Mac the chimpanzee dies at Houston Zoo

HOUSTON -- Mac the chimpanzee was euthanized Monday at the Houston Zoo.

The chimp was 20 years old and considered the leader of the chimp group which is made up of 15 others. There are six males and nine females remaining.

Zoo veterinarians say Mac was undergoing a routine physical and was put under anesthesia. That measure is routine for chimp exams.

However, Mac lost oxygen levels to his brain during the procedure.

"There was evidence of brain swelling, which could happen if the brain doesn't receive enough oxygen," explained Dr. Lauren Howard. "We had a bunch of theories -- drug reaction, some sort of heart condition."

Vets are still waiting on autopsy results to find out what exactly went wrong.