The thesis of this heuristic discussion is that the frog morphotype arose via a regulatory mutation that truncated vertebrae-forming somitogenesis and not via selection on structural genes. This truncation, along with many collaborative events (e.g., other skeletal elements, viscera, jaws, and mouthparts) required to maintain a viable organism, produced the essence of a prototadpole. With the presumed confines of metamorphosis, only something resembling a frog could metamorphose from such a highly paedomorphic larva. Larvae and adults were further altered by other less deep regulatory changes and subsequent selection to produce characters correlated with systematics and ecology.