How Did Prehistoric Sharks Gets so Big?

A great white shark on the hunt

Post Author - J. Carlin Decker III

Sharks have notoriously gotten a bad rap in in our culture for being violent and dangerous, but most species actually tend to be rather docile, and not at all aggressive. The horrors portrayed on the big screen, making the sharks seem bigger and scarier than real life, may not be like the sea predators of today, but during the Cretaceous Period, sharks might have been similar to those inspirations.

About 122 million years ago, the oceans were significantly warmer, and the heat had many species of sharks adapt and grow to larger sizes. The peak temperatures of the Cretaceous oceans were around 83 degrees Fahrenheit, while the average temperatures of the oceans today are about 68 degrees Fahrenheit. Most species of shark are benthic, or bottom feeders, and they can live on the sea floors. Recent research suggests that Cretaceous ocean floors may have been oxygen-scarce regions, and forced benthic sharks to adapt to open-water lifestyles.

Data tracking muscle cycle frequency in sharks, allowing for speculation in their swimming speeds

With this adaptation comes an increase in size. To chart through the open seas, the stubby fins of the benthic lifestyle simply wouldn’t do, and sharks developed longer pectoral fins to swim through the ocean. The warmer waters also would help the sharks’ muscles contract quicker, and they were able to move their fins faster, thus allowing them to swim faster. This allowed these Cretaceous sharks to expand their range, catch faster prey, and outswim larger marine predators. 

The rise of the Cretaceous ocean temperatures forced many species of shark to grow large and assimilate, however, not all species were able to adapt, and the rising temperatures resulted in mass extinction. As the Earth’s current sea temperatures are rising at dramatic rates, would it be possible to observe such gigantism in marine life? It is unlikely as the ocean temperature rise is extreme, and such evolutionary change takes place over millions of years.