The Denver Zoo says George, a 28-year-old rhino, was humanely euthanized because of health problems including diverticulitis, chronic diarrhea and continued weight loss.
George was the ninth oldest black rhino in the world.
The Denver Zoo says that animal care staff had been monitoring and treating George for his health problems. After finding him unable to stand in his indoor habitat zookeepers and veterinary staff made the difficult decision to humanely euthanize early Tuesday morning. Animal autopsy results found that George's spleen had ruptured.
"All of us at Denver Zoo will miss George greatly. He was a wonderful animal and a great ambassador for his wild brethren," Denver Zoo spokesperson Tiffany Barnhart said in an email.
According to Barnhart, black rhinos are critically endangered in the wild, and are less than 90 in North American zoos.
George was born on Jan. 11, 1983 and came to Denver in 1984 from the Cincinnati Zoo. George fathered a calf named Tony with a female named Onyx.
The black rhino's slow reproductive rate combined with the threat of poaching has left the animal critically endangered. Poachers use their horn for traditional Chinese medicine and dagger handles in Yemen. Only 3,700 remain in the world, according to the International Union of Conservation of Nature.
Leo Wolfson contributed to this report.
(KUSA-TV © 2011 Multimedia Holdings Corporation)