Evaluating ontogeny is tricky. Without a good sample size, it's not easy to differentiate juveniles from adults. Even in this case, it's still not a slam-dunk that Dracorex is a juvenile of Pachycephalosaurus. It might just be a juvenile of an animal we haven't found the adult form of.
This is actually a big problem in ceratopsian systematics. Ceratopsians go through pretty radical cranial changes as they get older, especially centrosaurines. At least two ceratopsians that have their own genus name (Brachyceratops and Avaceratops are most likely juveniles of other genera. But without a good sample size, you can never tell.
Let's say you find Brachyceratops, which is clearly a juvenile, in the same formation as Centrosaurus and Chasmosaurus (this would never happen, it's just hypothetical). Given that all juvenile ceratopsians pretty much look alike, how would you know whether Brachyceratops goes with Centrosaurus or Chasmosaurus? Without more intermediate age groups, it's impossible to tell.
Other potential synonymes: Nanotyrannus is probably a subadult Tyrannosaurus, and Torosaurus may just be an old adult Triceratops (I'm not sold on that last one).
So I don't think this will spark a re-examination of existing taxa, just because it's impractical and entirely dependant on existing specimens. Great question, though.
Also, the Brachiosaurus/Brontosaurus thing you mention...there's no such thing as Brontosaurus, and here's why: Back during the Great Bone Wars of the late 1800's, Cope and Marsh basically gave a different name to every bone they pulled out of the ground (they were competing with each other). As a result, they royally screwed up Morrison dinosaur taxonomy. At one point, Allosaurus fragilis had nine different names.
Anyway, the same thing happened to Apatosaurus. It was found intially based on incomplete remains. Years later, another specimen was dug up and given the name Brontosaurus. Several decades later, a paleontologist studied both specimens and determined that they're the same animal. Because Apatosaurus was named first, that's the name that sticks.
This matter was further confused because at the time, the only good sauropod skull was from Camarosaurus (a relative of Brachiosaurus), so the guy who mounted the composite "Brontosaurus" skeleton thought it had the same kind of skull. This later turned out to be totally incorrect, of course. Macronarian sauropods have leaf-shaped teeth while diplodocoids have narrow skulls and chisel-like teeth.
Topic: Halbred's Paleo-News Thread (Read 118380 times)
