COLUMBUS, Ohio - An Ohio zoo says necropsy results for the world's first gorilla born in a zoo indicate she probably died of a heart attack.

The 60-year-old Colo had been the country's oldest known living gorilla, having surpassed captive gorillas' usual life expectancy by two decades. She died in her sleep at the Columbus Zoo and Aquarium in mid-January.

The zoo's vice-president of animal health tells The Columbus Dispatch that age takes its toll on gorillas as it does with humans. Veterinarians had removed a malignant tumour from Colo, but the necropsy found no indication that the problem returned.

Colo was born at the zoo in 1956. She eventually became a mother of three, grandmother of 16, great-grandmother of 12 and great-great-grandmother of three.