Growth rings in the Dueling tyrannosaur's leg bones indicate it was about 20 years old and fully grown when it died, rather than being a juvenile Tyrannosaurus rex.
Sources
- Mini-tyrannosaur lived alongside T. rex, extraordinary fossil confirms (science.org)
- https://www.nationalgeographic.com/science/article/nanotyrannus-t-rex-dueling-dinosaur-fossil-debate (nationalgeographic.com)
- https://news.ncsu.edu/2025/10/nanotyrannus-confirmed-dueling-dinosaurs-fossil-rewrites-the-story-of-t-rex/ (news.ncsu.edu)
- https://www.sciencenews.org/article/nanotyrannus-not-teenaged-t-rex (sciencenews.org)
- https://earthsky.org/earth/nanotyrannus-a-t-rex-mini-me-coexisted-with-big-guys/ (earthsky.org)
- https://www.abc.net.au/news/science/2025-10-31/new-research-t-rex-nanotyrannus-debate-duelling-dinosaur/105946658 (abc.net.au)