Reptile husbandry has had an interesting history. The word "reptile" is generally defined as any of the class of terrestrial vertebrates characterized by having a cylindrical, or tapering, body that tapers to a point. The term is sometimes used to designate any of the higher vertebrates with a notochord. In 1755, Linnaeus coined the term in the first edition of Systema Naturae, and he listed seven orders as reptiles. There have been numerous additions to the original seven reptile orders since then, including many newly defined reptile suborders. The reptiles include the Amphisbaenia (worm lizards), Anguidae (slowworms), Anura (frogs, toads, and other amphibians), Caudata (salamanders and newts), Crocodilia (alligators and crocodiles), Gavialidae (gharials), Gekkonidae (geckos), Lacertilia (lizards), Rhynchocephalia (tuataras), Testudines (tortoises), and Chelonia (turtles).
In the original edition of Systema Naturae, published in 1755, Linnaeus listed seven orders of reptiles: Serpentes, Crocodilia, Lepidosauria, Ungulata, Chelonia, Pisces, and Avia. He placed serpents in the same order as his "Amphibia" with "testaceous species," and he included "all the four-footed serpents with the batrachians." The original edition of Systema Naturae included 25 different orders of reptiles. By the tenth edition (1766), however, he reduced the number to 21. In the tenth edition, he split two orders into two and added some new orders, giving us the twenty-four extant orders that we have today. We know now that all 25 orders are descended from only three original orders of reptiles: Serpentes, Crocodilia, and Lepidosauria.
During the 17th, 18th, and 19th centuries, various naturalists, including Carl Linnaeus, Georges Cuvier, Alcide d'Orbigny, Philip J. V. von Martens, Charles Darwin, and Richard Owen, among others, explored and classified the reptiles of the world. Today, reptiles are placed in three different groups in the Linnaean classification: lizards, snakes, and amphisbaenians. In modern taxonomy, turtles and tortoises (testudines) are placed in a separate group (Dermoptera) from lizards and snakes (Sauria).
The turtles were originally placed in a genus of the order Testudines, which contains three extant orders of tetrapods: the extant turtles (the largest living turtles are the leatherback sea turtle, the loggerhead sea turtle, and the green sea turtle), the extinct Testudinidae, which are known only from the fossil record, and the Tuatara. In the taxonomy of Livingston (1978), the living turtles (excluding the Tuatara) were placed in the order Chelonia and included with their closest relatives in the family Chelydridae, which includes the extant snapping turtles, the softshell turtles, and the painted turtles.
At one time, both freshwater and saltwater turtles were placed in the family Carettochelyidae and included with their closest relatives in the families Geoemydidae (pond turtles) and Emydidae (terrapins). This now obsolete grouping still appears in the classification of some older herpetological manuals.
Classification
REPTILES: THE CLASS FAMILY TURTLE FAMILY. — Testudinidae, the "turtle-family" (formerly known as the Testudines). Testudines are distinguished from lizards and snakes by their elongated, curved shells (carapace). The turtle family contains about 80 extant species, and some of the species are aquatic (saltwater and freshwater). Unlike other turtles, the sea turtle species have a plastron (a soft ventral bony structure), rather than a carapace, and the leatherback turtle has one of the longest, thickest, and heaviest shells of all of the extant species in the family.
The turtles are distinguished from the lizards by their shell covering and from the snakes by their legs. Unlike the snakes, most turtles have legs that have ankles that are equipped with claws (as opposed to webbed feet), and the feet also possess claws. The most distinguishing characteristics of the turtle group are the hinged lower jaw and the hinge that connects the upper jaw to the cranium (at the base of the brain). Unlike the lizards and snakes, the turtle has a lower jaw that opens and closes at the hinge. The hinge is actually located just behind the lower jaw, and when the lower jaw is closed, the upper jaw swings upward and slightly forward. The hinge permits the jaws to function much more efficiently than a hinge found in any other group of vertebrates. The mouth of a turtle is located in front of the eyes, and the tongue is extensible to facilitate eating. Unlike the lizards, snakes, and caecilians, which have extensible tongues located in the mouth, the turtle's tongue is contained in an internal groove in the roof of the mouth.
The reptilian skin of turtles is covered by scales, which are flat with no keels. Although the body is segmented, there is no tail. The limbs are usually covered by a claw, and the feet lack webbing between the toes. Many are covered by a horny carapace, but those that do not have a bony carapace are known as "mosaic terrapins."
TESTUDINIDAE — turtles. Family turtle. — A family of reptiles with a carapace, or shell, that may or may not be covered by scales; limbs with two claws, teeth, and no tail; a toothless jaw hinged to the cranium; no external ears, but two openings behind the external ears on the front part of the skull that transmit sound into the brain; a horny or pliable carapace. Abundant in all the warmer waters of the world, including in salt- and freshwater habitats, they are found on every continent and even in the polar regions of northern Antarctica. Their eggs are laid in the sand or in other shallow water, and the hatchlings are helpless and unable to survive independently. There are numerous subspecies and many individual species of turtles, most of which are considered threatened or endangered by the International Union for Conservation of Nature (IUCN). More than 90 percent of the world's approximately 250 species of turtles are found on only seven continents: the African continents of Africa, Madagascar, and the Comoros; the Asian continent of Asia; the continents of North and South America; and Australia. Their distribution is restricted to the Old World.
ORDER CROCODILIA. — The crocodilians are distinguished from the turtles by their snouts, which do not contain hinge jaws. The most conspicuous feature of these reptiles is their long, fleshy tongue, which, in spite of its name, is usually found in most individuals folded back against the side of the throat; many crocodilians also have a dewlap, which is an elongated flap of skin extending over the neck from the base of the lower jaw to the throat. These animals are also equipped with a hinged lower jaw and teeth.
CROCODILIA — crocodiles and gharials. Family Crocodilia. — A family of carnivorous reptiles that inhabit a variety of aquatic and semiaquatic habitats; they are distinguished from the other reptiles by their teeth; the long, conical tail is capable of rotation and is used to propel them through the water. The crocodile has both a broad and a narrow (snout-like) shape. The gharial is considered a distinct species and can reach a length of 3.5 meters (11 feet). The largest crocodile is the saltwater crocodile, or Nile crocodile, and it grows up to 10 meters (32 feet) in length. Although found in freshwater habitats, this crocodile is most common in the estuaries and coastal regions of the Indian Ocean and northern Australia.
ORDER SQUAMATA. — Lizard order. — A group of reptiles characterized by having a flexible tail; feet with a single toe; a skull in which the orbit is large; and jaw muscles that have a single head with the same number of rows of masticatory teeth as the total number of tooth rows of the lower jaw. This group is commonly referred to as lizards. In modern classifications, there are four extant orders of lizards: the geckos, the skinks, the anguids (monitor lizards), and the iguanas. The Iguanas include the iguana of Central and South America and also the marine iguana, which is found only in the waters off the coast of Mexico, Panama, and Costa Rica. The skinks and anguids have a hinged jaw, and like all of the reptiles, there is no tail, which means that the reptiles with tails are classified as snakes. There are no true snakes in this order of lizards. The geckos have hinged jaws,
