growth rates and body changes during maturation, Lyson said. There are only a handful of such fossils available for research. It appears this one is slightly larger than another juvenile Tyrannosaurus fossil called “Jane” at the Burpee Museum of Natural History in Rockford, Illinois, Lyson said.

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

A documentary crew was present during the excavation with the film “T. REX” will be released on June 21.