When did lungfish first appear in the fossil record?

Lungfish, which belong to the subclass Dipnoi, first appeared in the fossil record during the Early Devonian Epoch, approximately 419.2 million to 393.3 million years ago.12

These ancient fishes are part of the class Sarcopterygii and are noted for their evolutionary history, which includes early genera such as Dipterus. Fossil evidence from the Early Devonian indicates that these early forms already possessed characteristic dipnoid skull and dental features, as well as traits shared with other sarcopterygian groups like coelacanths.2