CLEVELAND – Zookeepers in Cleveland are the ones feeling slow because after more than 50 years, the tortoise they called “Mary” is actually a male.

Officials at the Cleveland Metroparks Zoo say it can be tough to establish the sex of a giant Aldabra tortoise because the reproductive organs normally aren’t visible. But Mary’s maleness was unexpectedly revealed earlier this month during a routine exam.

Spokesman Tom O’Konowitz said Wednesday that the zoo has decided to rename the tortoise Terry.

When the 400-pound (180-kilogram) reptile arrived at the zoo in 1955, it was assumed he was a she because of a flatter shell, shorter tail and all-around smaller size than most males.

The tortoise is estimated to be between 75 and 100 years old.