Turtles are diapsids of the order Testudines characterized by
a special bony or cartilaginous shell developed from their ribs
and acting as a shield. Turtle may refer to the order as a whole (American English) or to fresh-water and sea-dwelling
testudines.The order Testudines includes both extant and extinct species. The earliest known members of this group date
from 220 million years ago,making turtles one of the oldest reptile groups and a more ancient group than snakes or
crocodilians. Of the 356 known species alive today, some are highly endangered.
Turtles are ectotherms—animals commonly called cold-blooded meaning that their internal temperature
to the ambient environment. However, because of their high metabolic rate, leather back sea turtles have a body temperature
that is noticeably higher than that of the surrounding water. Turtles are classified as amniotes, along with other
reptiles, birds, and mammals. Like other amniotes, turtles breathe air and do not lay eggs underwater, although many species
live in or around water. The study of turtles is called chronology, after the Greek word for turtle. It is also sometimes called testudinology, after the Latin name for turtles.
Watching a baby turtle (known as a "hatchling") struggle out of the nest and make its way to the water is
experience. Everything from footprints to driftwood and crabs are obstacles, though this gauntlet is important for its survival.
Birds, raccoons, and fish are just a few of the predators these vulnerable creatures face; some experts say only one out of a
thousand will survive to adulthood under natural conditions.After an adult female sea turtle nests, she returns to the sea,
leaving her nest and the eggs within it to develop on their own. The amount of time the egg takes to hatch varies among the
different species and is influenced by environmental conditions such as the temperature of the sand.
The hatchlings do not have sex chromosomes so their gender is determined by the temperature within the nest.