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One of evolution’s most intriguing peculiarities is its tendency to repeat patterns across different species.

A new study in Nature Communications has unveiled a unique similarity between dinosaur and human development. Qi Zhao from the University of Bristol, lead author of the study, has found that like humans, some dinosaurs began life on all fours and transitioned to walking on two limbs during their young adult years.

Zhao’s research team carefully analyzed 16 fossil Psittacosaurus lujiatunensis specimens from the Liaoning Province in China. The genus Psittacosaurus—Greek for “parrot lizard”—is comprised of 10 known species of large, horned herbivores who lived during the Lower Cretaceous. Psittacosaurus fossils are diverse and especially well represented in the fossil record, making them an excellent candidate for measuring how limbs changed and developed over various ages.


A Psittacosaurus skeleton on display at The Children’s Museum of Indianapolis.

The scientists intentionally looked at specimens of varying age—between 1 and 10 years—in order to determine more about the process of limb development on the skeletal level. Using patterns made by blood vessels and orientation, as well as the comparison of body size to limb size, the team was able to determine how much bone was being deposited and where, for specimens of varying ages—thus indicating where growth was most rapid.

They discovered that the youngest dinosaurs had arms that were proportionally long and relatively short legs. Their posture was such that they walked on all fours between ages 1 and 3. But between the ages of 4 and 6, their hindlimbs grew at a much faster rate than their forelimbs, and consequently as adults, had long legs and shorter arms and stood on two hindlimbs.

The research team cites these findings as evidence that Psittacosaurus was once a quadrupedal creature, and evolved to walking on only two legs. The quadropedality characteristic remained in only early developmental stages for more evolutionarily advanced species. Throughout the course of their evolution, those who had long legs and used only hindlimbs to walk became better adapted, and the process of natural selection worked its magic, resulting in dinosaurs who stood tall on two legs, just like us.

The Psittacosaurus study was published in the journal Nature Communications on June 28, 2013.

The Paleontological Research Institution, Ithaca, New York, is pleased to sponsor Paleontology content for This View of Life. Founded in 1932, PRI has outstanding programs in research, collections, and publications, and is a national leader in development of informal Earth science education resources for educators and the general public.

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Published On: July 16, 2013

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