Amphibians & Reptiles Info
Reptilia is a class of vertebrate animals that includes the snakes,
lizards, crocodiles, alligators, turtles,
and the tuatara (only found in New Zealand).
Reptiles occupy an evolutionary position between amphibians, on the one
hand, and the birds and mammals on the other.
Reptiles can be technically described as being air-breathing vertebrates
with internal fertilization and a scaly body covering instead of hair
or feathers.
Australian - Distribution
The Australian reptile fauna comprises 2 species of crocodiles, over
20 tortoises and turtles and more than 800 lizards and snakes. One species
of tortoise, 40 lizards and 8 snakes inhabit the ACT region.
The Australian region is the only area in the world in which venomous
species of snakes outnumber harmless ones. The family Colubridae,
comprising the majority of the non-venomous or slightly venomous snakes
of the world, is poorly represented in Australia, which has only 12
species. The Australian region has many snakes of the cobra family (family
Elapidae), but no vipers. The fauna also include several pythons and
minute blind snakes (family Typhlopidae); a variety of geckos, skinks,
and agamid lizards; side-necked turtles; and two species of crocodiles.
Size range
Australia's largest snake is the Amethyst Python (also known as the
Scrub Python) has been known to grow to 7-8 metres.
One of the Australian saltwater crocodiles (Crocodylus porosus) can
approach 9 metres.
The largest modern lizard is a monitor, the Komodo dragon of the East
Indies; it attains a length of 3 metres. Two or three Australian species
of monitors can reach 1.8 metres.
The smallest reptiles are the geckos, some of which grow no longer than
three centimetres. Certain blind snakes (Typhlopidae) are less than 10
centimetres in length when fully grown. The smallest turtles weigh less
than 450 grams and reach a maximum length of 12.5 centimetres.
Feeding habits.
With few exceptions, modern reptiles feed on some form of animal life:
insects, mollusks, birds, frogs, mammals, fishes, or other reptiles.
Land tortoises are vegetarians, eating leaves, grass, and in some cases
even cactus. The majority of carnivorous reptiles have non-specialized
diets, feeding on a variety of animals. In general, the smaller the
reptile, the smaller is its prey.
Thermal relationships.
Reptiles are often described as being cold-blooded, which is not always
true. Their body temperatures are not always low, but they have no internal
mechanism for regulating body temperature and thus approximate closely
the temperature of their surroundings. This condition is termed poikilothermy.
Mammals and birds maintain their relatively high body temperatures at
a fairly constant level by physiological means that are independent
of the external environment, a condition called homoiothermy. When the
body temperature of a dog or a man falls below the normal range, he
begins to shiver, blood vessels in the skin contract, muscular activity
generates heat, and the contraction of the superficial blood vessels,
by reducing the volume of blood flow at the surface, reduces heat loss
by radiation. By contrast, a reptile, when its body temperature falls
below the optimum, must move to some portion of the environment having
a higher temperature; in less than optimal temperatures, its activity
drops, its movements become sluggish, its heartbeat slows, and its rate
of breathing drops. In short, it becomes incapable of the normal activities
required for growth, reproduction, and survival.
Mammals and birds have some physiological means of cooling their bodies
(e.g., panting and sweating, expansion of superficial blood vessels),
but a reptile must ordinarily move away from a spot in which the temperature
is too high or it will perish very quickly. Some reptiles also pant,
but most of their temperature accommodations are behavioral (e.g., orienting
to sun or wind, raising body from the ground).
Each group of reptiles has its own characteristic thermal range. One
genus of lizards, for example, may require temperatures of 29-32 C for
maximum efficiency, and another may require 24-27 C. As a result of
such physiological differences, lizards of the two groups will be active
at different times of the day or occupy slightly different habitats.
In general the normal activity temperatures of reptiles are lower than
those of most mammals, the majority of lizards have normal activity
temperatures in the 27-35 C range.
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