Evolution of Elephant | Zoology Optional Notes for UPSC PDF Download

Introduction

Elephants, the largest land animals, belong to the proboscidean family Elephantidae, the only surviving family in this group. Three existing species are recognized: the African bush elephant, African forest elephant, and Asian elephant. Elephantidae includes extinct members such as mastodons, mammoths, and straight-tusked elephants.

Physical Characteristics and Distribution

• African elephants have larger ears and concave backs; Asian elephants have smaller ears and convex or level backs.
• Distinctive features: long trunk, tusks, large ear flaps, massive legs, and sensitive skin.
• Found in various habitats: savannahs, forests, deserts, and marshes.
• Herbivorous and considered keystone species due to their environmental impact.

Social Structure

• Fission–fusion society: multiple family groups come together to socialize.
• Female (cow) family groups led by the oldest cow (matriarch).
• Male (bulls) leave family groups at puberty, living alone or with other males.
• Bulls interact with family groups during mating; exhibit musth, a state of increased testosterone and aggression.
• Calves are central to family groups, relying on mothers for up to three years.

Communication and Intelligence

• Communication through touch, sight, smell, and sound; use infrasound and seismic communication.
• Comparable intelligence to primates and cetaceans.
• Display self-awareness and empathy for dying family members.

Conservation Status and Threats

• African bush and Asian elephants listed as endangered; African forest elephants as critically endangered by IUCN.
• Ivory trade poses a significant threat, leading to poaching.
• Other threats: habitat destruction and conflicts with local communities.

Human Interaction

• Historical use in war; contemporary use as working animals in Asia.
• Controversial display in zoos and entertainment in circuses.

Etymology

The term "elephant" originates from the Latin "elephas" and Greek "ἐλέφας," likely via Phoenician. In Middle English, it appeared as "olifaunt" borrowed from Old French "oliphant."

Taxonomy and Phylogeny

• Belonging to family Elephantidae, within the order Proboscidea and superorder Afrotheria.
• Closest relatives: sirenians and hyraxes, forming the clade Paenungulata.
• Elephants and sirenians grouped in the clade Tethytheria.

A cladogram of the elephants within Afrotheria based on molecular evidence

Proboscidea phylogeny based on upper molars.

Phylogeny of modern elephants and close extinct relatives based on molecular evidence.

Evolution and Extinct Relatives

• Over 180 extinct proboscidean species.
• Three major radiations: the African Eritherium heralded the first, followed by the appearance of deinotheres and mammutids, and finally the elephantids.
• Proboscideans experienced size increase, limb elongation, and development of specialized cheek teeth.

Continuation of Evolution and Extinct Relatives

• Pleistocene marked high speciation and arrival of giant species.
• Palaeoloxodon namadicus, the largest terrestrial mammal.
• Proboscideans experienced insular dwarfism on islands during Pleistocene.

These colossal beings, with their intricate history and remarkable characteristics, continue to captivate human fascination, leaving an indelible mark across various aspects of culture and nature.

Anatomy and Morphology

Size

African bush elephant skeleton.

Elephants, the largest terrestrial animals, exhibit significant size variations among species and genders:

• African Bush Elephants:

  • Males: 304–336 cm tall at the shoulder, 5.2–6.9 t
  • Females: 247–273 cm tall at the shoulder, 2.6–3.5 t

• Asian Elephants:

  • Males: 261–289 cm tall at the shoulder, 3.5–4.6 t
  • Females: 228–252 cm tall at the shoulder, 2.3–3.1 t

• African Forest Elephants:

  • Males: 209–231 cm tall at the shoulder, 1.7–2.3 t

Male African bush elephants are typically 23% taller than females, while male Asian elephants are only around 15% taller than females.

Bones

The elephant's skeleton consists of 326–351 bones. Tight joints limit backbone flexibility. African elephants have 21 pairs of ribs; Asian elephants have 19 or 20 pairs.

Head

• The elephant's skull is resilient, flattened at the back, and spread out to protect the brain.
• Air cavities in the skull reduce weight, giving it a honeycomb-like appearance.
• The lower jaw is solid and heavy.
• Lacking a lacrimal apparatus, elephants rely on the harderian gland to moisten their eyes.
• Elephant vision is compromised due to eye location and limited mobility.
  

African bush elephant with ears spread in a threat or attentive position; note the visible blood vessels

Ears

• Elephant ears have thick bases and thin tips.
• Capillary-rich ear flaps release excess body heat, especially in African bush elephants.
• Elephants hear at low frequencies, being most sensitive at 1 kHz.

Trunk

• The trunk is a fusion of the nose and upper lip with up to 150,000 muscles.
• It is used for breathing, olfaction, touching, grasping, and sound production.
• The trunk can lift up to 350 kg, reach heights of 7 m, and dig for water under mud or sand.
• African elephants have two finger-like extensions; Asian elephants have one.
  

African bush elephant with its trunk raised, a behaviour often adopted when trumpeting.

Teeth

Closeup of the cheek teeth of a dead juvenile bush elephant.

• Elephants usually have 26 teeth: incisors (tusks), deciduous premolars, and molars.
• Tooth replacement occurs throughout their lives, with six sets of chewing teeth.
• Tusks, modified second incisors, grow continuously, serving various functions.

Skin

• Elephant skin is tough (2.5 cm thick on the back), sensitive, and covered in sparse hair.
• Mud is used as sunscreen to protect from UV light; regular mud baths prevent damage.
• Hair concentrations remain on the tail, chin, genitals, and around the eyes and ears.

Legs, Locomotion, and Posture

• Elephant limbs are positioned vertically under the body to support their weight.
• Circular feet with cushion pads distribute weight and facilitate standing for extended periods.
• Elephants can move both forwards and backward, using a walk and a faster gait similar to running.
• They are incapable of trotting, jumping, or galloping.

Organs

• The elephant's brain weighs 4.5–5.5 kg, larger than a human's but proportionally smaller.
• The heart weighs 12–21 kg, has a double-pointed apex, and beats around 30 times per minute when standing.
• Elephants have a well-developed larynx, hindgut fermentation system, and a unique temporal gland associated with sexual behavior.

Body Temperature

• Elephants are homeotherms, maintaining an average body temperature of ~36 °C.
• They lack sweat glands but cool down through water diffusion, flapping ears, mud bathing, and other behaviors.
• The interconnected crevices in their skin aid in thermoregulation, impeding dehydration over time.

Behaviour and Life History

Ecology and Activities

Habitat and Preferences

• African Elephants: Found in diverse habitats - dry savannahs, deserts, marshes, lake shores.
• Asian Elephants: Prefer areas with a mix of grasses, low woody plants, and trees.
• Feeding Habits: Herbivorous, consuming leaves, twigs, fruit, bark, grass, and roots.
• Digestion: Born with sterile intestines, need bacteria from mother's feces to digest vegetation.
• Feeding Behavior: Major bouts in the morning, afternoon, and night; rest midday; sleep at night lying down.
  

Movement and Migration

• Daily Movement: Males and family groups move 10–20 km a day.
• Seasonal Migrations: Elephants migrate for food, water, minerals, and mates.
• Extreme Migration: Recorded herds traveling up to 325 km in Botswana.
• Ecological Impact: Keystone species, transform environments by uprooting trees, creating waterholes.
• Seed Dispersal: Important seed dispersers, particularly in African and Asian ecosystems.
• Dung's Ecological Role: Provides food for other animals; can have negative impacts on ecosystems.

Social Organisation

• Matrilineal Structure: Female elephants in tight-knit family groups led by the matriarch.
• Matriarch's Role: Leads until death or inability; faecal corticosterone increases in group after matriarch's death.
• Succession: Eldest daughter takes over leadership, irrespective of the presence of a sister.
• Group Dynamics: Family groups may split due to resource constraints.

Interaction Beyond Family

• Interactions in Amboseli National Park: Females' lives involve interactions with other families, clans, and subpopulations.
• Bond Groups and Clans: Formed during dry seasons, indicating a higher level of social organization.
• Population Division: Amboseli population divided into "central" and "peripheral" subpopulations.

Social Structures in India and Sri Lanka

• Social Units: Family groups, bond groups, and possibly clans observed in Indian and Sri Lankan elephant populations.
• Male Social Behavior: Male elephants spend more time away as they mature; sometimes form groups.
• Male Dominance Hierarchy: Dominance based on age, size, and sexual condition.

Sexual Behaviour

Musth

• Musth Definition: Increased testosterone state in adult males.
• Age of Onset: Typically starts around 25 years; characterized by temporal gland secretions.
• Aggressive Behavior: Musth bulls exhibit aggression, dominance; intense encounters with other males.
• Mating Relevance: Musth linked to mating behavior, with musth males guarding oestrous females.

Mating

• Polygynous Breeding: Elephants are polygynous breeders; copulations most frequent during the wet season.
• Female Signals: Females release pheromones to signal readiness; bulls assess with the flehmen response.
• Oestrous Cycle: Lasts 14–16 weeks; bulls engage in mate-guarding behavior.
• Copulation: Involves laying the trunk over the female's back; lasts about 45 seconds.

Birth and Development

Gestation and Birth

• Gestation Period: Around two years; births often during the wet season.
• Calf Characteristics: Born 85 cm tall, weigh around 120 kg; usually single births.
• Prolonged Pregnancy: Five corpus luteums extend the pregnancy, allowing for better development.

Early Development

• Calf Dependency: Relies on mother for nutrition and protection; unsteady on feet initially.
• Suckling and Independence: Calves rely on milk for the first three months; gradually become more independent.

Adolescent and Adult Stages

• Sexual Maturity: Females mature around nine years, males around 14–15 years.
• Adulthood Onset: Typically around 18 years; long lifespans reaching 60–70 years.
• Memory and Cognitive Abilities: Exhibit mirror self-recognition, use tools; possibly have cognitive maps.

Communication

Communication Modes

• Touching: Important in greetings, discipline, and mother–calf communication.
• Visual Displays: Used in agonistic situations to appear threatening; often involve ear-spreading, head-shaking.

Vocalizations

• Types: Trumpets, roars, barks, snorts, growls, and rumbles; short and long-range communication.
• Infrasonic Rumbles: Produced for long-distance communication, with potential ranges up to 10 km.

Seismic Communication

• Seismic Signals: Produced during running or mock charging; travel distances of up to 32 km.

Intelligence and Cognition

• Mirror Self-Recognition: Indicates self-awareness; elephants also use tools.
• Memory: Possibly exceptional; cognitive maps for large-scale spaces.
• Emotion: Debated among scientists; show interest in bones of their kind; possibly exhibit concern for the dying or dead.

Conservation

Status

A family of African forest elephants in the Dzanga-Sangha Special Reserve wetlands, This species is considered to be critically endangered.

African bush elephants and African forest elephants face significant conservation challenges. As of 2021, the International Union for Conservation of Nature (IUCN) classified African bush elephants as Endangered and African forest elephants as Critically Endangered. In 1979, Africa boasted an estimated minimum elephant population of 1.3 million, potentially reaching 3.0 million. However, by 1989, the numbers plummeted to 609,000, with varying regional declines. Notably, East Africa witnessed a staggering 74% decrease from 1977 to 1989. Post-1987, the decline accelerated, with an 80% drop in savannah populations from Cameroon to Somalia. The rainforest-dwelling African forest elephants suffered a 43% loss during this period. Conversely, studies in 2005 and 2007 suggested population growth in eastern and southern Africa at an average annual rate of 4.0%. As of 2016, the IUCN estimated a combined total population of approximately 415,000 individuals for both African elephant species.

Threats

Poaching

The illicit trade in elephant ivory, meat, and hides poses a significant threat to elephant populations. Historical demand for elephant ivory led to a severe decline in African elephants, prompting international bans on ivory imports, starting with the United States in June 1989. CITES, in 1990, approved a global ban on ivory, with exceptions for certain countries. Recent efforts by China and the United States, two major markets, to ban ivory trade have been significant milestones. However, poaching remains a concern, and occasional devastating incidents, like the killing of 650 elephants in Bouba Njida National Park, Cameroon, in 2012, highlight ongoing challenges.

Men with elephant tusks at Dar es Salaam, Tanzania, c. 1900.

Habitat Destruction

Elephants face threats from habitat destruction and fragmentation, particularly in Asia. The Asian elephant's habitat overlaps with regions of high human population density, leading to conflicts. Mitigation strategies, such as the creation of wildlife corridors, are proposed to reduce human-elephant conflicts and ensure the long-term viability of elephant populations.

Association with Humans

Working Animal

Elephants have a historical association with humans as working animals, dating back to the Indus Valley Civilization. In modern times, around 13,000–16,500 elephants were employed in Asia in 2000. Tasks include hauling loads, moving logs, transporting tourists, and agricultural activities. The capture of wild elephants for work has evolved, incorporating tranquilizers since 1950. However, concerns over abuse and the impact on elephant health persist, leading to protective legislation like India's Prevention of Cruelty to Animals Act of 1960.

Warfare

Historically, elephants played a formidable role in warfare. Equipped with armor and trained for combat, war elephants were used extensively in South Asia and later in Persia and Southeast Asia. However, with the evolution of counter-measures, the strategic advantage of war elephants diminished, and they became impractical and expensive for use by the Romans and Parthians.

Zoos and Circuses

Elephants have been part of human entertainment for centuries, from ancient Roman gladiator events to modern zoos and circuses. Controversy surrounds the captivity of elephants, both in zoos and circuses. Critics argue that elephants in captivity experience physical and mental stress, leading to stereotypical behaviors. The debate continues, with zoos claiming to contribute to conservation efforts and critics highlighting ethical concerns.

Attacks

Elephants, known for their generally gentle nature, can exhibit aggressive behavior, posing a threat to humans. Instances of destructive actions against villages and attacks on humans have been recorded, often attributed to factors like habitat loss and human-elephant conflicts.

Cultural Depictions

Elephants hold cultural significance globally, symbolizing strength, power, wisdom, and various virtues. Depictions of elephants in art, literature, and religious contexts are widespread, showcasing their revered status. The elephant's portrayal in popular culture, as seen in political symbols and children's stories, further solidifies its position as a symbol of the exotic and admirable qualities.