Mesozoic mammals of Madagascar

This led its discoverers to propose that the ancestors of tribosphenic mammals arose in the south (Gondwana), not, as generally assumed, in the north (Laurasia).

In 2001, however, paleontologist Zhe-Xi Luo and colleagues alternatively proposed that Ambondro was part of a clade with Ausktribosphenos from the Cretaceous of Australia and the monotremes that developed tribosphenicity independently from other mammals (Boreosphenida).

Other paleontologists have disagreed with this interpretation and proposed different models; for example, in 2001 Denise Sigogneau-Russell and colleagues proposed that although Ausktribosphenos and monotremes were related, Ambondro was not and was in fact more similar to boreosphenidans, and in 2003 Michael Woodburne and colleagues excluded monotremes from Australosphenida and placed the remaining australosphenidans close to placentals.

[1] The Mahajanga Basin of northwestern Madagascar has produced a rich late Cretaceous fauna, including various dinosaurs and crocodyliforms as well as mammals, found by the team of David W. Krause since 1993.

Many of these taxa show affinities with similarly aged South American and Indian animals, also parts of Gondwana.

[10] In addition to these fragmentary teeth, the Maevarano Formation has also yielded a nearly complete, articulated skeleton of an immature, cat-sized mammal that has not yet been fully described.

[11] In a 2000 abstract, Krause identified it as a therian (a member of the group that includes marsupials, placentals, and their closest extinct relatives) more derived than the early Cretaceous Vincelestes of Argentina, but in 2006 he and colleagues instead refused to place it in any existing higher-order mammalian group and claimed that "it represents a major new nontherian clade".