Image: Opalised jaw of Steropodon, backlit Steropodon galmani
Archer. One of Australia's oldest mammal fossils, from the Early
Cretaceous rocks at the opal fields of Lightning Ridge, New
South Wales. - Carl Bento - © Australian Museum Steropodon
galmani, a platypus-like monotreme from the Early Cretaceous,
was the first Mesozoic mammal discovered in Australia. It is
known from this opalised lower jaw with molar teeth. The teeth
of Steropodon are similar to those of later fossil platypuses
although its molars are more archaic in form.Steropodon lived
alongside dinosaurs, crocodiles, early birds and other early
mammals on the forested shores of the inland Cretaceous Eromanga
Sea.