Stegodon ganesa was an ancient cousin of mammoths and modern day elephants. The name Stegodon means ‘roofed tooth’, and referred to the shape of the teeth resembling a roof. Stegodons, there were several sub-genus, lived in many parts of Asia, from the Indian subcontinent to as far east as Japan. Fossils have been found that date the animal’s existence up until the Pleistocene. The Geological Survey of India, founded by the Coal Committee of the British East India Company to explore and record the mineral resources of India for further development, was commemorated with a stamp issue in 1951 depicting the Stegodon ganesa.
Indian Stegodon First Day of Issue to Netherlands
This cover bears a commercially used pair of the 1951 issue. It was mailed on the first day of issue (Jan. 13 1951) from Bombay, India to Dalfsen, Netherlands at the first class international surface rate of four Annas. The typewritten text in the upper left indicates the year as 1950 – which is a typographical error. This stamp has the distinction of being the first postage stamp to depict a reconstruction of a prehistoric animal.
The Mesozoic Times 
A while ago I was really puzzled why Stegodons are chosen to commemorate a century of Geological Survey of India. It took me a while to find the answer:
In 1928 century 3 meter long fossil tusk of an elephantine mammal Stegedon ganes
a found in India by Dr. Darashaw Nosherwan Wadia (October 25, 1883 – June 15, 1969) who pursued his personal research on stratigraphy, structure and palaeontology of the Kashmir Himalaya with single-minded devotion. Having a very keen eye for observation, he worked towards identification of broad structural elements of the NW Himalaya. The fossil tusk is now kept at the Museum of the Geology Department of the Jammu University. The discovery of this skull, which was found in association with fossil ganoid fish and pteridospermous plants, led to the fixing of the age of an important geological rock formation in the Kashmir Himalaya to the Permo-Carboniferous time (355 250 million years).
more information about this stamp is here: http://www.paleophilatelie.eu/description/stamps/india_1951.html