CHICAGO--For the first time, scientists have determined the lifelong growth pattern for the Tyrannosaurus rex. T. rex reached its massive adult size due to an extraordinary growth spurt that stretched from about 14 to 18 years of age. Furthermore, the surge was followed by about 10 years of little or no growth as an adult, according to a study that will be the cover story of Nature Thursday, Aug. 12, 2004.

During the peak in its growth spurt, T. rex gained 2.1 kilograms (4.6 pounds) per day, developing into a more than 5,000-kilogram (11,000-pound) giant, one of the largest terrestrial carnivorous animals ever.

"Knowing the lifeline is important because we now understand the evolution of T. rex's giantism, one of the most fascinating aspects of dinosaurs," said Peter Makovicky, PhD, Dinosaur Curator at The Field Museum and a coauthor of the study. "With the life history parameters, we can better understand T. rex evolution, biology, biomechanics and population dynamics."

Makovicky and his colleagues determined T. rex's growth pattern and lifespan using an innovative technique that could be applied to many other dinosaurs. They determined the age by counting growth lines in T. rex bones and calculated the corresponding body size from circumference measurements of the femur. Correlating these two sets of data results in a growth curve.

It has long been known that large weight-bearing dinosaur bones display growth lines, but they are hard to read. This is due to the way these large bones form: their marrow cavity expands and changes shape as they grow, erasing some of the internal lines.

This study, however, focuses on smaller, nonweight-bearing dinosaur bones, including ribs, gastralia, and fibulas. These bones do not develop hollow cavities or remodel as they grow, so growth lines
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