Turtles are reptiles of the order Testudines characterised by a special bony or cartilaginous shell developed from their ribs and acting as a shield.
Reptiles are tetrapod animals in the class Reptilia, comprising today's turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives.
A shield is a piece of personal armour held in the hand or mounted on the wrist or forearm.
In vertebrate anatomy, ribs are the long curved bones which form the rib cage.
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"Turtle" may refer to the order as a whole or to fresh-water and sea-dwelling testudines.
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The order Testudines includes both extant and extinct species.
In biology, a species is one of the basic units of biological classification and a taxonomic rank.
The earliest known members of this group date from 157 million years ago, making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians.
Crocodilia is an order of mostly large, predatory, semiaquatic archosaurian reptiles, known as crocodilians.
Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes.
Of the 327 known species alive today, some are highly endangered.
Turtles are ectotherms—their internal temperature varies according to the ambient environment, commonly called cold-blooded.
An ectotherm, is an organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature.
However, because of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably higher than that of the surrounding water.
The leatherback sea turtle, sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtles and is the fourth-heaviest modern reptile behind three crocodilians.
Turtles are classified as amniotes, along with other reptiles, birds, and mammals.
Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles and birds by the possession of a neocortex, hair, three middle ear bones and mammary glands.
Like other amniotes, turtles breathe air and do not lay eggs underwater, although many species live in or around water.