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29.4 The Amphibians -- Part 1
There are seven characteristics that define the salamander.
There are two hypotheses that explain the evolution of amphibians.
Frogs, toads, newts, and salamanders are examples of living both on land and in water.
Most members of this group lead a lifestyle that includes a stage that lives in the water and an adult stage that lives on land.
Caecilians are fossorial, wormlike salamanders that spend most of their life underground.
There are thousands of known species of animals.
As mentioned before, most of the time, salamanders are referred to as tetrapods.
The skin, which is kept moist by the mucous glands, plays an active role in water balance and can help in temperature regulation when on land.
A thin, moist skin means that most of the time they stay close to the water.
If lungs are present, they are relatively small, and respiration is supplemented by exchange of gases across the porous skin.
Sight, hearing, and smell are special to land.
The cerebral cortex is more developed in Amphibians than in fish.
These animals have special tongues for catching prey and for keeping their eyes moist.
The temperature of the environment in which fishes live varies greatly, but they are able to live there.
They become inactive and enter torpor in the winter.
The European common frog can survive in the cold.
Many return to water for the purpose of reproduction, so their name is appropriate.
The eggs are protected by a coat of jelly.
The tadpoles feed and grow in the water when they hatch.
Amphibians have evolved mechanisms that allow them to reproduce on land.
Amphibians evolved from fishes with lungs.
There are two hypotheses about the evolution of the salamanders.
Some fishes had an advantage over others because they could use their fins to move from pond to pond.
The supply of food on land in the form of plants and insects promoted further adaptation to the land environment.
The limbs of ancestral amphibians are linked by this transitional form.
salamanders and newts, frog and toads, and caecilians are the three groups of salamanders and newts.
There are two pairs of limbs for salamanders and newts.
Most of the limbs are set at the right angles to the body.
They have side-to-side, S-shaped movements.
The members of this order have unspecialized limbs and a tail throughout their lives.
The members of this order have limbs that are specialized for jumping.
The caecilians are burrowers.
Both salamanders and newts feed on insects and other small animals.
Depending on the species, fertilized eggs are laid in water or land.
The mudpuppy of eastern North America remains in the water and retains its gills.
Frogs and toads, which range in length from less than 1 cm to 30 cm, are common in many climates around the world.
The head and trunk of these animals are fused, and the long hind limbs are used for jumping.
All species have a lot of specializations, depending on their habitats.
The poisons in the skin make the animals distasteful to eat and protect them from infections.
The bright colors of some tropical species are a warning to potential predator.
Caecilians range in length from 10 cm to 1 m and are often sightless.
Most burrow in moist soil.
Some species have folds of skin that look like earthworms.
Hundreds of pharmaceutical products come from other animals, and even those that produce poisons and toxins provide medicines that benefit us.
The black-and-white spitting cobra of Southeast Asia paralyzes its victims with a potent venom, which eventually leads to respiratory arrest.
The venom can be used to make the drug Immunokine, which can affect the immune system.
It is approved in Thailand for use in fighting the side effects of cancer therapy, and it is being studied for use in treating AIDS, autoimmune diseases, and other disorders.
Venom can relieve pain, even though snakebites can be very painful.
The black mamba is one of the most lethal snakes on the planet.
These compounds were as effective as morphine when tested in mice.
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