A Tyrannosaurus rex fossil has been discovered in Montana by paleontologists with the Burke Museum of Natural History and Culture and the University of Washington. The remains contain an estimated 20 percent of the carnivorous dinosaur — which lived 145-66 million years ago at the end of the Cretaceous Period — including an intact skull, vertebrae, ribs, hips and lower jaw bones.

The fossils were discovered in Hell Creek Formation in northern Montana when two museum volunteers, Jason Love and Luke Tufts, saw bone fragments on sandstone. Upon further examination, Love and Tufts found a large fossilized vertebrae protruding from a rock. The size of the bone and the “honeycomb-like structure” suggested it belonged to a T. rex .

The remains, which have been nicknamed “Tufts-Love Rex,” weigh 2,500 pounds and measure 4 feet in length. The right side of the skull is complete and the team believes the left side is intact as well.

“There’s a very good chance that the other half of the skull is there,” said Gregory P. Wilson, who co-led the excavation team and is a biology professor at the University of Washington, in a statement. “But the more we expose [of the skull out in the field], the greater the risk of damage.”

The size of the skull leads paleontologists to believe this specimen is roughly 85 percent of the size of the largest T. rex ever found. The Tufts-Love Rex is 66.3 million years old, according to Burke paleontologists, and based on the location of the remains, it lived at the end of the Cretaceous Period—the dinosaur became extinct 66 million years ago during the Cretaceous-Paleogene mass extinction. Skull size also indicates that the dinosaur was roughly 15 years old when it died; adult T. rex lived up to 25 to 30 years, for reference.

"We think the Tufts-Love Rex is going to be an iconic specimen for the Burke Museum and the state of Washington and will be a must-see for dinosaur researchers as well," said Wilson.

The new fossils are rare because of their level of completeness—the skull is the fifteenth mostly complete T. rex skull to be found in the world. According to experts, the remains will shed insight into the creature’s eating habits and growth.

"Having seen the 'Tufts-Love Rex' during its excavation I can attest to the fact that it is definitely one of the most significant specimens yet found, and because of its size, is sure to yield important information about the growth and possible eating habits of these magnificent animals," said Jack Horner, former curator of paleontology at the Museum of the Rockies and current Burke Museum research associate, in a statement.

In an interview with The Seattle Times, Wilson added: “There’s a great deal we still don’t know about these animals. Having this gives us an opportunity to fill in some gaps about how they lived and how they died.”