Mammals of Australia introductions of placental mammals into Australian fauna were about (rats), several thousand years ago (dingo), and 200 years ago (many species); the last two were made by humans. Some claims were made about placental mammal fossils from the Eocene of Australia, called "Tingamarra". These claims are based on only one found tooth having some characteristic features of condylarth, and were discussed widely. But both the age and placental nature of these fossils were challenged by other researchers. Monotremes are mammals with a unique method of reproduction: they lay eggs instead of giving birth to live young. Two of the five
Steropodon typical for Mesozoic mammals. Woodburne (2003, p. 212) reports that the holotype is a right mandible named AM F66763. The preserved molars are m1–m3. Page 237 includes: "In "Steropodon", the mandibular canal suggests the presence of a bill, with a bill also known in "Obdurodon dicksoni" and "Ornithorhynchus anatinus"." A fine photo of the opalised lower jaw can be found on page 182 in: Steropodon Steropodon galmani was a prehistoric species of monotreme, or egg-laying mammal, that lived about 105 million years ago (mya) in the Lower Cretaceous period. It is one of the oldest monotremes discovered, and is one