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Three Dinosaur Species Become One

Researchers used 3D scans to compare specific "landmarks" on the psittacosaur skulls to test taxonomic distinctions between species. (Image credit: PLOS One, doi:10.1371/journal.pone.0069265.g001)

Gazelle-sized dinosaurs in the Psittacosaurus genus roamed Earth between 120 million and 125 million years ago, eating plants and cracking nuts with parrotlike beaks. They represent one of the most species-rich groups of dinosaurs known today, with at least nine different psittacosaurs identified since their discovery in 1923. But their ranks may have just gotten smaller.

Specimens that had been classified as three distinct psittacosaurs actually represent just one species, according to a new 3D-fossil analysis.

Scientists of the past may have been too eager to separate Psittacosaurus skeletons into different dinosaur species, because the effects of burial and compression can give fossils misleadingly distinct features.

"Because of the vagaries of fossilization, no two fossils are the same," study author Peter Dodson, a professor of anatomy and paleontology at the University of Pennsylvania, explained in a statement. "Animals are alive and they die, but what's crucial in paleontology is what happens to the animals after they die."

Hundreds of psittacosaurs have been found across Mongolia, China and Russia, but Dodson and colleagues focused on those that have been found in the Lujiatun beds of the Yixian Formation, a fossil-rich deposit in northeastern China famous for its feathered dinosaur and early bird remains.

They used a technique known as three-dimensional geometric morphometrics — which used lasers to make 3D images of each specimen, similar to a CT scan— to analyze 30 of the dinosaur skulls.

Their study revealed that two species from the Lujiatun beds —P. major and Hongshanosaurus houi — are likely just juvenile specimens of P. lujiatunensis.

"Our study found all of these false 'species' that are not biological species but are apparent species caused by the process of fossilization," Dodson said.

The findings are detailed in the journal PLOS ONE.

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Megan Gannon
Megan has been writing for Live Science and Space.com since 2012. Her interests range from archaeology to space exploration, and she has a bachelor's degree in English and art history from New York University. Megan spent two years as a reporter on the national desk at NewsCore. She has watched dinosaur auctions, witnessed rocket launches, licked ancient pottery sherds in Cyprus and flown in zero gravity. Follow her on Twitter and Google+.