One Dinosaur Too Many?

Are there too many dinosaurs? Paleontologist Jack Horner thinks so, and he explained his reasoning in a short TED talk last month in Vancouver, Canada.

Over the past several years, Horner has been picking over the skeletons of Late Cretaceous dinosaurs from North America in an attempt to figure out whether some of the dinosaurs labeled as distinct species are actually growth stages of a single species. In 2009, for starters, Horner and Mark Goodwin proposed that the dome-headed dinosaurs Dracorex and Stygimoloch were actually immature representatives of the larger Pachycephalosaurus. Last year, Horner and colleague John Scannella made a bigger splash when they published a Journal of Vertebrate Paleontology paper suggesting that the broad-frilled, horned dinosaur Torosaurus was the adult stage of Triceratops (though this hypothesis has been contested). In the video, Horner also suggests that the hadrosaur Edmontosaurus was the subadult stage of the larger Anatotitan.

This kind of revision isn’t new. Many dinosaurs specimens that were once thought to be pygmies or oddly-proportioned adults of new species have turned out to be juveniles, such as the diminutive sauropodomorph Mussasaurus, hadrosaur specimens previously assigned to “Procheneosaurus,” and the ever-contentious Nanotyrannus. What’s different now is that paleontologists have more powerful techniques to investigate and compare specimens from well-sampled areas. Scientists can now look into the bone itself to estimate age, for example, allowing researchers to see if a seemingly small form was truly an adult or still had a bit left to grow.

I wouldn’t say that we have too many dinosaurs, though. Many new species are coming from areas that have not been previously explored or are poorly understood. Given how little we know about the past and how few paleontologists there are,many, many dinosaurs are undoubtedly yet to be discovered. These new species will be subjected to in-depth scientific investigations and in time, paleontologists will gain a deeper understanding of how dinosaurs grew up.

For another take on the same video, check out Love in the Time of Chasmosaurs.

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.