How Do Scientists Study Young T. rex?

by AMNH on

On Exhibit posts

Model of a T. rex hatchling with feathers. Like the Late Cretaceous theropod Ornithomimus, T. rex may have sported feathers. For hatchlings, feathers would have provided warmth and camouflage.
D. Finnin/©AMNH

Scientists have yet to find a Tyrannosaurus rex hatchling fossil, and even juvenile fossil specimens are very rare. But there are other methods of learning what young T. rex may have been like before it grew to be a giant.

Recent studies based on the growth curve of T. rex suggest that these animals would have been around 2 feet long straight out of the egg.

These gangly dinosaurs would have had long legs and proportionally longer arms than adults. They also would have had the ability to run quickly—a useful trait for a relatively defenseless youngster trying to survive to adulthood.

And many didn’t: about 60 percent likely died in their first year of life, according to Gregory Erickson, a biologist at Florida State University and consultant for the new exhibition T. rex: The Ultimate Predator.

Paleontologists also look to other tyrannosaurs—a group that’s bigger, and better studied, today than ever before—for additional clues about how T. rex may have developed and behaved. “Over half the animals on the tyrannosaur family tree were unknown 20 years ago,” says Mark Norell, Macaulay Curator in the Division of Paleontology and curator of the new exhibition.

Erickson has looked to Tarbosaurus, a tyrannosaur that lived 70 million years ago in what is now Asia, to glean more clues about young T. rex. As a youngster, Tarbosaurus had a short snout and teeth designed for slicing flesh—but not yet adequate for crushing bone. Young Tarbosaurus would have pursued smaller, perhaps faster prey until it grew into the body mass and bite force to go after larger game.

Model of a T. rex hatchling with feathers.
Visitors to the exhibition T: rex: The Ultimate Predator can see the skull of an adult Tarbosaurus that weighed six tons, and the small skeleton of a two-year-old that weighed just 70 pounds (32 kg).
R. Mickens/©AMNH

Juvenile T. rex fossil specimens are very rare, and even when a specimen is discovered, paleontologists run up against another problem: how to confirm that a fossil is of a young animal, not of an adult of a smaller, totally new species?

In 2003, scientists from the Burpee Museum of Natural History in Illinois discovered a nearly complete tyrannosaur skeleton in northwest Montana that measured 20 feet long and 7 feet tall. Whether “Jane,” as the specimen is known, is a juvenile T. rex or a yet-to-be described smaller tyrannosaur species has experts divided to this day.

Erickson is squarely on the Jane-the-T. rex-juvenile side of the debate, putting the animal’s age at 11. “We know from looking at other tyrannosaurs, such as Tarbosaurus, there are similar characteristics suggesting Jane is a juvenile: the proportions of the skull, the bone fusions, how big the eye is, and the shape of the bone over the nose and eyes that change as they mature,” says Erickson. “My data suggest it’s an animal still growing. It fits right on the T. rex growth curve.”

Illustration of T. rex juvenile.
Juvenile T. rex had a different body form and hunted different prey than adults, occupying different ecological niches as it matured.
Illustration by Zhao Chuang; Courtesy of PNSO

But even nearly complete fossils like Jane offer scientists an incomplete picture—small pieces of a large, complex puzzle. “One of the bigger challenges of paleontology is often we don’t have much to work with,” says Erickson. “We’re like forensic scientists, except that we’re looking at 65-million-year-old remains.”


For more about Tyrannosaurus rex throughout its life, visit T. rex: The Ultimate Predator.

A version of this story appeared in the Winter issue of Rotunda, the Member Magazine.