More than 100 million years ago, researchers believe that sharks evolved into larger, faster, and more powerful predators due to warming seas and reduced oxygen levels. A recent study published in the journal Current Biology examined the fin sizes and body lengths of 500 extinct and living sharks, comparing this data with the evolutionary shark family tree. The findings suggest that during the Cretaceous period, when ocean temperatures rose dramatically, some sharks transitioned from living on the seafloor to swimming in the open ocean. This change in habitat likely influenced their fin and body structures, leading to alterations in size and swimming capabilities.
Contrary to popular belief, not all sharks resemble the terrifying creatures depicted in movies like “Jaws.” Many sharks are benthic, meaning they feed on the ocean floor. Unlike their pelagic counterparts, benthic sharks do not need to constantly swim to breathe, as they can rest on the seafloor. However, the need for oxygen may have driven some sharks to migrate higher into the water column during the Cretaceous period. The researchers suggest that as oxygen levels decreased on the ocean floor, sharks adapted by moving to higher altitudes.
The study highlights the changing pectoral fins of ancient pelagic and benthic sharks as evidence of this habitat shift. Pelagic sharks typically have elongated fins, while benthic sharks have shorter fins. According to Lars Schmitz, a biology professor at Claremont McKenna College and co-author of the paper, these fin differences reflect the evolutionary changes that occurred as sharks adapted to new environments.
Overall, the research sheds light on the remarkable evolution of sharks in response to environmental shifts millions of years ago. By understanding how these ancient creatures adapted to changing conditions, scientists can gain valuable insights into the resilience and versatility of sharks as a species. The study serves as a fascinating glimpse into the deep history of these iconic predators and how they have evolved over time.
