Duelling Dinosaurs fossil identified as Nanotyrannus lancensis

A nearly complete tyrannosaur skeleton unearthed in Montana and long known as part of the Duelling Dinosaurs has been identified as an adult of a smaller, distinct species rather than a juvenile Tyrannosaurus rex, researchers reported Thursday. The specimen, found in 2006 in the Hell Creek Formation and acquired by the North Carolina Museum of Natural Sciences in 2020, was analyzed by a team that concluded the animal was a mature Nanotyrannus lancensis roughly 20 years old when it died, about 5.5 meters long and far lighter than an adult T. rex.

The conclusion rests on multiple lines of evidence reported in a paper published in Nature. Scientists examined growth rings in limb bones, patterns of bone fusion in the spine, and anatomical features of the skull. They found that the specimen’s cranial nerves and sinus patterns, higher tooth count, enlarged forelimbs, shorter tail and other skeletal details are inconsistent with normal ontogenetic changes observed in large theropods and modern reptiles such as crocodiles. These traits, the authors say, would not be expected to appear or disappear simply through growth from juvenile to adult T. rex.

“This fossil doesn’t just settle the...