Study: Growth rates among dinosaurs were highly variable

BLACKSBURG, Va., Dec. 5 (UPI) -- New research suggests growth rates among dinosaurs were highly variable, just as they are among humans.

Humans populations have evolved to yield a variety sizes -- short, tall and everything in between. But not only do humans fill a wide range of heights, they also arrive at their apex at varying rates.

Early dinosaurs were much the same way, according to new analysis by geoscientists at Virginia Tech.

Scientists examined 174 fossils representing hundreds of Coelophysis specimens, a small carnivorous dinosaur, that died en mass when a river suddenly flooded 208 million years ago in what's now New Mexico. Discovery of the ancient die-off allowed scientists to study varying rates of growth among a group of early dinosaurs.

"Fossils of even a single partial skeleton of an early dinosaur are exceptionally rare, so to have an entire group of a single species that lived and died together provided an unparalleled opportunity to study early dinosaur growth like never before," Christopher Griffin, a doctoral student in the department of geosciences, said in a news release.

Their analysis revealed a variety of body sizes and growth rates: fast-growing small dinosaurs and slow-growing large dinosaurs.

"Not only were there many different pathways to grow from hatchling to adult, but there was an incredible amount of variation in body size, with some small individuals far more mature than some larger individuals, and some large individuals more immature than we would guess based on size alone," Griffin explained.

Markings on the fossilized bones helped scientists determine the maturity of each dinosaur specimen.

"As these animals grew, muscle attachment scars formed on the limb bones, and the bones of the ankle, hips, and shoulder fused together, similar to how the skull bones of a human baby fuse together during growth," Griffin said.

Griffin and his colleagues compared the growth rates of Coelophysis to those of modern birds and reptiles, two of dinosaurs most closely related living relatives, and found early dinosaurs featured grater variability.

"Large variation in early dinosaurs may have allowed them to survive harsh environmental challenges like dry climate and high levels of carbon dioxide," said Sterling Nesbitt, an assistant professor of geosciences at Tech. "Understanding why dinosaurs were so successful has been a great mystery and high variation may be one of the characteristics of dinosaurs that led to their success."

Unfortunately, scientists can't say for certain whether the growth variability of Coelophysis was an evolutionary response to the environment or simply an example of genetic luck.

Researchers published their findings in the Proceedings of the National Academy of Sciences.

[Correction: A previous version in this story incorrectly identified the journal as PLOS One. The study was published in the Proceedings of the National Academy of Sciences.]