Petal was 52 when she succumbed June 9 to several underlying health problems, all linked to her age.
Animal health director Dr. Keith Hinshaw says Petal had arthritis and heart and lung problems, but "the most significant finding was fairly significant heart disease."
Zoo officials say that the morning of her death Petal fell into a deep sleep, collapsed, and toppled over from her upright sleep position. The autopsy concluded that because of her arthritis, the aged elephant was unable to get back up.
When handlers found her, Petal was exhausted and there was nothing they could do to help. She died a short time later.