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I was watching a talk by Michio Kaku and he mentioned that crocodiles (or possibly alligators, I forget offhand) don't actually age -- they can die, but they essentially go through no aging process beyond adulthood

Can anyone link me any sort of detailed information on this?

Amory
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1 Answers1

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Well, this needs to be broken down into two parts. Do Crocodilians age (undergo senescence), and are Crocodilians immortal (will only die of external causes)?

Are Crocodilians immortal? - No. They appear to live about as long as humans before they die.

Measuring crocodile age is unreliable, although several techniques are used to derive a reasonable guess. The most common method is to measure lamellar growth rings in bones and teeth—each ring corresponds to a change in growth rate which typically occurs once a year between dry and wet seasons. Bearing these inaccuracies in mind, the oldest crocodilians appear to be the largest species. C. porosus is estimated to live around 70 years on average, with limited evidence of some individuals exceeding 100 years. One of the oldest crocodiles recorded died in a zoo in Russia. A male freshwater crocodile at the Australia Zoo is estimated to be 130 years old. He was rescued from the wild by Bob Irwin and Steve Irwin after being shot twice by hunters. As a result of the shootings, this crocodile (known affectionately as "Mr. Freshy") has lost his right eye.

Do Crocodilians undergo senescence (show signs of aging)? Well, if this study from "Gerontology" written by Patnaik BK in 1994 is to believed... Maybe not.

Evidences and mechanisms of rapid or negligible senescence in reptiles are still fragmentary and unclear... neither the increase in mortality rate and accumulation of lipofuscin nor the reproductive senility have been shown conclusively in ageing reptile populations.

So, while Crocodiles and Alligators (both Crocodilians) definitely have a finite lifespan, because they just continue to grow it's hard to tell how long they have left until the day they die.

MCM
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  • Good answer, but I strongly disagree with the definition of immortal as "will only die of external cause". Immortal means that it does not die, whatever the cause. If they only died of extrenal causes it would just mean they they could not die of old age. – nico Nov 12 '12 at 17:12
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    @nico - Which is precisely why I defined it in my answer. Talk to any Highlander fans, and Immortal means you can only die by having your head cut off - which also differs from your definition. :) – MCM Nov 12 '12 at 17:39
  • Let's stick to the definition of the dictionary which is (OED): "Not mortal; not liable or subject to death; deathless, undying; living for ever. In wider sense: Not liable to perish or decay; everlasting, imperishable, unfading, incorruptible.". Immortal is just the wrong word to use in this context. – nico Nov 12 '12 at 20:46
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    Similarly in Tolkein, elves are immortal but can die in battle or from heartbreak. Both uses of "immortal" are common, and so MCM did the right thing by clarifying which way he was using it. – Noah Snyder Nov 13 '12 at 20:26
  • @nico I don't think theres a need to be that pedantic about the definitions if they are defined in the question and in general. After all Turritopsis nutricula is called "The Immortal Jellyfish" and I'm pretty sure they aren't bullet proof. – James Aug 01 '13 at 03:55
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    @Good Gravy: [un]fortunately in biology definitions are extremely important. In any case let's stick to the question, which states that they die, i.e. they are not immortal. The question is whether they do not age which is a completely different thing biologically speaking. For instance, do crocodiles show signs of cellular aging, like telomeres shortening? Sorry but if we want to talk about elves or Highlanders I am very happy to do it, just not on a biology Q&A site. As I said before, I have nothing against MCM answer, just pointing out that the term immortal is misplaced here. – nico Aug 01 '13 at 07:04
  • I would like to point out that, according to dictionary.com at least, immortality is also definable "not liable to perish or decay." More importantly, I have had several discussions about immortality with my colleagues (we study aging and lifespan) where we take immortality to mean "not dying of intrinsic causes" i.e. not dying of old age. This is because defining immortality as being immune to extrinsic causes (predation, environmental change, asteroid collisions etc.) is a highly improbable scenario due to the innumerable possible extrinsic causes. – rg255 Aug 01 '13 at 14:53
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    Other than external causes, what are the causes for a crocodile to die? Does an increase of aging increase the chances of organ failure? – brillout Nov 30 '13 at 21:55
  • I believe that to define something as immortal as being limited to total imperviousness to death is to reduce that term to being meaningless. Immortality is meant only to mean an imperviousness to death from old age. If you drop a vampire on the surface of the sun, they will cease to exist, but that doesn't mean that they're not immortal. – Yevgeny Simkin Dec 30 '13 at 19:10