The demise of nature’s most vicious killer
AREN'T sharks scary enough? The biggest of them all - the megalodon - has been dead three million years. And, yes, if they were alive now, palaeontologists would say - get out of the water, now!
Huge. Insatiable. Unstoppable.
There's no doubt the megalodon was amazing.
Nobody is suggesting that the new action movie The Meg- which burst to the top of international box offices at the weekend - is even remotely scientifically accurate. It's a romping, stomping, frightening yarn.
But there are few things more fascinating than sharks.
As the biggest and most powerful of them all, megalodon holds a special place in the nightmares of many. And because its smaller cousins still roam the waters (if you call white pointers small), they seem so much more … real.
And that's the point.
There's actually a remote reality we may become a confused shark's lunch. But a Predator's prey, or an Alien's nest? Not so much.
So sharks, even extinct ones, have real fright power.
Carcharocles megalodon roamed the world's coasts for a very long time. Evidence shows them being around as far back as 16 million years ago, and as recently as 2.6 million years ago.
And, yes: they did have very big teeth.
That's what megalodon means (enormous tooth).
The biggest so far found measures some 18cm.
They're not exactly rare. Fossilised examples have been found across the world.
"Teeth are common around the globe in marine deposits," Flinders University Strategic Professor in Palaeontology John Long says, "but not common enough that at each site they are easy to find."
These teeth tend to be scattered, and not in context. This is compounded by them having been a favourite object for collectors over recent centuries.
"In all my years as a kid collecting fossilised shark teeth around Victorian sites (I had over 500 specimens), I only ever found one half of a large megalodon tooth," Professor Long says.
Apart from these teeth, and a few fossilised vertebrae, we don't have much of an idea of what they looked like.
Almost every movie, picture and model of a megalodon usually shows it as simply being a scaled-up great white.
That's not quite right.
Palaeontologists say it more closely resembled a mako shark with sleek, streamlined, even delicate lines.
And another common misconception is size.
Fossilised clues point to megalodons being up to 18 meters in length: not the 25m or so often claimed. And even 18m is on the freak side.
Calculations of an average megalodon over its 14 million year reign of terror come in at about 10m. Putting that in perspective: the biggest great white ever recorded was 6.4m.
Palaeontologist and science communicator Dr Paul Willis says he can't help but be sceptical of megalodon's size.
"All the estimates are pretty hairy because we don't find complete skeletons of megaldon, mostly just the teeth," he says.
"Many of those size estimates are based on scaling up the teeth from living sharks. It's often as crude as 'if the length of this living shark is 50 times the length of its biggest teeth, and I have a fossil tooth that is 10cm long, then it must have come from a shark 500cm long'. The reality is that an extinct shark known only from teeth could have been much larger (having comparatively small teeth) or much smaller (with relatively big teeth).
"We will probably never know."
Megalodon is often depicted as aggressively ramming its prey. It also has a tendency of tearing large speedboats in two.
Yes, say palaeontologists.
Sharks sometimes do physically crash into their prey. And there is fossil evidence megalodons used this tactic to stun their favourite meal - baleen whales.
And its jaws were the most powerful - ever.
"Its jaws were like the gates of hell - 6ft high by 4 feet wide (182cm x 121cm), lined with serrated teeth like steak knives, capable of slicing flesh off their prey with the greatest ease," Professor Long says.
Palaeontologists have modelled the bites of modern and ancient predators, ranging from the Tyrannosaurus rex and Liopleurodon through to sabre-toothed tigers and Australia's marsupial lions.
Pit them all against the megalodon, and they look puny.
Its enormous jaws exert some 18,000kg of force. No other animal, living or extinct, even comes close to it.
When it came to snack time, megalodon probably wouldn't have been interested in a lone surfer or swimmer. But a popular beach would be another matter.
"If there were many people in one area, it could get a real mouthful!" Professor Long quips.
You'd think megalodon would be safe at the top of the predatory tree.
It was. For several million years.
"It's fairly clear that megalodon was a top predator that fed off baleen whales - some whale vertebrate have meg teeth still stuck in them from head-on attacks," Professor Long says.
But, first, it had to grow and age to that size. A juvenile megalodon might have been a simple fish feeder with more slender teeth.
But, about nine million years ago, competition materialised.
Livyatan had arrived.
An ancestor of the modern sperm whale, Livyatan didn't have megalodon's powerful bite. It was possibly a little bigger. But its teeth definitely were.
At 30cm, these short ivory swords are the biggest teeth ever found.
Eventually, sharks as we know them - and pods of killer whales - also arrived on the scene. These were probably more efficient at tackling the same prey. And a cooperative group of killer whales may have been able to take on a lone-wolf megalodon if it needed to.
Now, megalodon's successors are themselves at risk.
Another top predator is killing sharks at the rate of 11,000 every hour.
THE ONE THAT GOT AWAY
Palaeontologists are quick to dismiss the prospect that megalodon somehow managed to avoid extinction.
From their fossils, we've learnt a lot about these ancient monsters of the deep.
What we know tells us that if they were around, we'd know about it.
Some palaeontologists argue the evidence point to megalodons only living in warm, shallow waters. They simply weren't designed to roam the open oceans, they say. They needed a constant supply of food, and their body and bone structure was not likely strong enough for the pressures of deep water.
So, no: The Meg's idea that megalaodons have been hiding in deep undersea trenches just doesn't fit. Instead, they were specialists at gorging on the fast food available along ancient shorelines.
And that's even if overweight bathers at Bondi Beach didn't prove tempting.
"If megs were out there today they certainly - 100 per cent - would have been found by now," Professor Long says. "Their only food source would be the large baleen whales. Through centuries of whaling they would have been found and exploited as a rich source of oil (their liver) and cartilage (for medicine). Like anything else valuable on this planet, we humans would have hunted them from way back, and thus we would certainly have historical record of them and specimens in our oldest museums by now."
Then there's what they are famous for: their teeth.
Modern sharks shed up to 20,000 each during their lifetimes. Megalodons possibly many more.
Beachcombers would have found teeth by now. And we're not talking fossils.
Why megalodon went extinct is not known.
But there are a few ideas.
One is that their primary prey - baleen whales - were shaped by 14 million years of being hunted. They became bigger. Harder to stun and take down.
Professor Long says the baleens may also have simply found a new hide-out:
"Palaeontology teaches us that even the biggest, scariest creatures had their weaknesses and eventually succumb to extinction," he says. "Why might megalodon have gone extinct is a very good question: their prey went to areas they couldn't, like colder Antarctic waters. I think baleen whales began migrating to Antarctica to feed and megalodon's couldn't live down there as it's too cold."
A recent study also indicates megalodon may have been the victim of a previously unknown nautical mass-extinction event. About the time it disappeared, the oceans lost some 36 per cent of their various life forms. Changing sea levels appear to have caused the era's shallow coastal waters to shrink, reducing megalodon's hunting habitat to dry up.
UNDER THE MICROSCOPE
Mega-shark discoveries are still being made. Earlier this month, the Museum of Victoria announced its palaeontologists had worked with a member of the public to uncover teeth from the prehistoric Carcharocles angustidens.
It's not a megalodon. It's older.
"I was walking along the beach looking for fossils, turned and saw this shining glint in a boulder and saw a quarter of the tooth exposed. I was immediately excited, it was just perfect and I knew it was an important find that needed to be shared with people," says Philip Mullaly of his discovery on Victoria's Surf Coast.
The 25-million-year-old tooth was 7cm long. The shark it came from could grow longer than 9m, twice the size of modern great whites.
Only three grouped examples of Carcharocles angustid (Great Jagged Narrow-Toothed Shark) have been found.
Dr Erich Fitzgerald, Senior Curator of Vertebrate Palaeontology at Museums Victoria, says he hoped there may yet be more fossils to be found in the rock at Jan Juc. So, in December and January, he led a team of palaeontologists and volunteers to dig out the boulder.
More than 40 teeth were recovered. But no fossilised bones were found.
Among the Carcharocles angustidens teeth were those of another shark, the Sixgill (Hexanchus).
Museums Victoria palaeontologist Tim Ziegler said these teeth appear to have come from several individuals and were likely detached as they feasted on the huge carcass.
"The teeth of the sixgill shark work like a crosscut saw, and tore into the Carcharocles angustidens like loggers felling a tree. The stench of blood and decaying flesh would have drawn scavengers from far around.
"Sixgill sharks still live off the Victorian coast today, where they live off the remains of whales and other animals. This find suggests they have performed that lifestyle here for tens of millions of years."
But not so Carcharocles angustidens. Nor Carcharocles megalodon.
"We palaeontologists know that we can never find everything that ever once existed," Professor Long says. "But its unlikely something bigger in the shark world than megalodon ever existed or at least we would have cluses about it - like a tooth or giant scale or something. Frankly nothing bigger than megalodon could have existed as there was likely not enough food to support it. It's the same argument why lions are top of the food chain in Africa today."
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