55 million years ago, early Eocene
It was a condylarth - a member of an ancient group of placental mammals. These include the ancestors of placental mammals such as dogs, cats, horses and whales.
Tingamarra appears to be the only land-based placental mammal to have arrived in Australia before about 8 million years ago. The only other native placental mammals in Australia are rodents and Dingos (which arrived here more recently), and bats (which presumably flew in).
A single tooth of Tingamarra was found at Murgon in southeastern Queensland in 1987. An ankle bone and an ear bone found at Murgon may also belong to this animal.
Did you know?
Many Australian mammals are marsupials. Scientists have long thought that when placental and marsupial mammals compete for resources, the placentals win. Before Tingamarra was found, it was thought that marsupials had done well in Australia because for many millions of years they had no placentals to compete with.
Discovery of Tingamarra surprised scientists, because it meant that placental mammals were indeed in Australia many millions of years ago, and the marsupials had flourished anyway.