The family primarily consisted of large quadrupedal terrestrial browsers, notably including the largest marsupial that ever lived, the rhino-sized Diprotodon.[2]Nimbadon, which is often considered a basal diprotodontid, was arboreal.[3] Diprotodontids were plantigrade (foot and toes flat relative to the ground). In most diprotodontids, the forelimbs were not specialised and were capable of being used for functions other than movement. Some later diprotodontids from the Pliocene onwards like Ambulator and Diprotodon developed elephant-like forelimbs specialised for walking with modified wristbones which functioned as a heel, along with the development of footpads, which means that the digits probably did not contact the ground, as evidenced by the lack of toes on footprints of Diprotodon.[4][5] In at least some representatives of the clade, the inside of the skull was lightened by large interior sinus spaces.[6]
Ecology
At least some diprotodontids such as Diprotodon are thought to have lived in herds.[7]
Taxonomy
Diprotodontids are members of the Vombatomorphia, meaning that their closest living relatives are wombats, though they are more closed related to Palorchestidae, with both families placed in the Diprotodontoidea.[8] Traditionally the family is divided into two subfamilies, Diprotodontinae and Zygomaturinae. The taxonomy of diprotodontids is in need of revision, as historically many diprotodontids were diagnosed solely on tooth morphology, however the morphology of the premolar teeth of diprotodontid species is highly variable between individuals, with the molar morphology often very similar in species that differ greatly in skeletal anatomy, making the taxonomic utility of morphological characters related to teeth questionable.[5]
The group first appeared during the Late Oligocene, with representatives that were mostly sheep-sized, and substantially diversified beginning during the Late Miocene, reaching an apex of diversity during the Pliocene with seven genera, likely due to the increase of open forested landscapes. The last known members of the group including Diprotodon and Zygomaturus from mainland Australia, and Hulitherium and Maokopia from New Guinea became extinct during the Late Pleistocene around 40,000 years ago as part of the Late Pleistocene megafauna extinctions, following the arrival of humans to Australia-New Guinea.[9]
Vertebrate Palaeontology by Michael J. Benton (page 314)
Wildlife of Gondwana: Dinosaurs and Other Vertebrates from the Ancient Supercontinent (Life of the Past) by Pat Vickers Rich, Thomas Hewitt Rich, Francesco Coffa, and Steven Morton
Prehistoric Mammals of Australia and New Guinea: One Hundred Million Years of Evolution by John A. Long, Michael Archer, Timothy Flannery, and Suzanne Hand (page 77)
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