It contains a single species, Steropodon galmani, that lived about 100.2–96.6 million years ago during the Cretaceous period, from early to middle Cenomanian.

[4] Edentulous partial mandible from the Finch Clay facies of the Griman Creek Formation was attributed to undescribed steropodontid by Musser (2013).

[4] The specific epithet is derived from the surname of the jaw's collectors, when combined with the genus name Steropodon is intended to translate as "Galman's lightning tooth".

[6] 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.

Examination of the jaw fragment revealed a mandibular canal, which has been proposed to indicate the presence of a bill, similar to those of the extinct species Obdurodon dicksoni and the modern platypus Ornithorhynchus anatinus.