Elephant

ByDr. Girish Chandra

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.

  • Huge body size, 10-13 feet tall, bulky body, weighing 6-7 tons.
  • Pillar-like legs, with five toes encased in a huge cushiony mass and plantigrade locomotion. Ulna is the dominant bone of fore leg.
  • Skull is large, height being more than the length and having air cavities (diploe). Neck is shortened to support large head.
  • Proboscis or trunk is formed by the elongation of nose and upper lip and is used for handling objects, more or less like human hand.
  • Elephants possess pharyngeal pouches for storing water.
  • Dentition is lophodont, adapted for grinding rough fodder. Second pair of upper incisors is modified to form tusks which grow throughout life and each one may attain a length of 9 feet, weighing 200 pounds. Male tusks are larger.
  • All molars do not grow at the same time but new ones appear on the posterior side and the older and worn out ones are shed on the anterior side by horizontal displacement.
  • Stomach is simple and liver 2-lobed, without a gall bladder.
  • Brain is small in comparison to the body and fore brain does not cover the hind brain. However, temporal lobes are well developed, which provide elephants with better sense of touch, smell, hearing and extraordinary memory.
  • They produce high frequency infrasonic sounds for communication.Changes during evolution of elephant

            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.

  • Height increased to 10-13 feet and weight 6-7 tons. Large size provided protection against predators. Modern elephants have no natural predators.
  • rectigrade locomoLimbs became long and pillar-like to support heavy weight of body and for the same reason feet developed huge cushion-like pads and tion.
  • To make the skull light air cavities called diploe were formed in the whole of skull.
  • As the neck became short to support heavy skull, upper lip and nose got elongated and highly muscular to form proboscis which functioned like hand for handling objects.
  • As the animal fed on rough and highly abrasive diet, its teeth became lophodont with silica deposited in the depressions. Teeth replaced by conveyer belt system.
  • Second incisors in the upper jaw attained hypertrophy to form tusks for digging roots and for removing barks from trees which elephants relish.
  • Elephants developed infrasonic sounds for communication over long distances.
  • As an adaptation to survive in arid climate they developed pharyngeal pouches for storing water.
  • Elephants show mosaic evolution in the development of body organs.

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. 

Animal Adaptations: Evolution of Forms and Functions


Features: Eurospan
By (author): R. K. Saxena, Sumitra Saxena

An adaptation, or adaptive trait, is any heritable trait, that enables organisms to survive through natural selection and reproduce better under prevailing environmental conditions. Natural selection tends to preserve beautiful adaptation in populations and discard harmful ones. The evolution of animal form and function is the conceptual backbone of this book. It not only provides the framework for Animal Diversity, but also shifts the paradigm from a chiefly descriptive discipline to a dynamic predictive science. It is a book narrating rambling series of stories or vignettes about randomly selected animals or model organisms and their unique way of life. Animals might not be able to speak or master advanced language techniques, but they certainly have other ways of communications. Species often rely on verbal and nonverbal forms of communication, such as calls, nonvocal auditory outbursts, like the slap of a dolphin’s tail on the water; bioluminescence; scent marking; chemical or tactile cues; visual signals and postural gestures. When it comes to acoustic communication, not every member of a species is just alike. Animals in different regions have often been overheard sounding off in different dialects. Communication between species can play important roles as well. One study suggested that the reason Madagascan spiny-tailed Iguana have well-developed ears, despite the fact that they don’t communicate vocally is so that they can hear the warning calls of the Madagascan paradise flycatcher. The book is weaved intricately around these bizarre adaptations.
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