Evolution of Birds – How Birds Began?
GEOLOGICAL TIME SCALE:
Various views exist regarding the formation and time of origin of earth. The available evidence indicates the age of the earth to be roughly 4500 million years or even more. But life existed on the earth for about 2700 million years. The entire life span of earth is called the ‘geological time’. By reading the fossils present in the rocks, the geologists have divided the geological times into intervals which are characterised by significant events occurred in the organisation of organisms in the past. These divisions are of different durations and of different categories. The major divisions of geological time are known as eras. These in turn are divided into periods that are further subdivided into epochs. The eras, periods, and epochs are arranged on the time scale, in an order of their age, and this arrangements is called geological time scale. It is broadly divided into six major divisions or eras in the following sequence. (i) Azoic (ii) Archeozoic (iii) Proterozoic (iv) Paleozoic (v) Mesozoic (vi) Coenozoic
AGE OF REPTILES:
The duration of this era is 150 million years. This is the period of middle life. During this era, reptiles dominated and hence the era is called the “Golden age of reptiles.” The Mesozoic era is divided into three periods namely Triassic, Jurassic, and Cretaceous. In the Jurassic period strange gigantic dinosaurs roamed and ruled the land. Archaeopteryx, the fossil bird, and the connecting link made its first appearance in the Jurassic period. . The reptilian characters are the presence of teeth, powerful legs and long tail, The avian characters are the wings and feathers. The feathers had claws. Perhaps Archaeopteryx could have used the claws and its powerful legs to climb trees.
The first of the flying animals
As we saw above, the age of reptiles existed for a long time in the life of earth. During that time the most common animals were the cold blooded animals covered with thick scales.
The moved their bulky bodies almost similar to crawling motion on all four of their legs. Remember! Human beings did not appear at that time.
We come to know of these facts from fossils evidence during that time.
Fossils are defined as the preserved remains of animals, plants, or their parts found in the various layers of the earth’s crust, some times in ice or amber. The word fossil (Latin Fossilium –some thing dug out) literally means anything dug out of the earth. The importance of fossils was first recognised by the Leonardo Davinci in 1800
Experts will be able to find our many facts from fossils. They can find out how the ancient plant or animal looked like, what were their food, and also tell what changes have taken place by comparing their present relatives. A few of the early reptiles developed wings and learnt to fly. They were called Pterodactyls ( ter-o-dak-tils). Their wings were not made up of Feathers as we see to day. But their wings were made up either membranes or skins. Hence they could not really fly; but were only gliding. Since pterodactyls did not develop feathers they died and became extinct. We know about them only in fossils.
HOW DID BIRDS EVOLVE?
Mainly FOUR STEPS COULD BE DESCRIBED on the evolution of birds THAT MUST HAVE TAKEN MILLIONS OF YEARS.
THE FIRST BIRD (ARCHAEOPTERIX- AR-KI-OP-TER-IKS)
Connecting links are hence extremely important to understand how evolution has taken place from reptiles to birds. One example is that of Archaeopteryx, a primitive bird whose fossil remains have been found, and from which, the present day birds are believed to have evolved. The Archaeopteryx had abundant true feathers and like birds, it could fly. However it also had toothed jaws, free fingers in the forelimb, a long tail with many vertebrae, and other reptilian features. This shows that birds have evolved from the reptiles.
Article by Mr. R Venkata Ramanan. Chennai based educational consultant. See linkedIn profile.
R Venkata Ramanan
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