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Book Review

Megalodon: a puzzle piece to understanding ecological concerns around apex predator extinction

A Prehistoric Nightmare?

The Megalodon (Carcharocles megalodon), or “big tooth” is arguably one of the scariest creatures that has ever roamed the ocean. You may have heard about the Megalodon as a prehistoric gigantic shark that dominated the ocean millions of years ago, or even that scientists are still looking for them today, just like the Loch Ness monster and Bigfoot. The mystery and interest around this species is based on our preconceived notions of sharks as man-eating monsters, which is amplified by the fact that these sharks were the biggest sharks to ever live. Consequently, there is a huge intrigue around the idea that these gigantic sharks may still be lurking around in our waters. Even though this idea is certainly captivating, it is as much of a myth as the existence of mermaids and dragons. Ironically, before being identified as shark teeth, the huge fossilized megalodon teeth, were mistakenly identified as rocks that had fallen from the moon, or as the petrified tongues of dragons and giant serpents. A naturalist made the discovery that the “tongues” were actually teeth in 1666, after studying those of great white sharks and recognizing the similar shape of the teeth.

Tooth size difference of Megalodon fossil (right) and a spot tail shark (left). Photo Credits: Author.

Megalodons were Chondrichthyes; which means their skeletons were made of cartilage, which does not fossilize. Fortunately, the teeth made of bone have left a geographical trace of their life history. Based on the location of the fossil records, scientists believe Megalodons lived in temperate, tropical, and colder waters, which may indicate they could regulate their body temperature. The fossil records don’t only give scientists information about their geographical distribution; they have helped determine their size. Using the teeth dimension to jaw dimension ratio of great whites, scientists have estimated Megalodons were between 50-78 ft. in length and weighed in around 70-100 tons. Interestingly enough, Megalodons evolved from an extinct line of sharks (Otodonus), so even though we may picture Megalodons as enormous great whites, it is unlikely they looked like them. They may have been closer in resemblance to sand tiger sharks. This means we may be underestimating their size by using the great white ratio of tooth to jaw ratio.

Faked picture evidence of a Megalodon shark from the documentary Megalodon: the monster shark lives (2014). Photo Credit: Discovery Channel.

The Sharks and the Media

Since the release of Jaws, which increased the interest and fear of sharks, the Megalodon has attracted attention from the media. The Megalodon has inspired several science fiction shark movies. In 2014, a documentary called Megalodon: The Monster Shark Lives, was released by discovery channel on shark week. The story, which had short disclaimers at the beginning and ending indicating that it was fictional, was centered around the survival of the prehistoric shark, and unfortunately was perceived as real by a large portion of the public. This documentary received severe criticism from scientists, who were offended that this fictional documentary had been aired on a channel known for credible science shows. It did certainly expose the state of the public perception of sharks, as well as the role of media in the negative perception of sharks. It showed the interest of humans to learn real science and how the media had been using the fear of sharks to create sensationalist ratings. Fortunately, unlike Jaws, these fake documentaries inspired a new era of scientists who spread factual information and increased interest in these facts among the general public.

Example of a Megalodon being portrayed in media in science fiction movie Shark Attack 3: Megalodon. Photo Credit: David Worth.

Megalodon: The monster shark can help us predict the future

Given their size and predatory behavior, the Megalodon may have been the most important apex predator of its time. Given the known catastrophic consequences of apex predator removal (as seen in cases such as the sea otter disappearance in California, which resulted in an increase in sea urchins who consumed the kelp forests on the sea floor, triggering devastating consequences to the ecological chain) the extinction of apex predators has long been of interest to modern ecology. Understanding the factors behind the extinction of Carcharocles Megalodon, could give ecologists insight into the threats that lead to the extinction of an apex predator. This knowledge improves our understanding of the responses of marine species to these changes, presenting a unique perspective for the conservation of modern ecosystems.

Portrayal of the size of a Megalodon in relation to prehistoric whales. Photo Credit: Kerem Beyit.

It has been suggested that this species lived from the middle of the Miocene to the Pliocene (15.9–2.6 Ma). A study published in 2015 used a model to predict that C. megalodon went extinct around 2.6 Ma, and that gigantism in filter-feeding whales was established after the extinction. This pattern gives the first clue into the effect of the apex predator removal. It has been hypothesized that the extinction of the megalodon was caused by biotic factors including a decline in the diversity of filter-feeding whales, competition with predatory whales, or climatic factors such as climate change. A paper published in 2016 found no direct evidence of an effect in global temperature on the population size of megalodons. However; they found a drop in the diversity of filter‐feeding whales and the appearance of new competitors such as large predatory whales and great white sharks did correspond to drops in megalodon populations. The last piece of the puzzle was solved in 2017, a study analyzed the bite marks on marine mammal remains from the late Miocene and proposed that small-sized baleen whales could have been one of the target prey species for this shark. With the observation that the extinction of megalodon coincides with the collapse of various lineages of small baleen whales; we can predict this process was linked. It is important to note that diatom diversity and temperature changes (indicated by oxygen stable isotopes) have been associated with the changes in the diversity of marine mammals throughout the Cenozoic, so climate change may still be a relevant factor for the extinction. This interdependence tells us that controlling factors within ecosystems is not limited to top-down processes (processes in which predators keep prey populations at levels below the population size that would be observed in the absence of them). Bottom-up effects (population is regulated by resources and prey) are also important drivers in marine ecosystem dynamics.

What we can learn from the extinction of Megalodon is that we should also focus on the effect of prey when studying the potential for extinction in our apex predators. It is also important to note that the disappearance of Megalodon likely did not cause catastrophic effects like the sea otter disappearance because great whites and predatory whales had the same prey, mitigating the disappearance of the Megalodon. We have a lot to learn from our past and studies like this help us reconstruct ecological dynamics in order to help us predict the future of our oceans and improve our conservation efforts of apex predators.

Articles:
https://doi.org/10.1016/j.palaeo.2017.01.001
https://doi.org/10.1111/jbi.12754
https://doi.org/10.1371/journal.pone.0111086

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