Albertosaurus turned mean at maturity

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This article was published 14/07/2006 (7186 days ago), so information in it may no longer be current.

EDMONTON — Life for Albertosaurus turned nasty, brutish and too-often short once Alberta’s namesake dinosaur reached sexual maturity, new research shows.

The big flesh-eater’s juvenile years had been a boy’s dream — wandering the shores of an inland sea with your buddies, eating smaller prey with no fears of becoming dinner yourself.

Then one day, around 13, male hormones kick in and during the quest for female favours, boyhood buddies start going for your throat.

In a paper to be published this month in the academic journal Science, paleontologist Philip Currie of the University of Alberta writes how, throughout much of its youth, the big dinosaur led a relatively safe life. Natural causes of death like disease, drought and famine killed relatively few of the ferocious beats. But when Albertosaurus began to reproduce, competition for mates killed off many of the males.

“The mortality rates remained low until about the 13th year of life, at which point they reached total lengths of six metres or 60 per cent of their maximum recorded size,” Currie says. “At that point mortality rates escalated to more than 23 per cent a year.”

The four-tonne males tore into each other with their dagger-like fangs. Paleontologists know this because the wounds can still be seen on the mature, 10-metre-long skeletons which have been dug out of alluvial deposits in the valley of Alberta’s Red Deer River.

Currie co-authored his paper with three colleagues from Florida State University — Gregory Erickson, Brian Inouye and Alice Winn. Many bone samples used in the research were extracted from other Alberta sites near Dry Island Buffalo Jump and the Drumheller Valley.

One millimetre-wide cores were drilled from foot and leg bones of the dinosaurs at Florida State University. Annual growth rings seen in those cores were analyzed and used in a statistical study to determine mortality patterns.

“It’s surprising that something like this study has never been done before,” Currie says.

Currie and his colleagues did not find what they expected to.

Studies of the fossils of other Cretaceous-era reptiles indicated those animals experienced virtually the same mortality rate throughout their lives. Those large reptiles included crocodilians — ancestors of today’s crocodiles. Talk to any resident of the Australian outback today and they will explain how most crocodiles die. They eat each other.

Albertosaurus wasn’t a cannibal, Currie says. Until they became sexual rivals they chummed around, a fact demonstrated by the skeletons of 22 of animals discovered at one site near Dry Island Buffalo Jump.

“It is the best evidence that exists to suggest that tyrannosaurids (large flesh-eating dinosaurs) may have been gregarious or pack animals,” Currie says. Until sexual maturity, that is.

— CanWest News Service