|Unit: Amphibians|| 2 Body structure|
Body structureSome modern fish can live out of water for long periods, such as eels, climbing perch and walking catfish. The mudskipper, PERIOPHTHALMUS,
is a fish which spend most of its time on land.
The selective advantages which have led to the modern mudskippers moving onto the land are probably similar to the factors which favoured the development of the earliest amphibians.
But mudskippers are not very well adapted for living on the land. In particular, they do not have lungs, or a strong fin
structure to support the weight of the body. The fish ancestors of the first land vertebrates must have had both these features. Lungs developed as simple pouches leading from the throat, which developed a rich supply of blood vessels. Limbs developed from the bony supports of the fins.
Many bottom-living modern fish use their fins to help them manoeuvre over the bottom. But the pattern of bones at the base of the fins of most modern fish are quite unlike those of the limbs of land vertebrates. However, the arrangement of bones within the base of the fin of the modern coelacanth
is very similar to the limb structure of land