Steropodon galmani was a prehistoric species of monotreme, or egg-laying mammal, that lived during the middle Albian stage, about 105 million years ago, in the Lower Cretaceous period. It is thought to be the second-earliest known relative of the platypus. Steropodon is known only from a single opalised jaw with three molars, discovered at the Griman Creek Formation, Lightning Ridge, New South Wales, Australia, by brothers David and Alan Galman.