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Sharks as a group have existed for at least 450 million years, surviving four out of five mass extinctions, including the catastrophe that wiped out the dinosaurs 66 million years ago.
For context, this makes sharks older than dinosaurs, which appeared roughly 240 million years ago, and even trees, which evolved on Earth about 390 million years ago.
So how have sharks, as a group, survived so long? What are the secrets of their success?
One explanation may be that sharks are capable of modifying their physiology in response to environmental conditions, such as decreasing in size when temperatures rise. This ability enables the species to quickly adapt to rapid changes in ecological areas, according to Kosovapress.
Christopher Lowe, a professor of marine biology and director of the Shark Lab at California State University Long Beach, told Live Science that some sharks have large genomes, which may contain genes that may have enabled them to tolerate the conditions. past climates.
Additionally, some species of elasmobranchii, a subclass of the cartilaginous fish group that includes sharks, can move between freshwater and saltwater environments—a major physiological challenge.
Carcharhinus leucas is one of the most well-known sharks that is capable of living in both fresh and salt water environments. This ability likely helped past shark species when global temperatures were changing and large amounts of fresh water were entering the oceans due to melting ice.
That versatility likely supports the sharks’ longevity as a group, said Gavin Naylor, director of the Florida Shark Research Program.
For example, sharks are found in a variety of places that live in deep oceans, shallow seas, and even rivers, and can ingest a variety of foods, including plankton, fish, crabs, seals, and even whales, according to Natural History Museum in London.
Put another way, if an area or food source is threatened, the diversity of sharks as a group means that while some species may experience hardship or even extinction, others are likely to survive.
We usually think of sharks as exclusively carnivorous, but now we know they’re more diverse eaters, according to a 2018 study in the journal Proceedings of the Royal Society B. This adaptability when searching for a meal may have also allowed them to survive times of scarcity.
But while sharks have managed to avoid previous mass extinctions with their adaptability, they are currently facing an unprecedented challenge: human activity.
“Sharks have been able to cope quite well with climate change in the past, but the biggest challenge for the world’s sharks and rays today is overfishing. There are no clever tricks that these animals can use to combat fishing out of the water,” Naylor said.
The effects of pollution and habitat loss may also contribute to their loss in some places.
The role of sharks in the overall ocean ecosystem cannot be understated. Because so many sharks are apex predators, they likely play important roles in regulating the stability of organisms lower in the food chain.
Predators are much less abundant than plankton, but they have a huge effect as they feed on predatory fish that feed on plankton-eating herbivores.
“If you remove top predators, that can result in all kinds of changes in the system,” Naylor said.
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