Evolution of whales of land to sailor beings
Cetaceans diverged land mammals between 56-50 million years during the Eocene. The cetaceans were specifically separated from quadruped artiodactiles, such as giraffes or rhinos today. Thus, it is known that the early cetaceans originated in Asia del Sur from these artiodactile, and these amphibious whale dispersed until they reached northern Africa and America before 41.2 million years. But recently, remains of a quadruped whale in Peru have been discovered, whose existence was dated about 42.6 million years. This discovery brings some light to the process of transition of cetaceans, of terrestrial animals to mandatory marine animals, and involves the first indisputable evidence of a quadruped whale in the Pacific Ocean and the southern hemisphere during this period. A fact to highlight this discovery is that this specimen maintained characteristics such as the pelvis firmly linked to the sacrum and the presence of small hooves with a flat anteroventral tip on the fingers of the hands and feet. This indicated that the early quadruped whales had a combination of terrestrial and aquatic capacities at the time the South Atlantic crossed and before dispersing north America . In this way, the transition process of the ancient artiodactile quadrupeds to the cetaceans was a long process, in which a large number of adaptations to this permanent aquatic life such as hair loss or the increase in the size of the circulatory system took place. It should be noted that some of these adaptations arose from the loss of unnecessary genes. In this text, various processes will be explained that led to the presence of current cetaceans and emphasis will be placed on the different feeding modes that these organism developed.
Within this group of early whales are the archaeoceti, of which modern cetaceans evolved and whose oldest member is pakicetus. The first fossils are found in Indo-Pakistan and the study of the 5 families that formed the archaeocetes can be extracted different degrees of adaptation to the aquatic environment. We are going to focus specifically on the study and results of 3 of these families, Remingtocetidae, Protocetidae, and Basilosauridae. These 3 taxa, and the study of their bones through the use of microphotographies, show that there has been an increase in their bone mass in their ribs, which lack an open medullary cavity, and in their femards, while their vertebrae are essentially spongy. Smoking and femures show opposite trends in the specialization that was carried out to obtain the independence of the cetaceans of a land environment. The slopes change from very compact to spongy which agrees with the progressive loss of the propellant function carried out by the previous limbs, which were used as management and stabilization tools. With regard to the posterior extremities of the Basilosouridae, they were largely reduced, becoming not participating in the locomotion. The study by Alexandra Houssate, demonstrates that the Remingtocetidae and Protocetidae were almost of aquatic locomotion, since they were surely swimmers suspended in deep waters. With regard to the basilosaurus they show bone specializations similar to that of the cetaceans. This indicates that like current cetaceans were open and active swimmers.
Once the locomotion of 3 of the families of the Archaeoceti is studied, and from which it can be extracted that the current cetaceans are more similar to the Basilosauridae group, it is worth highlighting the different forms of food developed by the cetaceans. Cetaceans developed 3 types of food mainly predation, suction and filtering. The predators are commonly called "bite feeders" (Bite or Pierce Feeders) that consume dams through their hunting and persecution, and which they catch with their jaws. This group includes dolphins and most seals, although marine leopards and murderous whales could also be included. Successors create a pressure difference in their oral cavities which drag their prey towards their mouths. The filters use specialized structures to filter the water and capture very small dams. This separation is very clear, although mixtures of both can be presented in both predatory behaviors that use the suction to hunt their prey, and the same occurs in water filtering specimens, they can present suction.
From this variety of types of food and the development of the current locomotion of cetaceans it can be extracted that many evolutionary processes have had to pass and therefore changes so that the ancient quadruped artiodactiles evolved to the current cetaceans. One of these most remarkable and discovered changes is recently the loss of genes. From the study of the genome that has been modified during this transition, the loss of 85 genes have been observed. Some of these genes were beneficial such as F12 and KLKB1, which avoided thrombus formation. Although others have helped cetaceans adapt to their new aquatic medium. Some of these changes include the development of more hydrodynamic bodies, hair loss, thicker skin that allows a greater presence of fat and physical properties that make it act as a barrier, the reduction of the olfactory and gustative system and the loss ofposterior limbs that were replaced by the propulsion of the tail fins. In addition, it is worth highlighting the widening of blood volumes and high concentrations of hemoglobin, myoglobin and neuroglobin in blood, muscles and brain tissue respectively. Finally we find a flexible rib crowd that allows them to collapse at high pressures.
Of the different studies conducted and treated in this text, it can be seen that the transition of ancestral artiodactiles to cetaceans has been a long process that has taken many millions of years to make a land group, become completely aquatic, suchChanges such as hair loss or a more hydrodynamic form have appeared thanks to the loss of genes that were related to these characters and due to the performance of natural selection that favored individuals who presented these modifications and made them better adapted andTherefore survive more in that new atmosphere that was the sea.
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