Perhaps the vaguely leglike use of fins is even older than lungfish. Bichirs, which are the basalmost branch of ray-finned fishes and also often depicted as living fossils, have rather interesting fins too. They have fleshy bases that make them look like the fins of the coelacanth or Australian lungfish, even though the internal structure is different. They use their fins to propel them through water, sometimes in alternative strokes. They also stand up on the bottom with their fins turned forward like toes, and drag themselves through vegetation with them.

They have other primitive characters as well, such as lungs, spiracles, external gills in larval stage and ampullae of Lorenzini.

The bichirs seem to have branched off the ray-finned fish lineage pretty soon after they branched off the lungfish-tetrapod lineage. I don’t know if their mode of locomotion is the primitive one, but judging by their other ancient characters, it might be.