Rare juvenile T. rex discovered by young fossil hunters

A young boy lying next to a fossil legbone. The rock beneath him is grey.
Sam Fisher texted this image to Tyler Lyson at the Denver Museum of Nature and Science. It was a photo of his son Liam lying next to what looked like a dinosaur bone, in the North Dakota badlands. The bone turned out to be the femur and tibia of a juvenile T. rex. Image via Sam Fisher.

A couple years ago, three young boys fossil hunting in the North Dakota badlands discovered some unusual ancient dinosaur bones. And on June 4, 2024, the Denver Museum of Nature and Science said its scientists later identified the bones as belonging to a rare juvenile Tyrannosaurus rex. The bones will be on view at the museum starting this month. And, it turns out, the fossil – nicknamed Teen Rex – is significant. That’s because few juvenile T. rexes have ever been unearthed. So this specimen is a valuable clue in understanding how these ferocious dinosaurs grew to adulthood.

Discovering the teenage T. rex

In July 2022, three young fossil hunters were searching the arid badlands near Marmarth, North Dakota, for fossils. Liam Fisher was eight years old at the time, his brother Jessin, 11, and their cousin, Kaiden Madsen, was 10. The kids were accompanied by the brothers’ father, Sam Fisher.

The young fossil hunters were amazed to discover large bones protruding from sedimentary rock that formed the badlands hills. Some bones were in fragments, weathering out of the rock. Sam Fisher sent photos of this unusual find to his friend, paleontologist Tyler Lyson at the Denver Museum of Nature and Science. Lyson immediately recognized it as dinosaur bone but could not identify it.

A dinosaur, T. rex, with a long tail running on two legs as it chases a bird.
An artist’s depiction of Teen Rex, the juvenile T. rex found by the young fossil hunters in 2022. Image via Andrey Atuchin and Denver Museum of Nature and Science.

A stunning realization

In July 2023, Lyson and his team went to the site to excavate the fossil. The young fossil hunters who made the discovery joined the expedition. While digging, Lyson unearthed teeth that clearly belonged to a T. rex. Based on the size of the exposed bone and teeth, he realized that the kids had made an extraordinary discovery, a rare juvenile T. rex.

Lyson recounted that stunning moment in an interview:

Sam’s oldest boy, Jessin, and I were digging and brushing and digging and brushing, and all of a sudden, a brush and a T-Rex tooth … pops off, and I pick it up. I look at Jessin. He gasps. He and I, like, share this moment. And then I started brushing where the tooth came out, and we could see three more teeth all lined up in a row.

We just uncovered the lower jaw of this juvenile T-Rex specimen. It was just one of the most remarkable, remarkable moments. And you were able to tell from the size of it that it was a juvenile. We could tell based both on the size of the teeth and then also the size of the leg bone, that we had a smaller dinosaur.

A long black tooth with a pointed edge. Next to it is a small paintbrush.
A fossil rooted tooth from the juvenile T. rex. Image via Tyler R. Lyson.

Extracting the juvenile T. Rex

For 11 days, the team carefully dug out a large chunk of rock that contained the fossil. They wrapped it in a jacket of plaster and burlap. Then, the 6,000-pound package was airlifted by a Black Hawk helicopter and placed in a heavy duty trailer. From there, it began its journey to Denver, Colorado.

A large white object (rock   surrounded by burlap and plaster) with a large net below it. Six people are standing around it.
A large chunk of rock containing the fossil was wrapped by the excavation team, pictured here, in a burlap and plaster jacket. They placed the package in a net so that a Black Hawk helicopter could lift it up and place it on a trailer for transport to the Denver Museum of Nature and Science. Image via Tyler R. Lyson.

At the Denver Museum of Nature and Science, scientists removed some of the burlap and plaster jacket that protected the fossil during transport. The museum has now begun the painstaking process of extracting the fossil from rock.

The museum announced that starting June 21, 2024, visitors will be able to watch scientists work in real-time as they carefully remove the fossil from the rock. They also said Teen Rex’s discovery and excavation will be featured in a new film about T. rex that is opening in IMAX theaters nationwide.

What we know about Teen Rex

Tyrannosaurus rex, often called T. rex, lived during the late Cretaceous epoch, which was 100 to 66 million years ago. Its fossils have been found only in western North America. T. rex was a large bipedal carnivorous dinosaur, with sharp pointed saw-edged teeth. Its powerful jaws and teeth could break bones. Scientists think adults reached a length of 40 feet (12 m) or more. And it could have weighed over 11,000 pounds (5,000 kg).

Teen Rex is a significant discovery. That’s because most T. rex fossils are adults. There aren’t many juveniles in the fossil record. Researchers need more juveniles to compare them, so they can better understand how these ferocious creatures grew and developed during their teenage years to adulthood.

The Teen Rex fossil was a partial skeleton consisting of sections of the skull, tail, leg and hip. It’s only about 30% of the total skeleton, but there’s still a lot scientists can learn from it.

A drawing of a T. rex skeleton, with some parts shaded blue.
The Teen Rex fossil is an incomplete skeleton consisting of a section of the skull, tail, leg and hip. Those parts are shaded blue in this diagram of a T. rex skeleton. Image via Scott Hartman.

Answers from the T. rex skeleton

For instance, how did they know that Teen Rex was a juvenile? Its tibia (or shin bone) provided the first clue. It measured about 32 inches (81 cm). A full-grown T. rex’s tibia would have measured about 44 inches (112 cm). Teen Rex’s teeth were also smaller than that of an adult.

In addition, based on the size of the bones, researchers think Teen Rex measured about 25 feet (7.5 m) long and 10 feet (3 m) tall. They believe the dinosaur weighed about 3,500 pounds (1,590 kg). But that’s just an initial estimate. They’ll need to recover more bones to get a more accurate idea of Teen Rex’s size.

A man and three kids standing against grey rock.
Paleontologist Tyler Lyson is pictured here with the 3 young fossil hunters who found Teen Rex: Liam Fisher, Jessin Fisher and Kaiden Madsen. Image via Kirk Johnson.

Bottom line: A family fossil hunting in the North Dakota badlands stumbled across an intriguing fossil that was later identified as a rare juvenile T. rex.


Denver Museum of Nature & Science Online Magazine

Denver Museum of Nature and Science

Press Release and Media Kit

June 13, 2024

Like what you read?
Subscribe and receive daily news delivered to your inbox.

Your email address will only be used for EarthSky content. Privacy Policy
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

More from 

Shireen Gonzaga

View All