65.3 Sunday, Jan. 6 Sexual maturity in subadult dinosaurs does not fit reptilian growth models LEE, A.H.*; WERNING, S.; Ohio University, College of Osteopathic Medicine; Univ. of California, Berkeley email@example.com
Age at reproductive maturity (RM) is largely unknown in extinct taxa because unambiguous indicators of RM are rare. One exception is medullary bone (MB), which is an ephemeral bony tissue formed in the marrow cavities of ovulating birds and was recently described in the saurischian dinosaur Tyrannosaurus rex. Here we report two new occurrences of MB: in the ornithischian dinosaur Tenontosaurus and in another saurischian dinosaur Allosaurus. We show by counting lines of arrested growth and performing growth curve reconstructions that Tenontosaurus, Allosaurus, and Tyrannosaurus were reproductively mature before they reached adult size. On the growth curves, the transition from growth acceleration to deceleration coincides with the skeletochronological ages at RM (8, 13, and 21 years, respectively). These ages are consistent with predictions based on reproductive scaling in organisms ranging in size from viruses to whales. Such consistency suggests that large size in dinosaurs precludes relatively slow reptilian growth and RM. Furthermore, when histological confirmation is not possible, the general scaling relationship between reproductive maturity and mass is an accurate means to predict the age at RM in non-avian dinosaurs.