The Case of the Imaginary Dinosaurs and Fossils

How Dinosaur Growth has Led Paleontologists Astray

Nov 10, 2009

Recently, paleontologists came to the realization that perhaps one-third of "discovered" dinosaur species are simply younger or older versions of other dinosaurs.

A new study by paleontologists from the University of California, Berkeley and the Museum of the Rockies suggests that a sizeable chunk of dinosaur species that have been identified as unique may just be fossils of the same dinosaur during different stages of life.

Denying a Third of the Dinosaurs

Dinosaur experts Mark Goodwin (of UB Berkeley) and Jack Horner (of Museum of the Rockies) recently published an academic paper in the online, peer-reviewed journal PLoS ONE, outlining the similarities between species in a specific group of dinosaurs: pachycephalosaurids.

Pachycephalosaurids (which loosely translates to “thick-headed lizard”) were creatures with dome-shaped, bony heads. Some may be familiar with the pachycephalosaurus from Jurassic Part 2: The Lost World, as they made a brief appearance as head-butting thwarters of the human hunters.

Horner outlines in his research three species of pachycephalosaurids that have been categorized as completely different dinosaurs altogether: Dracorex hogwartsia (juvenile), Stygimoloch spinifer (sub-adult), and Pachycephalosaurus wyomingensis (adult). Horner and Goodwin argue that these dinosaurs were not simply similar pachycephalosaurids, but only representations of different stages of the same dinosaurs.

Based on their conclusions, Horner and Goodwin feel that it’s quite plausible that dinosaurs, through the uncovering of fossils, have been grossly overrepresented. If the three successive stages of the pachycephalosaurid listed above are any indication of how species have been classified up to this point, the paleontologists believe that nearly a third of already-discovered species may, in fact, be moot.

Finding the Evidence

Jack Horner and Mark Goodwin primarily discuss the development of the skulls of the three creatures featured in their study. By studying the microscopic structures of the skulls, the scientists determined that there were many features that suggested the bones were in a transitional stage that comes between different stages of maturity.

“Dracorex's flat skull, nodules on the front end and small spikes on back, and thickened but undomed frontoparietal bone all confirm that, ontogenetically, it is a juvenile Pachycephalosaurus," Goodwin said.

The tissues in the domes of the three pachycephalosaurids were all in different stages of development. In the juvenile, it was evident that the tough dome would develop, but hadn’t yet. The sub-adult’s cranial structure, with its growing tissue and unfused dome, suggests it was a creature that hadn’t yet reached sexual maturity.

What This Means for Paleontology

Though this is a major discovery for modern paleontological studies, Jack Horner doesn’t want to jump to any conclusions. "What we are seeing…suggests that we may be overextended by a third," Horner said, talking about the current catalogue of species. He admits, however, that this is a so-called “wild guess,” and simply because this applies to the pachycephalosaurids, doesn’t mean it will apply across the board.

Whether this realization can be applied to other dinosaur species or not, this new information will potentially provide helpful insight into the biology and lives of dinosaurs.

Horner JR, Goodwin MB, 2009 Extreme Cranial Ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus. PLoS ONE 4(10): e7626. doi:10.1371/journal.pone.0007626

The copyright of the article The Case of the Imaginary Dinosaurs and Fossils in Paleontology is owned by Kristina Bjoran. Permission to republish The Case of the Imaginary Dinosaurs and Fossils in print or online must be granted by the author in writing.