The fossil record of extinct kangaroos is incredible. Not only do we have the remains of heavily-built giant roos, we also have omnivorous and even predatory species of rat-kangaroo and smaller varieties no bigger than today’s smallest wallabies. This especially goes for some of the early species that were found all over Riversleigh, one of the most famous Australian fossil sites and a UNESCO World Heritage Site. The fossil site as a whole is made up of limestone deposits occurring in freshwater pools, and this allows the extinct creatures to be preserved in all three dimensions. Riversleigh has cast new light on pre-outback Australia and its colorful cast of animals, including tiny ancestral koalas, cow-sized wombats and fearsome land crocodiles. Altogether the site preserves roughly 20 million years of evolution that range from the end of the Oligocene to the dying days of the Miocene. This period is known as the heyday of mammalian evolution everywhere and this held true for Australia as well.
The evolution of kangaroos at the site was in overdrive here with many different genera. They ranged from being quite recognizable to being completely bizarre. One of the newest kangaroos from Riversleigh is the oddly named Cookeroo. The fossils were studied by a team comprised of Kaylene Butler and other researchers from the School of Earth Sciences at the University of Queensland in Australia.Two species of Cookeroo existed here, somewhere between 23 and 18 million years ago during a time known as the early Miocene. They were at the lower end of the scale in terms of dimensions, equaling a very small wallaby in size. Butler and team classified the new animal by using a sample of about 69 other kangaroo species.