By about 1970, some scientists were sitting around and they thought, "What in the world -- Look at these dinosaurs, they're all big. Where are all the little ones?"
And it comes down to a couple of things. First off, scientists have egos, and scientists like to name dinosaurs. They like to name anything. Everybody likes to have their own animal that they named.
Nobody noticed the gnarly stuff sort of looked alike. But they did look at these three and they said, "These are three different dinosaurs, and Dracorex is probably the most primitive of them. And the other one is more primitive than the other." It's unclear to me how they actually sorted these three of them out. But if you line them up, if you just take those three skulls and just line them up, they line up like this. Dracorex is the littlest one, Stygimoloch is the middle-size one, Pachycephalosaurus is the largest one. And one would think, that should give me a clue.
So if we cut open Dracorex -- I cut open our Dracorex -- and look, it was spongy inside, really spongy inside. I mean, it is a juvenile and it's growing really fast. So it is going to get bigger. If you cut open Stygimoloch, it is doing the same thing. The dome, that little dome, is growing really fast. It's inflating very fast. What's interesting is the spike on the back of the Dracorex was growing very fast as well. The spikes on the back of the Stygimoloch are actually resorbing, which means they're getting smaller as that dome is getting bigger. And if we look at Pachycephalosaurus, Pachycephalosaurus has a solid dome and its little bumps on the back of its head were also resorbing.
So just with these three dinosaurs, as a scientist, we can easily hypothesize that it is just a growth series of the same animal. Which of course means that Stygimoloch and Dracorex are extinct.