Kids discover extremely rare teen T. rex fossils sticking out of the ground during North Dakota Badlands hike

A boy lying next to a partially exposed fossil in the ground.
Liam Fisher lying next to his discovery — the femur and tibia of a juvenile T. rex. (Image credit: Sam Fisher)

Three kids hiking in North Dakota made a larger-than-life discovery: a rare teenage Tyrannosaurus rex. The fossil specimen, now nicknamed "Teen Rex," could shed light on how the mighty Cretaceous dinosaur matured.

The three children, ages 7 to 10, came across the young-T. rex fossils while walking in the Hell Creek Formation in the Badlands of North Dakota in 2022, and they helped excavate a series of its bones in 2023.

The partial skeleton, one of only a handful of juvenile T. rex specimens ever discovered, will go on display at the Denver Museum of Nature and Science later this month, coinciding with the cinematic release of a new documentary featuring the discovery, titled: "T. rex."

"Juvenile [T.] rex specimens are extremely rare," Tyler Lyson, a vertebrate paleontologist at the museum who led the "Teen Rex" excavation, said in a statement released by "T. rex" producer Giant Screen Films. "This find is significant to researchers because the 'Teen Rex' specimen may help answer questions about how the king of dinosaurs grew up." 

"Teen Rex" was 25 feet (7.6 meters) long and weighed about 3,500 pounds (1,600 kilograms) when it died more than 66 million years ago, according to Catalyst, the museum's online magazine. For comparison, a full-grown T. rex reached about 40 feet (12 m) in length and weighed around 8,000 pounds (3,600 kg). 

Related: T. rex was as smart as a crocodile, not an ape, according to study debunking controversial intelligence findings

Brothers Liam and Jessin Fisher, 7 and 10 years old, were with their father, Sam Fisher, as well as their 9-year-old cousin Kaiden Madsen, when they noticed a large fossil sticking out of a rock formation. Sam Fisher was a former classmate of Lyson, so he alerted the paleontologist to their discovery of the then-unidentified dinosaur. 

Denver Museum of Nature & Science volunteer Aidan Skelly poses by the partial juvenile T. rex skeleton.  (Image credit: Dr. Tyler R. Lyson)

Lyson began excavating the fossil site 11 months later with a team that included the three boys and Liam and Jessin's sister, 14-year-old Emalynn Fisher, according to the statement. The team unearthed a series of fossils, including a tooth that Lyson quickly identified as belonging to a T. rex

Lyson and his colleagues estimated the size of the adolescent T. rex based on its tibia (lower leg), which was 32.3 inches (82 centimeters) long. An adult T. rex tibia was about 44 inches (112 cm) long, suggesting the dinosaur was a teenager, according to "Teen Rex" documents released by the museum.

67 million years ago Tyrannosaurus rex would have preyed upon Denversaurus and other animals that lived during this time. (Image credit: Andrey Atuchin (artist) and Denver Museum of Nature & Science)

Researchers will analyze the bones in greater detail to confirm the dinosaur's age and learn more about T. rex growth patterns and bone development. This work will be done in public at the museum as part of a new temporary exhibit called "Discovering Teen Rex," which opens June 21.

The "T. rex" documentary, scheduled to premiere the same day, will feature footage from the "Teen Rex" discovery and use computer-generated imagery to bring T. rex to life, from hatchling to adult. 

"It's remarkable to consider how T. rex might have grown from a kitten-sized hatchling into the 40-foot, 8,000 pound adult predator we are familiar with," Thomas Holtz, "T. Rex" lead adviser and a vertebrate paleontologist at the University of Maryland, said in the statement. 

"Scientists can really only speculate on how 'Teen rex' might have lived and behaved, so discoveries like this one have the potential to provide important new information about those earlier life stages, when [the] fastest growth likely occurred," he added. 

Patrick Pester
Live Science Contributor

Patrick Pester is a freelance writer and previously a staff writer at Live Science. His background is in wildlife conservation and he has worked with endangered species around the world. Patrick holds a master's degree in international journalism from Cardiff University in the U.K.