Mysterious sharks can walk on land without legs -thanks to evolution

A team of researchers from Florida Atlantic University and Australia’s James Cook University study a unique species of shark called epaulette sharks. Young members of this species have learned to walk on land using their paddle-shaped fins. They can also live without oxygen for about two hours and search for prey in reef regions where most other sharks would never come.

Since epaulette sharks are known to feed only on aquatic animals like small fish and not on land animals, they mostly walk in and around the reef. However, during the study, the researchers noticed that sometimes the sharks walked up to 30 meters on the dry land using their fins. The epaulette sharks' strange abilities are being viewed as an evolutionary step toward surviving the ongoing climate crisis.

The study's authors explained this further, “such locomotor traits may not only be key to survival but also may be related to their sustained physiological performance under challenging environmental conditions, including those associated with climate change.”

Are there any other sharks that can walk?

The scientific name of the epaulette shark studied by the researchers is Hemiscyllium ocellatum. Interestingly, they are not the only shark species that can walk. A study published in 2020 reveals that at least nine shark species have developed the ability to dwell on land using their fins.

They all belong to the genus Hemiscyllium, and most members of the genus are limited to reefs in the Malay Archipelago region. However, Hemiscyllium ocellatum is the first Papuan epaulette shark species (sharks dwelling around the coast of Papua New Guinea) known to have developed the walking ability.

It also plays an essential role in ensuring their survival. For instance, when a predator follows epaulette sharks, they can walk into small reef crevices with the help of their fins, or if needed, they can also drag themselves to dryland. Moreover, their walking ability allows them to forage where they are likely to face less competition.

These walking sharks are evolving fast to survive climate change

During their study, the researchers found that compared to many other aquatic species, epaulette sharks are better equipped to face climate change. Their ability to survive without oxygen makes them well-suited to meet increased CO2 concentration and tolerate conditions like hypoxia (oxygen deficiency in blood and body tissues) that may arise due to climate change.

The rate of evolution is also pretty fast in epaulette sharks. For instance, it took them only about nine million years to develop fins that could help them walk. The unique long-tail shark, the thresher shark, had to wait for 55 million years to evolve. Moreover, despite having less genetic diversity in their population, they are giving birth to new species at incredible speeds.

The researchers claim that when it comes to survival-focused evolutionary development, epaulette sharks break all rules. However, more research is required to investigate further the factors affecting the walking and other unique talents of the epaulette sharks.

The study is published in the journal Integrative and Comparative Biology.

Abstract:

The epaulette shark, Hemiscyllium ocellatum, is a small, reef-dwelling, benthic shark that—using its paired fins—can walk, both in and out of water. Within the reef flats, this species experiences short periods of elevated CO2 and hypoxia as well as fluctuating temperatures as reef flats become isolated with the outgoing tide. Past studies have shown that this species is robust (i.e., respiratory and metabolic performance, behaviour) to climate change relevant elevated CO2 levels as well as to be hypoxia and anoxia tolerant. However, epaulette shark embryos reared under ocean warming conditions hatch earlier, smaller, with altered patterns and colouration, and with higher metabolic costs than their current-day counterparts. Findings to date suggest that this species has adaptations to tolerate some, but perhaps not all, of the challenging conditions predicted for the 21st century. As such, the epaulette shark is emerging as a model system to understand vertebrate physiology in changing oceans. Yet, few studies have investigated the kinematics of walking and swimming, which may be vital to their biological fitness, considering their habitat and propensity for challenging environmental conditions. Given that neonates retain embryonic nutrition via an internalized yolk sac, resulting in a bulbous abdomen, while juveniles actively forage for worms, crustaceans, and small fishes, we hypothesized that difference in body shape over early ontogeny would affect locomotor performance. To test this, we examined neonate and juvenile locomotor kinematics during the three aquatic gaits they utilize—slow-to-medium walking, fast-walking, and swimming—using 13 anatomical landmarks along the fins, girdles, and body midline. We found that differences in body shape did not alter kinematics between neonates and juveniles. Overall velocity, fin rotation, axial bending, and tail beat frequency and amplitude were consistent between early life stages. Data suggest that the locomotor kinematics are maintained between neonate and juvenile epaulette sharks, even as their feeding strategy changes. Studying epaulette shark locomotion allows us to understand this—and perhaps related—species’ ability to move within and away from challenging conditions in their habitats. Such locomotor traits may not only be key to survival, in general, as a small, benthic mesopredator (i.e., movements required to maneuver into small reef crevices to avoid aerial and aquatic predators) but also may be related to their sustained physiological performance under challenging environmental conditions, including those associated with climate change—a topic worthy of future investigation.