(ORDO NEWS) — Traditionally, it was believed that whales originated from purely terrestrial animals that lived in the coastal zone in southern Asia.
But now scientists have discovered that the last common ancestor of the fin whale and bottlenose dolphin was already an excellent diver, whose eyes were adapted to see in the twilight of the deep sea.
The transition to an aquatic lifestyle was one of the great events in the evolutionary history of mammals, along with the adaptation to flight or the beginning of upright walking.
Although the ancestors of whales were terrestrial ungulates related to modern hippopotamuses, just a few million years later, their descendants showed features characteristic of swimming animals: at first they looked like otters, then like seals, and finally like whales.
To understand how quickly the transition of cetaceans to a new way of life occurred, scientists from the University of Toronto (Canada) studied the evolutionary history of whales at the molecular level and focused on the protein rhodopsin , which absorbs light and sends a signal from the retina to the brain.
Scientists explained their choice by the fact that rhodopsin is responsible for the perception of light, and the air and water environments differ quite strongly in illumination.
Animals adapting to swimming have to adapt to life in a new, darker world, and judging by the results of the study, the last common ancestor of whales that lived on land could already see underwater.
By studying the rhodopsin genes of modern whales and their closest relatives, scientists were able to reconstruct the rhodopsin gene that was characteristic of the whales’ land ancestors.
This “ancient” rhodopsin was then inserted into the DNA of laboratory cell cultures to produce the protein itself, which was then purified and used for further study.
It turned out that rhodopsin in the eyes of whale ancestors was already much more sensitive to blue light (it penetrates the deepest into the water column) than one would expect from a land animal.
Also, the biochemical properties of the obtained protein prove that the eyes of these long-extinct animals could quickly change between different levels of illumination, which is typical for diving species, such as seals.
Probably, the ancestors of the whales not only lived on the coast, but also willingly dived for food into the depths of the sea, looking for food there or escaping from predators.
In the end, their hooves became flippers, and the first protokite, similar to a giant otter, descended from the shore for the last time, never to return to land.
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