When we think of the Tyrannosaurus rex, the first thing we usually think of is a massive, fearsome predator. But everyone has to start somewhere, and just as LeBron James was once a tiny, non-basketball-playing baby, even the largest land predator was once a youngster. Paleontologists digging in Hell Creek, Montana, confirmed this timeless truth on Thursday, when they announced that they’d excavated the fossilized remains of a dinosaur that’s likely a young T. rex.

The University of Kansas researchers say they’ve found an upper jaw section with all teeth intact, as well as parts of the dinosaur’s skull, foot, hips, and backbones.

“This is probably the most preserved and most complete” juvenile T. rex specimen ever found at Hell Creek, Kyle Atkins-Weltman, a fossil preparator who’s working on the small tyrannosaur, told Live Science. “This is a 1-in-100-million specimen,” says the assistant fossil preparator at the University of Kansas. Atkins-Weltman tells Live Science that the researchers suspect the animal was between 6 and 8 years old when it died.

t. rex jaw
The fossilized jaw, glowing under blacklight, as fossils often do.

Famous for its huge number of dinosaur fossils, the Hell Creek Formation spans four states — Montana, North Dakota, South Dakota, and Wyoming — and contains fossil remains from animals that lived near the end of the Cretaceous Period, which ended 66 million years ago. The T. rex lived for the last 2 million years of the Cretaceous, dying out along with 75 percent of life on Earth. Analysis revealed that this particular T. rex lived about 66.5 million years ago.

tyrannosaurus rex skull
The Tyrannosaurus rex skull being prepared in the lab.

Whether it’s actually a T. rex or not is subject to some debate, though, as some paleontologists sometimes think small tyrannosaur fossils belong to a different species altogether: Nanotyrannus. The controversy is understandable since the anatomy of a juvenile tyrannosaur could potentially have been much different from that of an adult, not just in size but also in proportions, like a “gangling, awkward youngster,” as the BBC suggested in 2016, when the outlet reported on this debate. Long story short, the available evidence suggests that Nanotyrannus isn’t its own species, but since researchers can only work with ancient fossil evidence, they’re keeping open minds until the evidence becomes more definitive. The Hell Creek fossil could be that evidence, though.

“The teeth suggest it’s a Tyrannosaurus rex; however, there is still more work to be done,” David Burnham, preparator of vertebrate paleontology at the KU Biodiversity Institute, said in a statement.

“With the specimens here at KU, we’ll be able to address the issue and make a declarative statement about Nanotyrannus,” Burnham tells Phys.org.

The team expects to publish its findings later this year.