for National Geographic News
If they survived the deadly toddler years, tyrannosaurs apparently had it pretty cushy, at least until they hit dinosaur puberty.
But after these dinosaurs reached sexual maturity, life's harsher realities kicked in again. Beginning at about age 14, tyrannosaurs suffered death rates of nearly 23 percent a year, according to a new study.
Threatened by disease, combat, and the stress of mating or raising offspring, most adults were lucky to hit their early 20s, the study says.
And just 2 percent "lived long enough to attain their maximal size and age" in their late 20s, the study authors write.
The study is the first to chart dinosaur survival ratesusing a technique that until now had only been applied to living animals.
Gregory M. Erickson, an evolutionary biologist and paleontologist at Florida State University in Tallahassee, led the research, which will be published in tomorrow's issue of the journal Science. Erickson is also a host of the National Geographic Channel TV series Hunter and Hunted, and the National Geographic Society has partially funded some of his research. (National Geographic News is part of the National Geographic Society.)
The researchers analyzed specimens from four North American tyrannosaur species: Albertosaurus sarcophagus, Tyrannosaurus rex, Gorgosaurus libratus, and Daspletosaurus torosus.
First discovered in 1910, a mass grave of 22 Albertosaurus fossils in Alberta, Canada, supplied the team with the most dinosaur obits (Canada map).
Part of a herd or simply close neighbors, the predators likely died over a period of weeks or months about 70 million years ago, perhaps due to a drought or similar catastrophe.
Using a technique pioneered by Erickson and others, the team counted growth ringslike those in treesin fossil leg and foot bones to determine how old each dinosaur had been when it died.
The researchers then plotted an age curve, or survivorship pattern, for the entire population.
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