Evolutionary Trend in Proboscidae | Geology Optional Notes for UPSC PDF Download

Evolution of Elephants

• Elephants Belonging to Order Proboscidea
• Origin of the Name Proboscidea
• Current Genera of Elephants
• Relationship with Sea-Cows and Manatees
• Characteristic Features of Elephants

Elephants are classified under the Order Proboscidea, a term coined by Carl D. Illiger in 1811. This name stems from the elongation of their nose and upper lip, forming the distinctive long proboscis or trunk. Presently, elephants are represented by two main genera: Elephas in Asia and Loxodonta in Africa. Their closest relatives are sea-cows and manatees, which belong to the Sirenia group. The following unique characteristics of elephants contribute to their fascination and admiration:

• Their massive size and weight
• Their tusks, used for various purposes such as defense, foraging, and social interactions
• Their impressive memory and cognitive abilities
• Their complex social structures and communication methods
• Their herbivorous diet consisting mainly of grasses, leaves, and fruits

These features collectively make elephants captivating subjects in the animal kingdom, showcasing a blend of physical prowess, intelligence, and social dynamics.

Elephant Anatomy and Physiology

• Body Size and Features:
  • Elephants are massive creatures, typically ranging from 10 to 13 feet tall, with a bulky body weighing around 6 to 7 tons.
  • They have pillar-like legs with five toes enclosed in a large cushiony mass, facilitating plantigrade locomotion.
  • The ulna is the dominant bone in their forelegs.
• Skull and Head:
  • The skull of an elephant is large, with the height exceeding its length and containing air cavities known as diploe.
  • They have a shortened neck to support their massive head.
  • The proboscis or trunk, formed by the elongation of the nose and upper lip, functions like a human hand for manipulating objects.
• Dentition and Tusks:
  • Elephants have lophodont dentition, specialized for grinding coarse fodder.
  • The second pair of upper incisors is adapted into tusks, which continue to grow throughout their life, with males typically having larger tusks.
  • Molars do not grow simultaneously; new ones emerge at the back while older ones are shed at the front due to wear.
• Physiological Features:
  • Elephants have a simple stomach and a 2-lobed liver devoid of a gall bladder.
  • Despite their massive body size, elephants have a relatively small brain that does not entirely cover the hindbrain.
  • The temporal lobes are well-developed, enhancing their senses of touch, smell, hearing, and memory.
• Communication and Evolution:
  • Elephants produce high-frequency infrasound for communication purposes.
  • Throughout their evolutionary history, elephants have undergone changes to adapt to their environment and lifestyle.

• Elephants' ancestors were small pig-like animals that lived in swamps without a proboscis and with enlarged tusks.
• Over time, as the swamps shrank, elephants adapted to a browsing or grazing habit on land.
• Height increased to 10-13 feet, weighing 6-7 tons, providing protection against predators.
• Limbs became long and pillar-like to support the body's weight, with feet developing cushion-like pads.
• Air cavities called diploe were formed in the skull to make it lighter.
• The neck shortened to support the heavy skull, leading to the elongation of the upper lip and nose to form a proboscis.
• Teeth evolved to be lophodont due to the rough diet, with silica deposited in the depressions.
• Second incisors in the upper jaw enlarged to form tusks for digging roots and removing tree barks.
• Elephants developed infrasonic sounds for communication over long distances.
• Pharyngeal pouches evolved for storing water as an adaptation to arid climates.
• Elephants exhibit mosaic evolution in the development of body organs.

Evolution of Ancient Elephants

• Moeritherium

  This ancient ancestor of elephants, originating from the Eocene Epoch, resembled the size of a pig or tapir, standing at about 3 feet tall. Notably, it lacked a proboscis but had a slightly elongated snout. Moeritherium sported one pair of slightly enlarged upper and lower incisors, stout legs that ended in broad feet, a diastema gap, and low-crowned molars.

• Phiomia

  Phiomia, larger than Moeritherium, had fossils discovered in Oligocene deposits near the Egyptian lake Moeris and in the Shivalik Hills of India. Its skull was sizable, featuring air cavities, and nasal openings positioned just in front of its orbits. Phiomia boasted elongated jaws with a pair of incisors that evolved into downwardly curved tusks.

• Palaeomastodon

  Living around the same time as Phiomia, Palaeomastodon stood at approximately 6 feet in height. While fossil records are limited, it's noted for having less complex molars compared to Phiomia.

• Dinotherium

  This genus thrived during the Miocene and Pliocene epochs, with fossils found in Europe and India. Dinotherium exhibited a unique feature of downward and backward-curving tusks in the lower jaw, used for digging roots. The upper jaw lacked tusks but had a small proboscis, indicating a probable swamp-dwelling nature, feeding on plant roots.

• Trilophodon (Gomphotherium)

  Trilophodon, or Gomphotherium, was discovered in Miocene rocks across Europe, Africa, and America. These creatures, comparable in size to Asiatic elephants, were known for their downwardly curved upper tusks and elongated lower jaws, which also featured a pair of tusks.

• Tetralophodon

  Fossils of Tetralophodon were found in Italy, India, and North America. Noteworthy for high-crowned molars with four cusps, this species had long, straight upper tusks and shorter lower tusks. Tetralophodon's upper jaw formed an extended proboscis, contrasting with the shorter lower jaw.

• Dibelodon

  Fossils of Dibelodon were found in Pliocene deposits in North America. They were likely the first elephants to reach South America. Dibelodons are identified by their shortened jaws and lack of lower tusks.

• Mastodons

  Several Mastodon species existed from the Oligocene to the Pleistocene in Africa and Eurasia. They had simple bilophodont molars (mastos = small cusps). True mastodons lacked lower tusks and had low-crowned molars, indicating they were likely foliage feeders.

• Stegodon

  Stegodon fossils have been discovered in South and Southeast Asia. They likely emerged in the Pliocene and survived until the Pleistocene. Stegodons had a short head, long proboscis, and a short tuskless lower jaw. Their molars had more roof-like ridges compared to mastodons, and their teeth were adapted for browsing on tough vegetation containing silica. Modern elephants are thought to have evolved from Stegodon.

• Mammonteus (Woolly Mammoth)

  Mammonteus, commonly known as the woolly mammoth (Mammuthus primigenius), was prevalent in the Arctic regions up to Spain, Italy, and North America. Frozen specimens have been found in the Siberian tundra in the Lena delta. These mammoths were well-suited to cold climates with a coat of coarse, long black hairs and a thick layer of brown wool underneath. Their tusks could be long and curved, and they could reach a height of about 9.5 feet.