I personally think it is a Pelvis and not a skull. One can clearly see that the lower section of the bone mass has sockets for ball-joint type legs just like in a monkey or a man... but the plate like structure is very strange. My guess is it's a deformity of some monkey, and a pelvis, not a skull. There's nothing skull-like about it, in fact. But perhaps it's the Pelvis' of a completely unknown species. I can't think of one with a plate like structure on its back, much less its front. It is a baffling object to be sure.