Ancient underwater volcanic eruptions may have made modern day sharks more fierce then their predecessors, a new study has found.
The infamous shark species we know of today evolved from stubby bottom dwellers around 93 million years ago when a spew of lava poured into the ocean, the study reported. This caused carbon dioxide levels to soar. This meant a drastic change in climate, making the ocean temperatures hotter than they had ever been.
And now, scientists have found that this was how some sharks developed their pectoral fins. They reached their findings by measuring over 500 sharks, and fossilized shark species, and published them in the journal Current Biology.
"The pectoral fins are a critical structure, comparable to our arms," University of California, Riverside doctoral student and the paper's first author Phillip Sternes said in a statement. "What we saw upon review of a massive data set, was that these fins changed shape as sharks expanded their habitat from the bottom to the open ocean.
"Their fins are comparable to the wings of commercial airplanes, long and narrow, to minimize the amount of energy needed for movement."
Today, most shark species still live on the ocean floor, in what scientists call the benthic zone. These benthic sharks are generally slender, flatter, and medium-sized predators, unlike the fierce, fast-swimming open-water sharks that dominate popular culture. Only about 13 percent of modern sharks are these swift open-water predators.
Researchers believe ancient sharks faced breathing difficulties due to low oxygen levels near the ocean floor during the Cretaceous period, prompting some to adapt to open waters.
During the Cretaceous period, sea surface temperatures were much warmer than today, averaging about 83 degrees Fahrenheit compared to today's 68 degrees. This high heat didn't happen overnight, and neither did the evolution of sharks.
"We had pretty warm open-sea surface temperatures throughout the era, and then a distinct spike that took place over a one- or two-million-year period," associate professor at Claremont McKenna College and paper co-author Lars Schmitz said in a statement.
As global warming drove the evolution of some animals, including sharks, it also led to the extinction of others.
However, predicting how sharks or other marine life will respond to current warming trends is challenging. Biologists have observed some sharks, including tropical species like tiger and bull sharks, moving farther north. Yet, it remains uncertain if these sharks can adapt to the rapidly increasing temperatures.
"The temperature is going up so fast now, there is nothing in the geologic record I am aware of that we can use for a true comparison," Sternes said.
The findings underline the complexity and uncertainty of predicting marine life responses to modern climate change, which is a topical concern for biologists and conservationists in the current day.
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