Parrot Dinosaur Switched from Four Legs to Two Legs After Childhood

Unlocking the mysterious of the past can be difficult, but that hasn't stopped one intrepid scientist from the University of Bristol. Using biomechanical analysis and bone histology, Qi Zhao, now part of the Institute for Vertebrate Paleontology in Beijing, has figured out how a dinosaur graduated from walking on four legs to two. 

It turns out that Psittacosaurus, better known as the "parrot dinosaur," spends it youth scuttling around on all fours before a growth spurt indicates it switches to walking on its hind legs as an adult. 

"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," said one of Zhao's advisors on the PhD study detailing the findings, professor Xing Xu from the Beijing Institute.

Psittacosaurus roamed around parts of China and east Asia some 100 million years ago, and over 1000 fossilized specimens of the dinosaur exist. Zhao studied two arm and two leg bones taken from 16 of the dinosaurs. 

"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," said Zhao. 

What was revealed is that during its childhood, Psittacosaurus arms and legs were relatively the same length, allowing for quadrupedal locomotion. At a certain point, between 4-6 years into the dinosaur's life, however, the legs experience a massive growth spurt while the arms slow down, indicating that from then on the dinosaur begins using its hind legs for bipedal movement. 

"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," explained another of Zhao's advisors, professor Mike Benton from the University of Bristol.

You can read the full published study detailing the findings in the journal Nature Communications.