The Evolution of Monotremes: New Fossils, New Insights

The origin and evolution of monotremes has long remained mysterious. New dating of monotreme-bearing Cretaceous deposits in eastern Australia reveal that the oldest known monotremes are Barremian in age – around 126 million years (ma) old. These shrew-sized ancestors share similarities with dryolestids, and lived well within the polar circle, enduring 3 months of darkness per year, and show adaptations to probe-feeding, like long-beaked echidnas (Zaglossus). By the Aptian (113 ma) monotremes had become cat-sized, and by the Cenomanian at least 6 genera (in 4 families, the largest diversity of monotremes known) co-existed in the Lightning Ridge fauna, New South Wales. They include a species that could have been functionally ancestral to both platypus (ornithorhynchids) and echidnas (tachyglossids), as well as an undoubted stem platypus. The oldest non-polar monotreme fossils are 26 ma ornithorhynchids from central Australia. Thus, for 100 million years, all known othithorhynchid fossils derive from sediments laid down south of 60S in latitude. As will be outlined, the Vogelkop region of the island of New Guinea may have played an important role in tachyglossid evolution. The Pleistocene saw rapid evolution of monotremes, with 2 genera of tachyglossids appearing, and the emergence of the first toothless ornithorhynchids (which may have evolved in response to the arrival of the Australian water rat Hydromys).

Tim’s visit is on the back of the rediscovery by James Kempton and colleagues of Attenborough’s echidna in New Guinea. Prof Flannery’s early research was on megafaunal extinctions and in more recent years he has focused on writing popular science books (books include The Weather Makers & The Future Eaters). He is a previous winner of Australian of the Year, a champion of climate change issues, and is an expert in biogeography, especially in New Guinea (hence his interest in the echidna).