At a remote outcrop at nightfall on the coast of Papua New Guinea on May 3, 2022, scientists encountered something extraordinary: a walking shark. Using its fins to drag itself along, the tiny tan and black spotted shark moved through a tide pool that barely held enough water to brush its belly, moving like a clumsy sea lion as it dragged its body across the shore.
The creature was a shoulder pad shark (Hemiscyllium ocellatum), and is unique among shark species in its ability to walk on land. Forrest Galante, conservationist and biologist, recently shared rare footage of this unusual species in a new special for Discovery Channel Shark week called “The Island of Walking Sharks (opens in a new tab). “
“This is the first time in history that one of the Papuan epaulet species has been documented walking,” Galante said on the show. “This is so amazing.”
Scientists think that epaulette sharks, a species found along the southern coast of New Guinea and the northern coast of Australia, developed the ability to walk because it helped them forage for food in environments where other sharks could not survive.
“All strokes are selected for when it allows [a species] to survive better and get an environment where they are safe and can get food, “said Gavin Naylor, director of the Florida Program for Shark Research at the Florida Museum of Natural History in Gainesville. Shoulder sharks, which grow to about 3 , 3 feet (1 meter) long, swim in shallow water coral reefs to hunt crabs and other invertebrates, their favorite food. When the tide goes out, they are perfectly happy to go out into the tide pools and nibble on these creatures. “But once they’re done, they’re trapped,” Naylor, who wasn’t involved in the TV special, told Live Science. “What the shoulder pads have learned to do is climb the reef and jump into the next tide pool.”
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Shoulder reef sharks can drag themselves 30 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 ashore on one breath, as previously reported by Live Science. This ability also helps the shoulder pads thrive in the low-oxygen waters of tide pools.
Epaulette sharks likely have developed the ability to walk over the past 9 million years, scientists reported in a 2020 study published in the journal Marine and freshwater research (opens in a new tab). It is incredibly fast for sharks; to put that into perspective, hammerhead sharks, one of the youngest shark groups, evolved about 45 million years ago, according to natural History Museum (opens in a new tab) in London. And shoulder reef sharks are potentially forming new species at a remarkably fast rate, Naylor said. Due to the unique mobility of sharks, small populations are often isolated.
“You may have one that is in a part of the reef; then he decides to take a tour of Australia,” Naylor said. A river or other geographic barrier could move just enough to isolate a small group of sharks from the main population. Over time, these populations can become genetically distinct, as their genes randomly mutate and adapt separately from other gene pools, Naylor said.
A big question about these sharks that scientists hope to answer is how a species with so little genetic diversity within populations can produce individuals that differ so much in their appearance. The patterns in the shark’s signature spots of the shoulder pads vary so widely that no two individuals are exactly alike, and Naylor and other scientists suspect that the shoulder pads can actually transform their color patterns at will.
“We haven’t proven it, but we think it’s happening,” Naylor said.
Originally published in Live Science.