|Paleontologists have uncovered the ages of a population of non-avian dinosaurs. (Credit: Zina Deretsky, National Science Foundation)
(Click image to enlarge)
For the first time, scientists have established the age structure of a
non-avian dinosaur population. Using this information, they inferred
which factors led to survival or death of group members.
Did these animals show survival patterns akin to extant living
dinosaurs, the birds, as did their crocodilian cousins? Or, did they
mirror that of more distantly related dinosaurs that lived in a similar
environment? A pile of bones from the North American tyrannosaur
Albertosaurus sarcophagus may hold the answer.
These animals "showed exceptional survivorship once they passed the
hatchling stage," said Gregory Erickson of Florida State University,
co-author of a paper reporting the results in this week’s issue of the
"Factors such as predation and [timing of] entrance into the
breeding population may have influenced survivorship," the researchers
say. Such patterns are common today in wild populations of long-lived
birds and mammals.
Why increased survivorship as juveniles? "In living populations it
occurs because animals reach threshold sizes, and predation pressures
decrease," said Erickson. "By age two, most tyrannosaurs were as large
or larger than nearly all other predators in their realm."
"Because most species of non-avian dinosaurs are known from just one or
a few specimens, very little is understood about the population biology
of these animals," said Richard Lane, program director in the National
Science Foundation (NSF)’s Division of Earth Sciences, which funded the
research."We now have a breakthrough in unraveling these dinosaurs’
The burial site was first found and partially excavated in 1910 by
famed dinosaur hunter Barnum Brown of the American Museum of Natural
History, who discovered it along the Red Deer River in Alberta, Canada.
The site was recently reopened by scientists from the Royal Tyrrell
Museum of Palaeontology in Alberta, Canada, on an expedition led by
co-author Philip Currie of the University of Alberta, Edmonton.
Erickson, Currie, Brian Inouye of the University of Alberta, and
Alice Winn of Florida State University, established how many dinosaurs
had died at the site. They concluded that at least 22 individuals
ranging from 2 to 28 years old were buried there, and found
considerably more adult specimens than juveniles.
They then studied and aged other North American tyrannosaurs. "These
specimens had been found individually throughout various formations in
the United States and Canada," said Erickson. "We found the same
situation–very few young animals–again."
Source: National Science Foundation. July 2006.