Study: T. rex took 40 years to reach full size
7 reported1 unconfirmed
A new study published in the journal PeerJ on June 22, 2026, suggests that Tyrannosaurus rex took about 40 years to reach its full size of roughly eight tons, extending previous estimates by 15 years. Researchers analyzed 17 tyrannosaur fossils using advanced imaging techniques and statistical models to reconstruct growth patterns. The study found that T. rex remained in a growth phase about 15 years longer than previously thought. The findings also indicate that some fossils traditionally assigned to T. rex may belong to other closely related species. Two famous specimens nicknamed "Jane" and "Petey" showed growth patterns that differed significantly from other fossils in the study. The researchers note that a separate recent study by Zanno and Napoli classified Jane and Petey as two distinct species of Nanotyrannus. The study was led by Holly Woodward of Oklahoma State University, with statistical analysis by Nathan Myhrvold of Intellectual Ventures and coauthor Jack Horner of Chapman University.
What’s reported
The study was published in PeerJ on June 22, 2026.
Researchers examined 17 tyrannosaur fossils spanning a wide range of ages.
T. rex likely took about 40 years to reach full size of roughly eight tons, extending previous estimates by 15 years.
The study used circularly polarized and cross-polarized light to reveal hidden growth rings in fossil bones.
Some fossils traditionally assigned to T. rex may belong to other closely related species.
Two specimens nicknamed "Jane" and "Petey" showed unusual growth patterns.
A separate recent study by Zanno and Napoli classified Jane and Petey as two distinct species of Nanotyrannus.
Open questions
Whether the fossils nicknamed "Jane" and "Petey" belong to different species or are simply unusual T. rex individuals remains unresolved.
Key figures
Holly Woodward, professor of anatomy at Oklahoma State University, led the research.
Nathan Myhrvold, mathematician and paleobiologist at Intellectual Ventures, led the statistical analysis.
Jack Horner, coauthor from Chapman University.
Zanno and Napoli, researchers of a separate recent study on Nanotyrannus.
Sources: ScienceDaily
