Although there have been eye-catching individual reports -- such as that of Jonathan the Seychelles tortoise who turns 190 this year -- these were considered anecdotal and the issue had not been studied systematically, Penn State wildlife ecologist David Miller, a senior author of one of the papers, told AFP.

Researchers have "done a lot more comparative, really comprehensive work with birds and animals in the wild," he said, "but a lot of what we knew about amphibians and reptiles were from a species here, a species there."

For their paper, Miller and colleagues collected data from long-term field studies comprising 107 populations of 77 species in the wild, including turtles, amphibians, snakes, crocodilians and tortoises.

These all used a technique called "mark-recapture" in which a certain number of individuals are caught and tagged, then researchers follow them over the years to see if they find them again, deriving mortality estimates based on probabilities.

They also collected data on how many years the animals lived after achieving sexual maturity, and used statistical methods to produce aging rates, as well as longevity -- the age at which 95 percent of the population is dead.

"We found examples of negligible aging," explained biologist and lead investigator Beth Reinke of Northeastern Illinois University.

Though they had expected this to be true of turtles, it was also found in one species of each of the cold-blooded groups, including in frogs and toads and crocodilians.

"Negligible aging or senescence does not mean that they're immortal," she added. What it means is that there is a chance of dying, but it does not increase with age.

By contrast, among adult females in the US, the risk of dying in a year is about one in 2,500 at age 10, versus one in 24 at age 80.

The study was funded by the US National Institutes of Health which is interested in learning more about aging in ectotherms, or cold-blooded species, and applying them to humans, who are warm blooded.

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