There's been a lot written about Carcharodon megalodon recently, so I thought I'd take this opportunity to quickly go through some of the major points of this awesome shark.

What's in a name?

Let's start with the simple stuff. Is it Carcharodon Megalodon or Carcharias Megalodon ?

While many marine biologists prefer the name Carcharodon, this name's only really accurate if the “Meg” is related to the great white shark ( Carcharodon carcharias ). Recent research suggests Meg's are actually the descendant of the 55 M.Y.O Otodus obliquus (of which there are now surviving members) , while the great white evolved from the similarly aged Isurus hastalis , making its nearest relative the Mako sharks. If this new hypothesis is true (which it looks like it is), then both sharks aren't that closely related, and any similarity they have is due to their similar diets (triangular teeth with serrated edges are perfect for mammal munching).

This means Carcharias Megalodon is the more correct, but damn if Carcharodon Megalodon doesn't sound cooler!

Just how big was it?

Well, now we're getting into a grey area. The original length for the shark of 30m (100ft) was based on the largest tooth sizes that were then placed into a hypothesized jaw. The problem with that was sharks don't have uniform sized teeth running through their mouth. The middle ones are the largest, but then they slowly taper away as they move towards the edges. Basing a mouth on just the same sized tooth will give you an enormous animal that simply never would have existed!

Instead if we take Meg teeth and build a jaw based on a great white, we get a body size of around 12 to 16m (40 to 50 ft), which is much more likely; yet still makes a shark nearly three times larger thn the great white.

As for its weight? Well at 6m a great white is around 2 tonnes, but you can't simply scale a Meg up at the same rate due to its size. The larger an animal gets, its mass increase even more as they need more muscle and bone mass to move the body, making them thicker and heavier. For instance at roughly 3 times the length, you'd think a Meg would weigh around 6 tonnes, instead it would have been more like thirty as everything increased (width, girth, height etc), not just its length. This makes a Megalodon slightly smaller than a humpback whale, a mammal that would definately have been on the menu for this monster shark.

Are they extinct?

Though the idea that these huge sharks are roving the world's oceans is often an attractive one, there's just no proof to support it. Recent, inaccurate reports of shark teeth being dredged from the ocean floor seems to be more of a misunderstanding than a direct attempt to fool people. For starters, these teeth are huge and tough and easily survive being eroded from one area and deposited in another, so if teeth are found in sediments that were laid down, say, 15 000 Y.A, it doesn't mean that's when the shark lost them. Another problem is these teeth have often been cleaned by the time people get to ‘study' them; so much of the surrounding material that had coated the teeth has already been removed. This is a real problem as these teeth are often perfect (remember they're extremely tough) so they often look brand new. To show you how well some of these teeth survive, many 55 M.Y.O fossil shark teeth are just as sharp as fresh ones!

Today there's still large sharks swimming the worlds oceans, with many as large as a Meg so these could often be mistaken for Carcharodons. Personally, I think only an expert diver would be able to keep their cool long enough when a basking or whale shark swam into their vision. Most of us would take a look, see the typical shark shape, and already be on the beach before we've had time to even mouth the word ‘shark'!

One of these giant modern species, the “megamouth' shark, is often used to prove the possibility of Megs being with us today. The first megamouth wasn't found until the 1970's, so people often ask, if one species of enormous shark could survive until quite recently without being seen, why not another?

It's a fair enough point…except…we are talking about two completely different animals here. By their very nature, megamouths are shy, solitary creatures, slowly ambling the world's oceans, often at great depths, constantly feeding on shoals of plankton. The equally large Meg, however, was another matter. Its size and dentition tell us this was no sardine-eating shark. To power such an enormous creature, Megs would have been voracious killers of the largest, most nutritious prey swimming their ocean…. whales.

Ask yourself, do we find a lot of half eaten whales floating in the worlds oceans? With the sudden loss of whales (thanks to human over hunting), have sharks started attacking other creatures in greater numbers? Lets face it, 15m sharks patrolling beaches where humans and seals congregate have never been reported and, it would only take one of these hungry guys to prove the existence of modern Megs.

It just doesn't happen so I'm sorry to say guys; they're just not out there!

I should point out this isn't to say no one's ever reported huge sharks patrolling their beaches, its just that estimating size at sea is a trickly thing. There have been a few reports, however, that make you think!

The best as far as I'm concerned comes from 1918 when Port Stephens fishermen refused to go to sea when an immense shark started devouring their crayfish pots (that were around 1m in diameter). This shark scared them so much they refused to go to sea for sometime, losing a substantial amount of money in doing so. I point this specific instance out because fishermen know their area (as well as fish you'd have to say), so when several claimed they saw an unusually large shark, you'd have to believe them.

This story does fall down (and proves my scepticism) when you look at the dimensions these fishermen claimed the shark was, with some saying 30m, while others suggesting it was 90m long!

Another interesting story is of an Australian Cutter called the Rachel Cohen that, after having run aground, had its hull inspected (in march 1954) at an Adelaide dry-dock for damage. Upon inspection a shark bite was discovered around the propeller that was far too large for any modern ‘toothy' shark to make. The tooth marks were about 10cm wide, while the largest great white has teeth only measuring 6cm.

The captain of the Rachel Cohen recalled a shudder on the ship as they were passing Indonesia , which he'd believed to be from hitting a floating tree trunk.

The big problem with this story is that there's no actual proof of this report, not a photo or true measurement of the teeth marks. Another problem is the only ship called the Rachel Cohen I could find was destroyed by fire in Darwin in 1924. This ship was famous for travelling around Australia and was even used (unsuccessfully) to take emergency supplies to Mawsons doomed expedition in Antarctica . This is a pretty famous ship that, surely, someone would have noted A. had survived far past when it was supposed to have burnt down and B. had been bitten by a huge shark at some time during its career.

Why did it go extinct?

Simply put, large animals are rare. An environment that might support thousands of house cats may only support a handful of lions, and the sea is no different. Megalodon was an enormous shark with an enormous appetite that would never have been numerous, even at its height. Yet within this ecosystem things were changing: such as the appearance of new, faster, more cunning predators, predators with an ingrained hatred of sharks!

Orcas, the killer whale ( Orcinus orca ), are tremendous predators of the deep, with the ability to hunt in packs like wolves. Recent footage has been collected of an Orca attacking and despatching a great white with seeming ease, yet as pups, the reverse is often true. Dolphins, seals and young Orcas make up the diet of the warm-blooded great white, and if its one thing we mammals don't do, it's forget! If you recall a time when giant sharks once swam the oceans, eating whales, dolphins, sea cows, turtles and just about anything else that ended up in front of their enormous snouts, then its likely every chance you get, you're likely to take out one of those sharks!

Adult Megs would have been too much, even for several Orcas to handle, but juvenile Carcharodons would have stood no chance at all.

Another problem was the appearance of new sharks out-eating Megs, like the great white and tiger shark. Again, though they posed no threat to adult Megs, the young would have had real trouble with these efficient predators, plus the smaller, but more numerous tigers and white pointers would have had a sever impact on the food supply of the Megs.

Another suggestion for their extinction is that the cooler waters forming during the Ice Age, drove many whale species into these northern and southern waters, places were the Meg was incapable of following. This is not a bad idea except Great Whites are warm-blooded sharks that can be found in some cooler waters, so its likely Megalodon could have handled these conditions as well.

This all had to have a huge effect on Meg populations until, finally, the Megalodon slipped into extinction.

So there you go guys, an update on what's been happening with everyone's favourite prehistoric shark, and knowing my luck, now that I've come out and publicly said there's no Megs alive today, you'll probably see footage of one on the news tomorrow.

BUT, we're not done here yet guys. Most people who follow prehistoric animals know about the colossal Megalodon, but what many don't know is that there were other giant toothy sharks!

Going backwards in time, first up is C. chubutensis. Living between 14 and 23 M.Y.A, C. chubutensis is almost certainly the direct ancestor of megalodon. Many teeth have been found reaching up to 13cm long, a mere 4cm shorter then a Megs. In fact the only real difference between the two species (that we know of) is that chubutensis teeth have two small cusps at the base of the tooth, where Meg teeth generally have a straight edge from tip to base. This is not always the case however, and can cause some confusion as juvenile Meg teeth sometimes have these cusps and are roughly the same size. It seems only their age can tell the two apart! The largest teeth suggest they could grow to around 13m and probably weigh around 12 tonnes. Another mega-toothed shark was Carcharodon subauriculatus ; in fact these teeth are so similar to both juvenile megalodons and C. chubutensis that they're often confused as each other. Its even being suggested now that C. chubutensis and C. subauriculatus are the same shark (and I gotta' tell you, the few teeth I've seen, they look the same), so lets just move on to our next shark.

Carcharocles sokolowi is considered the oldest of this branch (or the first if you want to think of it another way), evolving straight out of the incredibly successful Otodus sharks such as O.obliquus . It was originally considered to be the oldest representative of the great white, but as we've seen, the recent shift of this group into the lamnid sharks (like the mako) means they're no longer closely related. In fact it's around the end of the dinosaur age (65 M.Y.A) that a lot of these early species converged, yet still there were giant sharks (such as Squalicorax and Cretoxyrhina ) that at least equalled the size and power of the great white. These ‘Ginsu' sharks from the warm waters of the Mesozoic were caught in an all out war with that other group of cretaceous marine predators, the Mosasaurs, so it would seem there's always been large sharks patrolling the shallows just of shore, waiting for something, anything, to foolishly wander into its domain!