Analysis of a fossil showing a triceratops and a tyrannosaur locked in combat has reignited debate over whether some smaller tyrannosaur specimens are actually a distinct species rather than juvenile Tyrannosaurus rex. The fossil, known as the 'duelling dinosaurs', was discovered in Montana in 2006 and only recently became available for scientific study after being acquired by the North Carolina Museum of Natural Sciences.
Researchers now argue that the tyrannosaur in the fossil is not a young T. rex but a fully grown adult of a different species, Nanotyrannus lancensis. Dr Lindsay Zanno, co-author of the study published in Nature, said the specimen weighed only 1,500 pounds after two decades of growth, and its anatomy—including higher tooth count, enlarged hands, shorter tail, and unique cranial features—is incompatible with it being a teenage T. rex.
The name Nanotyrannus lancensis was first used in 1946 for a small skull found in Montana, but experts later dismissed it as a juvenile T. rex. The new study, however, suggests that both that skull and another juvenile skeleton named Jane are actually Nanotyrannus, a species that lived alongside T. rex in the same ecosystems.
Dr Zanno noted that previous studies using Nanotyrannus specimens as models for teenage T. rex—examining locomotion, growth, diet, and life history—may need to be revisited. Professor Steve Brusatte of the University of Edinburgh, who was not involved in the study, said the new evidence shows he was 'wrong—at least in part' about considering such specimens as T. rex juveniles, but cautioned that not every small tyrannosaur skeleton should be classified as Nanotyrannus, as some must be juvenile T. rex.
