Magazine article Science News

Growth Spurt: Teenage Tyrannosaurs Packed on the Pounds

Magazine article Science News

Growth Spurt: Teenage Tyrannosaurs Packed on the Pounds

Article excerpt

Detailed analyses of fossils of Tyrannosaurus rex and some of its more ancient kin suggest that the creatures experienced an extended surge in growth during adolescence, putting on as much as half their adult weight in a mere 4 years.

T. rex, one of the most fearsome meat eaters ever to stroll the planet, weighed more than 5,000 kilograms as an adult. Scientists have long debated whether such large dinosaurs achieved their bulk through rapid growth when young, delayed adulthood that enabled a longer growth period, or both. After scrutinizing the remains of four tyrannosaur species, researchers suggest that the beasts went through a substantial teenage growth spurt.

Many dinosaur bones show annual growth rings, as trees do, says Gregory M. Erickson, a paleobiologist at Florida State University in Tallahassee. In large, weight-bearing bones, some of the rings deposited early in life are erased as the bones' marrow cavities expand. However, some other bones don't have such cavities and so preserve all their growth rings.

Erickson and his colleagues counted the growth rings in fossil remains of seven specimens of T. rex, a species that lived in North America between 68 million and 65 million years ago. The smallest animal, which was 2 years old when it died, weighed about 30 kg. The largest--the specimen dubbed Sue, which is now housed at the Field Museum in Chicago--was also the oldest. Sue weighed 5,650 kg when she died at age 28. …

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