The jaws of megalodon in the American Museum of Natural History |
Discovery and Fossils
A megalodon tooth next to a banana for scale |
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 |
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 |
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 |
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 |
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
Thanks again for reading. For future blog updates please catch our Facebook or catch me on Twitter @LewisTwiby.