Paleontologists Uncover How 'Parrot' Dinosaur Switched from Four Feet to Two

First Posted: Jun 28, 2013 10:27 AM EDT

Understanding the growth of dinosaurs is difficult. It largely depends on the fossil record and what has been preserved for paleontologists. Now, though, scientists have discovered exactly how one of the best-known dinosaurs switched from four feet to two feet as it grew, revealing a bit more about dinosaur adaptation.

The dinosaur is Psittacosaurus, also known as the "parrot dinosaur." This species is known from more than 1,000 specimens from the Cretaceous period. Living about 100 million years ago, this dinosaur roamed China and other parts of east Asia. It had self-sharpening teeth that would have been useful for cropping and slicing through plant material; yet they didn't have grinding teeth. Most likely, this species swallowed stones to wear down food as it passed through the digestive system--rather like the birds of today.

In order to better understand this dinosaur, the researchers examined the bones of babies, juvenile and adults. They also sectioned two arm and two leg bones from 16 individual dinosaurs that ranged from less than one year to 10 years old. This allowed them to receive a better understanding of the growth of these dinosaurs.

"Some of the bones from the baby Psittacosaurus were only a few millimeters across, so I had to handle them extremely carefully to make useful bone sections," said Qi Zhao, the head researcher, in a news release. "I also had to be sure to cause as little damage to these valuable specimens as possible."

So what did they find? It turns out that the one-year-olds had long arms and short legs. This hinted at the fact that the dinosaurs scuttled on the ground on all fours soon after hatching. From the ages of four to six, though, the growth of these arm bones slowed down. The leg bones then received a massive growth spurt which eventually allowed the dinosaur to adapt its adult posture on its hind legs.

"These kinds of studies can also throw light on the evolution of a dinosaur like Psittacosaurus," SAID Mike Benton of the University of Bristol, Zhao's thesis supervisor, in a news release. "Having four-legged babies and juveniles suggests that at some time in their ancestry, both juveniles and adults were also four-legged, and Psittacosaurus and dinosaurs in general became secondarily bipedal."

The findings are published in the journal Nature Communications.

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