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Kingdom: Animalia

Phylum: Chordata

Superclass: Tetrapoda

Class: Amphibia Clade: Lissamphibia

Amphibians are ectothermic, tetrapod (4 legged) vertebrates of the class Amphibia. They inhabit a wide variety of habitats with most species living within terrestrial, fossorial (that habitually burrows or digs), arboreal (tree living) or freshwater aquatic ecosystems. 

A red eyed green tree frog. image: wikipedia

Overall description and lifecycle 

Amphibians typically start out as larva 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 upon skin. 

A Hellbender salamander. image: wikipedia/Brian Gratwicke

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.

Evolution of amphibians

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 spotted salamander (Ambystoma maculatum) .

 image: Scott Camazine /wikipedia

Dermophis mexicanus a kind of caecilian . image: Franco Andreone/ wikipedia

The three modern orders of amphibians are:

      Anura (the frogs and toads), 

     ▪ Caudata/Urodela (the salamanders), and 

     ▪ Gymnophiona/Apoda (the caecilians). 

The total number of known amphibian species is approximately 7,000, of which nearly 90% are frogs. 

The sizes of amphibians

The smallest amphibian (and vertebrate) in the world is a frog from New Guinea (Paedophryne amauensis) with a length of just 7.7 mm. 

The largest living amphibian is the 1.8 m  Chinese giant salamander (Andrias davidianus) but this is dwarfed by the extinct 9 m  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.

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