Turtles

Turtles are reptiles belonging to the order Testudines (also known as Chelonia), characterised by their bony or cartilaginous shell that acts as a shield for protection. They are among the most ancient reptilian groups, with a lineage dating back over 220 million years to the late Triassic period, making them older than snakes and crocodiles. Turtles inhabit a wide range of environments across the world, from oceans and freshwater lakes to deserts and forests, and play an important ecological role in maintaining biodiversity.

Classification and Anatomy

Turtles are classified within the class Reptilia and the order Testudines, which includes two major suborders:

• Cryptodira – turtles that retract their heads straight back into the shell (e.g., sea turtles and freshwater turtles).
• Pleurodira – side-necked turtles that fold their heads sideways under the shell (mostly found in the Southern Hemisphere).

A turtle’s most distinctive feature is its shell, comprising two main parts:

• Carapace – the upper, dome-shaped part.
• Plastron – the flat underside.

The shell is made of fused bones and covered by horny plates called scutes, which provide durability and protection. Unlike many reptiles, a turtle’s ribs and spine are fused to its shell, meaning the animal cannot shed or remove it.
Turtles have no teeth, but instead possess a sharp, beak-like mouth adapted to their diet, which may include plants, invertebrates, or small fish. They have strong limbs, with variations depending on habitat: flippers in marine species for swimming and sturdy, clawed legs in land-dwelling species for digging and walking.

Types and Habitat Distribution

Turtles are broadly divided into three ecological groups:

• Marine Turtles (Sea Turtles): Live primarily in oceans, coming ashore only to lay eggs. Examples include the Green Turtle (Chelonia mydas), Loggerhead Turtle (Caretta caretta), Leatherback Turtle (Dermochelys coriacea), and Hawksbill Turtle (Eretmochelys imbricata).
• Freshwater Turtles (Terrapins): Found in rivers, ponds, and lakes. They are semi-aquatic and capable of living both in water and on land. Examples include the Indian Flapshell Turtle and Red-eared Slider.
• Land Turtles (Tortoises): Primarily terrestrial, with heavy shells and column-like legs. The Aldabra Giant Tortoise and Galápagos Tortoise are notable examples.

Turtles are distributed across every continent except Antarctica. Tropical and subtropical regions host the greatest diversity due to their favourable climates and abundant aquatic habitats.

Evolution and Fossil Record

Turtles are among the oldest living reptiles, with fossils tracing back to over 200 million years ago. Their ancient ancestors, such as Proganochelys, already possessed a shell-like structure, indicating early development of this defining feature.
Unlike many other reptiles, turtles have changed little in their basic body plan through evolutionary history. Genetic and fossil evidence shows that turtles diverged early from other reptilian lineages, possibly sharing a common ancestor with crocodilians and birds. Their unique evolutionary adaptations, particularly the shell, contributed significantly to their survival through multiple mass extinctions.

Behaviour and Reproduction

Turtles exhibit a range of behaviours depending on species and habitat. Most are ectothermic (cold-blooded), regulating body temperature through external heat sources such as sunlight. They are generally slow-moving and long-lived, with many species living for several decades; some tortoises exceed 150 years of age.
Reproduction is oviparous, meaning all turtles lay eggs. Females typically come ashore or dig nests in sandy or soft soil to deposit eggs, which are then left to incubate under natural conditions. Temperature during incubation often determines the sex of the hatchlings — higher temperatures favour females, while lower ones favour males, a phenomenon known as temperature-dependent sex determination (TSD).
Newly hatched turtles, especially sea turtles, face high mortality rates due to predation and environmental challenges. Only a small fraction survive to adulthood.

Diet and Feeding Habits

Turtles display diverse dietary patterns:

• Herbivorous species (e.g., Green Sea Turtle, tortoises) feed on sea grasses, algae, and vegetation.
• Carnivorous species (e.g., Snapping Turtle) consume fish, insects, and small amphibians.
• Omnivorous species combine both plant and animal matter.

Their digestive systems are adapted to slow metabolism, enabling long periods without food, particularly during hibernation or migration.

Ecological Importance

Turtles play an integral role in maintaining ecological balance. In marine ecosystems, sea turtles help maintain healthy seagrass beds and coral reefs by grazing, which supports biodiversity. Freshwater turtles assist in nutrient recycling by feeding on detritus and aquatic vegetation. Tortoises, as grazers, influence vegetation structure and seed dispersal in dry habitats.
Their nesting behaviour also contributes to nutrient transfer from sea to land ecosystems, as unhatched eggs and eggshells enrich the coastal soil.

Conservation Status and Threats

Despite their resilience through geological history, many turtle species are currently endangered due to human activity. Key threats include:

• Habitat destruction from urbanisation, agriculture, and deforestation.
• Poaching and illegal trade for meat, shells, and traditional medicine.
• Pollution, particularly plastic waste, which marine turtles often ingest.
• Climate change, affecting nesting beaches and altering sex ratios.
• Bycatch in fishing operations, which accidentally capture and kill sea turtles.

Conservation efforts at national and international levels aim to protect turtle populations. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) regulates international trade, while organisations such as the World Wide Fund for Nature (WWF) and Sea Turtle Conservancy conduct awareness, research, and habitat protection programmes.
India, home to species like the Olive Ridley, Green Turtle, and Leatherback Turtle, has implemented conservation measures such as the Odisha coast’s mass nesting protection programmes and the Wildlife Protection Act (1972). The annual mass nesting of Olive Ridley turtles at Gahirmatha Beach is one of the world’s largest natural breeding phenomena.

Cultural and Symbolic Significance

Throughout history, turtles have held profound symbolic meaning across cultures. In Hindu mythology, the god Vishnu’s second incarnation, Kurma, took the form of a turtle to support Mount Mandara during the churning of the ocean. In Chinese culture, the turtle symbolises longevity, stability, and wisdom**, and in Native American traditions, it is often associated with the creation of the Earth, symbolised as “Turtle Island.”
Their enduring presence in art, folklore, and religion reflects human admiration for their patience, endurance, and connection to both land and water.

Modern Research and Ecological Awareness

Contemporary scientific research continues to explore turtle biology, migration, and conservation genetics. Satellite tracking has revealed remarkable long-distance migrations, such as those of the Leatherback Turtle, which can travel thousands of kilometres across oceans. Studies of their shell morphology and longevity also contribute to understanding vertebrate evolution and ageing.
Public awareness campaigns emphasise reducing plastic pollution, protecting nesting sites, and promoting eco-tourism to sustain turtle populations.