Ambondro mahabo is a mammal from the Middle Jurassic (Bathonian) Isalo III Formation (about 167 million years ago) of Madagascar.

In 2001, however, an alternative suggestion was published that united it with the Cretaceous Australian Ausktribosphenos and the monotremes (the echidnas, the platypus, and their extinct relatives) into the clade Australosphenida, which would have acquired tribosphenic molars independently from marsupials and placentals.

[1] Ambondro was described on the basis of a fragmentary right mandible (lower jaw) with three teeth in it (Figure 1), interpreted as the last premolar (p-last) and the first two molars (m1 and m2).

It is wider than long[4] and contains a well-developed cusp, the hypoconid, on the outer side and a depression, the talonid basin, in the middle.

Further towards the inner side, a crest, the entocristid, rims the talonid basin; on m1, it is swollen and on m2, it contains two small cuspules, but a distinct entoconid cusp is absent.

[9] Asfaltomylos Henosferus Ambondro Ausktribosphenos Bishops Monotremata Metatheria Eutheria Monotremata Metatheria Eutheria Ambondro Asfaltomylos Ausktribosphenos Bishops In their paper, Flynn and colleagues described Ambondro as the oldest mammal with tribosphenic molars—the basic molar type of metatherian (marsupials and their extinct relatives) and eutherian (placentals and their extinct relatives) mammals, characterized by the protocone cusp on the upper molars contacting the talonid basin on the lower molars in chewing.

The discovery of Ambondro was thought to extend the known temporal range of tribosphenic mammals 25 million years further into the past.

[11] They cited the retention of a distal metacristid and an "open" trigonid as characters separating Ambondro from more modern tribosphenidans.

[2] In 2001, Zhe-Xi Luo and colleagues alternatively proposed that a tribosphenic molar pattern had arisen twice (compare Figure 3, top)—once giving rise to the marsupials and placentals (Boreosphenida), and once producing Ambondro, the Cretaceous Australian Ausktribosphenos, and the living monotremes, which first appeared in the Cretaceous (united as Australosphenida).

[5] The next year, Luo and colleagues published a more thorough analysis confirming their previous conclusion and adding the Cretaceous Australian Bishops to Australosphenida.

[14] They mentioned the condition of the hypoconulid, which is inclined forward, rather than backward as in boreosphenidans, as an additional australosphenidan character[15] and noted that Ausktribosphenos and monotremes were united, to the exclusion of Ambondro, by the presence of a V-shaped notch in the distal metacristid.