Dinosaur Skull Analysis Shows Three Species Are Actually One
August 11, 2013

Dinosaur Fossil Analysis Reveals Three Species Are Actually The Same

redOrbit Staff & Wire Reports - Your Universe Online

A number of Psittacosaurus fossils, once believed to represent three different species, actually all belong to a single dinosaur species, researchers from the University of Pennsylvania claim in a new study.

Differences in the specimens had led scientists to label them as separate species, senior author Peter Dodson, a professor of anatomy in Penn's School of Veterinary Medicine and professor of paleontology in the School of Arts and Sciences' Department of Earth and Environmental Science, and his colleagues report in their soon-to-be-published paper.

However, after analyzing the fossils using three-dimensional geometric morphometrics – a new technique that uses lasers to generate data about the shape of different specimens – they discovered they all originated from the same creature. Their study, which is to be published in the journal PLOS One, marks the first time this method has been used to study dinosaur remains and could lead to a re-evaluation of the taxonomic classifications of other types of dinosaur and other long-extinct fossil organisms, they said.

The dinosaur fossils analyzed by Dodson and his colleagues all originate from the genus Psittacosaurus, a type of ceratopsian dinosaur that lived in what is now Asia during the Early Cretaceous Period, approximately 130 to 100 million years ago. Psittacosaurus, which means “parrot lizard,” was a semi-aquatic dinosaur, bipedal herbivore that was originally discovered by paleontologist Henry Fairfield Osborn in 1923.

It has been recognized as the most species-rich dinosaur genus, with nine to eleven recognized species from fossils found in different regions of modern-day China, Mongolia and Russia, as well as a possible species originating from Thailand. Species of Psittacosaurus, which varied in size and specific features, included P. mongoliensis, P. major, P. neimongoliensis, P. xinjiangensis, P. sinensis, P. meileyingensis, P. lujiatunensis and P. sibiricus.

The fossilized remains analyzed by Dodson’s colleagues had originally been identified as belonging to three different species, P. lujiatunensis, P. major or Hongshanosaurus houi, the researchers explained. They were discovered in the fossilized ashes of the Lujiatun beds of northeastern China's Yixian Formation.

“To compare and contrast the specimens, the researchers used two techniques,” the university explained in a statement. “First they conducted a traditional study in which they examined every skull that had been classified as one of those three species – a total of 74 specimens – for a variety of characteristics that had been used in prior studies to distinguish the species. The Penn team also compared these fossils to skulls that had been classified as belonging to eight other Psittacosaurus species.

“Next they completed a more high-tech analysis of 30 skulls from the three named species,” the institution added. “Using a hand-held stylus that captures a point in space relative to a transmitter, they pinpointed 56 ‘landmarks,’ or particular anatomical locations, on each fossil and compared the relative position of those marks between specimens. They also used a hand-held, laser-emitting scanner to make a three-dimensional image of each specimen, similar to a CT scan, from which they also collected landmark data.”

Based on an examination of the physical skulls, the research concluded all three supposed species were actually all members of the same species: P. lujiatunensis. The results of their geometric morphometric analysis supported their conclusion, though by itself the technique is not sufficient to classify species. Furthermore, their investigation suggests the way in which an animal’s body was crushed as it was fossilized (whether it was crushed from the top, from the side, or twister) could result in inaccurate species determinations.

Back in June, an international team of paleontologists explained how members of the Psittacosaurus genus switched from four feet to two as it grew. They sectioned two arms and two leg bones from 16 individual dinosaurs between the ages of one and 10 years, when they would have been fully grown.

The youngster of these creatures had long arms and short legs, and moved around on all fours soon after hatching, the paleontologists said. Those between the ages of four and six had slower arm growth, but experienced a massive growth spurt that ultimately left their legs twice as long as their arms. Eventually, Psittacosaurus moved from a quadrupedal lifestyle to becoming an upright bipedal dinosaur, they concluded.