How old is an Aldabra giant tortoise? Records, rings and guesses

A tortoise named Jonathan lives in a paddock at Plantation House on St Helena, a remote island in the South Atlantic. He arrived in 1882 as a fully grown animal, and news reports in October 2026 gave his age as about 194 years. Nobody has his birth certificate. The number is an estimate, and the scientists who study him say so. He is, in short, a very old tortoise with a very loose paper trail.

That is the real story of how long turtles and tortoises live: the headline numbers are huge, and the proof is thin. This article looks at the Aldabra giant tortoise (Aldabrachelys gigantea) through that lens. It covers what the records say, why shell rings make a shaky calendar, what a 2022 study found about slow aging in turtles, and why the species’ conservation category is something we could not confirm.

Meet the Aldabra giant tortoise

The Smithsonian’s National Zoo places the species on Aldabra Island, one of the Seychelles, in the Indian Ocean. A NASA image caption puts the atoll more than 400 kilometers (about 250 miles) northwest of Madagascar. The Zoo’s own page says the island lies northeast of Madagascar, so the two disagree on direction, and we use NASA’s. The Zoo says Aldabra tortoises were apparently introduced to Mauritius and Réunion.

Look at that last row. One page, three numbers. The Zoo says it is believed that tortoises are the longest lived of all animals, but adds that this is hard to prove, because records were poorly kept and researchers have outlived their subjects. Press coverage of Jonathan uses a narrower label, the world’s oldest known land animal.

Males can weigh up to 550 pounds, so this article is not a guide to approaching or handling these animals. Wild and zoo tortoises are best watched from a distance.

Ways to read a tortoise’s age

There is no tortoise odometer. Scientists lean on three imperfect clues, and the table shows what each one gives and where it breaks.

Rings first. A news report on Jonathan says growth rings on the shell plates can estimate a young tortoise’s age, but adults are harder. A 2015 study in Acta Herpetologica tested the idea on a different species, the spur-thighed tortoise (Testudo graeca), in southeastern Iberia. The team followed 156 recaptured animals from 2004 to 2010. Only 57.4% showed one ring per year, and the rings tended to undercount, missing about one year in every three or four. The authors concluded that the one-ring-per-year assumption is too simplistic. We found no study among our sources that tests ring counts on Aldabra tortoises, so this is a warning from a relative, not a measurement of this species.

Records next. Records are better when they exist. The Zoo’s page calls its own Aldabra tortoises about 80 years old in one section, and says that is a guess because they arrived as adults. In another section it estimates two of them, Chyna and Rulon, at between 80 and 100. Even a single zoo page gives two answers.

Jonathan: a 194-year estimate

Jonathan is described in coverage as the world’s oldest known living land animal. He was brought to St Helena in 1882 as a gift to the governor and was fully grown, likely from Aldabra Atoll or the Granitic Seychelles, according to the KSL report. Counting back from 194 years puts his hatching around 1832, which one outlet states directly. Benjamin Vaisvil, a co-lead author of the 2026 study, said Jonathan has the most documentary evidence of any Aldabra tortoise claimed to be this old, and also that historical records are unreliable. Both can be true. He has better paperwork than his rivals, and the paperwork is still thin.

A study reported on October 7, 2026 in Science Advances sequenced his genome and looked at his epigenome. That word means the chemical tags that switch genes on and off. Because a blood draw was not permitted, the team used cheek scrapes and saliva, and compared him with four other Aldabra tortoises ranging from juveniles to older adults. The reported findings:

• He has 287 genes with variants not seen in the comparison tortoises. One outlet describes the same result as 287 unique variants, so the exact count depends on what is being counted.
• In certain gene-regulating regions, his methylation entropy, a measure of how disordered the chemical tags are, was lower than in every tortoise studied except a 5-year-old juvenile.
• The authors hypothesize that a low-disorder state helps important genes work accurately.

The caveats are large. Vaisvil said the team cannot say for certain that this is the reason for his long life. The study has one exceptionally old tortoise and four comparisons, so it is unclear whether his traits are unusual or shared by long-lived tortoises. And the report notes that he lives on a tropical island with a carefully managed diet, which may matter too. This was a study of aging, not a way to date him from DNA.

Why turtles seem to age slowly

Zoom out from one tortoise. In 2022, a team of 114 scientists with first author Beth Reinke published a study in Science using wild data from 107 populations of 77 species of reptiles and amphibians, according to a Flinders University news report on the study. Turtles, crocodilians and salamanders had particularly low aging rates and long lifespans for their size. The turtle results gave the strongest support to the protective phenotypes idea: traits such as shells, armor, spines or venom may slow aging and extend life.

The study also reported negligible aging. In Reinke’s words in the Flinders report, it means the likelihood of dying does not change with age once animals are past reproduction. If the yearly risk is 1% at age 10, it is still 1% at age 100. The page we read does not say whether Aldabra tortoises were among the species studied, so this is the backdrop, not a result for them. Other turtles come with their own lifespan figures and their own caveats: see the Eastern box turtle, Loggerhead sea turtle and Green sea turtle articles.

What this looks like in practice

When a headline announces a record-old tortoise, a short checklist helps you judge it.

• Is there a written hatch date, or only an arrival date?
• Was the animal fully grown when it arrived? If so, the age is a guess about the years before.
• Does the claim rest on shell rings? If so, treat it as rough.
• Is the number given as “about” or “estimated,” or as exact?
• Do other sources agree, or does one page give several different numbers?

Jonathan scores well on some of these and badly on others, which is why the careful coverage says “estimate.”

Common mistakes and myths about tortoise age

Myth: count the rings to get the age. The spur-thighed tortoise study found one ring per year in only 57.4% of animals and a tendency to undercount.

Mix-up: a zoo’s stated age is a documented age. The Smithsonian’s National Zoo calls its Aldabra tortoises about 80 and says that is a guess, because they arrived as adults. Another section of the same page puts two of them at 80 to 100.

Mix-up: negligible aging means immortal. It means the risk of dying does not rise with age after reproduction. The risk is still there every year.

Myth: Jonathan’s genes are the secret to a long life. The researchers say they cannot be certain, and the study has one very old tortoise plus four comparisons.

Mix-up: every number on a page is the same fact. The Zoo’s own page gives “more than 100,” “up to 150” and “over 150” for the species.

Conservation status

We could not confirm the current IUCN category on the day this article was written. GBIF, the Global Biodiversity Information Facility, is the public database we use to read IUCN Red List categories, and it returned no IUCN record under this name when we looked on November 9, 2026. That is a gap in the data, not a rating, so it does not mean the species was judged safe or at risk. Where this site shows a status label for the species, it is marked pending. Read that as “not confirmed,” not as an IUCN decision.

The sources do describe pressures and a recovery. The Smithsonian’s National Zoo says the original population included at least 18 species and that all but the Aldabra tortoise were driven to extinction, by sailors’ hunting and introduced predators. It also says the species was one of the first to be protected. A report on a 2026 survey by the Seychelles Islands Foundation and the University of Exeter says heavy exploitation in the 19th century cut the island population to fewer than 1,000, that the atoll became a strict nature reserve in 1981 and a World Heritage site a year later, and that counts from 2018 to 2022 point to about 180,000 tortoises, compared with about 100,000 in the late 1990s. The report names longer, more frequent droughts and rising seas as threats, and notes that dense vegetation makes counting hard. We have not opened the survey itself and do not know whether the two counts used the same methods, so we call the rise reported, not a confirmed trend.

The official category lives on the IUCN Red List at iucnredlist.org, and that is the page to check before you quote one.