Turtles are reptiles classified into the taxonomic
order testudines. They are characterized by the shells
that cover much of their bodies. Turtles can be found
on all continents except for Antarctica, and tend to
inhabit areas with temperate and tropical climates.
Some species of turtle are specialized to live in water,
while others reside mostly on land. There are about
300 extant species of turtle.
A turtle's shell is comprised of an upper shell and
a lower shell, which are connected by a bony structure
at the turtle's side. Each shell consists of multiple
segments that fit together to form the respective shell.
It is generally made up of an inner layer of bone, which
is connected to the turtle's internal bone structures;
this layer of bone is most often covered by a horn material
made of the protein keratin. A turtle's shell serves
to protect it from any potential predators by providing
a sturdy protective structure into which it can withdraw
all exposed body parts when it feels threatened.
In addition to their shells, turtles are characterized
by four limbs, a lack of teeth, tails, and necks that
either fold or contract back into their shells. Land
turtles, most accurately called tortoises, have bent
legs and short and hefty feet. Amphibious turtles, or
those that can live on both land and in water, tend
to have similarly structured legs and feet, only their
toes are webbed and have long claws. Entirely aquatic
turtles have flippers instead of legs.
Turtles can be found in a wide range of sizes. The
smallest living turtle is a South African species called
the speckled padloper tortoise, which is a maximum of
about 3 inches in length and an average weight of about
5 ounces. The largest extant turtle is the critically
endangered leatherback sea turtle, which is a maximum
of about 6.5 feet in length and may weigh over 2,000
The diet of turtles depends heavily on their habitat.
Tortoises in drier regions tend to be herbivores, and
are not known to be selective in choosing their food.
Tortoises living near or in water are more often omnivorous,
and may feed on aquatic plant life, insects, and sometimes
dead aquatic life. Sea turtles are primarily carnivorous,
and may eat marine organisms with soft bodies or shellfish;
some species, however, are entierly herbivorous, and
eat plant life such as algae.
Turtles reproduce by laying eggs that are either spherical
or elliptical in shape. Mother turtles leave large numbers
of eggs in holes in mud or sand, and generally leave
the site in which they laid their eggs soon after; mother
turtles do not care for their offspring in their youth.
Eggs then incubate for an average of two to four months.
After hatching, some sea turtles tend to seek water
immediately, while tortoises may remain in an embryonic
sac until they are strong enough to move and find food
in their environments. Turtles may go on to live for
20-150 years, depending on species.