(CNN)Federal authorities made a grim and unexpected discovery in an unattended bag last week at a Detroit airport.
Inside, the bag held a young dolphin's skull, the US Customs and Border Protection said in a news release Friday.
The bag was separated from its owners while traveling and when it arrived in the US, a routine screening at the Detroit Metropolitan Airport revealed what appeared to be a skull-shaped object, CBP said in the release.
"Upon further examination by CBP and US Fish and Wildlife Service officials, it was determined the skull was from a young dolphin," the release said.
The skull was turned over to US Fish and Wildlife Service inspectors for further investigation.
"The possession of wildlife items, especially those of protected animals is prohibited," Robert Larkin, the area port director, said in a statement. "We take wildlife smuggling seriously and work closely with our federal partners at the US Fish and Wildlife Service to protect wildlife and their habitats."
There are restrictions and requirements around importing and exporting certain fish, wildlife and products that come from them -- and it's not the first time US authorities make a similar seizure.
In December, CBP officers seized zebra and giraffe bones from a woman at Washington's Dulles International Airport. The woman, who was traveling from Kenya, had kept the bones as souvenirs, authorities said at the time.