The very first representatives of sharks originate more than 400 million years ago. A new work by an international team of scientists, published in the journal Marine and Freshwater Research, traces the evolution of the Indo-Australian feline shark (Hemiscyllium), also known as "walking" sharks. These cartilaginous fish, first discovered in 2006, split from their ancestor only nine million years ago, and can be considered the youngest shark species today, according to scientists.
Small sharks Hemiscyllium, reaching 1.2 meters in length, live in the waters of northern Australia, in eastern Indonesia and near the island of New Guinea, have an elongated cylinder-shaped body, spiracles (spiracles), small antennae, spotted "camouflage" color and live at the bottom, on which they seem to "walk" with the help of fins. Moreover, such sharks often "come out" to the shore and roam the sand.
“At an average of less than a meter in length, walking sharks pose no threat to humans, but their ability to withstand low oxygen environments and walk on fins gives them a remarkable advantage in capturing small crustaceans and molluscs,” writes Christina Dudgeon, Marine biologist from the University of Queensland, one of the authors of the article. "These unique features did not go to their closest relatives - bamboo sharks - or more distant relatives - carpet sharks, as well as whales."
In the study, which lasted 12 years, nine species of "walking" sharks (Hemiscyllium henryi, Hemiscyllium ocellatum, Hemiscyllium freycineti, Hemiscyllium galei, Hemiscyllium michaeli, Hemiscyllium halmahera, Hemiscyllium stramishanium, hallcyllare) were studied. As scientists note, each of these species "are similar in body size and morphology, but can be easily differentiated based on color patterns." In addition, according to the authors of the work, all species "have a unique way of locomotion", "wandering" on the seabed in search of food on their muscular fins.
“We found that sharks, which use their fins to 'walk' on shallow reefs, evolutionarily split from their closest common ancestor about nine million years ago and have since split into a group of at least nine sharks,” says Mark Erdmann, co-author of the study. “It may seem like it happened a long time ago, but sharks have ruled the oceans for over 400 million years. This discovery proves that modern sharks have remarkable evolutionary endurance and the ability to adapt to environmental changes."
Hemiscyllium galei / © Gerald R. Allen, Department of Aquatic Zoology, Western Australian Museum, Perth
Hemiscyllium freycinceti / © Raja Ampat
According to scientists, the environment, including changes in sea level, the appearance of terrain, the formation of reefs and the spread of sharks in new places, played a decisive role in the formation of this species and their evolution. Analysis of mitochondrial DNA shows that Hemiscyllium emerged after a group of sharks migrated from their original population - Chiloscyllium punctatum, a brown-striped cat shark - and subsequently, due to adaptation to new tropical habitats, acquired genetic differences.
Phylogenetic tree showing the relationship between Hemiscyllium species relative to the original population of Chiloscyllium punctatum / © Marine and Freshwater Research
Three species of "walking" sharks have already been included in the Red Book of the International Union for Conservation of Nature. In the near future, the list may be supplemented by other representatives of Hemiscyllium. In addition, biologists do not exclude that even more relatives of these fish will be found in the future.
“Global recognition of the need to protect these sharks will help ensure their prosperity. - adds Erdmann.“It is important that local authorities, governments and the entire international community continue to work towards establishing marine protected areas to conserve ocean biological diversity.”