By Bary Alyssa Johnson ( | First Posted: Jun 30, 2013 04:02 PM EDT

New research coming from the University of Bristol suggests that, similar to a toddler who moves around on all fours before developing to walking on two feet, the Psittacosaurus, or "parrot" dinosaur similarly started off walking on four feet and then graduated to two.

The University of Bristol reports that researchers involved in the study, along with colleagues from the University of Bonn and Beijing Institute used a combination of bio-mechanical analysis and bone histology to demonstrate how the parrot dinosaur switched from four to two legs as it aged. The research was led by Qi Zhao as part of his PhD thesis and the results were published in the journal Nature Communications. 

"These kinds of studies can throw light on the evolution of a dinosaur like Psittacosaurus," said Professor Mike Benton of the University of Bristol, Zhao's PhD supervisor. "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 parrot dinosaur lived during the Cretaceous period, 100 million years ago, in China and other parts of Asia. Over 1,000 fossil specimens have been found and preserved for this species and for this study, Zhao carried out his work using bones of babies, juveniles and adults.

At a palaeohistology laboratory in Bonn, Germany Zhao intricately sectioned two arm and two leg bones from 16 different dinosaurs that ranged in age from one year to 10 years old, or fully grown.

The study showed that the one-year-olds had long arms and short legs and moved around on all fours after hatching. Research on the bone sections illustrated that the arm bones grew fastest when the dinosaur was between one-to-three years old.

From four-to-six years of age, arm growth slowed and the leg bones underwent a significant growth spurt, ending up twice as long as the arms. These growth patterns were necessary for an animal that stood up and walked like a human on two legs, as an adult.

"This remarkable study, the first of its kind, shows how much information is locked in the bones of dinosaurs," said Professor Xing Xu of Beijing Institute, another one of Zhao's PhD supervisors. "We are delighted the study worked so well, and see many ways to use the new method to understand even more about the astonishing lives of dinosaurs."

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