The diphyletic origin of marsupials

According to
the large reptile tree (LRT, 2340 taxa) marsupials had a single origin, splitting from monotremes in the Late Triassic.

Rich, Flannery and Vickers-Rich 2026
proposed a diphyletic origin of marsupials based on dental records and geography.

The authors did not provide a cladogram with separate origins for one set of marsupials vs another set of marsupials.

The authors wrote,
“There is ample evidence that one group of marsupials, the ameridelphians, arose during the late Early Cretaceous in the Northern Hemisphere and subsequently dispersed to South America.”

In the LRT the earliest marsupials come from Early Cretaceous China = East Asia with descendants in the Early Jurassic. So the dichotomy points to a Late Triassic origin or earlier.

The authors wrote,
“Australian marsupials are the product of a 125 million-year-long evolutionary marathon that began in China before sledging on through Europe, North America, South America, Antarctica and, by at least 55 million years ago (Ma), finally Australia – the last piece of land on the then remnant of Gondwana.’ But is this what necessarily happened? What now leads to a reason to possibly question that view has been the discovery of late Early Cretaceous tribosphenic mammals that could be the source from which arose the marsupials endemic to Australia and New Guinea.”

“Three lines of evidence now are known in the Early Cretaceous fossil record of Australia that suggest that a mammalian stock then existed on the continent that could have given rise to the metatherians: (1) a premolar-molar pattern plausibly ancestral to that of metatherians; (2) ‘twinning’ of the hypoconulid and entoconid cusps on the talonids of Ausktribosphenos and Bishops; and (3) a maxillary fragment with two upper molars, which have a protocone and occlusal outline similar to those seen in insectivorous australodelphians, and stylar cusps, a feature distinguishing basal metatherians from basal eutherians.”

I am respectful of and wary of dental traits
being used sans the broader range of traits from nose to toes tested in the LRT. This after having seen what happens to odontocete molars and marsupial canine-like premolars – plus the three origins for the placenta, the triphyletic origin of flukes and other convergent traits that Larry Martin would have had fun tempting students with while teaching them to be wary.

Not much else to say here
other than taxon exclusion is the number one problem hobbling paleontology today. Cladograms are the number one tool for demonstrating hypotheses of interrelationships.

References
Rich TH, Flannery TF, Vickers-Rich P 2026. The diphyletic origin of marsupials. Australian Zoologist (2026) 45 (2): AZ26012.

https://doi.org/10.1071/AZ26012