Paleo Profiles: Megalodon

The jaws of megalodon in the American Museum of Natural History

Welcome to our first Paleo Profile! As mentioned in our Introduction I am not a palaeontologist but rather a palaeontology enthusiast so this is not going a more authoritative look at the past. Anyway, with that out of the way we can jump right in. Millions of years ago a monster swam through our oceans which dwarfed the great white shark. This monster was a shark which fed on whales: Megalodon. O. megalodon has become well renowned across the world for its giant size earning it a place in the media whenever a giant shark is needed. As I am currently writing a new blockbuster called The Meg has a megalodon as the creature hunting down and eating swimmers. Often overlooked is that megalodon, despite its immense size, was a real creature, just as real as the great whites and tiger sharks which stalk the world's oceans today.

Discovery and Fossils

A megalodon tooth next to a banana for scale

Megalodon has been somewhat known by people for centuries but not in the way that you would imagine. The giant teeth of megalodon, and other large sharks, would be found by people who assumed that they were the petrified tongues of dragons. This was a regular occurrence with fossils - ammonites at one point were believed to be petrified snakes turned to stone as punishment from God for tricking Adam and Eve, and some less scrupulous individuals would carve snake heads onto them to trick buyers. It would take until 1667 when Danish naturalist Nicolas Steno in The Head of a Shark Dissected correctly identified the teeth as belonging to a large shark, but it would take a lot longer for the shark to be described. By the 1800s palaeontology was emerging as a new field of study as naturalists started realising that some of the skeletons they had been discovering were not just larger variants of extant animals. Sometime before 1837 Swiss naturalist Louis Agassiz described the shark who the teeth belonged to, but it took until 1843 for him to formally describe the shark. He named it Carcharodon megalodon - Carcharodon being the genus which the great white belonged to and megalodon meaning 'big tooth'. However, an different naturalist, Edward Charlesworth, in 1837 (citing Agassiz) called it Carcharias megalodon. This will become important later on.

We have a lot of specific fossil evidence of megalodon and most of it happens to be the teeth of the shark. Sharks can go through up to 40,000 teeth throughout their life and megalodon was no exception to that. Naturally we have lots of teeth believed to be from megalodon. It is a misconception though that we only have teeth from the shark, in reality we also have vertebra from megalodon. Unlike the rest of a shark's skeleton, made from 'soft' cartilage, the vertebrate is made of harder calcified cartilage which is more likely to be fossilised.

What type of shark is megalodon?
You may be wondering why within a few years Carcharodon and Carcharias were used for megalodon within a space of a few years. Originally it was believed that megalodon was an extinct larger great white as they were, and are, large predatory sharks and that they had similar teeth. However, the only similarity is that they are triangular and serrated, on closer look you notice more differences. Among these is that great whites have thinner teeth for their size compared to megalodon. As a result palaeontologists started suggesting that megalodon belonged to Carcharias instead where both sharks shared a common ancestor with some palaeontologists also suggesting that megalodon was a transitional fossil between older shark groups and the modern great white. There was some pushback to the transitional fossil theory as great whites lived alongside megalodon but it has been pointed out that transitional fossils can live alongside their later relatives, as shown with the Smilodon (sabre-toothed cat) whose species lived at the same time. However, other megatooth sharks were discovered and in 2012 an extinct relative of great whites was discovered showing a closer relation to makos than megatooths. As a result the megatooths were assigned the genus Carcharias. Our story does not end here. One family of shark yet to be mentioned are the Otodontids (now extinct). The Otodontids, of which Otodus was the most famous genus to comprise it, were closely related to Lamnidae, which the great white belongs to. Through research palaeontologists now believe that Carcharias is no longer a valid genus and that megalodon is really a species of Otodus with great whites sharing a common ancestor, and therefore being more closely related, with the mako shark. The reason for the similarity between great whites and megalodon is believed to be convergent evolution - the same way in how birds and bats fly despite having no shared ancestors. Hence, it is now Otodus megalodon instead of Carcharodon or Carcharias megalodon.

Biology

The size of megalodon from Prehistoric-wildlife.com

The reason why megalodon is so famous is because of its size. The issue is we have no idea how large the megalodon really was with estimates ranging from 15 metres long at its smallest to 20 metres at its largest (just ten metres shorter than the largest blue whales) - in contrast the largest great whites are just under 5 metres and the fictional shark from Jaws is almost 8 metres. Regardless of its size megalodon was a giant. How did they get these sizes though? In 1973 John E. Randall used the height of tooth enamel to give a size of 13 metres which was seen as inaccurate as he based this method on using white shark teeth and although similar they were very different. Even then enamel can have different thickness tooth to tooth never mind between individual animals thanks to wear, (and also preservation). In 1996‭ Michael D.‭ ‬Gottfried,‭ ‬Leonard J.‭ ‬V.‭ ‬Compagno and S.‭ ‬Curtis Bowman decided to measure the length of the cutting length of the tooth which gave an estimate of 19 metres, and in 2002 Clifford Jeremiah used the width of the tooth to find the width of the jaw and from there got an estimate of 15.5 metres. The same year Kenshu Shimada using a tooth from Panama used the tooth crown to get an estimate, seen as fairly accurate, of about 15.1 metres. As a result between 15 and 17 metres is seen as megalodon's length. However, sharks are very muscular so with muscles comes weight which is hard to estimate for an animal only known by teeth and some vertebra. Weight does not increase at a constant with length so we have a very wide range of proposed weights ranging from 47 metric tons for at 15.9 metre long shark to 103 metric tons for a 20 metre long one.

Most reconstructions portray megalodon as a massive great white but recently this has changed among paleoartists at least. Mainly this is due to how we now know that it is unlikely that megalodon was in the same genus as the great white. Some have suggested that they would look like a tiger shark as Otodus is thought to resemble tiger sharks but again this is seen as unlikely. Megalodon lived like a great white so it is quite likely that at a glance they would look similar - animals which evolved to fill similar niches often resemble one another. However, there would be noticeable differences. For example, the jaws would have thicker and the shark overall would appear thicker itself as it would need to be in order to power such a long body. The megalodon would have fairly long fins, particularly the tail fin, in order to reduce drag while swimming and when you look at the fins of whales, tuna and large sharks like whale sharks they are long for this reason. Below is a photo of a whale shark which shows just how big their fins can get.

As you can see on the photo the whale shark is being followed by smaller fish. Today great whites are also followed by smaller fish like remoras so it is likely that they would follow megalodon as well. It has been suggested that barnacles could even grow on elderly megalodon like on some whales. Megalodon could have an entire micro-ecosystem living around it with fish picking up stray bits of flesh from its last meal, parasites feasting on the shark itself, and also other animals eating the parasites. How did megalodon survive as an animal itself? Megalodon had a high metabolism to power its body and was likely mesothermic meaning that it was both cold and warm-blooded much like tuna and white sharks of today. This allowed it to possibly send warm blood to its head allowing its brain and sensory organs work along warm-blooded metabolic levels. The sheer size of the shark would also allow it to be gigantothermic where, thanks to its size, the outer layers of skin and muscles would insulate the shark. Finally, we have the jaws. Like modern sharks it would be able to move its upper jaw when biting and the bite of a megalodon was phenomenal. In 2008 a computer model was made to estimate the bite force of white sharks which was applied to the megalodon they found out just how powerful its bite was. A 16 metre long shark was found to have a bite force of 108,514 Newtons, or around 11 metric tons, while a 20 metre long shark 182,201 Newtons, or over 18.5 metric tons. That meant that the lower size estimate possibly had a bite force greater than that of a Tyrannosaurus rex! Finally, megalodon is believed to be long lived. Great whites can live to be 75 and generally larger animals live longer than smaller ones so megalodon could possibly live to be a century.

When and Where

The shark's distribution on a modern map from Prehistoric-Wildlife.com

Despite being shown in the media megalodon did not live alongside the dinosaurs. Non-avian dinosaurs (basically dinosaurs which aren't modern birds) went extinct around 66 million years ago and megalodon did not appear until around 23 million years ago in the early Miocene. It lasted a very long time with it going extinct in the Late Pliocene, or more specifically c.2.6 million years ago. To put it in perspective the first members of our genus, Homo, evolved 500,000 years after the extinction of this giant shark. Megalodon was truly the apex predator of the oceans with its teeth being found everywhere from Essex in England, to New Zealand's north island, to Peru and Panama. The only place where it was not known to live in were the waters of the Arctic and Antarctic. Global temperatures were warmer than today so it could survive everywhere and likely competed against white sharks. It has been theorised that white sharks and megalodon would migrate to avoid competing against one another. Even the shallows were not out of bounds. Pups occupied the shallows which brings us to our next point...

Birthing a Monster
Like most modern large sharks megalodon gave birth to live young but we don't know if they grew in an egg inside the mother or if they had no egg and received nutrients via an umbilical cord. Mothers didn't give birth anywhere. They gave birth in shallower and safer water in 'nursery grounds' much like modern sharks. We know where nursery grounds are by higher concentrations of smaller teeth and one key area has been identified by Catalina Pimiento, Dana J. Ehret, Bruce J. MacFadden, and Gordon Hubbell in the Gatun Formation in Panama facing the Caribbean. When megalodon swam the seas the Isthmus of Panama did not yet exist with the Central American Seaway instead taking its place. This area created an area, much like the Sea of Cortez where great whites now give birth, of shallow water safe for young megalodon to grow up in peace from larger predators. Most of the individuals from this area measure between 2 to 3 metres but we don't know if they are born that size or grow to be that size later on. In the nursery grounds the pups would eat anything they could get their jaws on ranging from turtles to cephalopods to smaller cetaceans (whales, dolphins and porpoises) like the tusked Odobenocetops from the shores of what would become Peru and Chile.

Diet and Hunting

A megalodon tooth in the vertebrate of a whale

Like the great white megalodon ate everything despite the stereotype of it only eating whales. They definitely did eat whales; one vertebrate had a megalodon tooth sticking out of it. However, it would not regularly target the large baleen whales; they could do serious damage to a shark making it undesirable to attack one. The megalodon would most likely target sick large baleen whales when the opportunity arose. Smaller whales, such as the 5 metre long Piscobalaena nana, would be the main food source for the megalodon. An orca would be the perfect size for a megalodon although orcas could potentially kill one being intelligent, social, and potentially dangerous cetaceans. Nothing was really out of bounds for a megalodon. Whales, sharks, sea birds, seals, turtles, and even aquatic sloths were on the menu for megalodon and smaller megalodon also could potentially be eaten. Cannibalism is common in many shark species, including the great white, so megalodon could eat smaller ones; the nursery grounds offered protection from adults as well as other predators. Like many predators megalodon scavenged and hunted. Sharks have an incredible sense of smell being able to smell blood from miles away so scavenging could be very easy for a megalodon in theory; other sharks would also be wanting to scavenge from a dead whale. Megalodon would hunt like a great white striking from below - being dark in colouring it would be hard to see them from above. With its powerful tail it could propel itself through the water like a torpedo striking the prey - we have fossil evidence of whales with damaged vertebrates indicating that they had been hit with some force. In particular they would target the rib cage where their strong teeth and jaws could tear through the ribs to get to the delicate internal organs. Even if the shark could not bite the whale it would stun them allowing the shark to take a bite; whales could escape as some have evidence of their ribs and spine healing. With the larger baleen whales the sharks could either hit them with their very strong tail or simply bite chunks out of the whale. It is thought that megalodon needed between 600 and 1200 kg of food a day to survive so hunting was needed more than scavenging.

Extinction
Megalodon was easily top of the food chain and dominated the world's oceans for around 20 million years, so why did it go extinct? The reason for their extinction is key considering that shark populations are dwindling. Climate change led to their extinction. Today climate change is decimating shark populations although human hunting and pollution is making a steady decline caused by human caused climate change turn into a very steep decline. Around 2.6 million years ago global temperatures dropped thanks to the arrival of the Ice Age. The Isthmus of Panama was formed connecting North and South America but also closing off the giant Seaway. As a result currents shifted changing whale migratory routes which in turn deprived megalodon of their primary food source around a major nursery ground. Although megalodon could have adapted to changing temperatures the whales they hunted could not; baleen whale diversity dropped from over 20 genera to just six extant ones. 36% of large sea life went extinct including 55% of large marine mammals, 9% sharks, 43% sea turtles and 43% sea birds. As a result megalodon lost a lot of its food source which was made worse when whales moved to colder climates where the mega shark could not follow. Nursery grounds needed shallow water, like in Panama, which vanished with the dropping of the sea level leaving pups exposed to predators. This was the primary reason although it has been suggested that increased competition sealed their fate. In the final few million years of the megalodon's existence more toothed whales including the giant sperm whale Livyatan and most importantly orcas evolved. Not only were they more versatile than the giant shark but they could bite back. As the great white's diet did not rely so heavily on whales their diet was less affected and their smaller size let them hunt and have nursery grounds closer to the shore compared to their larger cousins. Through all of this what made megalodon so powerful for twenty million years ended up sealing their fate.

Still Alive?

The infamous 'documentary' providing evidence for the shark's continued existence

The Meg and the book it's based on has the megalodon woken from being frozen in prehistoric ice but there are genuine theories that the megalodon exists to this day. These range from cryptozoologists to Young Earth Creationists. Curator of Palaeobiology at London's Natural History Museum sums it up well: No. It's definitely not alive in the deep oceans, despite what the Discovery Channel has said in the past. Mostly as we would see signs of attack on whales as we do with giant squid and where they could safely hide out are cold which is the exact reason why they went extinct to start off with. In 1873 the crew of the HMS Challenger picked up a megalodon tooth which gave an age of 10,000 years when tested in 1959. Did this mean that megalodon at least managed to last until humans started agriculture? The answer is no. Other than it being the only tooth to be found they had tested the tooth for manganese dioxide which is very unreliable. When it was later carbon dated they found it had too little nitrogen to be dated; this meant it was too unstable to be properly dated so it can't really be used to prove that it was from 10,000 years ago. Most 'sightings' of the shark are really misidentified megamouth sharks and younger looking teeth are due to preservation, not age. In recent years the conspiracy of the existing megalodon roared into existence again thanks to a Discovery Channel mockumentary called Megalodon: The Monster Shark Lives. In 2013 Animal Planet made a fake documentary called Mermaids: The Body Found which presented 'evidence' that mermaids existed confirmed by 'scientists' (really just actors) along the lines of What we do in the Shadows or Trollhunter. It was clearly fake but it was convincing - although 17 year old me saw it clearly as being fake I was convinced by some of their evidence - so convincing that people didn't realise it was a fake, especially coming from a respected channel like Animal Planet. Despite criticisms that the channel had not made it clear that it was fake it got many views so their sister channel, Discovery, decided to copy the format. In Mermaids a megalodon was seen eating mermaids 1.6 million years ago (albeit at that time it was thought that the shark existed until 1.8 million years ago) so Discovery chose to use the giant shark for Shark Week. Again featuring actors as scientists it featured a crew being attacked by the shark off the coast of South Africa. Like Mermaids it received criticism for featuring a mockumentary on a factual and reliable channel, and despite disclaimers claiming it was fake those who tuned in late or only saw the advertising thought it was real. Not learning from their mistake the next year the re-aired it with no further disclaimers and even made two more mockumentaries about the shark! Basically, the shark is very much extinct despite best efforts from cryptozoologists, poor dating, and Discovery Channel's marketing team.

Thank you for reading. We now have a list of future Paleo Profiles. The sources I have used are as follows:
-Alberto Collareta, Olivier Lambert, Walter Landini, Claudio Di Celma, Elisa Malinverno, Rafael Varas-Malca, Mario Urbina, and Giovanni Bianucci, 'Did the giant extinct shark Carcharocles megalodon target small prey? Bite marks on marine mammal remains from the late Miocene of Peru', Palaeogeography, Palaeoclimatology, Palaeoecology, 469, (2017), 84-91
-Catalina Pimiento, Dana J. Ehret, Bruce J. MacFadden, and Gordon Hubbell, 'Ancient Nursery Area for the Extinct Giant Shark Megalodon from the Miocene of Panama', PLoS One, 5:5, (2010), 1-9
-Catalina Pimiento and Christopher Clements, 'When did Carcharocles megalodon become extinct? A new analysis of the fossil record', PLoS One, 9:10, (2014), 1-5
-C. megalodon, Prehistoric wildlife.com, Accessed 15/08/2018
-Josh Davis, 'Megalodon: the truth about the largest shark that ever lived', Natural History Museum, (06/08/2018), Accessed 17/08/2018
-Trey the Explainer, 'Paleo Profile - Bunch of Prehistoric Fish', YouTube, (05/12/2017), Accessed 19/08/2018
-Trey the Explainer, 'Paleo Profile - Megalodon', YouTube, (22/06/2015), Accessed 19/08/2018

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