amphibian - History of amphibians, Classification, Reproduction

A vertebrate animal of class Amphibia (c.4000 species), exhibiting a wide range of characters and lifestyles; usually four legs and glandular skin, lacking scales or other outgrowths; larvae usually live in water and breathe through feathery external gills; undergo a metamorphosis during development, when the gills shrink and disappear; adults breathe using lungs (and partly through the skin); three major groups: salamanders and newts (Order: Urodela or Caudata), frogs and toads (Order: Anura or Salientia), and the legless caecilians (Order: Gymnophiona or Apoda).

iAmphibians Fossil range: Carboniferous - Recent
White's Tree Frog (Litoria caerulea)
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Amphibia Linnaeus, 1758
Subclasses and Orders
Order Temnospondyli - extinct Subclass Lepospondyli - extinct Subclass Lissamphibia   Anura   Caudata   Gymnophiona

Amphibians (class Amphibia; Amphibians are able to breathe through their skin making them very sensitive to anything they come in contact with, including human hands.

History of amphibians

Amphibians developed with the characteristics of pharyngeal slits/gills, a dorsal nerve cord, a notochord, and a post-anal tail at different stages of their life. Though early tetrapods (which appeared 390 million years ago in the Devonian period) are often referred to as "amphibians", the first true amphibians (of the order Temnospondyli) appeared during the early Carboniferous period. During the late Carboniferous, Permian and Triassic periods, amphibians were extremely diverse, including many large and in charge forms, some newt and salamander-like, others resembling snakes or eels, and some large-snouted forms that were very like small (about 1.5 meter long) crocodiles (e.g. However both large and small amphibians still continued to flourish in rivers and lakes of the Late Permian, alongside the diverse therapsids that were the dominant land animals of that time. Apart from a few stragglers, all these large amphibians died out at the Triassic-Jurassic extinction event, and the majority of Jurassic amphibians belonged to modern groups, and would look familiar today.

The names of many of these Palaeozoic basal tetrapods and amphibians end in -gyrinus.

Throughout their history, amphibians have ranged in size from large forms, such as the above mentioned Triassic genera, the 5 foot (150cm) long Eryops of the Permian period, and the Giant Japanese and Chinese Salamanders of today, down to the tiny Brachycephalus didactylus (Brazilian Gold Frog) and Eleutherodactylus iberia (leptodactylid frog) from Cuba, with a total length of 9.6-9.8 millimeters (0.4 inches).

Classification

Traditionally the amphibians have included all tetrapods that are not amniotes. They are divided into three subclasses:

Subclass Labyrinthodontia (diverse Paleozoic and early Mesozoic group) Subclass Lepospondyli (small Paleozoic group) Subclass Lissamphibia (frogs, salamanders, etc)

Of these only the last includes recent species. Generally amphibians are defined as the group that includes the common ancestors of all living amphibians (frogs, salamanders, etc) and all their descendants. This means that there are a now large number of basal Devonian and Carboniferous tetrapod groups, described as "amphibians" of earlier books, that are no longer placed in the formal Amphibia.

All recent amphibians are included in the Lissamphibia, which is usually considered a clade (which means that it is thought that all Lissamphibians evolved from a common ancestor apart from other extinct groups), although it has also been suggested also that salamanders arose separately from a temnospondyl-like ancestor (Carroll, 1988).

Authorities also disagree on whether Salientia is a Superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia.

Family Albanerpetontidae - Jurassic to Miocene (extinct) Superorder Salientia Triadobatrachus (Triassic) Order Anura (frogs and toads) Jurassic to recent - 5,296 recent species Order Caudata or Urodela (salamanders): Jurassic to recent - 555 recent species Order Gymnophiona or Apoda (caecilians): Jurassic to recent - 171 recent species

Reproduction

For the purpose of reproduction most amphibians are bound to fresh water.