Potential Discovery of 66.5 Million Year Old Baby Tyrannosaurus Rex Fossil Could Solve Puzzle of What It Looked Like

Updated | Hell Creek, Montana, was definitely hellish for one dinosaur that died there, about 66.5 million years ago—but the site was heaven for the team of scientists that stumbled on that dinosaur's remains there in the summer of 2016.

Uncovering the specimen has been a long process—the excavators didn't really know what they had found until they could return the next summer and find the 2-foot-long toothy skull, which told them it was a tyrannosaur, and one in quite good condition. They announced the discovery on Thursday, although it has not yet been published in a scientific journal.

"This is a one in 100 million specimen," Kyle Atkins-Weltman, an assistant fossil preparator at the University of Kansas who is working on the project, told Live Science.

Read more: Teenage Dinosaur Fossil Discovery Reveals What Puberty Was Like for a Tyrannosaur

Finding such a well-preserved small tyrannosaur sparked the team's interest because small tyrannosaurs, it turns out, are quite contentious. Over the years, scientists have found a handful of fossils that seem like they could be the remains of very young Tyrannosaurus rex individuals.But for three decades now, other paleontologists have argued that these fossils are actually from a related but different type of dinosaurs, which they have dubbed Nanotyrannus.

But right now, scientists haven't studied enough fossils to solve the dilemma. "We don't have a lot of juvenile Tyrannosaurus rex specimens," Randall Irmis, a paleontologist at the Natural History Museum of Utah not involved with the new discovery, told Newsweek. "Having a third could really make a big difference."

The new specimen, which is about 17 feet long all told, fits perfectly into that disputed area. The excavating team currently suspects it belonged to a T. rex that was six, seven, or perhaps eight years old at its death. It fits right between already discovered specimens that scientists have theorized might be from T. rex individuals that died at about three and 11 years old.

The fossil skull is being cleaned at the University of Kansas. David Burnham

But the team working with the new fossil can't be sure whether it represents a young T. rex or a full-grown Nanotyrannus until they've managed to study the specimen fully. That's why they are working to compare the skull with other known specimens.

"Paleontology is not just about finding new species," Imis said, adding that scientists need fossils from a whole range of individuals to understand an animal's biology and how it interacted with other species. "I think the biggest thing is this really shows why it's important to find multiple specimens of species."

The team is also headed back to Hell Creek this summer in hopes of finding still more pieces of this dinosaur—and maybe even other specimens—to study.

This story has been updated to include comments from Randall Irmis.