It seems likely to me that a large portion of those skulls came from the Predator's homeworld itself.
1st. The "T-Rex" skull. We've got mandibles as well as jaws, so it seems like this critter came from the same evolutionary system as the Preds. There are a lot of holes on the side of its head, too; maybe it has multiple (more than 2) eyes? Man it's got a lot of teeth, though, some of which seem to still be coming down into the mouth. Could be like a shark, in that they continually grow new teeth, which would make it an A-number 1 predator (little p). Could be it's mutated too; as advanced as the Predators are, how badly polluted do you think their world is?
2nd. Monkey Predator. Immediately to the left of the Alien skull, there's one that looks kinda like a Predator skull, only with a big ridge over the top of the head. It might even have mandibles, though its really hard to see, based on how dark everything is. This could be the Predator homeworld equivalent of a Gorilla, a big fierce beast that's vaguely related to the Predators, but still dangerous enough to hunt. It, like the 1st skull, also seems to have holes for more than one pair of eyes. So either it came from the same world as #1, or the Predator homeworld is more (and different) variety than previously pondered.
3rd. Wacky skull. The thing on the other side of the Alien skull is just plain weird. No mandibles like the other two, a very sloping head, and tusks that seem to start at the back of their head and curve all the way over. Huge teeth, that almost seem like fingers; ew, creepy thought. And it looks like a weird claw or starfish thing is growing off the back. There might even be a hint of a more conventional skull back there, too. Whatever this thing is, it is very alien (little a), and I'd be interested to see concept art of it.
4th. BIG skull. It isn't in those pictures, but if you watch Predator 2 again, watch during the actual fight between Harrigan and the Bill Paxton Predator (he's their alien equivalent, I figure (the oomans are all around man! What are we gonan do? What are we gonna do?!)). Anyway, there's another, larger skull above all those that we don't see in the main shot, and it seems to have horns or something that go all the way across the case. That's the one I wanna see a beast for.
Overall, I wonder if there's any concept art or production photos of this set. It really would be neat for future movies to incorporate the living versions of these critters.
-Pax
