Penn researchers determine three dinosaur species are actually one

Dinosaur Research

Peter Dodson, a professor with appointments in Penn Vet and the School of Arts & Sciences, and Brandon Hedrick, a Ph.D. student in the Department of Earth and Environmental Science.

Psittacosaurus (sih-TACK-oh-sore-us) is a genus of short, beak-faced dinosaurs that lived in Asia 120-125 million years ago, roaming China, Mongolia, Siberia, and possibly Thailand.

The plant-eaters lived for about 10 million years in an era after Stegosaurus and before Tyrannosaurus rex, at a time when most dinosaurs were small.

Three- to six-feet long, its name comes from the Greek word for “parrot lizard,” an ode to its beaked, turtle-like face.

“They were really quite short,” says Peter Dodson, a professor of anatomy in the School of Veterinary Medicine and a professor of paleontology in the Department of Earth and Environmental Science. “If one stood up and it had a bad attitude, it might reach your waist.”

First unearthed in 1923, Psittacosaurus is one of the most abundant dinosaurs known to science, with hundred of specimens—including 300 complete skeletons.

“With most dinosaurs, you only have one specimen, and it doesn’t have to be a great specimen,” says Brandon Hedrick, a Ph.D. student in the Department of Earth and Environmental Science. “With some dinosaurs, it’s a couple of thumbs.” With Psittacosaurus, there are many.

Using conventional paleontology research procedures and 3-D geometric morphometrics, a cutting-edge technique that uses lasers to generate data about the shape of different specimens, Dodson and Hedrick discovered that a number of Psittacosaurus specimens—once thought to represent three species—are actually members of a single species. Their findings were published on Aug. 9 in the journal PLoS ONE.

The scientists analyzed high-quality Psittacosaurus skulls found buried in the fossilized ashes in northeastern China.

“The advantage of this study is that all the fossils come from a single location,” Dodson says. “It’s hard to say that a fossil from Mongolia or Siberia is the same. But here, when it comes from a single spot in the ground, you know they’re all the same.”

Paleontologists had previously determined that the skulls were members of three different species, Psittacosaurus lujiatunensis, P. major, or Hongshanosaurus houi. Dodson and Hedrick conclude that all three can be considered members of the species P. lujiatunensis, and the disparity among fossil skull remains is explained by how the dinosaurs were buried and compressed.

The researchers employed traditional methods of examining fossil skulls, including examining every skull that had been classified as one of the three species—a total of 74 specimens—to confirm that the supposed three species were indeed one.

The scientists then conducted a geometric morphometric analysis of 30 skulls—using a hand-held stylus and portable laser-emitting scanner that enabled three-dimensional imaging—to support their findings. Results from the analysis supported the conclusion that the way in which an animal’s body was crushed as it fossilized could lead to inaccurate species determinations.

Hedrick says a lot of the characters that were being used to distinguish the different species were based on the different types of compression. Paleontologists believed there were three different species because of the different shapes of Psittacosaurus fossil skulls. He maintains that the skulls were buried in similar condition, and the differences in shape are the result of the long process of fossilization, and of millions of years of moving Earth.

Dodson and Hedrick’s study was the first time 3-D geometric morphometrics has been used on the study of dinosaur skulls.

Dodson has used calipers to measure dinosaur fossils for 40 years, a trusty tool indeed, but, he admits, it is “the kind of technique you could have used in the 19th century.” He sees 3-D morphometrics as an emerging and valuable technology.

“This is a very powerful method of data capture,” he says. “I think this study is likely to be a model for future studies, and I think other researchers can take our techniques and apply it to their own fossils.”

Originally published on September 12, 2013