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In the history of life on earth, the emergence, dominance and extinction of dinosaurs, meaning 'terrible lizards' is one of the most fascinating chapters. To many it may be surprising to know that the tiny house lizard is but a midgety representative of this group of animals which not only ruled on land but also in water and air. Dinosaurs appeared on our planet in the course of evolution through a small dog-like reptile group called Thecodont. This was about 230 million years ago, at the begining of the Triassic period. Initially some of them were as small as a fowl. But gradually they evolved into larger and larger forms - that was during 180 to 140 million years ago, in the Jurassic period. By the end of the Cretaceous period, about 65 million years ago, the dinosaurs became extinct, and some of their skeletons got entombed in sediments by chance and petrified to tell their facinating tale. On account of their mighty size, they acquired the name 'terrible lizard'. They varied in appearance, size, and habits. Many dinosaurs had long necks and tail (Brontosaurus). The body was either smooth or covered with heavy horny scales or bony plates (Stegosaurus) that acted as formidable bony armour in self defence. Dinosaurus had two pairs of limbs, usually the hind limbs were long and supported the body. The head was very small compared to the large body size. Dinosaurus are broadly divided into two subdivisions :
(a) Saurischia, meaning reptile-hipped and (b) Ornithischia, meaning
bird-hipped.
Some of the thecodonts which evolved into dinosarus found that they could run
faster on two legs and that the front limbs could be used to catch the prey.
They had to develop their hind legs under their bodies, as in the case of birds
of today; long tails also developed to balance the body. This is how the
Ornithischia group of dinosarus evolved; these are characterised by the deep
sockets for upper leg bones and the strongly attached back bones to the hip
bones. It is studying the hip bones that dinosarus are divided into Ornithischia
(bird-hipped) or Saurischia (reptile-hipped). The char on the back cover
illustrates the evolution of these two different dinosaur groups.
The fascinating chapter of dinosaurs in the long history of life on earth
came to an end at the close of the Mesozoic era, about 65 million years ago. The
different branches of dinosarus - those which lived on land, in water and air -
all became extinct with the advent of what geologists call 'Cenozoic era'. The
cause of this extinction is a field of research where Palaeontologists feel that
there are lessons to be learnt by man on the importances of protecting his
environment.
Evolution of Life
Fossils and Palaeontology
Geological timescale and Life events
Construction of Lifesize Prehistoric animal models by the geological Survey of India
Details of Prehistoric animal models constructed at Nehru Zoological Park
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