Steropodon (subclass Prototheria, order Monotremata) The earliest Australian mammal and the only known Mesozoic representative of the monotremes. It is known only from opalized jaws and teeth found in Cretaceous deposits at Lightning Ridge, central Australia (the name is from the Greek sterope, ‘lightning’). The pattern of the molar teeth suggests that monotremes, like Eupantotheria, may be derived from Theria and not from a separate protomammalian stock.

Steropodon The earliest Australian mammal, a monotreme known only from opalized jaws and teeth found in Cretaceous deposits at Lightning Ridge, central Australia (the name is from the Greek sterope, meaning ‘lightning’). The pattern of the molar teeth suggests that monotremes may be derived from Theria and not from a separate protomammalian stock.