Amphibians are among the oldest tetrapods (four legged animals) on the planet, evolving during the Devonian period (about 400 million years ago) from the bony fishes. They have the ability to live on land and in water, alternating between the two, they usually have to return to water to breed.
Amphibia - Amphibians
- both, Bios - life, refers to the fact that they can live in
or out of water
A characteristic of the group is metamorphosis from aquatic larval stages (tadpole or tadpole-like), into terrestrial (and aquatic) stages, through the release of the hormone thyroxine from the pituitary gland. Some do not undergo metamorphosis and remain in their juvenile stage while becoming reproductive, so adults that still still look like the larval stage, this phenomena is known as neoteny and can be seen in the Axolotl.
A typical toad, a "Southern Toad" - Anaxyrus terrestris from the USA
note the overall sturdier and heavier build with relatively shorter limbs when compared to the frog above, also warty rather than smooth skin.
picture Aurelius787, used under CC3 Attribution Share Alike Unported license
Fire Salamander Salamandra salamandra from Europe
the name probably comes from the habit of hiding in old logs that may be thrown onto the fire causing the salamanders to (unsurprisingly) leave rather quickly. This developed into a myth whereby salamanders could not only withstand fire but lived in it, even to be born from it.
picture Danny S.used under CC3 Attribution Share Alike Unported license
An axolotl, Ambystoma mexicanum.
This is an adult which retains the form of the juvenile without going through metamorphosis. It is fully aquatic and has external gills like tadpoles do. They grow up to 30cm (12") and can be induced to undergo metamorphosis into a salamander with a thyroxine injection. They are used in scientific research into stem cells as they can regenerate limbs.
picture LoKiLeCh, used under CC3 Attribution Share Alike Unported license
Poison dart frogs of the family Dendrobatidae are small frogs in the region of 2.5cm (1") long. They vary in toxicity though are often brightly colored as a warning to potential predators. The common name comes from their use by native peoples to tip hunting darts.
The Spanish ribbed newt or Iberian ribbed newt, Pleurodeles waltl.
Also known as the sharp-ribbed newt, the brown bumps along its side are tubercules through which it can push its sharp ribs as a defence mechanism. These have been used as a model organism on at least six space missions to study the effects of microgravity.
picture - David Perez, used under CC3 Attribution Share Alike Unported license
Kingdom - Animalia
Phylum - Chordata
Subphylum - Vertebrata
Class - Amphibians
Amphibia is a Class in the Subphylum Vertebrata of the Phylum Chordata, so they have all of the characteristics of both of these groups in addition to the following:
- Thin smooth permeable skin though which gas exchange (oxygen in, carbon dioxide out) can take place, gills are usually also present in the larvae and lungs in adults.
- Ectothermic, cold blooded.
- Soft unshelled eggs which must be laid in freshwater.
- Most members undergo a metamorphosis from larval (usually purely aquatic) to adult stage
Many Amphibia are highly toxic, the toxins being produced by poison glands on the skin. This toxicity often comes from the diet, taking on chemicals such as alkaloids from prey animals and synthesizing them into poisons.
Modern amphibians are experiencing declines in populations and extinctions, that have exceeded that of any other class over the last millennia. Of the 5,743 species of Amphibia, 32% are classed as at least threatened, compared to 12% of birds and 23% of mammals.
Population declines are associated with many factors, habitat loss through overexploitation of natural resources affects almost all threatened species, as well as the effects of climate change, and the fungal disease Chytridiomycosis (Batrachochytrium dendrobatidis) causing catastrophic levels of mortality.
What do amphibians eat?
Amphibians, for the most part are generalist carnivores. This means they will eat what they can get, what is abundant, and what they can fit in their mouths. The majority of the time this includes invertebrates such as insects, worms, slugs etc, as well as smaller and larval stage amphibians.
Some bigger amphibians can feed on larger animals like birds, or mammals such as the giant salamanders which are capable of feeding on small mammals such as rodents.
What eats amphibians?
Lots of things. Amphibia play an important role in food webs, and many species of bird, mammal, reptile and larger amphibians rely on them as an energy source. The conservation of amphibians is of great importance, not only for their own sakes, but for trophically higher organisms and the whole ecosystem.
The group includes:
The names of Amphibian groups should be taken as a work in progress, as they are revised; changed; and revised again.
Anura: Frogs and toads.
An = Without Uro = Tail
Four legged, generally have large hind limbs for jumping (saltatorial), swimming (natatorial), climbing, hopping or burrowing.
The largest Amphibian order, the Anura make up 88% of all Amphibians, containing more than 6100 species, found all over the globe except Antarctica.
Eggs are generally termed as a 'spawn' when laid in a gelatinous grouping, and laid in water, producing aquatic larvae called tadpoles. Some species however can develop directly on land, those of the genus Nectophrynoides and Nimbaphrynoides give birth to live young rather than eggs, a process known as viviparous spawning.
Ranidae - These are the 'true frogs' and what you are most likely to imagine when thinking of a frog. A family of 371 species, showing a general frog body plan and aquatic larval stage. Common frog -Rana temporaria.
Bufonidae - These are the diverse 'true toads' of which there are 577 species. They have shortened forelimbs (strong and used for mate retention in males during mating), dry, warty / bumpy skin and eggs are laid (generally) in strings as opposed to clumps like many frogs.
Cane toad - Bufo marinus (Introduced in Australia to limit rodent and beetle pests but now a massive problem as it has very toxic skin secretions which makes it immune to most predators.
Desert toad - Bufo alvarius Burrows underground in arid areas, only surfacing to feed. Takes up water from the ground through a patch in the pelvic region.
Urodela / Caudata
Uro = tail Delos = evident
Over 500 species making up approximately 9% of all Amphibia, legged and non-legged forms.
Giant Californian salamander - Dicamptodon ensatus (can 'bark').
Great crested newt - Triturus cristatus, Fire salamander -Salamandra salamandra, Spanish newt - Pleurodeles watl (rib popping).
3 toed amphiuma -Amphiuma tridactylum.
Gymnophiona: Gymno = naked
The Caecilians, with 3% of all Amphibian species. Being elongate, legless, and with a segmented look from skin folds, they are often compared to worms or eels.
All species require moist conditions. The name Caecelian is derived from the Latin 'Caecus' meaning blind, with most species living underground, eyes are rudimentary and scarcely function or completely gone, with a strong skull and head muscles for burrowing. Sensory information is picked up through chemo and tactile sensory organs in tentacular openings in the head. Fertilization is internal, with viviparity (live birth) and oviparity (egg laying) exhibited by various species.
Life in Cold Blood - Amazing Rain Frogs - David Attenborough - BBC Wildlife
Life in Cold Blood - Golden Frog - David Attenborough - BBC Wildlife
Top banner picture - Italian tree frog - Hyla intermedia, picture Benny Trapp, used under CC3 Attribution Share Alike Unported license.