Cassius, the world's biggest captive crocodile, may have been over 120 years old when he died

Close-up profile photo of the world largest crocodile showing its teeth.
Cassius the giant crocodile died on Nov. 2 after 40 years in captivity. (Image credit: Australian Associated Press / Alamy Stock Photo)

Cassius, the world's largest captive crocodile, has died in Australia after his health started declining in mid-October.

"It is with deep sadness that we share the passing of our beloved mate Cassius," Marineland Melanesia Crocodile Habitat & Gift Shop wrote in a Facebook post announcing his death. "He was more than just a Crocodile, he was a cherished member of our family and brought joy and companionship to his best mate George for over 37 years."

The saltwater crocodile (Crocodylus porosus) — who was 17 feet and 11.75 inches (5.48 meters) long — received the Guinness World Record as the largest living captive crocodile in 2011. But, as no one measured him since, he could have grown even bigger. The species can grow up to 23 ft (7 m) long.

Cassius had lived at Marineland Melanesia Crocodile Habitat on Australia's Green Island since 1987. He was captured in the Finniss River, near Darwin, in 1984 because he was acting aggressively and causing problems.

A person hanging raw meat from a pole to feed a saltwater crocodile.

Cassius in his enclosure being fed by George Craig at the Marineland Melanesia Crocodile Habitat. (Image credit: Australian Associated Press / Alamy Stock Photo)

"As an apex predator, this big crocodile was getting into all sorts of trouble, from catching and eating cattle to attacking boat propellers," Marineland Melanesia's representatives wrote on its website. "It is believed this is where and how he sustained his many battle scars, including losing his front left leg, part of his snout and around 15 cm [6 in] off the end of his tail."

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Cassius was moved to an "assisted care residence" in Cairns on Oct. 5 and his health started declining shortly after. He died on Nov. 2. "He was very old and believed to be living beyond the years of a wild croc," according to Marineland Melanesia's post.

Although experts aren't sure, they think this massive croc may have been over 120 years old when he died. When he was caught, Cassius was estimated to be between 30 and 80 years old. Crocodile growth rates slow significantly once they reach adulthood.

"There is no way of knowing Cassius' actual age as he was born in the wild and the age is just an estimate," Toody Scott, one of Cassius' keepers at Marineland Crocodile Park, previously told Live Science, adding that his birthday "was essentially made up."

Despite his enormous size, Cassius wasn't the largest crocodile ever kept in captivity. This record goes to a saltwater crocodile named Lolong, who was caught in the Philippines in September 2011, and measured over 20 ft (6.17 m) before his death in 2013.

Melissa Hobson
Live Science Contributor

Melissa Hobson is a freelance writer who specializes in marine science, conservation and sustainability, and particularly loves writing about the bizarre behaviors of marine creatures. Melissa has worked for several marine conservation organizations where she soaked up their knowledge and passion for protecting the ocean. A certified Rescue Diver, she gets her scuba fix wherever possible but is too much of a wimp to dive in the UK these days so tends to stick to tropical waters. Her writing has also appeared in National Geographic, the Guardian, the Sunday Times, New Scientist, VICE and more.