Amphibians

 The amphibians are the first terrestrial vertebrates, but that depend still narrowly on the aquatic way, since only in they can be reproduced. His four extremities are alone sufficient to move with slowness for firm land.
 It has cartilaginous skeleton, with the cranium joined the vertebral column by means of two cóndilos and with the ribs, when they exist, without joining the breastbone. Is observed in them already the beginning of reproduction of the number of cranial bones that they characterize to the terrestrial vertebrates. They can have tail or not.