Eriorguez: what's the conensus these days re Stygimoloch being sunk into Pachycephalosaurus? Would it become its own species, ie. P. spinifer? (I really need to sign up to the DML. Will do today or tomorrow I think.)
The original paper. ALL subsecuent studies have disagreed with that.
The consensus for Stygimoloch is "needs more data". We know that it is very close to Pachycephalosaurus, that a fully grown specimen would be very Pachycephalosaur-like, and that a Pachycephalosaurus in the same growth stage as the known Stygimoloch would look remarkably like them, BUT, we need more data to go either way.
Same as Triceratops and Torosaurus; One looks like what the fully grown other would look like from what we know and vica-versa, but we need more data.
Dracorex looks just like a smaller, younger Stygimoloch without a dome. That dome could be grown. Same with Homalocephale and Prenocephale, that one is even more widely accepted, mostly from the description of both of them being on the same paper, and Bakker not being obnoxious about it.
Plus, there is a large bias torwards splitting taxa. It is all a subjective matter, but still, ontological issues are ontological issues.