When we asked people – what the most indestructible
animal to have ever lived on Earth was, we were hit with a barrage of different suggestions.
Everything from dinosaurs and reptiles to invertebrates and fish were thrown into
the ring, but what’s the actual answer?
Well if you Google – ‘most indestructible animal’,
this little critter pops up with headlines claiming
that they can survive incredible levels of radiation,
live at the bottom of the ocean, or in the vacuum of space. Now, I don’t want to say Google is wrong,
but it’s definitely not right either. So what is the most indestructible animal
to have ever lived on Planet Earth? Let’s unpick this tangled web of Earth’s
greatest survivors! I’m Stu, this is Debunked, and we’re here to sort the Truths from the Myths, and the Facts from the Misconceptions. With so many pretenders for the crown of – most
indestructible animal, let’s start, with some of the oldest candidates.
I’m talking seriously old, prehistoric in fact. Going all the way back to the Cretaceous Period; you might expect fan-favourite dinosaurs like
the T-Rex to be pretty hardy. Problem is, these carnivorous eating machines
weren’t really built for defense, they were built to kill,
which means evolution didn’t really equip them with much in the way of defence mechanisms.
In fact their only real defense was also their weapon – their bone crunching jaws. Instead it turns out that the most indestructible
dinosaurs weren’t the ones trying to kill each other
but rather those critters who just wanted to eat their greens in peace. One such species of dinosaur was the Ankylosaur,
which might easily be mistaken for a tank. The Euoplocephalus is probably the best example
of this genus, covered with thick spines across its back
and sides of its head for protection. Even its eyelids were armoured. Its skull was so thick, that an attack from
a raptor like a Deinonychus would leave barely a scratch, and it could
withstand a bite from a Tyrannosaurus Rex! While some dino experts even believe that
their armour could stop small gun fire. And, Fossils show that if one of these bad
asses swung, well, its ass, then its club-like tail, could break the legs
of a T-Rex. Now, obviously, Ankylosaurs aren’t invincible,
otherwise they’d still be roaming around today. In fact, even back when they were around they
occasionally ran into difficulty. You see, they had one fundamental weakness. If something managed to flip it over onto
its back, its soft armour-free belly would be exposed
and that often meant gameover for an Ankylosaur. Think of it like a giant, sad turtle. But according to Paleontologist Kenneth Carpenter
this wouldn’t have been easy for a predator to achieve. “IT WOULD BE DIFFICULT EVEN WITHOUT THE ARMOR
TO GET A PURCHASE ON IT BECAUSE ITS BODY IS RELATIVELY FLAT.” Combine this with their incredible defenses
and most predators just left them alone in favour of easier prey.
Can’t say I blame them, eating a tank wouldn’t be easy. But I’m afraid it doesn’t matter if the
Euoplocephalus was the most indestructible dinosaur, because around 66 million years
ago, it’s fair to say there was a little incident. And by little incident, I am of course, referring
to that time a huge meteorite slammed into Earth, causing the mass extinction of the
dinosaurs and 75% of all species. That still leaves an awful lot of survivors
though, so surely some of them must have a claim to
the title of most indestructible animal? How about the humble crocodile? Other than
size, this modern-day living fossil hasn’t really evolved in around 200 million years
– fitting the definition of ‘if it ain’t broke don’t fix it’.
So how did it survive a near apocalypse. Well, to start with, the Cretaceous–Tertiary
Extinction, as it’s known, wasn’t an overnight event,
it took place over a few hundred to a few thousand years. So while crocs have an impressive armoured
skin similar to the late Ankylosaurs, it wasn’t defense mechanisms like this,
that were key to its survival. The species that survived were those that
were best adapted to the aftermath and not necessarily the initial event.
Blast a crocodile with an asteroid and you’ll end up with a dead crocodile.
What worked in their favour, however, was their habitat. While this extinction event wiped out land-dwelling
dinosaurs, pterosaurs and the majority of marine reptiles, crocs got off relatively
lightly. Living between land and freshwater lakes or
salt water estuaries, allowed them to avoid the worst hit environments
on land and in saltwater oceans. Crocs are also cold blooded, allowing them
to slow their metabolism and survive when food was in short supply,
which it most definitely was in the post-apocalyptic world following the KT extinction.
Plus, most paleontologists now consider dinosaurs to be
at the warm blooded end of the spectrum, and when food became scarce, so did they.
These factors are believed to have contributed heavily to the survival of the crocodilian
lineage. While we’re right to be impressed with how
crocodiles survived when lots of other creatures died out,
they weren’t exactly the only species to make it through those dark times.
There were plenty of other species that had the ability to endure those trying conditions.
I mean, we wouldn’t be here today without the survival our early primate relatives.
In fact a whole host of animals you know today have barely evolved since they lived alongside
the dinosaurs. There’s the Duck Billed Platypus, Sharks,
and Green Sea Turtles, but one little critter, has been around long
before all of these aquatic greats. Crawling along the present day seafloor we’ll
find the Horseshoe Crab. This humble animal might not look like much,
but they’ve withstood 3 of the planets mass extinctions, and date back 450 millions years!
Having lived through some of the most dramatic environmental changes – Earth has ever seen,
they’re an incredibly adaptable species. They can feed on nearly any organic matter,
have an armoured shell that can heal over pretty much any wound
and they can survive with very low levels of oxygen. There’s just one problem. Us.
Yep, despite surviving nearly half a billion years, in 2016
the International Union for the Conservation of Nature put these guys on the vulnerable
list. Aside from habitat loss, these creatures are harvested by the pharmaceutical industry
for their bacteria indicating-blood. The net result has been a steady decline in their
population. As unfortunate as that is, we can’t exactly
have the most indestructible animal sitting on a vulnerable list.
With humans now being the biggest threat to these epic survivors,
let’s bring another destructive man-made force in to the mix… nuclear bombs. Surely anything that can get through a nuclear
blast must have a shot at the title of most indestructible
animal. Now, I’d imagine the creature that springs
to mind is the formidable little cockroach. The idea that they can handle a nuclear explosion
has been around since reports circulated that these mini-beasts were the only survivors
found in the rubble following the Hiroshima and Nagasaki atomic bombs. But the fact is,
cockroaches can’t withstand the intense energy released by a nuclear explosion.
Their presence after the atomic bombs was due to their ability to withstand extreme
levels of radiation. As a point of reference the aforementioned
atomic bombs released radiation levels of around 100 Grays each, roaches can withstand
up to 1,000 Grays! Why are these little guys so resilient to
radiation? Well it’s all down to their their body’s
simple design and slow cell cycle. You see, cells are particularly susceptible
to radiation when the’re dividing and renewing. The human cell cycle is fairly constant and
takes place every 24 hours. Cockroaches, comparatively, change once a
week and it takes 48 hours, so their window of vulnerability is much narrower. These guys won’t be walking away from the
HYPOCENTER of a nuclear bomb and, to be honest, no animal can, but they CAN hold their own
post-nuke. They’ve also got a pretty good track record
of survival, having evolved around 200 million years ago, living alongside the Crocodile
and surviving the KT extinction. Look, so far, I think we’ve been too easy
on the animal kingdom. We need to up the stakes. And really ramp up the level of destruction.
What could possibly survive a huge asteroid hitting the planet, throwing billions of tons
of rock into the air whilst simultaneously a series of the biggest volcanic eruptions
take place, filling the atmosphere with ash, blocking out the Sun?
Actually, that’s not enough. Let’s detonate a whole bunch of nuclear bombs for good measure.
Now we should have the biggest mass extinction ever to occur on our planet.
And what animal could get through all that? Well, somewhere amongst all the rubble and
fallout of our once thriving planet, you’ll find those little fellas we mentioned
at the start, a creature known as a Tardigrade. These guys have been on Earth for around 520
million years, and can be found in pretty much every environment
imaginable. They can survive in the vacuum of space, withstand the pressures of the deepest
oceans, go without food or water for 30-40 years, be frozen at -328°F (-200°C) or be
heated to more than 300°F (149°C). They can even cope with radiation levels up
to 6,000 grays, a human for comparison would be lucky to walk away from 5 grays.
There’s just one problem. No, for once, it’s not us pesky humans. It’s more to do with
how we’ve classed Tardigrades. Now, take this little Tardigrade, it would
have died during the apocalypse. You see Tardigrades, as they exist from day
to day, aren’t very indestructible at all, in fact you could kill them pretty easily
if you catch them going about their daily business.
To become ‘indestructible’ these micro-animals put themselves in to a protective state called
cryptobiosis, where they tuck their little legs in and excrete 97% of the moisture from
their body. Like this they become what’s known as a
Tun. Tree ha lowce
They produce a form of antifreeze called ‘glycerol’ and convert jelly-like proteins into glassy
cocoons that protect all parts of the Tardigrade that are sensitive to dehydration.
As a Tun, the Tardigrade reduces its metabolism by 99.99%
and then simply waits for a more habitable environment to become available.
However, here comes the biggest misconception about these cuddly, little, pig-faced creatures;
they can’t all survive all extreme environments. The headlines that made them so popular
were based on a study by theoretical physicists who lumped all the Tardigrades
and their abilities together, when, in fact, there are around 1,250 species.
They usually have names like ‘Water Bear’ and ‘Moss Piglets’, which relate to the
environments that best suit them. It is true that they can survive in the most
extreme of environments, but the deep ocean-dwelling Tardigrades who
can survive pressures of 6,000 atmospheres, (that’s nearly six times the pressure of
water in the deepest ocean trench) may not be able to withstand the high temperatures
and radiation levels that the landlubbers can, and vice versa. William R Miller an expert on Tardigrades
explains that merging all of their abilities together simply doesn’t work.
“[it’s like saying] a sixgill shark at the bottom of the ocean is the same as a snow
leopard in Siberia.” When approaching it from a biological point
of view lumping them all in as one is just unfair
when trying to establish the most indestructible animal, and in fact Miller points out how
unjust their popularized indestructible status is:
“they’re quite easily murdered,” “We kill thousands of them every day.” In an apocalyptic sense, however, it would
take the world’s oceans to boil away before all these tough little creatures would be
wiped out, so in that sense they deserve their indestructible credentials. Problem is, in real-life scenarios you could
quite easily just squish them, and ‘ferocious’ predators like snails routinely
do, as they chomp down on them for a tasty meal. *NOTE: Although they’d still be resilient
to getting squashed between your fingers because they’re so small they’d probably just
hide in the irregularities of your fingerprints. Right, while we can agree that Tardigrades
are incredibly resilient, they can die, but what about animals that like to laugh
death in the face. Ones that have been squished and chopped up
but, in true Terminator-style, they regenerate back to life. Surely that
is what indestructible is really about? And incredibly there are a lot of animals
out there with regenerative powers, from salamanders regrowing their tails to
sea cucumbers regrowing their organs! When we’re talking about regenerative animals
however, I’m afraid it pretty much excludes mammals,
as our regenerative powers tend to be far more limited than that of invertebrates
and evolutionarily primitive vertebrates. Okay, let’s start with probably the cutest
of the candidates so far, the Axolotl. This little fella can regrow one of the most
important organs of all! Not only can they regenerate a missing limb,
tail or even their lower jaw, but also parts of their brain and heart! “If they’re paralyzed in the back they
can recover the functions of their legs … They can make all new neurons and new connections
that allow them to use their legs again, which is really one of the most incredible examples
of recovery.” But as incredible as this is, that’s still
only regenerating parts of the body. Now I’m sure I’m not the only one who heard
the rumour at school about earthworms. You know the theory. If you chop one in two,
it will generate into 2 living earthworms! But, here’s the bad news, this is not true.
The head end may survive and regrow a stunted tail but once the nerve endings have stopped
it wriggling around, you’ll most likely just end up with two halves of a dead earthworm.
There is however, distant relatives known as Planarian Flatworms
and scientists are describing these incredible creatures as having Regenerative Superpowers!
Research has looked at a range of these species since 1901,
but it’s only today that scientists are beginning to understand its true abilities.
This creature can regrow its entire head but, not only that, it retains learned information
as though it had never been decapitated. And it doesn’t stop there. This incredible little worm can regenerate
from as little as 10,000 cells, which is around only 1⁄ 279th of a Planarian Flatworm’s
body. How do they do it? Well it’s all down to
the fact that their Adult Stem Cells are “pluripotent” – meaning they can potentially become any
cell in the body. With other animals, once they hit adulthood
their stem cells become limited and can only produce cells for specific purposes – blood
stem cells produce blood cells, for example, but they can’t produce skin cells.
With Planarians, special adult stem cells called Neoblasts
can produce all the different types of cells that make up a complete Planarian.
Essentially you could chop one worm in to 279 pieces and so long as each part contained
one of the special Neoblast cells then you’d have 279 new worms within about 2 weeks.
And this process isn’t limited to one round of regeneration,
these creatures are, in a way, immortal. Seems impossible?
But in order to heal or regenerate, Stem Cells divide.
In other animals, as this process is repeated, the cells start to decay and show signs of
ageing. When they age, stem cells can no longer divide
and so can’t replace the exhausted cells in our bodies.
However, Stem Cells in Planarian Flatworms don’t stop dividing and so avoid the ageing
process. What does kill these little guys however is
radiation, but so long as there remained enough healthy
cells in the worm they could recover. In fact, scientists at MIT have discovered
that by transplanting one Neoblast cell called a Clonogenic Neoblast from a healthy worm
to a worm that received a lethal dose of radiation, then that one cell will regenerate the entire
worm. So with all these incredible candidates with
amazing abilities, which animal comes out on top?
Well, to answer this fairly you need to split them into categories.
If a nuclear apocalypse or the ultimate planet-wide extinction fell upon us
then Tardigrades would inherit the Earth. (You-Oh-Plo-ceph-alus)
In the more day-to-day scenario of fighting off predators
then the Euoplocephalus would live to fight another day.
But, if a bizarre situation occurred where you were chopped up, stamped on and smushed
then the Planarian Flatworm would be the only creature
eventually wriggling away to live another day.