
Credit: Phillip Sternes/UCR. Top row: Pelagic Sharks - open water/in the water column; middle row: Benthopelagic sharks - near bottom, sometimes in water column; Bottom row: Benthic sharks - live on the bottom/seafloor.
Key points:
- A global warming episode millions of years ago triggered the evolution of fast-swimming, open-water sharks from bottom dwellers.
- These sharks responded to the heat with elongated pectoral fins that allowed them to swim in ocean regions with more oxygen.
- Researchers are unable to accurately predict how sharks and other marine life will respond to the current rapid warming trends.
A new study, published in Current Biology, reveals that today’s sharks evolved from bottom dwellers during a global warming episode millions of years ago. Their findings suggest that some sharks responded to this dramatic heat with elongated pectoral fins.
Researchers collected body length and fin measurements from over 500 living and fossilized shark species. This data allowed them to correlate higher temperatures, tail movement, and swimming speeds. They found that during evolution, open water sharks became faster relative to bottom dwelling sharks due in part to their longer pectoral fins.
“The pectoral fins are a critical structure, comparable to our arms,” explained study author Phillip Sternes of University of California – Riverside. “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.”
Most living shark species are bottom dwellers and only about 13% of modern sharks are fast-swimming open-water predators. Based on their analysis, the research team believes that these species are a result of decreased oxygen levels near the bottom of the ocean during the Cretaceous period that would have made breathing challenging for their ancient relatives.
Despite their findings related to global warming’s ability to drive shark evolution, researchers are unable to predict how sharks and other marine life will respond to the current warming trends. Some sharks – tropical species including tiger and bull sharks – are starting to swim farther north, but scientists do not know if sharks will be able to successfully adapt where they live and survive the rapidly increasing heat.
“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 comparison,” said Sternes.