Introduction
Amphibians
Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. Modern amphibians are all Lissamphibia. They inhabit a wide variety of habitats with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Amphibians typically start out as larvae living in water, but some species have developed behavioural adaptations to bypass this. The young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin. They are superficially similar to reptiles but, along with mammals and birds, reptiles are amniotes and do not require water bodies in which to breed. With their complex reproductive needs and permeable skins, amphibians are often ecological indicators and in recent decades there has been a dramatic decline in amphibian populations for many species around the globe.
The earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, but were later displaced by reptiles and other vertebrates. Over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura (the frogs and toads), Urodela (the salamanders), andApoda (the caecilians). The number of known amphibian species is approximately 7,000, of which nearly 90% are frogs. The smallest amphibian (and vertebrate) in the world is a frog from New Guinea (Paedophryne amauensis) with a length of just 7.7 mm (0.30 in). The largest living amphibian is the 1.8 m (5 ft 11 in) Chinese giant salamander (Andrias davidianus), but this is dwarfed by the extinct 9 m (30 ft) Prionosuchus from the middle Permian of Brazil. The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology.
Task
Amphibians Quiz
Click on the radio button in front of the correct answer to the question.
1. The word amphibian means
a. Frog
b. Both sides of life
c. Toad
2. Estivation means
a. Going into hiding and sleeping through the winter
b.Going into hiding and sleeping through the summer
c. Migrating south during the winter
3. Amphibians are among the largest vertebrates
a.True
b.False
4. Amphibians are cold blooded
a.True
b.False
5. Which group of animals are amphibians?
a.Frogs & Toads
b.Snakes & lizards
c.Cats & dogs
6. Amphibians have
a.Radial Symmetry
b.Asymmetry
c.Bilateral symmetry
7. The amphibians babies are called
a.Cubs
b.Tadpoles
c. Chicks
Process
Evaluation
Criteria
Conclusion
One-third to one-half of the world’s approximately 7,500 known amphibian species could go extinct in our lifetime. This would be the largest mass extinction since the disappearance of the dinosaurs. Amphibians are considered canaries in the coal mine: they are among the first species to be affected by environmental stressors, so when they show declines in the wild, it is a warning to other species, including humans. Their population declines and extinctions signal that changes are occurring in the environment that will also negatively impact humans.
Amphibians are dying in alarming numbers. About 122 species are believed to have become extinct since 1980. About half of the world’s 7,500 species could become extinct within our lifetime with at least 500 species facing imminent extinction. This rate of extinction is unprecedented since the demise of the dinosaurs.
Destruction of habitat, invasive species, pollution, global warming and other human influences threaten many species throughout the animal and plant kingdom. In addition to these challenges, amphibians are being attacked by a lethal disease that has caused unprecedented and unexpected losses, called chytrid fungus. Chytrid quickly and quietly destroys entire species when introduced to new populations in the wild. Chytrid fungus has now been identified in association with amphibian die-offs on every amphibian-inhabited continent. This disease has decimated or wiped out species that had not been considered critically endangered. It happens so quickly that species disappear before anyone realizes they are in trouble.
Amphibian chytrid is a disease that infects the skin of amphibians, a vital organ through which many drink and breathe. It was discovered a decade ago; dozens of frog species have already vanished because of it. In environments where it thrives, the fungus can kill 80 percent of the native amphibians within months. Currently, it is unstoppable and untreatable in the wild, even in ‘protected’ areas. Amphibian chytrid is believed to have originated in Africa. The export of African clawed frogs (likely resistant carriers of the fungus) around the world for human pregnancy testing and lab studies spread this disease worldwide. Recently, the food and pet trades may have contributed to the problem as well. The chytrid’s spread and effects may be exacerbated by climate change – warmer temperatures dry the moist areas where amphibians live, causing stress that may lead to greater susceptibility to the disease.
For amphibians, the potential impact of chytrid fungus across all species is probably underestimated, and a significant number of amphibian species that have been described are too rare and too poorly known to assess their level of endangerment.
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