Lesson 5) Just When You Thought It Was Safe To Go Back In The Water...

Good afternoon, students, and welcome to your fifth Prehistoric Creature Feature lesson! For those of you who haven’t encountered me in the classroom yet, I am Professor Mirabelle Fairclough. I have to admit I am rather excited to be presenting today’s lecture, as this creature is actually one of my favourites to have ever existed. So please prepare yourselves as we dive into the depths of the ocean to explore the world of the megalodon!

The megalodon, as illustrated in the picture above, is an extinct species of shark. In fact, it was the biggest shark to ever exist! Imagine a modern-day great white shark and then triple or quadruple that in size, if not more. That’s how big this fish was, and it is a truly terrifying, yet amazing prospect to think about! For those of you who prefer a more precise measurement, the average megalodon was believed to be between 14 and 20 metres long (46ft- 66ft). In terms of its weight (or mass), some were thought to have been as heavy as 100 tonnes! Typically they weighed around 70 tonnes, though.

Below is a comparison chart so you can see for yourself how mighty this fish was! The red and grey sharks are the minimum and maximum ranges for the megalodon, the purple one represents a whale shark, and the green one is indicative of a great white shark.

The word ‘megalodon’ comes from the Greek words ‘megas’ and ‘odous,’ meaning ‘giant’ and ‘tooth,’ respectively. As a whole, the word literally translates as ‘giant tooth’ which is quite an apt name for this particular creature, as you will see in due course. The megalodon is also frequently known by its scientific name of C. megalodon.

So, when did this shark actually exist? There isn’t an exact time or date, I’m afraid, but people have generally accepted that it was somewhere around 15-25 million and 1.6 million years ago in the Miocene and Pliocene epochs. This time period was slightly warmer than today in terms of climate, and the sea levels were much higher, making it a suitable environment for the megalodon. 

External Shark Anatomy 

If I had asked you all to picture a shark in your mind at the start of the lesson, I’m sure that you all would have come up with something like this, right?

Even though this is a great white shark, it isn’t too different from the megalodon visually or anatomically. Without anything to show scale, one couldn’t even be faulted for saying that it was a megalodon.

Now, I want you all to look at this labelled diagram of a shark’s external features. You can even compare it to the shark image we just looked at to get a better understanding.

This is the most basic depiction one can have. Every shark, including the megalodon, is made up of three main sections - the head , the trunk, and the tail. From there, there is a significant amount of diversity. Each species of shark is different, and may possess variations in the number of fins or gills they have, for example, or maybe a different type of tail. Each variation serves a purpose and helps that particular species of shark survive in its habitat. I won’t go into detail for every feature mentioned above and their different variations throughout the many families of sharks, as we could be here until your next Creature Feature lesson! 

Skeleton and Teeth 

Unfortunately, there is not as much fossil evidence of the megalodon as I - or many scientists - would like. The main source of information we acquire comes from their teeth, which I will get into in a minute. First, let’s have a very quick discussion about their skeleton. 

Obviously the megalodon had some sort of skeletal frame, but it wasn’t composed of bones, as you might expect. The skeleton was made up of a material called cartilage; a connective tissue that we would primarily associate with our knees or noses. A skeleton composed of cartilage would have helped the megalodon, as the strong, resilient material was lighter than bone and aided their buoyancy. Now, I might add here that cartilage is a substance that doesn’t fossilise easily, hence the reason we are unable to find any proper skeletal remains of the megalodon. There may be the odd fragment here and there, but nothing really substantial enough. However, we are fortunate enough in that we can find fossils in the form of teeth.

Let’s start the topic of teeth and jaws with a fun fact. Did you know that megalodon teeth were misidentified up until 1667? Muggles genuinely believed that they were finding fossilised dragon tongues! Yes, tongues, of all things! With that in mind, let’s take a look at some examples of megalodon teeth. You can all thank Ms. Hackett the next time you see her for providing us with these wonderful specimens!

The average megalodon tooth is 7.5 cm to 12.5 cm (three to five inches) long. Although, some teeth have been found a little over 18 cm (seven inches) in height, which is exceptionally rare. If you compare this to a modern-day great white’s tooth (the record size being just under three inches long), you can really grasp how huge this tooth actually is. The teeth are also perfect for tearing the flesh off prey. Each one is triangular but the edges aren’t smooth - they are actually serrated. 

Because of the scarcity of fossils, the teeth serve many purposes for researchers. Muggle scientists developed techniques which allowed them to determine the age at which the megalodon died, simply by counting the number of rings on a tooth. It’s a very similar process to the one we use today when determining the age of a tree! Scientists further developed their research by using the colouration of the tooth as well as the distance between the various rings to calculate the growth rate of the shark despite it being dead for millions of years. Impressive stuff, right?! 

The first jaw reconstruction took place in 1909 under the watchful eye of Bashford Dean (right). His model wasn’t entirely accurate though - he actually made it too big and therefore had it scaled down to a more suitable size (approximately 70% of the size it started at).  Over time, many have tried to create their own set of megalodon jaws. For those who don’t have the time, energy, money, or patience to construct their own set of jaws, there are many different examples in various museums around the world, so if you are lucky enough to have access to one, I urge you to go and see it, as I assure you that you won’t be disappointed!

If you were brave enough to look into the jaws of a megalodon, past the front teeth you would see several more rows of teeth. The front row of teeth were usually fully grown and the biggest, but because sharks have a tendency to lose and replace teeth on a fairly regular basis, these are not their only teeth. The extra rows that you can see in the image to the left would replace any of the teeth lost in the row in front. It was a pretty effective system! Some sharks have been believed to go through thousands of teeth in a single lifetime. It is thought that the megalodon had approximately 46 front teeth, with many extra rows. The exact number of extra rows isn’t known, but reasonable estimates indicate five or six, which would equate to a single shark having between 230 and 276 teeth at any time!  

Diet and Hunting Techniques

With the megalodon being the size it was, it was able to hunt all types of creatures like seals and fish, much like today’s sharks. However, they were also believed to eat much bigger sea-dwelling organisms such as dolphins and even whales. The combination of strong teeth and powerful jaws would have even allowed them to crush through a giant sea turtle’s shell with ease. You could essentially say that the megalodon ruled the seas and ate whatever it wanted, as there wasn’t really any competition that could match it in terms of size or strength. They were thought to have consumed at least 1300 lbs (590 kg) every single day to survive. To put that into perspective, that’s almost equivalent to the weight of a bison or buffalo!

Now that you know what the shark liked to eat, I think we should discuss some of the various techniques it used to catch its prey. There are a number of methods a megalodon would employ, and the technique used would usually depend on how far away the prey was. The diagram below gives a better idea of how this works:


Let’s start with hearing capabilities.

  1. A megalodon had exceptional hearing capabilities. Its ears were an internal structure. They had no visible outer ear like humans do. In their place were miniscule holes on the side of its head that led to the internal auditory system.

    Sharks, in general, have a hearing range between 10 and 800 Hz. The lower end of the spectrum (between 10 and 20 Hz) is actually lower than we are able to hear. They are even able to hear different sound frequencies from distances of over 1 kilometre! This all applied to the megalodon too, however, it is interesting to note that the giant shark was particularly drawn to the lower frequencies for one very specific reason.  Fish, especially when injured or wounded, would emit tones from the lower half of that range. To a shark, this would be a signal that its dinner was nearby. It would then hone in on the sound and consume the fish. 
  2. In terms of the sense of smell, megalodons possessed a pair of nostrils on their snout, like most other animals and fish. These were extremely receptive to different scents, as they were lined with very sensitive sensory tissues. The water would flow into the nostrils and any differences, including small chemical deviations, in the water could be easily detected. Please note that the nostril passages of the megalodon were only used for their sense of smell and not for breathing purposes.

    The shark’s ability to smell was so strong, it could detect a single drop of blood in a million drops of water. So, if there was an injured, bleeding organism in the vicinity, you can be sure that the megalodon would have soon picked up and followed the scent. Once locked onto a potential trail, the giant shark would keep track by moving from side-to-side so that the smell wouldn’t become lost and remained fresh, much in the same way a dog follows a scent. 

  3. The megalodon also detected meals by vibrations via the lateral line system (also known as the lateralis system). Through this method, the megalodon would detect pressure and vibrational differences in the water. The shark actually possessed a line, or canal, down the side of its body which could be located via a series of pores along the line. Inside the canal were hundreds upon thousands of tiny hair cells (a type of sensory cell). Water would flow into the canal and these cells would pick up on any unusual vibrations in the surrounding water and register it in the brain before the shark made its move. This ability gave the megalodon a great sense of direction.

  4. Electroreception is an amazing ability that the megalodon would have likely possessed. In the most basic terms, the shark would have been able to detect all electrical currents. It was, by far, their most sensitive technique, but it was also the one with the shortest range. This ability allowed the shark to be alerted to any movements by prey within the vicinity without having to rely on any other senses. It was very effective in darker waters and it meant that prey couldn't hide, as their muscles expanding and contracting or a single heartbeat would have been detected!

    How did this work? Electroreception was a technique that could only happen with certain cell types and these were very limited; so limited, in fact, that they could only be found on the snout of the beast. 
  5. Finally, there is breaching. This technique is one that was used by the megalodon and is still used today by the modern-day great white shark. I must say that it is definitely one of the most impressive methods visually. When a shark hunts food using this method, it would often lurk in the depths below and wait for potential prey to swim near the surface. The shark did this for a number of reasons: so that it couldn’t be seen, it wouldn’t scare its food away, and it would have enough power and momentum for the next stage of the attack. Once the prey had finally been located, the megalodon would swim so that, from below, it directly lined up with the creature at the surface. Then, using its powerful muscles, the shark would propel itself upwards at an incredibly high speed to attack the prey. It would breach the surface and leap into the air, biting or knocking its prey away. Depending on the creature the megalodon was attacking, it would either stun and paralyse it, if it was a bigger creature like a whale, or directly kill it upon impact.

    The video shows multiple sharks breaching the surface:
    https://www.youtube.com/watch?v=CcAfUMPpooU

As a  last resort, there was scavenging. Obviously, if there was a dead whale carcass or some other creature drifting in open water, the shark wouldn’t turn its nose up at free food. On a long term basis, the megalodon just wouldn’t survive through this particular method of acquiring food. Its other hunting abilities were much more reliable.

Breeding and Nursing

Due to the lack of fossil evidence, the breeding and nursing techniques of the megalodon are still largely unknown. However, some Muggle scientists speculate that the age at which the giant shark would reach sexual maturity (estimated to be somewhere between 15 and 30 years)  and their gestation periods (estimated to be 11 months) would correspond to those of a great white shark, due to their notable similarities. Do not take that as fact, though; as I said, these exact figures are still a mystery to us! 

Considering their size, it would make sense that a megalodon would have given birth to live pups as opposed to laying a number of eggs on the ocean floor, which is how smaller shark types typically reproduce. For all live-birthing sharks, there are two different ways in which the mother can potentially look after the pups prior to birth:

  1. Viviparously - The pups would have an umbilical cord inside their mother to receive all of their nutrients.
  2. Ovoviviparously - The pups would be within an egg inside the mother and receive all the nutrients from the egg in which they were contained. When born, the pups would hatch from their eggs, still inside the mother, and be a live birth.

We can assume that the megalodon reproduced in one of these two manners. It isn’t known how many offspring would have been produced at any single time either, but regardless, they were assumed to still be large pups measuring almost two metres (6.5 ft), if not slightly less, in length. 

It is firmly believed that after megalodons gave birth, they would have left all offspring in a nursery. These were areas that would allow the young sharks to thrive in an environment safe from the majority of predators. There would have also been a lot of opportunities for the younger sharks to practise and hone their hunting skills on smaller prey, as they could obviously not eat full grown whales at birth! 

So, how do we know that younger megalodons grew up in nurseries? Once again, it is down to fossil evidence. Large numbers of incredibly small fossilised teeth belonging to this species of shark were found grouped together in areas known to have shallower waters in the Miocene and Pliocene epochs. For example, countries like Panama and Costa Rica that exist today would have been underwater in the times of the megalodon. Large parts of this submerged area, known as the Central American Seaway, would have been shallow and warm enough for the megalodon pups to live and grow in, but it would have been too shallow for any lurking predators looking for an easy feast. Eventually, the pups would outgrow the nursery and have to move on to tackle larger prey and live in more dangerous environments

Possible Extinction Factors

The megalodon was a creature that lived all throughout Earth’s oceans. This can be confirmed by the number of megalodon teeth that have been discovered in many different countries across the globe. With this in mind, we can assume that it wasn’t a single event that caused this creature’s ultimate demise, but more a series of simultaneous occurrences and changes that gradually became increasingly problematic over a period of time.

Environmental Factors
In the span of the 14 to 21 million years when the megalodon ruled the seas, there were a number of environmental changes that may have reduced the population of the giant shark. Global temperatures were decreasing quite rapidly, resulting in the polar regions of Earth freezing over to form glaciers. The increasing number of glaciers meant that the sea levels began to decrease, which would have had an impact on all sea creatures.  All marine life, particularly in the shallower waters, would have suffered and either had to adapt or die out, leaving a gap in the food chain. The numbers of secondary and tertiary predators would have also dwindled to some capacity due to the lack of food available, leaving the megalodon with little to eat.

As always, land masses moved, changing the oceans as a result. New stretches of water formed while other older ones ceased to exist. This led to coastal areas disappearing and breeding and nursing grounds drying up. Other oceanic predators used this opportunity to their advantage and feasted upon the young megalodons.

Megalodons dying due to starvation, as well as very few surviving the nursing stage of life, would have led to the fall of the population quite quickly.

Evolutionary Fail?
Some sharks, like the great white and the mako, both members of the Lamnidae family, have the ability to generate heat in their muscles as they swim, which then transfers into their blood. When a shark with thermoregulatory abilities enters colder waters than it is accustomed to, it  adapts its own body temperature with this specially generated heat to make it more bearable. Unfortunately, the megalodon did not possess such an ability and was limited to the warmer, more temperate waters it already used for hunting activities and general living. Much like the previous point, food became more scarce as the area of warm water shrank and what was left wasn’t enough to sustain a creature of the megalodon's size, therefore pointing to starvation as a cause of extinction once again.

With that, we have come to the end of this rather lengthy lesson on the megalodon. I hope you all enjoyed it and have learnt a thing or two about this amazing creature. I also want to thank Professor Anne and Professor Cattercorn for giving me the opportunity to lead this class today. I will now leave you with one mandatory essay and a couple of extra credit ones to complete if you wish to do so. Good luck with the rest of Prehistoric Creature Feature! 

All pictures are found using the Google Images search engine, and belong to their owners. Photograph of three shark teeth taken by Ms. Hackett.

Welcome to Prehistoric Creature Feature! During the course, you will learn about seven different prehistoric, extinct (possibly?) creatures that roamed the Earth. The biggest question: are you ready to meet some of these creatures, or would you rather they stay extinct? Find out this week in Prehistoric Creature Feature! This is the third Creature Feature to be released.

Currently open from July 1, 2019 through October 31, 2019 as part of the activities during the break between years.
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