We as humans have an inherent drive to question the unthinkable and dive face-first into the unexplored mysteries our planet has to offer. We fanaticise and relish the idea of what our planet once looked like leaving us captivated by how our world today, came to be. To some, no such venture into the past is more alluring, than delving into the life behind the ocean’s largest ever apex predator, Otodus megalodon.
From the middle Miocene to the early Pliocene, 15.9-2.6 Ma (Million years ago), Otodus megalodon roamed our oceans. Spreading in range from tropical to temperate regions, this behemoth shark was found worldwide with abundant fossil evidence being found on every continent except Antarctica.
These sharks’ physical attributes are still debated but it is believed that Otodus megalodon ranged in length from 14.2-15.3 meters with suggestions from some scientific studies saying it could reach 18 meters in length. Nevertheless, these size estimations of the largest shark that ever lived, are simply of monstrous proportions.
In order to crush bone and incapacitate prey Otodus megalodon had immense bite force. A study by Stephen Wroe and colleagues from the University of New South Wales, reconstructed the bite mechanism of this shark yielding a bite force result of between 108,514 and 182,201 N (Newtons) in a posterior bite. In comparison, the largest ever recorded great white shark has an estimated bite force of 18,216 N.
With serrated teeth up to 7 inches long and the predicted most powerful bite force ever seen in the animal kingdom, Otodus megalodon would have had a majorly decisive role in the structuring of marine ecosystems in its era.
To understand Otodus megalodon’s past role in the global oceans, we must question what selection pressures and environmental factors allowed this animal to evolve to be so big. How do we piece this together from a palaeobiological standpoint? And lastly, how did an animal that evolved to be so dominant ever disappear?
At Napier aquarium in New Zealand a reconstruction of the Otodus megalodon jaws has been created with a cast model, not real fossils, to reveal the size of the jaws this animal possessed.
PHOTOGRAPH COURTESY OF Wiki commons
Otodus megalodon was the biggest member of the megatooth lineage, which is an extinct group of predatory sharks. Over geological time, from the early Eocene to the early Pliocene (54-2.6 Ma), the species of the megatooth lineage evolved larger teeth. From these extinct sharks, we mainly have tooth fossil evidence at our disposal, however these are a good indicator of the body size in lamnoid sharks such as Otodus megalodon. Paleobiologists use the crown height of the shark’s teeth to estimate the total length that the shark reaches. By utilising this method, it indicates that as tooth size increased in the lineage over geological time, there was a macro-evolutionary increase in the shark’s body size. Why did the Otodus megalodon get so big?
At such an immense size, this shark had the capability to eat a vast spectrum of prey types whilst it sat at the top of trophic levels. From analysing bone scrapes on ancient fossils of whale bones, paleobiologists have been able to piece together the makeup of its diet. The shark was believed to have fed upon many cetacean species such as dolphins and mysticetes along with bony and cartilaginous fish, sea birds and marine reptiles.
During the middle Miocene the fossil record indicates the appearance of a high diversity of small-bodied mysticetes, these are whales that feed using a filtering mechanism made up of baleen plates. In our oceans today we have large mysticetes such as humpback whales (Megaptera novaeangliae). This diversification in these species coincides with the appearance of Otodus megalodon. It is believed that this available food source had a role in driving the shark’s evolution in body size as it allowed them to obtain a greater quantity of fat to meet its ravenous calorific demands.
The illustration shows the massive proportions Otodus megalodon was predicted to reach. It is proposed that the diversification of mysticetes in the Miocene era provided the calories needed for such a huge animal to sustain its energy demands.
ILLUSTRATION BY Matt Martyniuk
Another suggestion as to how this shark reached these outlandish proportions was due to a selection pressure favouring larger sharks because of an ontogenetic dietary shift. To simplify this idea, it involves the principle that smaller shark individuals tend to avoid large prey as it is potentially dangerous to attack which risks possible injury or death. However, larger individuals with their increased size advantage can consume these bigger more dangerous prey types along with all the other smaller animals, allowing them to have a broader range of prey overall. This therefore implies that the size reached by the Otodus megalodon was due to a long-term selective pressure on large sharks favouring the consumption of a wider range of prey.
Due to such a range of prey, Otodus megalodon would require varying hunting techniques to tackle its victims. Bite marks on large extinct cetacean flipper bones and tail vertebrates suggest that Otodus megalodon would immobilize its prey before eating it. However, these bite marks may have been the result of scavenger sharks preying on already deceased cetaceans. The consumption of this energy-rich whale blubber could have been an important addition to Otodus megalodon’s diet and allowed it to reach its colossal size. The extant great white shark, which is believed to share many behaviours with Otodus megalodon, relies on whale carcasses for calories, commonly scavenging from them. Therefore, it may have been possible that this megatooth shark did the same.
There are clear unknowns surrounding the evolution of gigantism within this shark species. However, further research on body size patterns of other extinct large apex predators, such as other megatooth sharks or toothed whales, could add to our understanding of how these body size increases evolve.
This fossil of an Otodus megalodon tooth reveals the sheer size of their teeth responsible for biting and tearing flesh from their prey. Over time the shark species belonging to the megatooth lineage have evolved larger teeth.
Photograph by David Eickhoff
Despite the wishes of some, the world’s largest ever shark Otodus megalodon no longer patrols our global oceans, but how did it go extinct? It is difficult to picture how such a dominant apex predator met its demise. The starter of our clues lies in the dates. Knowing the time period at which this shark went extinct is vital for our insight into the ecology of the habitat and understanding the effects that its loss had on ancient communities. Therefore, this makes the subject highly debatable.
A recent study by Robert Boessenecker and colleagues in 2019, analysed a revised global dataset of Otodus megalodon fossils, revealing results that this shark was extinct by the end of the early Pliocene, 3.6 Ma. This is a somewhat older age than previously thought. A study before this put the date at 2.6 Ma for when Otodus megalodon went extinct. The variation in the believed ages of extinction can slightly alter the precited main reasons for why they went extinct.
The extinction of Otodus megalodon has been linked heavily to varying biotic factors, in particular competition from newly evolved species. It is not believed that this shark had any predators due to its size, but it had competition with other species over prey. Unexpectedly, the modern great white shark, Carcharodon carcharias, is the supposed culprit.
Evolving 5-6 Ma, the great white shark is believed to have competed with juvenile individuals of Otodus megalodon as both species would have been the same size at this growth stage. This is believed to have restricted a vital growth stage in the Otodus megalodon halting their development. This idea is supported by tooth fossil evidence. Otodus megalodon and the great white shark share similar tooth morphology which is a reliable indicator of diet type suggesting that these sharks competed for similar resources such as cetaceans and small whales. Coincidently, the loss of Otodus megalodon according to the earlier extinction date of 3.6 Ma, matches with the great white shark’s global expansion in our oceans. Therefore, this alludes to how as they became more widespread, their impact may have been ever more influential.
The evolution and global spread of the modern great white shark, Carcharodon carcharias, is believed to be a major factor in the extinction of Otodus megalodon in the early Pliocene.
PHOTOGRAPH BY Elias Levy
An additional reason believed for the extinction of Otodus megalodon is the loss of prey. The decline in global abundance of this shark species matches the drop in diversity of mysticetes, a believed prominent food source for these sharks. It is suggested that this triggered a process of co-extinction between predator and prey. However, the revised extinction time of 3.6 Ma from Boessenecker’s study, pre-dates the extinction of many of these mysticetes suggesting that this could not have had an impact on the shark’s extinction.
Further study of the late Pliocene marine mammals is definitely required to unearth the role they played in this extinction. For now, there appears to be more supported coherent evidence favouring the theory that the great white shark had the largest impact on Otodus megalodon extinction.
Following the idea that these sharks ate a wide variety of prey types, their loss would have had massive consequences for the ecosystem, opening up new niches to fill. It is proposed that this shark species extinction allowed for the establishment of gigantic filter-feeding baleen whales we see today to evolve due to reduced hunting pressures.
Although the extinction of the iconic Otodus megalodon may be upsetting for some, its loss may have helped open up a niche for the largest animals ever on this planet to evolve. If Otodus megalodon still roamed our seas today, we may have had a very different composition of marine fauna swimming through our oceans.
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