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:
MESOZOIC ERA
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
MIILIONS OF YEARS.