Open access article:

The Gondwanan Origin of Tribosphenida (Mammalia)

Abstract

A review of the Southern Hemisphere Mesozoic tribosphenic mammal
fossil record supports the hypothesis that Tribosphenida arose in the
Southern Hemisphere during the Early Jurassic, around 50 million years
prior to the clade’s reliably dated first appearance in the Northern
Hemisphere. Mesozoic Southern Hemisphere tribosphenic mammals are
known from Australia, Madagascar, South America and the Indian
subcontinent, and are classified into three families: Bishopidae (fam.
nov.), Ausktribosphenidae and Henosferidae. These are stem therians,
and considerable morphological evolution occurred within the lineage
between the Jurassic and late Early Cretaceous. Important dental
modifications include a graduated transition between premolars and
molars, development of molar wear facets V and VI, loss of facets for
postdentary bones, reduction in the Meckelian groove and development
of a true dentary angle. Previous classifications of Southern
Hemisphere tribosphenic mammals are ambiguous because information from
the upper dentition has been lacking. Upper molars attributed to the
late Early Cretaceous (Albian) Southern Hemisphere group Bishopidae
fam. nov. are now known to possess a prominent protocone and stylar
cusp C. We thus consider bishopids to be the sister group to Theria.
https://www.tandfonline.com/doi/full/10.1080/03115518.2022.2132288