The parrot dinosaur — Psittacosaurus — switched from four-legged locomotion to bipedalism as it matured from a juvenile to an adult, according to new research from the University of Bristol. By utilizing a combination of biomechanical analysis and bone histology, the researchers — with help from colleagues at the University of Bonn and Beijing University — were able to demonstrate how the well-known species of dinosaur made the switch from four feet to two as it grew.
Psittacosaurus is a very well-known species as a result of the more than 1000 specimens of the dinosaur that been recovered so far — making the species one of the few where complex studies of the animal’s growth processes can be done. The species — popularly known as the ‘parrot dinosaur’, due to its head/beak structure — lived during the Cretaceous, around 100 million years ago, throughout much of what is now China and east Asia.
The new if dings are the result of an ‘intricate study’ on the bones of babies, juveniles and adults, of the species. Dr Qi Zhao, of the Institute for Vertebrate Paleontology in Beijing, said: “Some of the bones from baby Psittacosaurus were only a few millimetres 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.”
To start with, the researchers sectioned two arm and two leg bones from each of sixteen separate individual dinosaurs, across a wide-range of developmental stages — ranging from less than a year old, to 10 years old, to fully-grown, etc.
The University of Bristol provides details:
The one-year-olds had long arms and short legs, and scuttled about on all fours soon after hatching. The bone sections showed that the arm bones were growing fastest when the animals were ages one to three years. Then, from four to six years, arm growth slowed down, and the leg bones showed a massive growth spurt, meaning they ended up twice as long as the arms, necessary for an animal that stood up on its hind legs as an adult.
Professor Xing Xu of the Beijing Institute stated: “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.”
Professor Mike Benton of the University of Bristol, one of Dr Zhao’s PhD supervisors, stated: “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.”
Interesting research — the growth processes of extinct species are often hard to glean from fossil records, it’ll be interesting to see further research in this vein. The switch from quadrupedalism to bipedalism is a rather rare one — as documented in the fossil record anyways — perhaps such research could shed further light on the evolutionary processes that select for bipedalism in species? There is still an enormous amount of debate in the scientific community with regards to why/how bipedalism developed in hominids.