Sipalocyon belongs to a group of extinct South American marsupials called borhyaenids. This mainly carnivorous group, known from the Paleocene through the Pliocene, is characterized by having carnassial teeth for shearing meat. However, the carnassials in borhyaenids are convergent with those in dasyurid marsupials from Australia and placental carnivorans. Within Borhyaenidae, Sipalocyon is a member of Hathlyacyninae, the clade that includes Notogale, Cladosictis, and Sallacyon.
About the Species
This specimen, a braincase, was made available for scanning by Dr. Richard Cifelli of the University of Oklahoma and Dr. Christian de Muizon of the Muséum National d' Histoire Naturelle, Laboratoire de Paléontologie. Funding for scanning was provided by Dr. Timothy Rowe of The University of Texas at Austin
About this Specimen
The specimen was scanned by Richard Ketcham, Greg Hoeft, Timothy Rowe, and William Carlson on 31 March 1997 along the coronal axis for a total of 45 slices, each slice 0.5 mm thick, with an interslice spacing of 0.5 mm. Many features of the internal cranial anatomy of Sipalocyon are readily discernible in the CT slices, including the passageways for the semi-circular and cochlear canals in the inner ears. These features are visible on the unreduced coronal slice (#16, top of page) through the braincase.
de Muizon, C. 1999. Marsupial skulls from the Deseadan (Late Oligocene) of Bolivia and phylogenetic analysis of the Borhyaenoidea (Marsupialia, Mammalia). Geobios 32:483-509.
de Muizon, C. 1998. Mayulestes ferox, a borhyaenoid (Metatheria, Mammalia) from the early Palaeocene of Bolivia: Phylogenetic and palaeobiologic implications. Geodiversitas 20:19-142.
Marshall, L. G. 1978. Evolution of the Borhyaenidae, extinct South American predaceous marsupials. University of California Publications in Geological Sciences 117:1-89.
Marshall, L. G. 1981. Review of the Hathlyacyninae, an extinct subfamily of South American dog-like marsupials. Fieldiana Geology 7:1-120.