The Earth is home to an incredible number of species: some are well known to scientists, while the existence of others is still shrouded in mystery.. It is known that whales are the largest animals on Earth, and their life expectancy may be twice as long as scientists previously thought, but this is not all the secrets of whales - in a new study, scientists have revealed details of the evolution of these sea giants, writes IFLScience.

It is known that the ancestor of all four-legged creatures on Earth crawled out of the ocean about 400 million years ago.. Then, 350 million years later, the ancestors of modern whale species crawled back into the ocean to thrive.. Descendants of these ancient creatures that roam Earth's oceans today may be some of the ocean's largest and most talked about species.. Scientists have already discovered that whales have an amazing lifespan, impressive hunting techniques and an interesting history.. They are also found in animals not only in the ocean, but throughout the planet.

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In a new study, scientists turned back time to reconstruct the evolutionary history of whales.. Surprisingly, the closest relative of whales is the hippopotamus - they are not at all similar, have different habitats, diets and distributions. And yet, despite its semi-aquatic lifestyle, the large land animal actually turned out to be extremely closely related to the largest mammal on Earth.

Scientists believe hippos evolved from a non-aquatic group known as anthracotheriums about 15 million years ago. At the same time, whales originated more than 50 million years ago from creatures that lived on land. Somewhere in the distant past in evolutionary history, hippos and whales shared a common ancestor that was also terrestrial.

It is believed that one of the earliest ancestors of land whales was the whale known as Pakicetus, also known as the " Scientists believe that this creature walked on four limbs and ate the meat of land animals and fish.. It was first discovered in 1983 and must have lived on the edge of the Tethys Sea in what is now Pakistan and India.. Fossils have shown that it had an auditory bone similar to modern whales, with a unique structure that could even allow Pakicetus to hear underwater.

Next, creatures evolved that moved further into the water, adapting to the new environment. One of them is considered to be Ambulocetus, who lived on the planet about 50-48 million years ago.. This species was distinguished by a long tail for swimming and four limbs, but could spend time both on land and in water.

After Ambulocetus, about 40–33 million years ago, dorudontids and basilosaurids appeared. The latter were distinguished by tiny hind limbs, and their nostrils were located further back - it is assumed that this is an intermediate stage between the snout and the blowhole. Dorudontids reached a length of about 5 meters, had tiny hind legs and flippers. They also spent all their time in the water.

According to cetacean researcher Dr. Ellen Coombs, over the course of 8 million years, whales' ancestors transitioned from a completely terrestrial lifestyle to a completely aquatic one.. By the way, from an evolutionary point of view, this is actually incredibly fast..

It is known that it was the descendants of Dorudon that actually became modern whales. Baleen whales began evolving their filter feeding with flatter skulls about 34 million years ago, while others retained their teeth and became killer whales, sperm whales and dolphins. In fact, it was during this period that the separation of toothed and baleen whales occurred - the animals underwent physical changes to adapt to new diets.

Genetic studies have shown that along with the hind limbs and physical changes seen in the fossil record, cetaceans lost much more than just legs when they returned to the ocean. Previous research has also shown that cetaceans have lost a gene that controls saliva production.. In addition, toothed whales also discovered most of their smell and taste genes. Scientists also believe that genetics will ultimately be able to explain why whales became the largest animals on the planet..

Previously, Focus wrote that scientists named the culprit for the complete extermination of two species of whales.