I think if you poured that from the back of the skull there aren't that many undercuts except around where the jaws meet. Still likely a 2 part mold but nothing overly complicated and putting the seam around where the jaws meets alleviate the undercuts there as well as helps hide the seam.

Or it could be a single metal mold utilizing the size difference after heat change to help release. Still poured from the back which we don't see in the pics.