In 1909 a rich accumulation of many thousands of bones was excavated from Mammoth Cave in Australia's south-west. Many of the bones far exceeded in size any modern-day native mammal, evidence that in prehistoric times giant mammals had roamed the Australian bush. They included a marsupial the size of a buffalo, kangaroos more than two metres tall, wallabies much bigger than any living species, a marsupial 'lion' about the size of a leopard, giant echidnas and wombats, plus the thylacine (Tasmanian tiger). What did these animals look like and how did they live? And how did they become extinct in a relatively short period of time?