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The oldest Cenozoic mammalian assemblages in South America have been recovered from levels of the Hansen Member of the Salamanca Formation, Punta Peligro locality in Argentina, and from the Santa Lucía Formation in Tiupampa, Bolivia. These faunas led to the recognition of the Peligran and Tiupampan South American Land Mammal Ages (SALMAs), each alternatively regarded as the oldest Paleocene SALMA. Due to the lack of radioisotopic dates for mammals bearing levels at these localities, no agreement has been reached yet about their relative ages. In this paper, the role of mammal faunas in age inference is discussed. Analysis of the SALMAs shows that the presence of non-therian mammals in the Peligran is of little consequence to the biochronological evaluation, reflecting instead a relict Mesozoic distribution. In contrast, therian mammals are particularly important in that (1) they were Lauraisan immigrants and (2) they support direct comparisons between the Tiupampa and Punta Peligro faunas. Parsimony and cluster analysis were used to quantitatively test hypotheses concerning the relative age of the Peligran and Tiupampan SALMAs. Our results support the hypothesis that the Tiupampan SALMA (early Danian) is older than the Peligran SALMA (early Selandian). This alignment results in an interpretation of the evolutionary history of South American land mammals that is more straightforward than the alternative. [ABSTRACT FROM AUTHOR]

The taxonomy, biostratigraphical and palaeogeographical distribution of the Lower Ordovician graptolite genus Bryograptus is evaluated. Bryograptus is recognized as a distinct triradiate anisograptid with a multiramous, pendent rhabdosome. The species of the genus Bryograptus can be interpreted as shallow water faunal elements with a strongly limited biogeographical distribution to the Atlantic Faunal Realm. Bryograptus is restricted to a narrow interval in the Upper Tremadocian, the Bryograptus Biozone of Scandinavia and South America (Argentina), making it a taxon with a high potential for precise biostratigraphical correlations. The proximal end development can be used to differentiate the genus Bryograptus from other pendent multiramous graptoloid genera with a homoplastic rhabdosome development. Characteristics of the proximal end development and structure easily differentiate these genera in relief specimens, but not in flattened material. [ABSTRACT FROM AUTHOR]

The trilophodont gomphothere group is a monophyletic group of genera separated from other proboscideans by one synapomorphy, the presence of trefoil-shaped wear patterns on the occlusal surfaces of their teeth. These wear patterns vary from being just a single trefoil, through double trefoils, to more complex combinations of trefoils. They are present in all of the genera studied here. Our cladistic analysis makes use of 12 genera as terminal taxa. It was performed using 43 cranial, dental and postcranial morphological characters. The polarity of characters was based on outgroup criteria using the genus Phiomia as the outgroup. All characters are considered to be unordered (34 are binary and nine are multistate). The present analysis leads us to reject the hypothesis that considered Rhynchotherium as a direct ancestor of South American gomphotheres and supports the hypothesis that Sinomastodon is the sister group of Cuvieronius and Stegomastodon. High congruence between the stratigraphical record and the phylogenetic hypothesis is observed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]