By Kate Bush
Whales are warm blooded mammals (vertebrate) whose females give birth to live young ones. Due to the nature of the environment they thrive in they have high metabolism which helps in producing heat and regulate their body temperatures. The adult whales temporarily acquire some body hair and sensory bristles in their mouth which is characteristic unmistakably mammalian.
The whales have some unique features that are not found in other mammals, many of these are not even found in other marine mammals such as pinnipends and manatees. Examples of these features include streamlined thick and rounded bodies. This feature is different from the fish bodies which have slim and elongated bodies. The whales also have a tail with horizontal fluke which it uses for its movement in water. The neck of the whale has vertebrae which is shortened and fused partially into its skeletal mass. The bones behind the neck are similar. The skull of the whale has jaws extended forward which gives them the feature of a long head. The whales rip cage is very mobile as compared to other mammals. The whales have no olfactory sense, glands on the skin nor the tear gland. These animals have a sharp sense of hearing although they don’t have an external ear opening. These are the key features that are distinct with the whale which shows its adaptations to the marine life. There are many features which show that the whale shares a common ancestor with the terrestrial mammals (McGraw-Hill Yearbook of Science &Technology, 2004).
Classification of the whales
Whales are classified in the class cetacean. In this class there are two general species of whales that exist on earth today, the whales with teeth known as, odontoceti and the toothless whale mystgiceti. The first group has simple uniform teeth found in the lower and the upper jaw. The mysticetes have a kelitinous tissue called the baleen on their jaws. The other group of whale is long extinct it called the Archaeocete which is only known from the fossils found to have existed 53 to 35million years ago. They had complex teeth formulae with molars with double roots, a feature found in the terrestrial mammals. The feature of this group of whales and the modern whales forms the basis that is used to explain the evolution of whales (McGraw-Hill Yearbook of Science &Technology, 2004).
Different arguments for evolution of whales
Theories have been developed that have convincing evidence that the ancestors of the whale were covered with fur and seldom got into water. Whereas the current whales are full aquatic and inhabit the rivers lakes and the ocean. These theories shows the whale ancestors had four limbs with hooves to walk on land. Whereas when we observe the whale today has modified fore limbs as flipper and they don’t possess the hind limb and they move by propelling themselves through the water using the powerful adapted tail. The evolution of whales is said to be a backward kind of macro evolutionally transition because they moved from the terrestrial life to aquatic life as compared to evaluation of other vertebrate evolution from aquatic life to terrestrial life.
The whales have long been known to be the ancestor of land mammal because of their physical characterizes, they have flippers which are similar to the forelimbs found in mammals and the movement of its spines. There some genetic relationship that has been identified between the whales and the terrestrial mammals. Due to various studies the scientist has been able to unearth the origin of whales. In the year 1693 John Ray brought to attention that whale were not fish but mammals. Century or so later William Henry flower discovered that whales had some vestigial features of a terrestrial mammal. This brought to attention that the whales might have originated from the terrestrial mammals rather than the earlier prediction that they were the ancestors of the modern terrestrial mammals (Raymond, n.d.).
From this time various scientist had come up with different hypotheses of the origin of whales. In the mid 18th century Charles Darwin suggested that the modern whales had originated from the bear. A point he withdrew later. In 1966 and 1969 Leigh van vale and F.S. Szaley respectively, independently noticed that the whales’ teeth resembled those of extinct carnivore’s ungulates known as mesonychids. This was the beginning of the modern evolution theory of whales. To be specific the earliest whale was said to look like a wolf and was of the genus sinoyx.
The morphological evidence was developed in the 1990s to give a better understanding to the development of whales. This theory shifted attention from van vale hypothesis to the group of mammals known as Artiodactyls which contains a wide variety of mammals including hippos, dog, and cows. Another twist in the evolution developed in the 2000 when Gingerish Philip discovered some fossils of an extinct whale sub-order which was linked with artiodactyls (Gingerich, 2002). Gentrich has been working in the field for many years and has contributed a lot to the evolution theory of whales. Most recently Hans Thewisssen found a 48 million year old fossil of an indohyus which is also linked with the evolution of whales.
In this paper I will analyze various theories that have been developed to support the Evolution of whales by various scientists in different disciplines.
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Bush, Kate "The Evolution Of Whales." The Evolution Of Whales. 27 Jun. 2010. uberarticles.com. 5 Oct 2014 <http://uberarticles.com/miscellaneous/the-evolution-of-whales/>.
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Bush, K (2010, June 27). The Evolution Of Whales. Retrieved October 5, 2014, from http://uberarticles.com/miscellaneous/the-evolution-of-whales/
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Bush, Kate "The Evolution Of Whales" uberarticles.com. http://uberarticles.com/miscellaneous/the-evolution-of-whales/
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