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.

Keywords:

• Gondwanatheria
• Theria
• Metatheria
• Bonapartheriiformes
• Diprotodontia
• occlusal wear

Acknowledgements

We thank the reviewers (Guillermo Rougier and Robin Beck) whose suggestions substantially improved this work. We thank Marcela Tomeo for her help in the composition of figures; Bruno Pianzolla for several of the photos that illustrate this work; Patricia Sarmiento (Servicio MEB, Museo de La Plata) for the SEM photos in Figure 4. NZ thanks to the curators of mastozoological collections of MACN (David Flores) and MLP (Diego Verzi) for allowing access to the studied materials. This work was partially funded by projects PICT 2014-2497 and PICT 201-0508 (Agencia Nacional de Promoción Científica y Tecnológica, Argentina) and IBIGEO-PUE. FJG thanks CONICET (Argentina, PIP 0361) and the Alexander von Humboldt Foundation (Germany).

Supplemental material

Supplemental material for this article can be accessed here: http://dx.doi.org/10.1080/14772019.2019.1706195.

Associate Editor: Pip Brewer