There is only Triceratops
3 Aug 2010
New Scientist reports that we might wrongly be classifying young and fully grown dinosaurs as separate species.
Paleontologists John Scanella and Horner propose that some dinosaurs underwent remarkable morphological changes during their growth and that we are confusing these differences between juvenile and adult with distinct species, specifically that
… Triceratops is merely the juvenile form of Torosaurus. As the animal aged, its horns changed shape and orientation and its frill became longer, thinner and less jagged. Finally it became fenestrated, producing the classic Torosaurus form
ScienceDaily has a similar story about the Pachycephalosaurus:
Many paleontologists now realize that the elaborate head ornaments of dinosaurs, from the huge bony shield and three horns of Triceratops to the coxcomb-like head gear of some hadrosaurs, were not for combat, but served the same purpose as feathers in birds: to distinguish between species and indicate sexual maturity.
“Dinosaurs, like birds and many mammals, retain neoteny, that is, they retain their juvenile characteristics for a long period of growth,” Horner said, “which is a strong indicator that they were very social animals, grouping in flocks or herds with long periods of parental care.”