CLEVELAND -- A 50-year resident of the Cleveland Metroparks Zoo revealed some startling personal information earlier this month.

A 400-pound tortoise named Mary is not a "she" after all. A recent veterinary examination determined that the Aldabra tortoise is actually male.

The zoo says it's very difficult to determine the sex of the species because it normally doesn't have externally visible sex organs. But during the exam earlier this month, Mary decided to “come out of her shell” and show the veterinary staff that he’s definitely a male.

Zoo staff thought Mary was female because the tortoise has a flatter shell and shorter tail than most males and also weighed less than the zoo's other Aldabra tortoises, Tom and Tim.

The zoo never did an invasive procedure to determine sex before because it was not medically necessary. Mary, Tom and Tim arrived at the Cleveland Zoo in 1955 from their native habitat of the Seychelles Islands, off the coast of Africa.

They are the oldest animals at the zoo and are estimated to be between 75 and 100 years old. Aldabra tortoises can live well beyond 100 years old.

The trio of tortoises are not on exhibit during the winter months but will be back at their outdoors exhibit in May of June.

The zoo's director hasn't decided whether Mary should be given a more masculine name.