The rodent species found in the stomachs were: Bolomys obscurus, Oligoryzomys flavescens, Calomys laucha and Oxymycterus rutilans with body mass ranges of 30–80, 18–39, 9–15.5 and 50–120 g, respectively (data from González, 2001). Monodelphis dimidiata is one of the best examples of a semelparous marsupial. Some dasyurid marsupials are semelparous, although females may live click here a second year (Lee & Cockburn, 1985). Adult male M. dimidiata disappears from the population in March, 2 months earlier than females, and thus exhibits a male mortality syndrome after mating (Pine, Dalby & Matson, 1985). Males have only one opportunity for reproductive

success and there may be severe competition for Osimertinib chemical structure access to females, with the larger, more aggressive and more canine-enhanced males having a competitive advantage (González

& Claramunt, 2000). Monodelphis dimidiata shows a broad repertoire for dealing with various kinds of prey, such as dehairing hairy caterpillars, crunching the heads of arthropods and killing mice by means of a neck bite (González & Claramunt, 2000). The authors described the following: ‘Laboratory mice are quickly and continually attacked until the opossum can grasp the mouse by the throat. The mouse is then held in that way until it stops moving’ (González & Claramunt, 2000). Generally, carnivorous marsupials use crushing bites directed to the anterior of the prey’s body and often strike the head, neck or even chest (Eisenberg, 1985; Croft, 2003; Jones, 2003). The reported killing behaviour of M. dimidiata, which avoids biting bones, could be analogous to the killing technique proposed for several extinct sabretooth predators (Biknevicius & Van Valkenburgh, 1996; Antón & Galobart, 1999; Salesa et al., 2005; Turner & Antón, 1997). Emerson & Radinsky (1980) described cranial features that distinguish sabretooths from living felids and marsupial predators. They concluded that sabretooth predators have modifications for a wider gape with the retention of a powerful Thiamet G bite force at the carnassial. Here we make morphological studies, using methods already

used in the study of the sabretooth condition, in order to determine how suitable M. dimidiata is as a living analogue of primitive sabretooth predators. We worked with an osteological sample of 44 individuals of living marsupials from South America (didelphids, 14 species) and Australia (dasyurids, 18 species). The sample includes four specimens of M. dimidiata, three males and one female. The specimens are housed in the collections of the Museo Nacional de Historia Natural in Montevideo and the Western Australian Museum. For details of the specimens, see Supporting Information Appendix S1. Using dial calipers, we took 15 linear measurements on each skull based on those of Emerson & Radinsky (1980) (see Figs 1 and 2). For comparing our data with those of Emerson & Radinsky (1980), we calculated 14 indices.