Fragment of the back piece (squamosal) of the skull from a baleen whale (Mysticeti)?|
This is hard to picture, since it is just a fragment of a skull piece.
The grooved section is where the bulla (ear bone) attatches to the skull
Back Left View|
The concave crevice is probably part of the brain case.
Cross your eyes, align the images into one, and focus.
You should see a 3-d version of the flat picture.