[Marius3188]

Still going with a Orca or similar whale.

[Arthalion]

Yep, mystery SOLVED! The skull, and apparently the entire body, are the remains of a beluga whale. Beluga's have a lot of fat on them making them appear fat and rounded, but when you strip it away this is what a Beluga skull looks like:



Look familiar? Even the notch in the upper skull is consistent.

[Mark Felton]

The teeth are all wrong for a whale. Whales have several layers of very sharp teeth to filter krill and shrimp.