The Living Was Easy for Young Tyrannosaurs

New Scientist Online ^ | 7/13/2006 | Jeff Hecht

[Al Simmons]

Youth was easy for big predatory dinosaurs – but adulthood and old age much harder to survive, a mass graveyard of tyrannosaur fossils suggests.

This first study of dinosaur population distributions shows that most juvenile tyrannosaurs survived to reach sexual maturity, but then their death rate increased sharply in adulthood. This life-pattern is similar to those of long-lived birds and mammals.

*SNIP

Biologists study population distributions of modern animals by counting individuals and keeping track of deaths. This is not possible for extinct creatures, and fossilised remains are also scant for many dinosaurs. But Erickson turned to the tyrannosaur family that roamed North America from about 80 to 65 million years ago, late in the Cretaceous period, which left abundant fossils.

His team studied a bone bed in Alberta, Canada, containing the bones of at least 22 Albertosaurus individuals which died during an unusually harsh period. They range in length from 2.2 metres to 10.1 m. By counting annual growth rings in the bones and measuring sizes of the femurs, Erickson's group estimated the ages at which the 22 animals died.

*SNIP*

The youngest animal was about two years old and 2.2 m long. About two-thirds of the animals had made it to age 13 or beyond, indicating that only 2% to 7% of juveniles died each year before reaching sexual maturity, at about 14.

But after that the death rate jumped to an average of 23% each year between the ages 14 and 23, and the oldest Albertosaurus died aged 28.

*SNIP*

[bornacatholic]

Luckily, the juveniles didn't have access to cars. Imagine the death rate for juv-tyrs if they had access to the ancient equivalents of GTO's.