In this article we will discuss about the various fossil flora’s found in India.
A study of the fossil plants of the different ages is the most direct evidence of the evolution of the Plant Kingdom.
The history of the different Plant Groups as evidenced by Palaeobotanic studies may be summarised as follows:
The distribution of the different groups in the different ages is shown more elaborately in Figure 511. The major groups forming the flora of the different ages can also be ascertained from the same figure. Figure 512 is an imaginary picture of a Carboniferous forest.
The groups which are of great interest from the Palaeobotanical point of view are given below. These are discussed in the two parts (Pteridophyta and Gymnosperms) that follow. An asterisk marks extinct groups which are represented only by fossils.
The Indian Gondwana Flora:
The most important fossil flora of India is what is known as the Gondwana Flora which covers the period Upper Carboniferous to Jurassic. Indian plant fossils are known before (a few) and after (quite a large number) this period but no flora is as interesting as the Gondwana Flora. Towards the end of the Palaeozoic were the great Hercynian mountain building waves.
This was followed in the Upper Carboniferous and the Permian by severe glaciation and the Permian in India is the greatest coal- forming age. The geography of the Earth at that time was quite different from what it is today (Fig. 513).
There were three continents—the Eur-American Continent (modern Europe and North America) to the North-West, Angaraland (Siberia and North China) to the North-East and a vast Gondwana land on the South which combined the land masses of India, Africa, Australia, South America and Antarctica. In between the continents was the great Sea of Tethys.
The Gondwana land has been named after the Gond tribe of Madhya Pradesh ruled by the famous Rani Durgabati during the reign of Akbar. The name was coined by H. B. Medlicott in 1872 but actually published by O. Feistmantel in 1876. The Gondwana land began to split in the Jurassic as shown by the intensive lava injections at that age.
There was drifting apart of the continents in the Cretaceous, gradually bringing them to their present positions. Another series of great mountain building waves built the present dominant Mountains (Himalayas, Alps, etc.) on the location of the Sea if Tethys.
The whole Gondwana land (now distributed over five continents) shows a uniformity of the Flora (and also the Fauna).
In Indian Geology the Gondwana rocks are considered to form a Group which is almost equivalent to an Era like Palaeozoic. Feistmantel (1882) divided the Gondwana into Lowor Gondwana (Permo-Carboni- ferous with Glossopteris Flora), Middle Gondwana (Triassic with Glossopteris-Thiimfeldia (Dicroidium Flora) and Upper Gondwana (Jurassic with Ptilophyllum Flora).
This three-fold division has been followed by many authorities like Wadia and Lele. But many other authorities prefer a two-fold division into Lower Gondwana (Upper Carboniferous to Lower Triassic) and Upper Gondwana (Lower Triassic to Jurassic, probably reaching Cretaceous).
The two-fold division is supported by the two (Glossopteris Flora and Thinnfeldia (Dicroidium)—Ptilophyllum Flora) distinct floras (and faunas) in the two divisions.
There is a sudden break between the two floras as during the Upper Permian and Triassic intensive glaciation and drought killed most of the previous early Gymnosperms and arborescent Pteridophytes giving place to the more modern Gymnosperms and herbaceous Pteridophytes (mainly ferns).
Indian Gondwana beds are named as shown in Table II. The two-fold system (i.e., only Upper and Lower Gondwana) has been followed in this book but the Middle Gondwana beds and fossils have also been pointed out.
As seen from the Table, places in Indian showing Gondwana rocks occur mainly in the Damodar, Sone, Narbada, Godavari and Mahanadi Valleys. There are also some exposure along the Himalayan foothills of Nepal, Bhutan and Arunachal and also in the Punjab, Himachal, Kashmir and Baluchistan.
Upper Gondwana rocks are more detached occurring in patches along Rajmahal-Cuttack to Kanya Kumari, in Madhya Pradesh, Rewa, Saurashtra, Kutch and in Ceylon. The Map in Figure 514 shows the principal outcrops of Gondwana rocks. It should be noted against that the Triassic beds (Maleri, Mahadeva, Pachmarhi, Parsora, Panchet) spreading from Sone to Godavari Valleys are placed by some in Middle Gondwana.