Short answers, pulled from the story.
Diprotodontia includes kangaroos, wallabies, possums, the koala, wombats, and many others, totaling about 155 living species. Extinct members include the hippopotamus-sized Diprotodon and Thylacoleo, the so-called marsupial lion.
Diprotodont means two front teeth, from the Ancient Greek words for two, first, and tooth. The name refers to a pair of large, procumbent incisors on the lower jaw.
Living diprotodonts are almost all herbivores, and most extinct ones ate plants too. A few are insectivorous or omnivorous, the Potoroidae are largely fungivorous, and the extinct thylacoleonids were the only group to show large-scale carnivory.
Diprotodonts are restricted to Australasia. Their earliest known fossils date to the late Oligocene, between 23.03 and 28.4 million years ago, though their origin lies earlier than the fossil record shows.
Many of the largest and least athletic diprotodonts became extinct when humans first arrived in Australia about 50,000 years ago. The cause was possibly hunting, but more probably widespread habitat changes from human activities, notably the use of fire.
Diprotodontia is identified by being diprotodont, meaning it has a pair of large lower incisors and a short jaw with no lower canines, and by syndactyly, the fusing of the second and third toes up to the base of the claws.