So – some sharks walk. Only not the scary ones.
While great whites haunt the depths, walking sharks are content to flee in shallow water.
They've been walking, or something like that, for at least 9 million years.
They are also evolutionary superstars: walking sharks may be the most recently evolved sharks on Earth.
This is according to the results published this week in Marine and Freshwater Research. Shark scientists have spent years sampling the DNA of the only known walking shark species to estimate when they evolved. They found four new species while they were there.
The youngest species may have evolved less than 2 million years ago. And by evolutionary patterns, this is recent – and a major contradiction to the widely held belief that sharks are slow to evolve.
"The discovery proves that modern sharks have remarkable staying power and the ability to adapt to environmental change," said Mark Erdmann, co-author of the article and vice president of Conservation International for Asia Pacific marine programs.
Sharks are older than dinosaurs, dominating the seas for up to 400 million years (the oldest dinosaur fossil it is believed to be about 240 million years old, in comparison). Therefore, the fact that sharks continue to evolve as recently as 399 million years later is quite remarkable.
How they walk and where they go
The walking sharks, also called "epaulette" sharks for their points that resemble military decoration, "walk" on their muscular fins to look for small fish along shallow reefs and sea grass.
It is a behavior partially driven by the change in sea level and the change in landscapes, which ended up influencing the place where most of the nine known species settled – eastern Indonesia and neighboring islands, New Guinea and parts of Australia.
Based on differences in shark DNA, scientists created estimated evolutionary schedules. They found that walking sharks began to separate from their evolutionary relatives about 9 million years ago.
During mass extinction events, carpet sharks, the group that includes walking sharks, were among the "most affected" animals, the researchers wrote. Sea levels have risen and ocean temperatures have dropped, causing sharks to migrate to warmer waters.
Sharks off the coast of Australia "hitchhiked" by moving plate tectonics to New Guinea, the researchers said. When the plates stopped moving, the land was established, creating barriers for species migration.
Perhaps this is why shark habitat rarely overlaps, they wrote.
Hope for the future of walking sharks
Erdman said the group hopes that its research will encourage conservationists to add some of the sharks to the IUCN Red List, a global inventory of threatened species, based on how little is known about them.
"A global recognition of the need to protect walking sharks will help ensure that they thrive, providing benefits to marine ecosystems and local communities through the value of sharks as a tourist asset," he said. "It is essential that local communities, governments and the international public continue to work to establish marine protected areas to help ensure that ocean biodiversity continues to flourish."