Three Genera... or One?

You may remember when the pachycephalosaur Dracorex hogwartsia was revealed to the public. The reason it garnered the amount of publicity it did was that its specific name (that would be the "hogwartsia") was inspired by a certain series of novels which in turn inspire hysteria in children. It was considered striking enough to grace the cover of the December 2007 issue of Nat Geo, featuring the John Updike article Big Bad Bizarre Dinosaurs.

Not to burst any muggle-bubbles, but according to Jack Horner and Mark Goodwin in Extreme Cranial Ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus, Dracorex and the slightly larger Stygimoloch aren't unique genera at all: they are juvenile specimens of the iconic "bone-head" Pachycephalosaurus. Horner and Goodwin took a close look at the available specimens and determined that they clearly share characteristics of juveniles. Their bones were still growing, and their domes weren't fully fused.

Though we may lament the loss of two such colorful dinosaur names, this does bring the pachycephalosaur family more in line with the ontological (a fancy word for growin' up) development of other dinosaurs, such as the ceratopsians and crested duck-bills, as well as birds like the modern cassowary. In all of these, juveniles begin with much different head ornamentation before developing ostentatious adult characteristics fairly quickly during puberty.


Cassowary, by rogersmithpix via flickr