The most popular hypothesis for much of the 20th century was that sparassodonts were closely related to opossums. In 1990, Marshall et al. (1990) considered the Cretaceous stagodontids to be members of Sparassodonta, but this was criticized by later authors. Marshall and Kielan-Jaworowska (1992) considered sparassodonts to be closely related to deltatheroidans, but this was also criticized. Most of these hypotheses were based on similar adaptations for carnivorous diets in sparassodonts, opossums, dasyuromorphians, stagodonts, and deltatheroidans, which are highly prone to convergent evolution within mammals. Szalay (1994) considered sparassodonts to be closely related to paucituberculatans based on features of the ankle. In recent years there has been a growing consensus that sparassodonts are positioned just outside of crown-group Marsupialia, in a broader clade (Pucadelphyida) including pucadelphyids as well as sparassodonts. Sparassodonts are currently considered to be endemic to South America, and have not even been found in nearby continents like Antarctica (which otherwise shares many groups of mammals with South America such as litopterns, astrapotheres, microbiotheres, and polydolopids). Paleobiology Diet Sparassodonts were carnivorous, and with the exception of some basal members of all members of this group were hypercarnivorous (having diets composed of more than 70% meat). Only Hondadelphys and Stylocynus appear to have exhibited adaptations for omnivory, and even then Stylocynus may have had a more mesocarnivorous diet similar to canids than an omnivorous one. Medium-to-large caviomorph rodents and rodent-like mammals (e.g., small notoungulates) appear to have been common prey items of sparassodonts. The subadult holotype of Lycopsis longirostrus preserves remains of the dinomyid Scleromys colombianus as fossilized gut contents. Sparassodont coprolites from the Santa Cruz Formation preserve the bones of chinchillid and octodontoid rodents inside them. Bite marks from medium-sized sparassodonts have been found on the small notoungulate Paedotherium. Stable isotope data from the early late Miocene Lycopsis viverensis and Thylacosmilus atrox suggests that these species fed on C3 grazers in open habitats, likely notoungulates. Bite marks likely pertaining to hathliacynid sparassodonts have been found on the remains of penguins and flightless marine ducks in ancient seabird nesting colonies, suggesting that sparassodonts raided seabird colonies for eggs, carrion, and other prey like many predatory mammals do today. Borhyaenid and proborhyaenid sparassodonts have been interpreted as being capable of crushing bones similar to modern hyenas, wolverines, or the Tasmanian devil (Sarcophilus harrisii) based on their deep jaws, bulbous premolars with deep roots and pronounced wear at their tips, extensive