There has been a lot written about Carcharodon megalodon recently, so I thought I would take this opportunity to quickly go through some of the major points of this awesome shark.
What's in a name?
Let us start with the simple stuff. Is it Carcharodon megalodon or Carcharias megalodon ?
While many marine biologists prefer the name Carcharodon, this name is only really accurate if the “Meg” is related to the great white shark (Carcharodon carcharias). Recent research suggests that Megs are actually the descendant of the 55 M.Y.O Otodus obliquus , while the great white evolved from the similarly aged Isurus hastalis, making its nearest relative the mako sharks. If this new hypothesis is true, 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 that although Carcharias megalodon is generally considered the correct classification, However Carcharodon megalodon does sound a lot cooler!
Just how big was it?
Well, now we are 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 not 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 this still makes a shark nearly three times larger than the great white.
As for its weight. At 6m a great white is around 2 tonnes, but you cannot simply scale a Meg up at the same rate due to its size. The larger an animal gets the more its mass increases as they need more muscle and bone mass to move the body. For instance, at roughly 3 times the length you would think a Meg would weigh around 6 tonnes, instead it would have been more like 30 tonnes 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 definitely 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 is 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 instance, these teeth are huge, 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 does not mean that is when the shark lost them. Another problem is that 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 in such good condition that (remember that they are extremely tough) they 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 are still large sharks swimming the world’s oceans, with many as large as a Meg so these could 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 have even 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 was found in the 1970's, so people often ask, if one species of enormous shark could survive until quite recently without being seen, why not another?
This is a fair enough point except that we are talking about two completely different animals here. By their very nature megamouths are shy, solitary creatures slowly ambling across the world's oceans at great depths, constantly feeding on shoals of plankton. The equally large Meg was another matter altogether. 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 world’s oceans? With the sudden loss of whales (thanks to human over hunting), have sharks started attacking other creatures in greater numbers? Let’s 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.
I should point out this isn't to say no one's ever reported huge sharks patrolling their beaches, it is just that estimating size at sea is a tricky thing. There have been a few reports, however, that might make you think!
As far as I am concerned, the best report 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 some time, 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 would have to say), so when several claimed they saw an unusually large shark you would have to believe them.
This story does fall down 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 had believed to be from hitting a floating tree trunk.
The big problem with this story is that there is 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 Mawson’s doomed expedition in Antarctica. This is a pretty famous ship that, surely, someone would have noted if it had survived far past when it was supposed to have burnt down or 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 peak. Yet within this ecosystem things were changing: like 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 them attacking and despatching an adult great white with ease. However, the pups of dolphins, seals and young Orcas regularly make up the diet of the warm-blooded great white. So it would have been an excellent way for Orcas to protect their young, if they could dispatch a young Megalodon while it posed a much less challenging target. 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-competing 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. In addition, the smaller but more numerous tigers and white pointers would have had a more severe impact on the food supply of the Megs.
Another suggestion for their extinction is that the cooler waters that formed during the Ice Age drove many whale species out of the reach of most sharks. However this is not particularly likely as some species like the great white shark are warm-blooded and regularly found in modern cooler waters. So it is likely that the prehistoric Megalodon could have handled similar conditions.
This all had to have a huge effect on Meg populations until, finally, the Megalodon slipped into extinction. So, there you go, an update on what has been happening with everyone's favourite prehistoric shark, and knowing my luck, now that I have come out and publicly said there are no Megs alive today, you will probably see footage of one on the news tomorrow.
BUT, we are not done here yet. Most people who follow prehistoric animals know about the colossal Megalodon, but what many do not 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 than a Meg’s. 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, whereas 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 are often confused as each other. It is even being suggested now that C. chubutensis and C. subauriculatus are the same shark (and I have to tell you, the few teeth I have seenlook the same), so let us 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 Otodus obliquus. It was originally considered to be the oldest representative of the great white, but as we have seen, the recent shift of this group into the lamnid sharks (like the mako) means they are no longer closely related. In fact it is 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 has always been large sharks patrolling the shallows just of shore, waiting for something, anything, to foolishly wander into its domain!