THE AUDITORY REGION OF EARLY PALEOCENE PUCADELPHYDAE (MAMMALIA, METATHERIA) FROM TIUPAMPA, BOLIVIA, WITH PHYLOGENETIC IMPLICATIONS

Abstract:  New petrosal bones, assigned to Pucadelphys and Andinodelphys , from the Lower Paleocene of Tiupampa, Bolivia, are described. These remains provide new information on the anatomy of the ear region of these taxa. The re-examination of characters from the petrosal and basicranium shed light on the phylogenetic relationships of the three Tiupampan genera known from complete cranial remains (i.e. Mayulestes , Pucadelphys and Andinodelphys ). The combination of dental, general cranial and basicranial characters led to two alternative hypotheses. The first is that borhyaenoids (including Mayulestes ) are nested within Notometatheria. Pucadelphyds (i.e. Pucadelphys and Andinodelphys ) are the sister group of a clade comprising MHNC 8369 (one isolated petrosal from Tiupampa) and Marsupialia. The second favours the paraphyly of 'borhyaenoids' (i.e. the exclusion of Mayulestes from borhyaenoids) and the polyphyly of 'Notometatheria'. In this case, Mayulestes and borhyaenids represent the stem group of a clade including Asiatic, American and Australian metatherians. This analysis of combined datasets (dental, general cranial and basicranial) highlighted contradictory information in the dental and cranial characters, serving to emphasize that in a large anatomical complex like an entire skull mosaic evolution of the characters is likely.