Editing Tetrapod (section)

==== Cutaneous respiration ====
Skin breathing, known as [[cutaneous respiration]], is common in fish and amphibians, and occur both in and out of water. In some animals waterproof barriers impede the exchange of gases through the skin. For example, keratin in human skin, the scales of reptiles, and modern proteinaceous fish scales impede the exchange of gases. However, early tetrapods had scales made of highly vascularized bone covered with skin. For this reason, it is thought that early tetrapods could engage some significant amount of skin breathing.<ref>{{harvnb|Clack|2012|pp=233–7}}</ref>