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T. Rex Reached Full Size Around 40, New Bone Study Finds

Cross-polarized microscopy with a composite growth curve from 17 leg bones revealed hidden rings that lengthened the species’ growth timeline.

Overview

  • Tyrannosaurus growth modeling based on femora and tibiae from 17 individuals produced the most detailed life-history curve for the species to date.
  • The best-supported model counted double and faint growth marks visible only under cross-polarized light, yielding lower peak growth rates and later size plateau estimates.
  • Two well-known immature specimens, nicknamed Jane and Petey, were statistically incompatible with the main growth series, leaving open taxonomic explanations that remain unresolved.
  • The authors report no strong evidence from living vertebrates that a growth curve’s inflection point marks sexual maturity, challenging a common assumption in dinosaur studies.
  • The study recommends revising standard protocols for counting growth marks, with implications for reevaluating growth dynamics across other dinosaur taxa.