Turtles are uniquely popular members of the reptile family, easily distinguished from other reptile species by their often brightly colored protective shells and their docile temperaments. Turtles can withdraw their heads, legs and tails into their shells to protect their soft body parts from their natural enemies. Many persons who are completely repulsed by all other families of reptiles, such as snakes and lizards, are often very fond of turtles and even keep them as pets.
Turtles, the order of reptiles known as "chelonians," are the oldest group of reptiles alive today, dating back 200 million years to the mid-Triassic Period, but now represent only about one tenth of the earth’s total number of living reptile species. Approximately 220 species of turtles are known to exist in the world today, living in a wide variety of habitats, including deserts, forests, plains, mountains and oceans. Antarctica is the only continent not inhabited by turtles. The structure of the shells of various turtle species can vary widely from hard and rigid to soft and flexible. Instead of teeth, turtles have beaks that are adapted to help them eat their primary food source, such as the sharp, hooked beaks of the carnivorous species and the flat, broad beaks of the vegetarian and mollusk eating species.
Turtles that live on land are often referred to as "tortoises." The term "terrapins" is often used to refer to freshwater turtles. Turtle sizes range widely from the 4.5 inch (11.2 cm) Musk turtle to the enormous 8 foot long (244 cm), 1,600 pound (726 kg) Leatherback sea turtle. The largest land turtle is the Galapagos Giant Tortoise of the Galapagos Islands, located in the Pacific Ocean 660 miles west of Ecuador, South America, which grows to a length of almost five feet and a weight of well over 500 pounds.
Sadly, most turtle species are now threatened with extinction, including all six known species of sea turtles, due to human hunting, collecting and destruction of natural turtle habitats. The Darwin Memorial Research Station, named for Englishman Sir Charles Darwin, who first studied the giant tortoises on the Galapagos Islands as part of his research on his theory of evolution upon his arrival on the islands in 1835, has been engaged in the captive breeding of Galapagos Giant Tortoises in an attempt to prevent the extinction of these magnificent creatures, so far having saved all but four of the Galapagos species.