A team at the University of New South Wales has described three fossil species from northwestern Queensland that it argues do not fit into any known branch of the marsupial family tree, and has proposed a new order to hold them.
The group has been named Keeunamorphia and is put forward as a sixth order within Australidelphia, the superorder containing Australia's marsupials, according to an announcement from the university carried by ScienceDaily. The work is published in the Journal of Paleontology, by Timothy James Churchill, Michael Archer, Suzanne J. Hand and Robin M. D. Beck.
What was found
The material is modest: teeth and pieces of jaw, recovered from what were once shallow cave pools at the Riversleigh World Heritage Area. The fossils are dated to roughly 18 million years ago, in the Early Miocene.
Riversleigh is one of the richest fossil deposits in the southern hemisphere, and its limestone has preserved a long sequence of Australian mammal life. Much of what is known about the continent's mammals between about 25 and 12 million years ago comes from it.
The researchers say the order may have persisted for around 35 million years before disappearing roughly 15 million years ago.
Why an order is a large claim
The significant word here is "order," and it is worth being precise about what is being asserted.
Describing a new species is routine work. A new genus is notable. An order is a rank several levels higher: in the marsupial context it sits alongside Diprotodontia, the group that contains kangaroos, koalas and wombats, and Dasyuromorphia, which contains the quolls and the thylacine. Proposing one means arguing that these animals sit outside every existing branch, rather than at the end of one.
Churchill put the claim directly in the university's announcement: "Not only is it a new order, it could also be the most ancient lineage of all Australian marsupials."
That is the part likely to attract scrutiny. Higher-level taxonomic claims built on teeth and jaw fragments are not unusual in mammal palaeontology, because teeth are hard, they preserve well, and their shape is genuinely diagnostic. They are also, however, a limited window. Whether other researchers accept the placement will depend on how the specimens are read against existing material, and that argument plays out over years in the literature rather than on publication day.
What it would mean
If the interpretation holds, it complicates a tidy account of Australian marsupial origins in which today's diversity descends from a relatively small ancestral stock. It would instead suggest that early Australia carried lineages that left no living descendants at all, and that the modern fauna is the surviving portion of something broader.
That is a familiar shape for evolutionary history rather than a surprising one. It is also difficult to demonstrate, precisely because extinct side branches leave less behind than lineages that continued.
A note on this report
This account is based on the University of New South Wales announcement and the published paper's details. We were not able to obtain comment from a palaeontologist unconnected to the study before publication, which is the usual check on a claim of this size. Readers should treat the order-level classification as the research team's proposal, now entering peer scrutiny, rather than as settled.
