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BIOLOGICAL SCIENCES / EVOLUTION
Sexual maturity in growing dinosaurs does not fit reptilian growth models
Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, CA 94720-3140
Edited by James H. Brown, University of New Mexico, Albuquerque, NM, and approved November 21, 2007 (received for review September 19, 2007)
Recent histological studies suggest relatively rapid growth in dinosaurs. However, the timing of reproductive maturity (RM) in dinosaurs is poorly known because unambiguous indicators of RM are rare. One exception is medullary bone (MB), which is an ephemeral bony tissue that forms before ovulation in the marrow cavities of birds as a calcium source for eggshelling. Recently, MB also was described in a single specimen of the saurischian dinosaur Tyrannosaurus rex. Here, we report two other occurrences of MB: in another saurischian dinosaur, Allosaurus, and in the ornithischian dinosaur Tenontosaurus. We show by counting lines of arrested growth and performing growth curve reconstructions that Tenontosaurus, Allosaurus, and Tyrannosaurus were reproductively mature by 8, 10, and 18 years, respectively. RM in these dinosaurs coincided with a transition from growth acceleration to deceleration. It also far precedes predictions based on the growth rates of living reptiles scaled to similar size. Despite relatively rapid growth, dinosaurs were similar to reptiles in that RM developed before reaching asymptotic size. However, this reproductive strategy also occurs in medium- to large-sized mammals and correlates with a strategy of prolonged multiyear growth. RM in actively growing individuals suggests that these dinosaurs were born relatively precocial and experienced high adult mortality. The origin of the modern avian reproductive strategy in ornithuran birds likely coincided with their extreme elevations in growth rate and truncations to growth duration.
life history | bone histology | medullary bone | bird | reproductive strategy
*Present address: College of Osteopathic Medicine, Ohio University, Athens, OH 45701.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0708903105/DC1.
To whom correspondence may be addressed. E-mail: lee{at}oucom.ohiou.edu or swerning{at}berkeley.edu
© 2008 by The National Academy of Sciences of the USA
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