LOS ANGELES (AP) _ Twinkletoes, a 2,000-pound black rhinoceros that lived at the Los Angeles Zoo since it opened in 1966, was euthanized this week after her internal organs began to fail.

Born in the wild in Kenya in the early 1960s, Twinkletoes was the oldest female black rhinoceros in North America. She was estimated to be in her late 30s.

Twinkletoes, who had five calves during her years at the zoo, began to experience problems over the weekend. She started having difficulty breathing and tests indicated liver and kidney failure. Her condition worsened and she was put down on Monday.

Other than being ``slow and forgetful,'' Twinkletoes had no previous signs of health problems, zoo officials said.

Captive black rhinos usually live into their early 30s, although there are two male rhinos in U.S. zoos that are in their 40s, according to the zoo.

About 2,500 black rhinos remain in the wild in Africa and there are about 150 in zoos, including three in Los Angeles.