World's largest captive croc turns 120, giving scientists 'serious knowledge on longevity'

The "big old gnarly crocodile" Cassius was kidnapped by scientists in 1984 because he was causing trouble on a cattle farm, and they transported him to Green Island, Australia, where he is still living today. The oldest captive crocodile in the world, Cassius, has celebrated his 120th birthday. Or at least that is the age that scientists estimate him to be.

The age of a crocodile cannot be inferred from its size. Crocodiles develop more slowly after reaching adulthood and finally stop growing altogether. When they are young, the biggest crocodiles often develop in irregular spurts, with males normally becoming larger than females.

Toody Scott, a crocodile keeper at Marineland Crocodile Park on Green Island who cares for Cassius, said to Live Science in an email, "There is no way to know Cassius' actual age as he was born in the wild and the age is just an estimate." It was "basically made up a few years ago" that the 5.5-meter (almost 18-foot) saltwater behemoth would turn 18; in addition, Scott noted that this time of year is "the wrong time of year for a crocodile to be born in northern Australia."

After the ranch owners reported they were losing animals, researchers managed to trap the crocodile on a cattle ranch southwest of Darwin, Australia, in 1984. Even at that time, Cassius was the largest crocodile ever captured alive in Australia and his age was believed to be between 30 and 80.

"He was 16 feet, 10 inches [5.13 m] with at least another 6 inches [15 centimeters] of tail missing and a bit of a snout missing," Grahame Webb, a crocodile researcher who assisted in the catch, said to ABC News. "Back then, he was a huge, old, nasty crocodile. Such large crocs are unusual.

The huge crocodile has lived on Green Island for 35 years and is still growing, which is "unusual for a big croc," according to Webb. It is also giving scientists "serious knowledge on longevity."

In the 1980s, Webb and his colleagues had a hard time catching Cassius. Researchers rarely got the chance to examine large crocodiles since they had been top targets for hunters. Adult crocodiles that made it through the hunting season "were very wary," according to Webb. (The Northern Territory of Australia outlawed crocodile hunting in 1971.) Now, according to his guardians, Cassius is everything but fearful. Scott told ABC News that the man "still has a lot of spark in him" and is "always up for an interaction." He's one of the liveliest crocodiles and is quite engaging, in contrast to other elderly reptiles who are often passive and indifferent.

According to the non-profit conservation group Oceana, saltwater crocodiles (Crocodylus porosus) often live for more than 70 years. Lolong, a 20.3-foot (6.17 m) long beast from the Philippines, was the longest saltwater crocodile ever to be caught.

Cassius, who has been in possession of the Guinness World Record for the largest captive crocodile since 2011, was far larger than the 15.4-foot-long (4.7 m) "salty" crocodile that was captured in Australia in 2018.