Page 36 - Reptiles & Dinosaurs (Britannica Illustrated Science Library)

32 REPTILES: BACKGROUND

A Skin with Scales APPROXIMATELY
This order constitutes the largest group of living 2,900
Squamata
eptiles are vertebrates, meaning that they are animals with a reptiles and includes more than 6,000 species of SPECIES OF
lizards and snakes. The majority of animals in this
spinal column. Their skin is hard, dry, and flaky. Like birds, order have bodies that are covered with corneous SNAKES EXIST.
scales. The squamata include three forms of reptiles
R most reptiles are born from eggs deposited on land. The SOLOMON that are somewhat different from each other: the
amphisbaenians, the lizards, and the snakes. It also
offspring hatch fully formed without passing through a larval stage. ISLAND SKINK contains certain extinct forms of reptiles, including
Corucia zebrata
The first reptiles appeared during the height of the Carboniferous pythonomorpha, which had snakelike bodies and
lizard-like feet.
Period in the Paleozoic Era. During the Mesozoic Era, they
evolved and flourished, which is why this period is also EMBRIONARY
MEMBRANES
known as the age of reptiles. Only 5 of the 23 orders that They develop two: a
protective amnion and a
existed then have living representatives today. respiratory allantoid (or ECTOTHERMIC SKIN
fetal vascular) membrane.
BOA CONSTRICTOR The body temperature of Dry, thick, and
Boa constrictor reptiles depends on the impermeable, it
environment—they cannot protects the body from
regulate it internally. This is dehydrating even in
why higher temperatures very hot, dry climates.
They regulate their increase their vitality.
temperature by taking
4,765 advantage of different
sources of external heat,
EYES NICTITATING such as direct sunlight and
are almost always small. MEMBRANE stones, tree trunks, and
In diurnal animals, the extends forward from SPECIES OF LIZARDS patches of ground that have
pupil is rounded. the internal angle of EXIST. been heated by the sun.
the eye and covers it. ROSY BOA
Charina trivirgata
Habitat Chelonians
Reptiles have a great capacity to adapt, since The order of the testudines differentiated itself
they can occupy an incredible variety of from the rest of the reptile world during the
environments. They live on every continent except THE TONGUE Triassic Period. Today it comprises marine turtles
Antarctica, and most countries have at least one Large, protractile, and terrestrial turtles. The species of this
order are unique. They are covered with
species of terrestrial reptile. They can be found in the and bifid, a reptile's shells that consist of a dorsal carapace
driest and hottest deserts, as well as the steamiest, tongue is very and a ventral plastron. These shells are
most humid rainforests. They are especially common short and thick, so much a part of these animals that
in the tropical and subtropical regions of Africa, and it contains the their thoracic vertebrae and ribs are
taste organs.
included in them. Since these rigid shells
Asia, Australia, and the Americas, where do not allow turtles to expand their chests to
high temperatures and a great diversity of breathe, these animals use their abdominal and
BLACK CAIMAN prey allow them to thrive. pectoral muscles like diaphragms.
Melanosuchus niger HERMANN'S TORTOISE
Testudo hermanni
300 SPECIES OF
Crocodiles TURTLES EXIST.
are distinguished by their usually large size. LUNGS
From neck to tail, their backs are covered in Since the ribs are fused with the shell,
rows of bony plates, which can give the turtles cannot move their ribs to
impression of thorns or teeth. Crocodiles inhale. They use the muscles in the
appeared toward the end of the Triassic
Period, and they are the closest living upper part of their legs to produce a
pumping motion and inhale air.
relatives to both dinosaurs and birds. Their
hearts are divided into four chambers, their
brains show a high degree of development,
and the musculature of their abdomens is
so developed that it resembles the SKELETON
gizzards of birds. The is almost entirely
larger species are very ossified (not
dangerous. cartilaginous).
THORAX AND ABDOMEN
are not separated by a
diaphragm. Alligators
breathe with the help of
OVIPAROUS muscles on the walls of
Most reptiles are their body.
oviparous (they lay eggs);
however, many species of
snakes and lizards are
ovoviviparous (they
give birth to live CENTRAL AMERICAN
offspring). AMERICAN ALLIGATOR
Alligator mississippiensis RIVER TURTLE
Dermatemys mawii