Turtles live in the water and on land. Some land-dwelling turtles are known as tortoises. All turtles, including tortoises, are part of the scientific order Testudines.
A group of turtles is collectively known as a “bale of turtles.”
The top of a turtle’s shell is called the carapace. The bottom is called the plastron.
The largest sea turtle on earth is the leatherback. The heaviest one ever recorded weighed 2,019 pounds, though the species more commonly weighs between 660 and 1,100 pounds. The largest land turtles are the famous giant tortoises that inhabit islands in the Galapagos Archipelago, and have been recorded weighing up to 882 pounds.
Male and female turtles are similarly sized, but males have larger and longer tails, and often have longer claws on their front feet. Male turtles have a concave plastron that allows them to more easily mount a female during mating, while females have a flat plastron that creates more room for eggs to be held inside.
Sea turtles can extract salt from seawater and excrete the excess salt through special glands in their eyes, allowing them to live indefinitely without access to fresh water.
Sea turtles can smell underwater by taking water in through their nostrils and pushing it out their mouth. Their vision is specially adapted for underwater sight. Out of water, they’re near-sighted. Although they have no external ears to enhance their hearing, their eardrum, middle- and inner-ear structures do give them a limited sense of hearing. They hear low-frequency sounds best.
Many sea turtles are adapted for impressively deep dives: Leatherbacks have been known to dive more than 3,900 feet while hunting jellyfish. Green turtles can spend up to five hours underwater, slowing their heart rate to just one beat every nine minutes to conserve oxygen.
Diego, a giant tortoise more than 100 years old, recently made headlines for “saving his species” in his 40+ years of service to a captive breeding program. The Giant Tortoise Restoration Initiative started in 1970 with just two male tortoises and twelve females – the last of their kind on Espanola Island. Thanks to their efforts, the island is now home to 2,000 tortoises – and paternity tests show that latecomer Diego, transferred from San Diego Zoo to the breeding program in 1976, is responsible for about 40% of the total population. In March, Diego at long last returned to Espanola Island, after nearly 80 years away from home. (Well done, Diego.)
Of the 207 species of turtle and tortoise alive today, 129 of them are listed by IUCN as vulnerable, endangered, or critically endangered – including nearly all sea turtles. According to the IUCN-SSC Marine Turtle Specialist Group, the biggest threats to sea turtles are habitat loss due to coastal development; poorly-managed fisheries that don’t use turtle-safe catch methods; illicit global trade; ocean pollution, including plastics, discarded fishing gear, and petroleum by-products; and climate change, which can throw the sex ratios of hatchlings out of balance, increase the likelihood of disease outbreaks, and escalate the frequency of extreme weather events that destroy nesting beaches and coral reefs.