The problem of determining the evolutionary relationships between different species of amphibians has been neglected for too long - the latest evolution tree of the amphibian was drawn in 1930 and it was created in particular based on the appearance of various species. Although in recent years, populations of amphibians such as frogs, have suffered significant declines due to habitat destruction in particular, scientists have discovered a series of new species. But it was not clear how these species are related to each other.
Biologist Darrel Frost and his colleagues at the American Museum of Natural History were occupied by this problem, making the largest study so far in this area. They analyzed DNA of 522 species of amphibians, which are considered representative for the nearly 6,000 known amphibian species that still are living on the Earth.
Evolutionary tree resulted has radically changed the perspective on the evolutionary relationships among amphibians.
Amphibians are the first quadruped that evolved from fishes, which are precursors of amniotics (reptiles, birds and mammals). Unlike amniotic, amphibians have a larval stage, in which the tadpole must look for food alone, in order to grow up, followed by a metamorphosis to the adult stage. For amniotic, from dinosaurs to humans, the larval stage was transformed into an embryo stage, when the animal is not forced to look for food alone but is fed (either passively, in case it develops inside an egg or actively by the mother, in case of mammals).
The Devonian Period was probably the first time the first major amphibian groups existed. They initially were fish-like creatures similar to the present day coelacanth. They had developed multi-jointed leg-like fins that enabled them to crawl along the sea bottom. However, Devonian Amphibians did not have the capabilities as to breed their eggs on surface.
In the Carboniferous Period, they began to eat insects and small aquatic creatures under water.
btw Reptiles used to be a form of an amphbian that developed thicker skin and a proper respiratory system.