Although all of these animals have been regarded as possible ancestors of the first tetrapods which colonized the land, their skull morphology is unlike the first fossil tetrapods which were amphibians. Neither Coelacanth nor Lungfish have a passage linking the nostrils with the roof of the mouth, a characteristic feature of all land vertebrates. However, another lobe-fin fish called Eusthenopteron, which only exists today as fossils, possessed such a passage and well developed lobes. Careful examination of the fins of these fossils revealed that the base of the lobe was supported by one stout bone close to the body, two bones joined to it and at the terminal end a group of small bones; an arrangement found in the limbs of land vertebrates.
A link between lobe-fin fish and amphibians has been found in the fossilizedIchthyostega found in Greenland in 1938. The swamps through which such animals waded was thick with horsetails and club moss trees which became fossilized as coal and also contained the first fossils of the terrestrialvertebrate (tetrapods) which belong to the class Amphibia.
These animals had evolved only 50 million years after the first bony fish and reached greatest expansion some 100 million years later in the Upper Carboniferous period. Some of these early forms grew to four metres in size and possessed jaws spiked with cone-like teeth. Today relatively few amphibians have survived, but they are nevertheless distributed in tropical and temperate areas of the world and in a variety of habitats. The modern amphibians differ considerably from their large ancestors. The living amphibian that most resemble early forms are the salamanders and the newts which collectively are called Caudata ("tailed ones"). The largest member of this group comes from Japan and has a body length of 1,7 m (Megalobatrachus).