How evolutionary changes in body size are brought about by variance in developmental timing and/or growth rates (also known as heterochrony) is a topic of considerable interest in evolutionary biology. In particular, extreme size change leading to gigantism occurred within the dinosaurs on multiple occasions. Whether this change was brought about by accelerated growth, delayed maturity or a combination of both processes is unknown. A better understanding of relationships between non-avian dinosaur groups and the newfound capacity to reconstruct their growth curves make it possible to address these questions quantitatively. Here we study growth patterns within the Tyrannosauridae, the best known group of large carnivorous dinosaurs, and determine the developmental means by which Tyrannosaurus rex, weighing 5,000 kg and more, grew to be one of the most enormous terrestrial carnivorous animals ever. T. rex had a maximal growth rate of 2.1 kg d -1 , reached skeletal maturity in two decades and lived for up to 28 years. T. rex's great stature was primarily attained by accelerating growth rates beyond that of its closest relatives.
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Acknowledgements We thank O. Rieppel and B. Simpson (The Field Museum), L. Chiappe (Los Angeles County Museum of Natural History), P. Larson and N. Larson (Black Hills Institute), B. Stein and M. Triebold (Triebold Paleontology), D. Evans (Indianapolis Children’s Museum), C. Mehling (American Museum of Natural History), S. Williams, M. Henderson and L. Cranford (Burpee Museum of Natural History), J. Gardner, D. Tanke and D. Brinkman (Royal Tyrrell Museum of Palaeontology), T. Carr (University of Toronto), F. W. King and K. Krysco (Florida Museum of Natural History), K. Womble (Florida State University), M. Bayless (Berkeley, California) and A. Woodward (Florida Fish and Wildlife Conservation Commission) for assistance with this research. The NSF and the College of Arts and Sciences of Florida State University generously funded this project.
Acknowledgements We thank A. Thorpe and M. Allen for encouraging the development of this project. We also acknowledge many Hadley Centre colleagues for their advice on model parameters and their uncertainty ranges, and for comments on earlier versions of the manuscript. This work was supported by the UK Department of the Environment, Food and Rural Affairs. D.A.S. was funded by the NERC COAPEC thematic programme.