Abstract

The description of a partial skull of a dog-like marsupial (Borhyaenoidea, Marsupialia, Mammalia) referred to Notogale and of the further-prepared ear region of the only known skull of Sallacyon hoffstetteri,, both from the Deseadan (late Oligocene) of Salla-Luribay (Bolivia), allows a revision of the basicranial characters of the Borhyaenoidea. These new data provide the opportunity of a reconsideration of the phylogenetic relationships of the superfamily, which was mainly diagnosed with dental characters, in some cases, belonging to the same functional complex. Several previous hypotheses on the affinities of the Borhyaenoidea are considered and close relationships with the North American Stagodontidae or with the essentially Asian Deltatheroida are regarded as unlikely. The Borhyaenoidea are included within the Didelphimorphia and could represent the sister group of the Didelphoidea. The key-synapomorphy of the superfamily is the contribution of the medial process of the squamosal to the construction of the lateral and dorsal wall of the alisphenoid hypotympanic sinus. Forty-five characters distributed among 13 taxa are analysed with the branch and bound search of Paup 3.1.1. Three of the taxa are the outgroup which includes the genera, Didelphis, Pucadelphys,, and Andinodelphys.. The borhyaenoids included in the analysis are genera represented by reasonably well preserved cranial remains (Mayulestes, Sallacyon, Notogale, Cladosictis, Sipalocyon, Lycopsis, Borhyaena, Prothylacynus, Paraborhyaena,, and Thylacosmilus)). The analysis confirms the monophyly of the Hathliacynidae (Notogale, Cladosictis, Sallacyon,, and Sipalocyon)) but definitely excludes Mayulestes from the family. Although the parsimony analysis included Sallacyon within the Hathliacynidae, this position is not very securely established because the basicranium of the only known skull is incomplete. Borhyaena and Prothylacynus belong to the monophyletic family Borhyaenidae, which does not include the genus Lycopsis. Paraborhyaena (Proborhyaenidae) and Thylacosmilus (Thylacosmilidae) are sister groups.