At a remote outcrop at nightfall off the coast of Papua New Guinea on May 3, 2022, scientists encountered something incredible: a walking shark. Using its fins to drag itself, the diminutive tan and black-spotted shark fluttered through a tidal pool that contained barely enough water to clean its belly, moving like a clumsy sea lion as it dragged its body along the shore.
The creature was an epaulet shark (Hemiscyllium ocellatum), and is unique among shark species in its ability to walk on land. Forrest Galante, a conservationist and biologist, recently shared rare footage of this unusual species in a new Discovery Channel special Shark week called “Walking Shark Island”. (opens in new tab).”
“This is the first time in history that one of the Papuan species of epaulettes has been documented to walk,” Galante said on the show. “This is so amazing.”
Scientists believe that epaulet sharks, a species found along the southern coast of New Guinea and the northern coast of Australia, evolved their ability to walk because it helped them search for food in environments where other sharks could not survive.
“All traits have been selected where possible [a species] to better survive and create an environment where they are safe and can get food,” said Gavin Naylor, director of the Florida Shark Research Program at the Florida Museum of Natural History in Gainesville. Epaulet sharks that grow to about 3.3 feet (1 meter) long, swim shallow coral reefs to hunt crabs and other invertebrates, their preferred food. When the tide goes out, they are perfectly happy hanging out in tide pools and munching on these critters. “But once they’re done, they’re trapped,” Naylor, who was not on the TV special, told Live Science. “What epaulettes have learned to do is climb into the reef and wash up on the next tide.”
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Epaulet sharks can be dragged 100 feet (30 m) or more across land, Naylor said. And walking with fins isn’t the only adaptation that allows them to do so; this species can survive when oxygen is scarce by spending up to an hour on land in one breath, Live Science previously reported. This ability also helps epaulettes thrive in the low-oxygen waters of tidal pools.
Epaulette sharks likely evolved their ability to walk in the last 9 million years, scientists reported in a 2020 study published in the journal Marine and Freshwater Research (opens in new tab). This is incredibly fast for sharks; to put this in perspective, hammerhead sharks, one of the youngest groups of sharks, evolved about 45 million years ago, according to Museum of Natural History (opens in new tab) in London. And epaulette sharks are potentially forming new species at remarkably fast rates, Naylor said. Due to the unique mobility of sharks, small populations often become isolated.
“You might have one that’s in one part of the reef; then he decided to go on an Australian walk,” Naylor said. A river or other geographic barrier can shift enough to cut off a small group of sharks from the main population. Over time, these populations can become genetically distinct because their genes mutate randomly and adapt separately from other gene pools, Naylor said.
One big question about these sharks that scientists hope to answer is how a species with so little genetic diversity in its populations can produce individuals that vary so much in appearance. The patterns in the epaulet shark’s distinctive spots vary so widely that no two individuals look exactly alike, and Naylor and other scientists suspect that epaulettes can actually change their color patterns at will.
“We haven’t proven it, but we think it’s happening,” Naylor said.
Originally published on Live Science.