But are Dracorex and Stygimoloch synonyms of Pachycephalosaurus? The diagram below says differently. Regardless, of the taxonomic situation, this is a great drawing representing the other lesser-known pachycephalosaurids, not just Pachycephalosaurus.
It has obviously been covered in other comments, but the suggestion is that the formerly considered synonyms are probably distinct from the Pachycephalosaurus as we know it. They could be just a different species to P. wyomingensis or fall under a combined Stygimoloch. It is a good diagramatic display of fossil material to show what we do know.
And I always try to show off as wide arange of species in a group that I can, including the lesser lights!
It’s funny to think these animals were once thought to have been the same thing as troodonts. How times have changed and how the fossils have amassed in the ensuing decades.
For how famous these guys are as stock dinosaurs, it’s surprising how rarely they show up in educational media. You’d think being a contemporary of T. rex and a stock dinosaur in general would warrant plenty of appearances for Pachycephalosaurus in educational media but not so much, only in Dinosaurs Decoded. Outside of that, there’s only Prenocephale from Dinosaur Planet and the genetic little dome-head from Dinosaur Revolution (confirmed to be a recycled Prenocephale from a scrapped segment, ironically enough).
One dome-head that really gets the shaft though is the polar pachycephalosaur, Alaskacephale, which is actually the first of the Prince Creek dinos to properly be described as its own species in 2006, but even that awful Walking with Dinosaurs 3D film, which took a lot of liberties to swell up its cast, didn’t include it.
But they did include Parksosaurus, which is like Alaskacephale, but less interesting? They didn't even bother naming Parksosaurus, so clearly they didn't care!
(Don't let us down forgotten bloodlines)
As the only evidence of small ornithischians from Prince Creek are teeth, so Parkosaurus can’t even be confidently assigned to the Prince Creek Formation (it’s more of a “best guess” scenario). Hesperonychus and Chirostenotes aren’t even known from the Maastrichtian, let alone Alaska, though the latter was likely based more on Epichirostenotes. It really is unjust that Alaskacephale meanwhile is being totally ignored.
Re: troodont connection. This was obviously based on the teeth, and it's possible that pachycephalosaurs may have been more omnivorous than previously thought or used the small sharp bladed teeth for snipping browse.
Re: fame. And one was also present in the second Jurassic Park movie, primarily to recreate the 'noosing rhinos' scenes of old safari films. That and for it to hammer a vehicle.
It is a surprise they aren't more popular, but it probably comes down to being relatively rare in the fossil record. Was a reason for wanting to depict them too!
I know why they mistakenly thought there was a connection back in the day, I just think it’s funny in hindsight, given how little these two groups had in common besides their teeth.
They are not that rare, given how most major fossil sites from Late Cretaceous North America and Asia have at least one species of pachycephalosaur (Hell Creek, Nemegt, Dinosaur Park, Kirtland, Horseshoe Canyon, Prince Creek, etc.). And I’m saying its weird they are so rare in media, especially documentaries, when Pachycephalosaurus is an iconic dinosaurs and many docus take places in a location where a pachycephalosaurs would logically turns up, especially Hell Creek.
They might be found in all the main fossil sites of Late Cretaceous North America and East Asia, but compared to other ornithischians they are a rare part of any fauna. Duckbills and ceratopsians make up a far larger percentage of the herbivore clade. But I do agree that for an iconic group they don't get much PR love.