A new metatherian order from Australia (Keeunamorphia, Metatheria), and new Early Miocene species from the Riversleigh World Heritage Area, northwestern Queensland

Abstract Three new species of small (~25–200 g) tribosphenic marsupials, including a new genus, are described from the Early Miocene deposits of the Riversleigh World Heritage Area. Phantasmodon travouilloni , Phantasmodon minuferox , and Keeunidae gen. and sp. indet. share dental apomorphies with the late Oligocene marsupials Keeuna woodburnei and Ankotarinja tirarensis (currently Australidelphia incertae sedis), and with Australia’s oldest and most plesiomorphic marsupial, the early Eocene Djarthia murgonensis. Parsimony analyses recover these taxa as a distinct clade, warranting recognition of a new marsupial order, Keeunamorphia. In contrast, Bayesian analyses do not support the inclusion of D. murgonensis in this group, instead placing it as a stem australidelphian or stem marsupial. When early Eocene South American and European metatherians are excluded, Keeunamorphia new order appears to be the most basal (parsimony analysis) or one of the most basal (Bayesian analysis) lineages of Australidelphia. However, when these taxa are included in parsimony analysis, Keeunamorphia weakly links to South American sternbergiids and European herpetotheriids, whereas Bayesian analysis suggests keeunamorphians (excluding D. murgonensis ) are more closely related to dasyuromorphians than to peramelemorphians, microbiotherians, D. murgonensis , and non-australidelphian metatherians. Keeunamorphia n. ord. may represent some of Australia’s earliest marsupials, with possible origins in Gondwana and a record spanning more than 35 million years before its apparent extinction in the Middle Miocene. UUID: http://zoobank.org/a2699457-5b2c-4f0c-b8b6-dd41401c3a17