tetrapod - Reflexions

tetrapod

An animal belonging to the sub-branch of vertebrates, whose skeleton has two pairs of limbs and whose breathing is by means of lungs. The oldest among them were difficult to distinguish from fish and lived in an aquatic environment. Ichthyostega is one of the best-known fossils representing this.
Today, the tetrapods include the amphibians, reptiles, the birds and mammals even though some have lost the characteristics of the group (legs in the case of snakes or upper limbs which became wings in the case of birds for example).