'Parrot Dinosaur' was a Quadruped at Birth and Grew to Walk on Two Legs, Study Finds

An intricate examination of fossilized bones from the "Parrot dinosaur" Psittacosaurus presents evidence that the ancient reptiles walked around on all fours in their youth and later grew into bipedal creatures.

Qi Zhao began his research at the University of Bristol and later carried out the study of Psittacosaurus bones from baby, juvenile and adult specimens at the Institute of Vertebrate Paleontology in Beijing. A total of 16 specimens were included in the analysis, ranging in age from less than 1 year old, to a fully-grown 10-year-old specimen. The youngest specimens of the 100 million-year-old creatures required special attention when being studied.

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

Zhao's analysis demonstrated that one-year-old Psittacosaurus specimens had long arms and short legs and therefore moved about in a quadruped fashion in their early years. When the dinosaurs were between 1 and 3 years old, their arm bones grew quickly. But arm growth was surpassed by a prominent spurt in leg growth when the dinosaurs were between 4 and 6 years old, resulting in the Psittacosaurus having legs twice as long as its arms, which would necessitate the creature to move about in a bipedal fashion.

"These kinds of studies can also throw light on the evolution of a dinosaur like Psittacosaurus. 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," said Mike Benton, Zhao's advisor from the University of Bristol.

Psittacosaurus is not as well-known as its distant relative Triceratops, but the scientific community places great value on Psittacosaurus because of the abundance of good fossil specimens of the creature. Fossils from more than 1,000 specimens have been collected so far, according to a report by University of Bristol.

Xing Xu, of the Institute of Vertebrate Paleontology, said the study was "remarkable" and a "first of its kind" which "shows how much information is locked in the bones of dinosaurs."

"We are delighted the study worked so well, and see many ways to use the new methods to understand even more about the astonishing lives of the dinosaurs," Xu said.