Sharks are hardly newcomers to our planet. As a group they already exist at least 450 million years (opens in new tab), surviving four of the “Big Five” Mass Extinctionsincluding the catastrophe that wiped out the nonavian dinosaurs 66 million years ago at the end of the Cretaceous.
For context, that makes sharks older than dinosaurs, which arose about 240 million years ago, and even treeswhich evolved On Soil about 390 million years ago.
So how did you? sharks, as a group, has survived so long? What are the secrets of their success?
Related: What is the oldest shark?
One explanation could be that sharks are able to adapt their physiology in response to environmental conditions, such as shrinking in size as temperatures rise. This ability allows species to quickly adapt to rapidly changing ecological niches.
Sharks are close relatives of skates, rays and chimeras, all of which belong to a group of fish known as the chondrichthyes, which are distinguished in that most of their skeleton is made of cartilage rather than bone. Gene expression studies in ice skates have shown their adaptability when the water they live in changes several degrees in temperature. For example, a population of winter skaters (Leucoraja ocellata) living in Canada’s southern Gulf of St. Lawrence was able to adapt to water temperatures rising 18 degrees Fahrenheit (10 degrees Celsius) over a 7,000-year period by “drasically reducing its body size” by 45%, a 2016 study in the news Royal Society Open Science (opens in new tab) found it. In evolutionary terms, 7,000 years is a short time, leading scientists to think that the rapid change in winter skate size was due to an epigenetic response, where gene expression is altered by environmental factors, rather than natural selection, gradually selecting for smaller ones. individuals.
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 are unique in that they have very large genomes, which can contain genes that, although not useful now, , may have enabled them to tolerate the climatic conditions of the past.
In addition, several species of elasmobranchii, a subclass of the cartilaginous fish group that includes sharks, can move between freshwater and saltwater environments — a huge physiological challenge. The notoriously aggressive bull shark (carcharhinus leucas) is one of the most famous sharks that is Able to live in freshwater and saltwater environments (opens in new tab). This ability likely helped earlier shark species as global temperatures changed and huge amounts of freshwater entered the oceans as a result of melting ice sheets.
This versatility likely supports shark longevity as a group, said Gavin Naylor, director of the Florida Program for Shark Research. Sharks, for example, are found in different parts of the water column — living in deep oceans, shallow seas and even rivers — and can gobble up a range of food, including plankton, fish, crabs, seals and even whales, according to the Natural History Museum (opens in new tab) in London. In other words, if an area or food source is under threat, the diversity of sharks as a group means that while some species may experience difficulties or even extinction, others are likely to survive.
We usually think that sharks are exclusively carnivorous, but we now know that they are more diverse eaters, according to a 2018 study in the journal Proceedings of the Royal Society B (opens in new tab). This adaptability when looking for a meal may also have enabled them to survive times of scarcity.
But while sharks have avoided previous mass extinctions with their adaptability, they currently face an unprecedented challenge: human activity.
“Sharks have been able to cope with” climate changes fairly well in the past, but the biggest challenge facing the world’s sharks and rays today is overfishing,” Naylor said. “There are no clever tricks these animals can resort to to battle being out of the water. be fished.”
“The effects of pollutionpollutants and habitat loss likely also play a role in their loss in some places,” Lowe added.
sharks’ role in the total ocean ecosystem (opens in new tab) cannot be underestimated. Because so many sharks are apex predators, they likely play an important role in regulating the stability of organisms lower in the food chain. Predators are much less numerous than plankton, but they have an outsized effect because they feed on predatory fish that feed on herbivores that feed on the plankton.
“If you remove the apex predators, it disrupts the apple cart and can lead to all kinds of changes in the system,” Naylor said.
To read more about sharks and find featured shows during Discovery Channel’s Shark Week 2022 (July 24-30), visit Live Science’s Shark Week streaming guide.
Originally published on Live Science.