Page 370 - (DK) Ocean - The Definitive Visual Guide

368 ANIMAL LIFE

Reptiles HUMAN IMPACT
EXPLOITATION

DURING THE JURASSIC PERIOD, over 140 million years ago, All marine reptiles, apart from
DOMAIN Eucarya sea snakes, have a long history
reptiles were the largest animals in the oceans. Their place has of exploitation by humans for
KINGDOM Animalia
since been taken by mammals, leaving few reptiles that are food, skins, or shells. Turtles face
PHYLUM Chordata the additional hazard of being
wholly marine. Of these, turtles are the most widespread, and accidentally caught in fishing nets,
CLASS Reptilia
sea snakes are the most diverse. Apart from the leatherback and numbers of all seven species
ORDERS 4 have steeply declined. Marine
turtle, almost all are confined to warm-water regions, with turtles are now protected by
SPECIES About 7,723
the largest numbers around coasts and on coral reefs. international legislation.
ILLEGAL SOUVENIRS
Stuffed marine turtles—seen here on a beach
Anatomy pointed scales streamlined in Peru—are still sold to tourists, despite
(scutes) shell (carapace) being liable to seizure by customs officials.
Marine reptiles have several adaptations for life in the sea. .
Turtles have a low, streamlined shell, or carapace, and
broad, flattened forelimbs that beat up and down like
head
wings. Marine lizards and crocodiles use their tails to
provide most of the power when swimming, while most
sea snakes have flattened tails that work like oars. Unlike
land snakes, true sea snakes do not have enlarged belly
scales, since they do not need good traction for crawling
on land. All reptiles breathe air, and marine species have valves or flaps
that prevent water entering their nostrils when they dive. Crocodiles
also have a valve at the top of the throat, which enables them to open
their mouths beneath the surface without flooding their lungs with
short rear flippers
water. Marine reptiles all need
long front flippers
to expel excess salt. Sea snakes
and crocodiles do this through STREAMLINED SHELL
salt glands in their mouths, while The hawksbill turtle has a tapering carapace
with conspicuous scales, or scutes. Unlike
marine turtles lose salt in their
most terrestrial tortoises, it cannot retract
tears. The marine iguana has salt its head or legs inside its shell.
glands located on its nose.
Food and Feeding
REPLACEMENT TEETH
A saltwater crocodile’s teeth are Most marine reptiles are carnivorous.
constantly shed and replaced. During Sea snakes typically feed on fish,
its lifetime, it may use over 40 sets. although a few are specialized
predators of fish eggs. They use
Habitat their venom mainly in feeding,
rather than for defense, killing
Most marine reptiles live close to the shore, or return to it to breed. their prey by biting it, and then
The only fully pelagic species are true sea snakes—those in the family swallowing it whole. Green turtles
Hydrophiinae. They remain in the open ocean for their entire lives. Sea feed on seagrass when they
snakes are also the deepest divers, feeding up to 330 ft (100 m) below the become adult, while other marine
surface. Apart from the leatherback turtle, most marine reptiles depend turtles are carnivorous throughout
on external warmth to remain active, which restricts them to tropical their lives. The marine iguana is
and subtropical waters. They also show striking variations in regional the only marine reptile that is a GRAZING ON ALGAE
spread. This is particularly true of sea snakes: up to 25 species are found fully herbivorous. When young, it Marine iguanas have blunter
in some parts of the Indo-Pacific, but the Atlantic Ocean has none. feeds on algae close to the waterline, heads than most lizards, enabling
them to tear seaweed from rocks.
but as an adult, it grazes seaweed Sharp claws act as anchors.
growing on submerged rocks.
Reptiles are cold-blooded
KEY
(ectothermic), so they use less
Number of sea
snake species energy than mammals or birds.
This means that they need less
12–25 species
PACIFIC ATLANTIC OCEAN food, and can go for long periods
OCEAN 2–12 species between meals. Sea snakes, for
example, can survive on just
INDIAN
1 species
OCEAN one or two meals a month.
OCEAN LIFE SEA SNAKES WORLDWIDE REEF SNAKE
SOUTHERN OCEAN
A yellow-lipped sea krait
Although diverse in the
searches for prey in a coral
Indo-Pacific, sea snakes are absent
reef. Reefs are prime habitats
from the Atlantic. Cold waters
for sea kraits, which generally
off southern Africa prevent them
live in shallow water.
from spreading west.