The affinities of Roberthoffstetteria nationalgeographica (Marsupialia) and the origin of the polydolopine molar pattern

Abstract

ABSTRACT A reanalysis of the upper and lower molar morphology of the early Paleocene marsupial Roberthoffstetteria nationalgeographica led to an interpretation of the molar homologies of the Polydolopinae (Polydolopimorphia). Several derived features support the attribution of Roberthoffstetteria to the Polydolopimorphia: thick dentary, molars with thick enamel, upper molars with reduced preparacrista that points to stylar cusp A, open centrocrista (that is, postparacrista not connected to the premetacrista), and metaconule large to very large, forming a “hypocone.” Other derived features support the monophyly of Roberthoffstetteria + polydolopines: alignment of paraconule, protocone, and metaconule in a lingual row; well-expanded anterior and posterior cingula, which are level with the trigon basin; variable occurrence of accessory cuspules at the labial face of the upper molars; and the labially placed paraconid with respect to the metaconid in the lower molars. Both Roberthoffstetteria and the polydolopines are plesiomorphic in having stylar cusp E, which is absent in most other South American marsupials. Several character complexes may be involved in the evolution of the polydolopine molar pattern.