These are real ricefield rat (Rattus argentiventer) skulls! Endemic to Southeast Asia, they live in large groups and feast on termites, insects, grasshopper, snails, seeds, nuts, rice, vegetables, and fruits.
Due to their habit of raiding homes for food, they are considered a pest by many and are often trapped or killed.
They measure ~1.25" long and can be shipped worldwide!
The jaws may be hot glued on to ensure the buyers receive the correct mandible. To remove the hot glue, simply wet the area with rubbing alcohol and it will loosen up.