EVOLUTION OF ELEPHANT
(By Dr. Girish Chandra)
Elephants belong to the Order Proboscidea, the name coined by Carl D. Illiger (1811), because of the long proboscis or trunk formed by the elongation of nose and upper lip. Only two genera exist today, Elephas in Asia and Loxodonta in Africa. Their nearest relatives are sea-cows and manatees (Sirenia). The following characteristic features make elephants subjects of curiosity and awe.
Ancestors of elephants were swamp dwelling small pig-like animals, which had no proboscis and enlarged tusks. During evolution as the swamps shrunk, they had to get adapted to browsing or grazing habit on land and underwent changes in accordingly.
Moeritherium: This is the earliest and best known ancestor of elephants from Eocene Epoch. It was a heavily built animal, the size of a pig or tapir, about 3 feet tall. Proboscis was absent but snout was slightly elongated. One pair of upper as well as the lower incisors was slightly enlarged. Legs were stout and terminated in broad feet. Diastema was present and molars were low-crowned.
Phiomia: Fossils of Phiomia were unearthed from Oligocene deposits near the Egyptian lake Moeris and also from Shivalik Hills in India. It was twice the size of Moeritherium. Skull was large with air cavities and nasal openings lay just in front of orbits. Jaws were elongated having one pair of incisors each, modified to form downwardly curved tusks.
Palaeomastodon: Lived almost at the same time as Phiomia. Fossil records are not very well documented. Height was about 6 feet. Molars were less complex than in Phiomia.
Dinotherium: This genus lived in Miocene and Pliocene epochs. Fossils have been found in Europe and India. There were no tusks in the upper jaw but lower jaw had tusks that curved downward and backward, suggesting that they were used for digging roots of plants. A small proboscis was present in the upper jaw. It was probably a swamp dweller digging and feeding on the roots of plants.
Trilophodon (=Gomphotherium): Fossils have been discovered from Miocene rocks in Europe, Africa and America. They were great migrants and widely distributed animals. Body size was nearly as large as the Asiatic elephant. Upper tusks were downwardly curved and lower jaw was enormously long also having a pair of tusks.
Tetralophodon: Fossils of this species were discovered in Italy, India and North America. Molars were high crowned with four crossing cusps. Upper tusks were long and straight while lower tusks were small. Upper jaw formed long proboscis while the lower jaw was short.
Dibelodon: Fossils of this species were recovered from the Pliocene deposits in North America. They were probably the first elephants to reach South America. They are characterised by shortening of the jaw and loss of the lower tusks.
Mastodons: Several species existed during Oligocene to Pleistocene in Africa, Eurasia and Africa. They had simple bilophodont molars (mastos = small cusps). True mastodons had lower jaw without tusks and molars were low crowned, indicating that they were foliage feeders.
Stegodon: Their fossils have been found in South and Southeast Asia only. They probably appeared in Pliocene and survived up to Pleistocene. They had short head, long proboscis and short tuskless lower jaw. Molars had more roof-like ridges as compared to mastodons. Teeth were adapted to browse on tough vegetation containing silica. Modern elephants are presumed to have evolved from Stegodon.
Mammonteus: Mammonteus (=Mammuthus) primigenius, commonly known as woolly mammoth is the best known elephant. It was abundant in arctic region up to Spain and Italy in Europe and also in North America. Frozen specimens were found in Siberian tundra in Lena delta. Recently more complete specimens have been recovered and preserved in frozen caves in Siberia. The animal was well adapted to withstand cold climate by having a coat of coarse, long black hairs and with a thick coat of brown wool beneath. Tusks were either long and curved. They attained a height of about 9.5 feet.