(NEXSTAR) – U.S. Customs and Border Protection agents made a fishy discovery last week at the Detroit Metropolitan Airport while inspecting unaccompanied international baggage.

The bag had been separated from owners during transit, the agency said in a news release, and underwent routine X-ray screening when it reentered the U.S.

During the screening, agricultural specialists noticed a skull-shaped object in the luggage. Officials with CBP and the U.S. Fish and Wildlife Service determined it was a skull believed to be from a young dolphin.

According to CBP, animal parts or products, including skulls, are subject to import and export restrictions, prohibitions, permits, or certificates. Importing or exporting marine mammals is prohibited.

“The possession of wildlife items, especially those of protected animals is prohibited,” said Area Port Director Robert Larkin. “We take wildlife smuggling seriously and work closely with our federal partners at the U.S. Fish and Wildlife Service to protect wildlife and their habitats.”

The skull was turned over to U.S. Fish and Wildlife Service investigators. Additional details, including where the dolphin skull may have come from, weren’t immediately available.

Routine luggage X-rays have uncovered other surprising discoveries at U.S. airports in recent weeks.

In November, TSA officials in New York found an orange cat in a checked bag at John F. Kennedy International. Days later, TSA agents found a small dog in a passenger’s bag at a Wisconsin airport. TSA agents found an “emotional support” boa constrictor in a carry-on bag at Tampa International last month.

Two months ago, CBP found giraffe and zebra bones in a Virginia woman’s luggage at Washington Dulles International. She admitted to collecting the bones in Kenya with the intention of keeping them as souvenirs, the agency said in a news release. The woman was not criminally charged.