Cranial anatomy and palaeobiology of the Miocene marsupial Hondalagus altiplanensis and a phylogeny of argyrolagids

New cranial material of Hondalagus altiplanensis, from the middle Miocene o f southern Bolivia, allows a rediagnosis of the genus and an assessment of its palaeobiology and phylogenetic relationships with other argyrolagid mar supials. The new specimens demonstrate several derived (synapomorphic) cran ial features shared by Hondalagus and Argyrolagus: a globular braincase, ve ntrally directed occipital condyles, a broad zygomatic arch, and a short, d eep dentary with a flat and long coronoid notch. Hondalagus had powerful ma sticatory muscles and its cementum-encased hypselodont cheek teeth suggests it had a very abrasive diet. The deep fossae on the lateral aspect of the skull of argyrolagids, interpreted by Simpson as large, laterally-facing or bits, are actually sharply margined temporal fossae. Hondalagus has a very large carotid foramen medially situated within the suture of the basispheno id and basioccipital. A phylogenetic analysis of five argyrolagid genera wa s conducted using 32 characters (16 cranial, 16 dental) and a didelphid and a caenolestid as outgroups. Hondalagus-Argyrolagus-Microtragulus form a mo nophyletic group with an undescribed gen. et sp. nov. (MACN-Ch-1305) from t he lower Miocene (Colhuehuapian) of Argentina as its sister taxon. Proargyr olagus appears as sister group to the other taxa of argyrolagids.