Learning Target: Amphibians are adapted for life on the land, but begin their life in the water.
There are four types of amphibians:
- Frogs
- Toads
- Salamanders
- Newts
The term amphibian means "two lives".
More than 350 million years ago, Earth was already inhabited by many species of vertebrate animals. All of them were fish. They lived only in the water. Over time the water became overcrowded with invertebrates and fish competing for oxygen and food. In times of drought this competition worsened. Animals that could survive on land would be better off than the fish that were stuck in the water. However, the gills of fish work only when they are wet. Fins can function to make fish move through water, but they are not good for moving on land. Water provides more support for the body than air. Plus, fish sensory organs are specialized for detecting sounds and smells in water, not in air.
It took millions of years and many generations before different adaptations occurred and amphibians became a distinct group. These early amphibians were able to survive on land. Today there are fish that can breathe air and fish that can walk for short distances on land. There are also some modern amphibian species that have adapted to life only in water.
It took millions of years and many generations before different adaptations occurred and amphibians became a distinct group. These early amphibians were able to survive on land. Today there are fish that can breathe air and fish that can walk for short distances on land. There are also some modern amphibian species that have adapted to life only in water.
Characteristics of Amphibians:
As adults, most amphibians have these characteristics:
As adults, most amphibians have these characteristics:
- They have two pairs of legs, or a total of four limbs
- They lay their eggs in water
- They obtain oxygen through their smooth, moist skin
- Many also have lungs
- Their sensory organs are adapted for sensing on land
External anatomy of a frog
Most amphibians live in moist environments. Their skin is a respiratory organ that functions only when it is wet. Most species of amphibians live close to water or in damp places. Most are active at night, when the ground is wet with dew. Others live mostly underground, beneath wet leaves, or under decaying trees.
Amphibian Life Cycle
When a young amphibian hatches, it is called larva. Larva is an early stage that is very different from the animal's adult form. The larvae of frogs and toads are called tadpoles. Tadpoles look and behave like fish. They breath with gills, eat mostly algae, and move with their tails.
After a few weeks, lungs and legs form, and the tail is absorbed by the body. They leave the water and begin their life on land. This process is called METAMORPHOSIS!
After a few weeks, lungs and legs form, and the tail is absorbed by the body. They leave the water and begin their life on land. This process is called METAMORPHOSIS!
Questions:
- Why do most adult amphibians stay near the water throughout their lives?
- Would a tadpole be able to live on land? Why?
- What invertebrate animal also breathes through its skin?
- Why are frogs and toads so vocal?
- Are amphibians endotherms or ectotherms?
ENDANGERED!!!!
Because of their special skin, amphibians require very specific living conditions. Too much sun can damage their cells. Too much wind can dry their skin and dehydrate the animal. As a result, amphibians are the first to die off when their habitats are disturbed or contaminated with chemicals like weed killer. This is the main reason over half of all frog species are in danger of extinction.
Because of their special skin, amphibians require very specific living conditions. Too much sun can damage their cells. Too much wind can dry their skin and dehydrate the animal. As a result, amphibians are the first to die off when their habitats are disturbed or contaminated with chemicals like weed killer. This is the main reason over half of all frog species are in danger of extinction.