Young dinosaurs lived in packs with nurturing parents like modern mammals, paleontologists who studied a group of fossils in Alberta's Badlands say.

Millions of fossils are scattered throughout the area, but one quarry is home to at least 22 individual Albertosaurus dinosaurs, a close cousin of Tyrannosaurus rex.

Phil Currie in the quarry which is home to at least 22 individual Albertosaurus dinosaurs.
(CBC)

The unique site gave scientists access to Albertosaurus specimens with a range of ages, allowing the team to map out the life span of the animals.  

Paleontologist Phillip Currie of the University of Alberta and his colleagues concluded predation led to high death rates among newborns until they reached a threshold size about age two. The dinosaurs then survived relatively well until about age 13, the team reports in Friday's issue of the journal Science. 

That would help explain the mysterious rarity of young adult bones. The fossils aren't found simply because the mortality rates for that age group were extremely low, the growth curves suggest.

Phil Currie of the University of Alberta.
(CBC)

At about age 14, when the dinosaurs reached sexual maturity, the death rate rose significantly, possibly because they were competing with each other for mates and food. 

"Up to that point in time, they seem to have been protected by the adults, to a large extent," Currie said.

Survivorship pattern

The study said the average mortality rate from ages two to 13 was about 3.7 per cent, jumping to 22.9 per cent between ages 14 and 23.

The survivorship pattern paints a picture of parents who shield their offspring until their young are old enough to breed. The behaviour is seen in large modern mammals, such as male elephants that usually stay with their birth herd until puberty.

The results reinforce the notion that dinosaurs were much more closely related to modern birds and mammals than they were to reptiles.

"It helps us understand why dinosaurs dominated over mammals for over 150 million years," Currie said.

"If dinosaurs hadn't died out, I'm not sure that mammals would have got an edge to outcompete them."

Information gleaned from the study will be applied to other dinosaurs in the hopes of learning more about the day-to-day life of dinosaurs and perhaps what led to their extinction.