Turtles are an ancient and diverse group of reptiles, found in various habitats across Earth. Their long evolutionary history has led to a remarkable variety in size, appearance, and habitat. From small pond dwellers to immense ocean voyagers, these shelled creatures exhibit a wide range of adaptations that allow them to thrive in diverse environments.
The Reigning Giant
The largest turtle species in the world is the Leatherback Sea Turtle, scientifically known as Dermochelys coriacea. This marine giant averages 1 to 1.75 meters (3.3 to 5.7 feet) in curved carapace length and can reach a total length of 1.83 to 2.2 meters (6.0 to 7.2 feet). Adult leatherbacks typically weigh between 250 to 700 kilograms (550 to 1,540 pounds), though some individuals have been recorded at over 900 kilograms (2,000 pounds) and nearly 3.05 meters (10 feet) from beak to tail.
Unlike other sea turtles, the leatherback lacks a hard, bony shell; instead, its carapace is covered by tough, rubbery skin, giving the species its name. This leathery shell features seven distinct longitudinal ridges running down its back. Their front flippers are proportionally the largest among all sea turtles, aiding in their powerful oceanic movements. Their coloration is typically black with distinctive white, pink, or blue splotches.
Life of a Colossus
The Leatherback Sea Turtle’s immense size is supported by its specialized diet and unique adaptations. These turtles primarily consume soft-bodied prey like jellyfish and salps. Their mouths and throats are lined with backward-pointing spines that help them secure and swallow their gelatinous meals. Despite the low nutritional content of jellyfish, leatherbacks consume vast quantities, enabling their rapid growth.
Leatherbacks are renowned for their extensive migratory patterns between nesting beaches and feeding grounds. For example, Atlantic populations migrate from the Caribbean to Canadian waters, while Pacific populations travel from Southeast Asia to the coasts of California and Alaska. These journeys are facilitated by remarkable physiological adaptations, including gigantothermy. This ability to maintain a body temperature higher than the surrounding water allows them to forage in colder, productive waters.
Their large body size, thick fat layer, and specialized circulatory system help them retain body heat efficiently. Leatherbacks are also exceptional divers, capable of plunging to depths of nearly 1,200 meters (4,000 feet) and remaining submerged for up to 85 minutes. Their flexible carapace is uniquely structured to withstand the extreme pressures of deep dives.
Giants of Land and Freshwater
While the Leatherback Sea Turtle is the largest overall, other notable species dominate in freshwater and terrestrial environments. The Yangtze giant softshell turtle (Rafetus swinhoei) is the largest freshwater turtle. This critically endangered species can exceed 1 meter (39 inches) in length and 0.7 meters (28 inches) in width, with the heaviest recorded specimen weighing 250 kilograms (550 pounds). Only a few individuals are known to exist. Another significant freshwater species is the Alligator Snapping Turtle (Macrochelys temminckii), known for its formidable size and powerful jaws.
On land, the Galapagos Tortoise (Chelonoidis nigra complex) is the largest land tortoise. Native to the Galapagos Islands, they can live for well over a century. The Aldabra Giant Tortoise (Aldabrachelys gigantea) is another large land tortoise, with individuals reaching weights up to 250 kilograms (550 pounds).
Protecting the Largest
Despite its impressive size and wide distribution, the Leatherback Sea Turtle faces significant threats to its survival. The species is globally listed as Vulnerable by the IUCN, with many subpopulations, particularly in the Pacific, considered Critically Endangered. In the United States, it is recognized as federally endangered.
Major threats include accidental capture in fishing gear (bycatch), which can lead to injury or drowning. Plastic pollution also threatens them, as leatherbacks often mistake plastic bags and debris for jellyfish, leading to fatal blockages. Habitat loss due to coastal development, which degrades nesting beaches, and climate change, impacting nesting temperatures and sea levels, also endanger the species. Additionally, illegal egg collection and hunting of adult turtles contribute to population declines.