Great Whites Competitors, Not Children of Megalodon

Imagine witnessing a white spot moving quickly up from below. From a blur of white and gray it turns into an open mouth, two black eyes and large winglike fins. In 3 seconds the image transforms from a vague spot to a great white grin. Five rows (with two protruding rows) of around 300 triangular serrated teeth line a jaw of cartilage around 1 meter (three feet) wide in a mature great white shark sized around 5-6 meters (16.5-20 feet).

Now image a shark 3-4 times larger with a mouth 2.9-3.7 meters ( 9.5- 12.1 feet) with teeth 18 centimeters (9.1 inches) long and with distinct serrations. The megalodon (Otodus megalodon), the largest shark ever to live, could grow up to 20 meters or 60 feet long. Based on descriptions from the fossil record, megalodon (Greek for big tooth) had six to seven rows of teeth. The front row teeth numbered around 46, with 24 in the upper jaw and 22 in the lower, with a total about 276 teeth.

This magnificent shark was the apex predator of the sea, until it went extinct about 2.6 million years ago.

Scientists are uncertain what caused the megalodon to go extinct, but the demise of the this shark occurred during a period of cooling and drying in many parts of the world at the end of the Pliocene, perhaps impacting its range and availability of prey species. Some scientists have proposed that competition for the same food source may have been a contributing factor.

A 2019 study suggested the possibility of the evolution of the great white shark (Carcharodon carcharias) may have contributed to the extinction of megalodon.

Now, a new study published in the journal Nature Communications has added to the theory that great white sharks may have helped push their larger cousins forever into the fossilized record.

The Truth is in the Tooth

Shark teeth are heavily mineralized and preserve well as fossils. Given that sharks can shed thousands of teeth over their lifetime, they provide unique clues into the past. The team lead by researchers at the  Max Planck Institute for Evolutionary Anthropology, in Leipzig, Germany measured zinc isotopes in fossilized teeth from both megalodon and white sharks.

Using teeth from more than a hundred sharks, drawing from species alive today and fossilized, the researchers confirmed that the zinc isotope values of sharks living today, reflect their place in the ecosystem. This work is based on a previous study showing zinc Isotope ratios are indicators of diet and trophic levels in arctic marine mammals. Zinc isotope levels in the teeth of present-day mammals correlate with where they fall in the food chain. The higher up the food chain an animal is, the lower the zinc isotope values they show. For example, sharks that eat small fish have higher values of zinc than sharks that are higher in the food chain that eat whales.

Based on mineral analysis, the authors suggest that ancient great white sharks consumed the same kinds of prey that the much larger shark ate. If the great white was eating the same kinds of prey, then the smaller sharks may have competed with the megalodon for food. If so, they might have contributed to its eventual demise, alongside potential changes in other aspects of the ecosystem, like climate. This evidence helps to support the theory that competition with the great white, might have been one factor that removed the mighty megalodon forever from the high seas.

Cousins Not Descendants

The similarity in shape and design of teeth between white sharks and Megalodon have lead to the perception that modern day white sharks are the smaller counterparts evolved from megalodon. Given the absence of a complete fossil record, scientists built the image of megalodon into a great white shark on steroids. This image of a ferocious ship swallowing super predator has intrigued many, and fueled many a Shark Week episode and films like The Meg.

The relationship between white sharks and megalodon was first formalized by the, a Swiss naturalist Louis Agassiz who first named megalodon (Carcharodon megalodon) in 1843. Agassiz, observed that great white shark teeth and the fossil megalodon teeth were both serrated, and placed megalodon into the same genus as white sharks, Carcharodon. However, new data analysing tooth morphology and root type confirmed that megalodon is not ancestral to the great white shark. Therefore megalodon was placed into a new genus, Carcharocles. Further investigation and analysis of dentition lead scientists to again reclassify megalodon into the genus Otodon, more closely related to the extinct O. obliquus and represents a separate lineage from the great white shark.

Instead, it is believed that white sharks are more closely related to mako sharks, both in the family Laminidae. Fossils of a newfound species of shark, Carcharodon hubbelli, suggest the modern great white actually may have descended from broad-toothed mako sharks. Using computer-assisted imaging and measurement methods Nyberg and Wray of Duke University and Charles Ciampaglio of Wright State University examined the similarities and differences among great white, megalodon and extinct mako teeth. They determined that the extinct mako and great white teeth and roots were similar in shape and clearly distinct from megalodon. Instead, white sharks evolved from a more moderate-size, smooth-toothed relative of mako sharks.

So much attention is given to white sharks, much of it negative. As we discover the relationships of sharks over time and their role in marine ecosystems, we cannot overlook the current crisis facing many species of shark’s survival. Over one third of shark species are threatened with extinction largely due to overfishing. If we do not act now, many modern-day sharks will follow the megalodon, and in a far shorter time span.