Also, with the exception of _Yaverlandia_, are
pachycephalosaurs known from the Early Cretaceous? And
if so where?
There is a lot of doubt over whether _Yaverlandia_ is actually a
pachycephalosaur. (As to what it actually is... your guess is as good as
mine. Any takers out there?) I have a reference somewhere that questions
the pachycephalosaurian status of _Yaverlandia_ - I can probably dig it up
tonight.
_Stenopelix waldensis_ is known from a partial postcranial skeleton from the
Wealden of northwestern Germany. It is of Early Cretaceous (Berriasian)
age, and appears to be some sort of marginocephalian, possibly a
pachycephalosaur.