About the Dipnoi
The earliest known Dipnoi date back from about 400 million years ago. During the Devonian the Dipnoi had dorsal, anal, and caudal fins. At the end of the Devonian these fins disappeared or merged to form one a single elongated caudal fin. This is a characteristic which all living lungfishes still have. It is believed that since the end of the Carboniferous lungfishes only inhabited freshwater. Later during the Permian they evolved the ability to aestivate, which means they can lie in a state of dormancy enclosed in the mud to survive long periods when a river or lake dries up, becoming active again when the rains arrive.