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1. Jurassic period

Jurassic period started from about two hundred million years ago and lasted for the next fifty five million years. Today diverse plant life and animal forms exist. Contrary to this, reptiles dominated during Jurassic period. Dinosaurs were the reptiles of that time. Mammalian animals were smaller and lived in the dense forests of the time. Reptiles of the Jurassic period lived on land and sea. Some fish also thrived in the sea. Animals and fish of the time were mostly larger than the animals we know today. Some of the smaller reptiles could fly. However, these reptiles were not birds. Later, feathered birds evolved from the smaller reptiles.

The large forests were made up of trees of limited diversity and supported the large reptiles. Some of the animals were predators while others were herbivores. Large terrestrial animals were referred to as sauropods. They were feeding on the trees, which were primarily coniferous plants. Diverse forms of ferns existed which served as food for small herbivores. Theropods, which were large dinosaurs resembling lizards, fed on herbivores. These reptiles were carnivorous and predators. Diplodocus was the largest herbivore of the time, while allosaurus was the largest terrestrial predator during that time. Pterosaur was a flying reptile and was larger than most birds of the present time (Enchanted Learning 2012).

During the Jurassic period, the massive dry land was breaking up and separating leading to creation of new coastlines. This brought water nearer to the most of the dry land and rain became frequent. Due to the rain more forests were formed and this supported more herbivores. In turn, the herbivores served as food for predators of that period. This explains the existence of large animals during that period. The food resources of the time could support large animals which required a lot of energy to survive.

2. Cenozoic period

Later, when a cataclysmic event wiped out dinosaurs, mammals emerged and dominated the terrestrial habitat. This period is known as the Cenozoic period. Mammalians occupied the terrestrial and marine habitat at the beginning of this age. This was facilitated by absence of the reptiles, which had formerly dominated the earth. Similarly, birds emerged in diverse forms and evolved into big avian species.

3. Paleocene

Mammal and birds emerged and evolved during the Paleocene period of the Cenozoic era. This era began about forty two million years ago. Earth’s surface temperature dropped considerably leading to formation of glaciers on the continent. This period is also divided into epochs that define various evolutionary stages of life on Earth. During this period mammals differentiated and this led to emergence of the primates.

4. Neocene period

Neocene began about twenty three million years ago. During this time, small mammals emerged. Continued cooling of the earth led to glaciations near the poles. On the other hand, quaternary period succeeded the Neocene period. The quaternary period started two and a half million years ago and lasts up to date. It is during this time the human being emerged and dominated over all other species.

5. Mesozoic period

The Mesozoic era began two hundred and fifty million years ago and lasted for one hundred and eighty five million years. During that time dinosaurs were the main animal form. The Triassic period is the first portion of this era during which marine and terrestrial life was exterminated by a single event for the first time (Enchanted Learning 2011). The Jurassic period then followed within the Mesozoic period. The last period of the Mesozoic era was the cretaceous period. During this time reptiles lived on terrestrial and marine habitat. At the end of this period, a complete extinction of the dinosaurs and other large reptiles paved the way for development of birds, mammals and the hominid species.