A new study based on an analysis of 17 Tyrannosaurus rex specimens suggests the prehistoric carnivore took up to 40 years to reach its full size, significantly longer than previous estimates of approximately 25 years. This research re-evaluates the T. rex growth rate and lifespan, proposing that the species spent a considerable portion of its life in a mid-body size range.
Methodology
The study employed advanced statistical algorithms and examined slices of fossilized T. rex leg bones. Researchers utilized polarized light, specifically circularly polarized and cross-polarized light, to identify previously undetected growth rings. This method allowed for a more complete and accurate reconstruction of tyrannosaur growth, as typical dinosaur growth rings often record only the last 10 to 20 years of an individual's life. By synthesizing growth records from specimens spanning various ages, the team constructed a comprehensive year-by-year growth timeline. This research represents the largest dataset ever assembled for Tyrannosaurus rex growth analysis.
Key Findings and Implications
- Extended Growth Phase: The study indicates that Tyrannosaurus rex achieved its peak size of approximately 8 tons between 35 and 40 years of age, extending the growth phase by 15 years or more compared to earlier estimations. Previous research suggested T. rex generally ceased growing around 25 years old and lived up to 30 years.
- Ecological Role: The slower, prolonged growth rate may have enabled younger tyrannosaurs to occupy diverse ecological roles and food niches throughout their lives. This flexible growth strategy is hypothesized to have contributed to their success as apex carnivores during the late Cretaceous Period.
- Species Classification Debate: Variations observed in the growth curves among different T. rex specimens contribute to an ongoing scientific discussion regarding whether Tyrannosaurus rex represents a single species or a complex encompassing multiple species or subspecies. The study notes that some specimens, such as "Jane" and "Petey," exhibit incompatible growth curves, suggesting they might belong to distinct species or subspecies. This observation aligns with previous research, including an earlier study that suggested a fossil identified as a juvenile T. rex was a separate species, Nanotyrannus. While the current findings do not definitively establish the existence of separate species, researchers consider it an intriguing possibility.
- Broader Paleontological Impact: The discovery of new types of dinosaur growth rings, visible under specific polarized light, may necessitate revisions to standard growth study protocols for other dinosaur species. Interpreting closely spaced growth marks is complex, and the study's insights could influence how paleontologists analyze growth rates across different dinosaur taxa.
Research Team
The research was led by Holly Woodward, a professor of anatomy at Oklahoma State University. Statistical analysis was provided by Nathan Myhrvold, a mathematician and paleobiologist, with contributions from Jack Horner. The study was published in the journal PeerJ. Steve Brusatte, a professor of paleontology and evolution at the University of Edinburgh who was not involved in the study, commented that the findings are significant and suggest greater variation among T. rex specimens than previously recognized.