11-year-old African elephant named Bets dies unexpectedly at Fresno Chaffee Zoo in California

An 11-year-old African elephant died unexpectedly over the weekend at a zoo in Fresno, California.

The female elephant, named Bets, died at Fresno Chaffee Zoo late on Saturday, just 36 hours after staff noticed she was "not behaving normally" and her health began to "rapidly" decline, according to a press release from the zoo.

The cause of death was unknown, pending a necropsy and pathology reports, the zoo said in the release.

"We consulted with zoo veterinarians around the country to devise our treatment plan. Bets had staff with her to monitor and care for her," Dr. Shannon Nodolf, the zoo's chief veterinary officer, said in a statement Sunday. "We did everything we could in a short amount of time."

Bets arrived at Fresno Chaffee Zoo in May 2015, where she shared a space with three other African elephants. Her remains and tissue samples will be analyzed for scientific study in hopes the findings will allow veterinarians to learn more about her health, according to the zoo's press release.

"We’re extremely saddened by the loss of Bets. This is a great loss to Fresno Chaffee Zoo and our community," the zoo's CEO, Scott Barton, said in a statement Sunday. "The team continues to work to understand the underlying cause."

Elephants are known to live long lives, but they have considerably shorter life spans in captivity than they do in the wild.

A six-year study published in the journal Science in 2008 revealed that wild African elephants in Kenya's Amboseli National Park lived more than three times as long as their captive counterparts living in European zoos.

The researchers found obesity and mental stress to be likely factors to their untimely deaths.