Why Did ‘Fish’ Go to Such Lengths to ‘Land’?

A spiny seahorse is 'walking' on the beach.The fish got on land, how could it survive?We all know that life originated in the ocean. The vast ocean occupies 71% of the Earth's surface and sustains a huge number of species.However,3.75 million years ago, a group of fish began to leave the aquatic environment, becoming the earliest tetrapods to settle on land.This is one of the most important events in the history of life.Which group of fish was the first to come ashore? What caused them to come ashore?What fish was the first to make this major move?Among the many fish fossils that flourished between 4.5 million and 7 million years ago, many fish have evolved muscles and bony structures in their fins.The most common of these are holosteoan fish.▲ The second spiny seahorse discovered, is the model specimen of the new species Indonesian spiny seahorse (Latimeria menadoensis).Therefore,In 1938, fishermen dragged a living spiny seahorse onto the South African coast.This excited evolutionists. It was a good opportunity to show the body structure and internal anatomy of these ancient fish. However, the fishermen destroyed the fish and threw away all the important internal organs.Subsequently, scientists searched again in the southern and eastern coastal areas of Africa, trying to find more samples. This search yielded abundant results, but they couldn't find any spiny seahorses.In 1952, they finally found another spiny seahorse.This was caught off the north coast of Madagascar. The locals didn't like this strange creature very much because its meat was not particularly delicious, and it would fight fiercely once hooked.▲ A specimen of the Sunda spiny seahorse in 1974. Sunda spiny seahorse, also known as East African spiny seahorse, is one of the species in the Holosteoan suborder. Fig/WikipediaEven so, locals still catch a few of them every year,Scientists then had a large number of samples for detailed study.Later, another population of spiny seahorses was discovered in Indonesia.Underwater photographers on a submarine took pictures of them,showing their swimming process. Spiny seahorses swim gracefully, sometimes using their strange and fleshy fins to push themselves along the seabed like a boat.Detailed anatomical studies showed that,spiny seahorses are a very ancient group,but despite this,they don't have any close relationship with the earliest tetrapods that came ashore.▲ The life reconstruction diagram of Titani. Fig/WikipediaTherefore, scientists began to study the common ancestors of terrestrial vertebrates again.In 2004, paleontologists discovered a more likely candidate on the northeast coast of Canada, Ellesmere Island. The Inuit people saw these fossils, calling them 'Tiktaalik',This is the name they gave to the codfish, which is a large fish that is frequently caught by locals in freshwater.Now, 'Tiktaalik' has become the scientific name of this fossil creature.However, Tiktaalik is unlike any fish or other living organism.▲ The redrawn diagram of Titani. Fig/WikipediaIt is about two meters long, with a large and flat head, eyes similar to crocodiles, and fins that resemble limbs.Its body is protected by scales, and it has a neck-like structure. Its importance lies in its 'limbs'.Its 'front limbs' have fins, which are familiar to you as fins of fish. But their muscle bases are bone-like and form joints at the elbows and wrists.This is obviously a limb that can help it leave the water.How did the fish survive on land?In order to complete this major crossing, 'Tiktaalik' like the first terrestrial invertebrates, had to solve two problems: first, how to leave the water; second, how to obtain oxygen from the air.We can refer to a living animal that can complete these two things at the same time, which is a spiny seahorse. Spiny seahorses and the pioneering spiny seahorses that came ashore don't have any close relationship because they don't have any genetic relationship. But even so, spiny seahorses can still give us some clues about how the first spiny seahorses completed this major move.▲ A picture of a Guangdong spiny seahorse, which is a species of spiny seahorse in the family of spiny seahorse. Fig/WikipediaSpiny seahorses are only a few centimeters long, you can find them in many tropical red mangrove swamp and muddy estuary,They often lie in the shimmering mud surface with glittering mud, some even cling to the arched pillars and breathing roots of the red mangrove, or crawl onto the branches. They are easily startled by sudden movement or noise, and quickly return to the water safely.They come out of the water to hunt insects and other invertebrates that gather on the soft mud surface.Spiny seahorses suddenly bend their bodies and jump to move, but they also use a more common and gentle way of movement, that is to use their chest fins to move forward. Each chest fin has a muscle base, and internally it has bone support. In fact, chest fins are like sturdy walking sticks, and with them, spiny seahorses are like having support points, and they can move forward.▲ A picture of a spiny seahorse on the beach. Fig/WikipediaBut how did it breathe in the water?Spiny seahorses use their mouths to suck in water, and by waving their heads, they make water rotate on the mucous membranes of their mouths, to obtain oxygen in the water.In addition, they also absorb some oxygen directly from the air through their moist skin,But these only allow them to stay out of the water for a short time. Within a few minutes, they must return to the water to moisten their skin and take a breath.Spiny seahorses cannot stay out of the water for too long, otherwise they will dry up and die. However, another creature has found a solution.▲ African Lungfish. In Africa, during the dry season, the surrounding flood plains were dried up by the scorching sun, and many swamps became hard soil. However, a fish – the lungfish – was able to survive.It has both gills and lungs,and lives in a nest on the bottom of the stream. When breeding, the lungfish becomes very similar to fish.It swims by moving its side fins and bending its body and flapping its tail. During courtship, some species have brightly colored 'head crests' on their backs, like finlets.Female lungfish lay large numbers of eggs, each egg attached to the leaves of aquatic plants. When the larvae hatch, they are even more like fish than their parents, because they don't have limbs and don't breathe with lungs, but they breathe with gill filaments, which will develop later.▲ An old goldbar lungfish. Fig/WikipediaSome lungfish have even further returned to aquatic life,they have completely lost their hind limbs and their forelimbs are greatly reduced and have no bones, only cartilage, so their limbs have no practical effect in movement.▲ A picture of a Goldenbar lungfish in Guangdong. Fig/WikipediaWith it coming from the same origin,the African lungfish,although it still retains limbs, but its limbs are very small, and it is necessary to observe carefully to find them. In fact, because the African lungfish looks very much like a fish, it is called 'Congoro Lungfish' locally.- END -Edited by: West Lake VinegarImages not attributed: 'The Evolution of Life'Part of the content is from 'The Evolution of Life', with modifications

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