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Dr. Peter Dodson, University of Pennsylvania – Lumping Dinosaur Species

In today’s Academic Minute, Dr. Peter Dodson of the University of Pennsylvania explains how the fossilization process can make individual fossils hard to interpret.

Peter Dodson is a professor of veterinary gross anatomy and vertebrate paleontology at the University of Pennsylvania. He and his graduate students have studied dinosaurs around the globe in places such as Montana, Egypt, Madagascar, Argentina, and China. He earned his Ph.D. at Yale University.

About Dr. Dodson

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Dr. Peter Dodson – Lumping Dinosaur Species

Dinosaur species are hard to determine. More than 600 species are known from around the world,  most known from fewer than six specimens, often represented only by a skull or a partial skeleton.

The best chance to determine species reliably is when we have a large sample. Psittacosaurus is a little plant-eater, barely four feet long, that lived 125 million years ago in Central Asia.  It is one of the most abundant dinosaurs known.  

15 species have been described, but we focused on three species from a single locality in northeastern China. These are Psittacosaurus lujiatunesis, P. major and Hongshanosaurus houi. All specimens come from the Yixian Formation, and lived together at the same time. Graduate student Brandon Hedrick and I studied 28 skulls ranging in length from 3 inches to 8 inches. We used powerful three-dimensional scanners and determined landmarks on skulls in 3D space. We subjected the data to computer analysis, and plotted the results. These show that specimens called Psittacosaurus lujiatunesis are preserved in the round with no crushing, specimens called P. major are flattened side to side, and specimens called Hongshanosaurus houi are crushed so that the back of the skull is pushed down. We conclude that the two distorted species are merely preservational variants of a single species.

Paleontologists have long understood that growth and sexual differences must be taken into account when defining species. Our study underscores the importance of post-mortem preservational effects, and demonstrates the value of powerful new technological tools in paleontology.

Production support for the Academic Minute comes from Newman’s Own, giving all profits to charity and pursuing the common good for over 30 years, and from Mount Holyoke College.

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