Henry the giant crocodile, who has sired 10,000 babies, celebrates 124th birthday

Henry the world's oldest known crocodile is celebrating his 124^th birthday at a conservation center in South Africa today (Dec. 16).

The Nile crocodile (Crocodylus niloticus) has lived at the Crocworld Conservation Centre in Scottburgh, South Africa since 1985. He was originally captured in the Okavango Delta in Botswana in 1903.

Henry, now a vigorous senior resident at the Crocworld Conservation Center, is said to have fathered over 10,000 offspring with numerous partners since he arrived there almost 40 years ago.

While his exact birthday is unknown, Crocworld representatives estimate he was born around 1900 and celebrate his birthday on Dec. 16 each year.

"He's clearly old," Steven Austad, a biologist studying animal aging at the University of Alabama, told Live Science. "Whether he's 100 or 130, we don't really know. An age of 124 is not inconceivable for a crocodile."

Reptiles are known for their impressive longevity. Usually, a good rule of thumb for an animal's lifespan is to look at their size — smaller animals typically live shorter lives because they have higher metabolisms, meaning that they burn more energy and age more rapidly as a result.

But even compared with other animals of roughly the same size, reptiles tend to be much longer-lived. Austad said that being cold-blooded allows them to conserve energy by relying on external heat sources to regulate their body temperature.

"A crocodile that was the same size as a person would only need to eat about 4% as much as a mammal like us," he said.

Crocodiles, like some other reptile species, continue growing with age. Henry weighs 1,540 pounds (700 kilograms) and measures 16.4 feet (5 metres), which is on the larger end for his kind. Their huge size keeps them safe from potential predators in their old age.

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Henry's life in captivity has also likely helped him reach such an old age, keeping him well fed and safe from accidents and disease.

"Animals that for whatever reason, happen to live in a safe environment, tend to live longer," Austad said.

Reptiles, compared to many other vertebrates, also do not show signs of noticeable decline in physiological abilities as they age.

Other biological traits may also contribute to Henry's longevity. Theories posit that proteins found in the blood of Nile crocodiles may have antibacterial properties and help them fight off infections and disease. Similarly, some researchers claim that their gut microbiomes could contribute to their robust immune system.

Studying the aging of crocodiles like Henry can be challenging since researchers have to catch them in their infancy, tag them, then follow them throughout their lives. Because of this, many theories around the secrets to reptilian aging are speculative, like the role of their immune system and microbiome, Austad said. "[Crocodiles] live longer than the careers of the scientist studying them," he said.