The main cusps, the buccal hypoconid and lingual entoconid, are opposite each other on the margins of the tooth ( the entoconid is further to the front in " Phenacopithecus " ).
22.
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.
23.
Averianov and colleagues noted that zhelestids, a placental group, share all those traits, though to varying degrees, and that the hypoconulid in similarly aged marsupials is even more lingually located, " twinned " to the entoconid ( the cusp on the back lingual corner of the tooth ).
24.
In " Indraloris himalayensis " lower molars, there are four main cusps ( protoconid and metaconid in the trigonid, hypoconid and entoconid in the talonid ), which give the crown a rectangular aspect, although the labial cusps ( protoconid and hypoconid ) are placed somewhat anterior to their lingual counterparts.
25.
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.
26.
Muirhead ( 1997 p . 372 ) describes " W . ridei " as having the following features that are unique : parametacrista on the first molar is straight, entoconid either missing of combined with the hypoconid in a more posterior position, the loss or reduction of styler crests, small metaconid, talonid basin reduced by the Ngamalacinus ", and that is the metaconid and protoconid are reduced.
