A reassessment of the genus Groeberia Patterson, 1952 (Mammalia, Metatheria): functional and phylogenetic implications

Abstract

With two recognized species, the extinct (late Eocene) Groeberia is periodically at the centre of systematic disputes. On the basis of its best-preserved specimen, we describe in detail the dental and functional morphology of the masticatory apparatus of Groeberia minoprioi. A review of its dental anatomy indicates that Groeberia has a tribosphenic molar pattern which confirms its therian affinities. Its dental formula of I2/1; C1/1; P3/1; M4/4 is compatible with the usual metatherian set of three premolars and four molars in the upper dentition, and with the common ‘pseudodiprotodont’ lower postcanine formula of one premolar (p3) and four molars. A cladistic analysis resulted in the inclusion of Groeberia among australidelphian metatherians, clustering with vombatiform diprotodontians in the strict consensus tree; however, these affinities require further testing. The functional morphology of the masticatory apparatus suggests distinct incisive and chewing phases. The incisive stroke was followed by a power stroke with a combination of proal and ectental motion of the jaw. Integrating the results of masticatory movements, occlusal tooth wear, infraorbital foramen size, and body mass estimations (90.2 g for G. pattersoni and 216.3 g for G. minoprioi), we suggest an omnivorous diet with a preference for plant material, like that characterizing living potoroids.