The skull of a young dolphin was found in a piece of luggage at Detroit Metro airport, the U.S. Customs and Border Protection reported.

The luggage was separated from its owner on an international flight re-entering the United States, and it was then scanned through an x-ray machine at Detroit Metropolitan Airport. A skull-like shape was detected, and agents from the CBP and the US Fish and Wildlife Service later identified it as a dolphin, according to the CBP.

"The possession of wildlife items, especially those of protected animals is prohibited," CBP Area Port Director Robert Larkin said. "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." 

Some fish and wildlife products are subject to restrictions, permits and prohibitions when entering and leaving the country, including "wild birds, land or marine mammals, reptiles, fish, shellfish, mollusks or invertebrates, and any animal part or product, to include skins, tusks, bone, feathers, or eggs," the CBP said. 

The U.S. Fish and Wildlife Service is now in possession of the skull and will be investigating further.