The fourth upper premolar ( P4 ) has not been recorded, but there is a specimen of its cusps ( protocone, paracone, hypocone, and metacone ) and lophs or crests ( protoloph, mesoloph, metaloph, and posteroloph ), separated by synclines or valleys.
22.
Based in part on Martin and Rauhut's earlier work on wear facets in australosphenidans, they questioned the presence of a true functional protocone on the upper molars of non-monotreme australosphenidans none of which are known from upper teeth and consequently suggested that australosphenidans may not, after all, have had truly tribosphenic teeth.
23.
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.
24.
However, there are also differences : there is no entoconid, and an absence of wear seems to suggest that the upper molars ( as yet unknown ) did not have a protocone, and so implying that there was a double origin of tribosphenic teeth, one group represented by the living placentals and marsupials, and the other group being the monotremes bearing'pseudo-tribosphenic'teeth.
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