The origins of our planet and its ancient history have fascinated human beings since the dawn of civilization. According to Science Alert, more than 35 million years ago, the ancestor of modern cetaceans—fully aquatic mammals like whales, dolphins, and porpoises—returned to the sea, aided by their unique eyesight that allowed them to see in the depths
It may surprise many people that cetaceans evolved from land-dwelling ancestors. This is evident from many of its characteristics. Cetaceans breathe air, nurse their young with milk, and their fins enclose the bones that mark five “fingers.” Before birth, the small hind limbs of their embryos disappear.
If you look at whales and hippos, which are close relatives, you will notice that the two have similar traits. Both whales and hippos evolved from four-legged, ungulate (ungulate) ancestors that roamed the earth about 50 million years ago. Today’s ungulates are animals such as hippos, giraffes, deer, pigs and cows.
The cetacean ancestors returned to the sea and, over 8 million years, evolved into sea-dwelling creatures.
Basilosaurus, which were these massive prehistoric whales, were originally thought to be dinosaurs, before scientists realized they were mammals. Basilosaurus was longer than modern whales, with smaller hind legs and front flippers. They had nostrils between the tip of Basilosaurus’s snout and forehead, as well as the same ear bones found in modern whales. Basilosaurus was halfway between the transition from prehistoric ungulate ancestors and the modern whale.
No one knows why some prehistoric ungulates returned to the sea. Some believe that they liked to feed on plants near large bodies of water because they could hide in the water whenever a predator approached. As they spent more time there, their bodies adapted to move in water, with their front legs turning into flippers, fat replacing their skin, and their bodies becoming smoother to move through. water more easily. Their tails become longer, stronger and larger, allowing them to move through the sea. Meanwhile, its hind legs shrank in size. The nostrils moved upwards, which allowed them to breathe without having to move their heads up while swimming. As their diet changed, some of them became bearded and lost their teeth.
One of the biggest questions scientists have wrestled with is figuring out how these animals have adapted to see in the deep. Recent evidence suggests that rhodopsin, or “virtual purple,” a protein found in a mammal’s eye, is responsible for this evolutionary leap.
Rhodopsin is a light-sensitive receptor protein that is important for visual phototransduction, the process by which light is converted into electrical signals in rod cells, cone cells, and ganglion cells photosensitive cells of the retina of the eye. Rhodopsin is very sensitive to light, which allows it to see clearly in low light conditions.
The researchers, Sarah Z Dungan and Belinda SW Chang, published a paper, “Ancient whale rhodopsin reconstructs dim-light vision over a major evolutionary transition: Implications for ancestral diving behavior,” which shows why whales were able to evolve the power of the view in depth.
Dungan and Chang reconstructed the ancient sequence in which whales learned to dive with their breath for underwater feeding purposes. This has always been very difficult to do, but they believed that by looking at their co-evolving sensory systems, they could gain insight into what this sequence actually looks like. They also used the protective resurrection to see how the activation of light occurred during the transition from the terrestrial to the aquatic world.
Whales have rhodopsin that is more sensitive to light in dim conditions than rhodopsin in land mammals. The authors found that the decay rates of these light-activated rhodopsins increased in prehistoric cetaceans, suggesting that dark adaptation occurred (relatively) very quickly. In general, they found, the prehistoric ancestors of whales were able to dive about 650 feet or more, in what is known as the mesopelagic zone, where light begins to wane. This happened before the split between toothed whales and whales.
So we can say that cetaceans had the same ancestor, which started with breathing diving and evolved into the present modern form. Subsequently, they evolved all the characteristics that facilitated their search for food in the sea.
In the past, researchers believed that prehistoric cetaceans were dolphin-like, with tail traits and vestigial hind limbs. However, before this work, scientists had not gone very far in determining how deep-sea vision evolved. What’s more impressive is that Dungan and Chang achieved these results without having to examine any fossils. This may surprise some people, but the reality is that prehistoric fossils are so old that it is extremely unlikely that a researcher will be able to obtain any DNA from them. Therefore, researchers must rely on computer models and gene samples from existing organisms to trace the evolutionary path of prehistoric creatures.