Page 68 - Reptiles & Dinosaurs (Britannica Illustrated Science Library)

64 TURTLES AND SNAKES REPTILES AND DINOSAURS 65

Slow but Steady Ocean Species SHELL
Small, flat, and joined
to the skeleton
are the rarest. They live in warm waters and are excellent swimmers.
ince their appearance on Earth about 230 million years They have flippers instead of feet. The front flippers move them
ago, turtles have changed very little. Turtles can live on HEAD forward, and the back flippers act as a rudder for steering. Their shells
of oceanic turtles are flattened into a streamlined shape. These turtles
S land, in freshwater, or in saltwater. However, they all has a have developed a dual respiratory system that allows them to remain
submerged for up to two hours.
need light and heat to survive, and they all lay their eggs on pointed
nose.
land. Although aquatic turtles are nearly all carnivorous,
some land-dwelling species are herbivorous. Turtles' most Hawksbill Turtle
noticeable trait is their hard shell, which encloses and Eretmochelys imbricata
protects the soft part of their bodies. It also camouflages Sea turtles are usually heavy and
large. This Caribbean species can
them for protection from predator species. weigh up to 141 pounds (64 kg).

NECK
Much longer
Freshwater Turtles than that of
APPROXIMATELY other species
Most turtle species live in freshwater. They are
distinguished by their feet, which are partially or totally 300-350 Concealed from Danger Head
webbed and are used for swimming, an activity at which SIDE-NECKED The neck STRAIGHT-NECKED TURTLE
they are highly skilled. They can also be identified by their Many scientists believe that turtles' shells TURTLE bends to
shells, which are flatter than those of land-dwelling turtles. TURTLE SPECIES EXIST. TYPES OF SHELLS enabled them to survive long ago, during a one side. Head
is pulled inside the shell
Some freshwater turtles are quite well adapted to living on Turtle shells differ according time when so many other reptile species, by a vertical pendulum
land. In general, they prefer warm climates with abundant to each species' habitat. including dinosaurs, perished. The shell consists of mechanism.
vegetation, so they commonly live near swamps and a domed back and a flat belly, joined by a bridge
rivers located in subtropical areas around the between the front and hind legs. The outer layer
world. Their shells may have particular is made of skin and hornlike plates, and the inner Legs
characteristics depending on the species. SHELL layer is made of bone. Turtles draw their heads and Tail
The American box turtle, for example, This species inside their shells in different ways depending on are always
can completely close its shell.. has a very whether their necks are straight or side-bending. outside the
shell.
soft, thin STREAMLINED Land-dwelling turtles have shells that enable Legs
shell. them to hide their legs, as well as their heads, and Tail
Leatherback Turtle fold upward
inside, protecting their entire bodies from threats. and are
The skeletons of ocean turtles, however, are brought inside.
completely integrated with their shells.
Chinese Soft-
Shelled Turtle
Pelodiscus sinensis A Turtle's Age
They live in swamps and FLAT SHELL Counting the successive
streams. Their diet consists Red-Eared Slider Made of shieldlike hornlike plates that
plates
of fish and mollusks. grow on the shell each
year allows us to
determine a turtle's age.

CRESTED
Alligator Snapping Turtle

On Solid Ground
Land-dwelling species have the best-
protected legs because they are covered
by large scales. They also have the most
dome-shaped shells. Many species have
front legs that are adapted for digging
deep burrows, which serve as a shelter in
Hermann's inclement weather and protect them from
Tortoise threats from other species. The Florida
Testudo hermanni gopher tortoise (Gopherus polyphemus)
can dig tunnels up to 33 feet (10 m) deep.
Some land-dwelling species can inflict
PLASTRON
Underside of very painful scratches.
the shell