Using biomechanical analysis and bone history, a group of paleontologists from the Bristol University, uncovered the mystery behind how the parrot dinosaur (Psittacosaurus), switched from walking on fours to twos.
The researchers carefully studied the bones of the baby, adult and juvenile parrot dinosaurs, as an attempt to track their growth, which is in general, difficult to achieve.
"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. I also had to be sure to cause as little damage to these valuable specimens as possible," Dr Qi Zhao, a staff member at the Institute for Vertebrate Paleontology, Beijing, explained.
After obtaining permission to use and section the bones of two arms and legs from 16 different parrot dinosaurs, all between the ages of 1 to 10 years, Zhao carried out delicate sectioning in a palaeohistology laboratory in Germany.
Careful observation of the sections revealed that the arm bones grew fastest between one to three years of age. The one-year olds had long arms and short legs, and walked around on all fours after hatching and the four to six year olds showed a slower arm bone growth and a speedy leg bone growth, the study revealed.
This leg bone growth spurt caused them to grow twice as long as the arm bones; a structure necessary for an animal to stand up on its hind legs.
"This remarkable study, the first of its kind, 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," thesis supervisor professor Xing Xu, added.
Similar studies may help scientists shed light on the evolution of the parrot dinosaur, professor Mike Benton claims. "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," he added.
The findings from this study are published in Nature Communications.