Five previously undescribed decapod taxa have been collected from lower upper Miocene rocks of the Puerto Madryn Formation, Península Valdés region, Chubut Province, Patagonia, Argentina. New species include Osachila valdesensis, Rochinia boschii, Romaleon parspinosus, Panopeus piramidensis, and Ocypode vericoncava. Chaceon peruvianus and Proterocarcinus latus are also reported from the unit, in addition to two indeterminate xanthoid species. Assignment of fossil taxa to genera within the Panopeidae Ortmann, 1893, is difficult due to the marked similarity in dorsal carapace characters among several genera. Panopeus whittenensis Glaessner, 1980, is herein referred to Pakicarcinus Schweitzer et al., 2004. The Puerto Madryn Formation exposed near Puerto Pirámide contains three distinct Facies Associations (1–3), each associated with specific paleoecological and paleoenvironmental conditions, and which recur throughout the section and represent trangressive systems tract (TST) deposits and highstand systems tract (HST) deposits. Within Facies Association 1, near the base of the section at Puerto Pirámide, three paleosurfaces containing invertebrate fossils in life position are exposed and have been carefully mapped in plan view. Because of their sedimentologic, stratigraphic, taphonomic, and paleoecologic features, these three paleosurfaces are considered to be obrution deposits, each preserving a slightly different paleoenvironmental regime in terms of water depth and position with respect to wave base. Paleosurfaces were formed during the waning stages of the transgressive systems tract.

Ear ossicles were extracted from the skull of 64 specimens representing 31 marsupial species; all major extant marsupial clades were sampled except for Notoryctes. Images of ossicles were obtained using a scanning electron microscope and exported digitally to a graphic computer software. Thirteen characters and 31 character states were defined and coded to encompass the observed morphological variation. A composite phylogeny summarizing published molecular and morphological data was used to map the characters, revealing homoplasy in all three ossicles. The majority of transformations recorded occur between species, genera, or subfamilies, while few of them characterize higher-level taxa. The two alternative phylogenies of phalangeriforms being monophyletic or paraphyletic receive equal support from ossicle characters.

Much debate exists over the taxonomic relationships among the river dolphins, which have traditionally been grouped at the superfamily level (Platanistoidea) or at the family level (Platanistidae), but monophyly of this group has been questioned by several recent studies. The present study uses endocasts from the river dolphin taxa and a variety of marine taxa in order to investigate this problem further. Endocasts from crania belonging to the river dolphins (Inia geoffrensis, Pontoporia blainvillei, Lipotes vexillifer, and Platanista spp.) were used to described various features of the brain and dural venous sinuses. Casts from Inia, Lipotes, and Pontoporia had large projections from the ethmoid region and Platanista unexpectedly had large projections from the optic nerve region. Overall patterns of dural venous sinuses were similar among all taxa for the dorsal sagittal sinus, the confluens of sinuses, and the transverse sinuses. The spinal venous plexus and longitudinal, basilar, and dorsal petrosal sinuses were highly variable among taxa. Based on the results of this study, we advocate conclusions reached by previous authors who have placed Inia and Pontoporia into one group, with Lipotes as a sister taxon and Platanista as more closely allied with the delphinids.