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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]

Mammals are the only surviving group of Cynodontia, a synapsid clade that first appeared in the fossil record in the late Permian, ~260 million years ago. Using three metrics that capture skeletal completeness, we quantify the quality of the early cynodont fossil record in time and space to evaluate the impact of sampling and preservational biases on our understanding of the group's evolutionary history. There is no consistent global sampling signal for early cynodonts. Completeness of the cynodont fossil record increases across the Permian–Triassic boundary, peaking in the Early to early Late Triassic. This peak is dominated by specimens from southern Africa and South America, where a highly seasonal climate probably favoured preservation. Completeness is generally lower thereafter, correlating with a shift from a Gondwanan to a predominantly Laurasian fossil record. Phylogenetic and stratigraphic congruence in early cynodonts is high, although their fossil record exhibits less skeletal completeness overall than other tetrapod clades, including the contemporaneous anomodont synapsids. This discrepancy could be due to differences in the diagnosability of their fossils, especially for small‐bodied species. Establishing the timing and assembly of derived ('mammalian') anatomical features in Cynodontia is obscured by sampling. Two of the major nodes at which acquisition of mammalian features is concentrated (Cynodontia and Mammaliamorpha) suffer from lengthy intervals of poor sampling before becoming abundant parts of tetrapod faunas. Low completeness in these intervals limits our ability to determine when certain 'key' mammalian characteristics evolved, or to identify the selective pressures that might have driven their origins. [ABSTRACT FROM AUTHOR]

The Middle Miocene has been identified as a time of great diversification in modern lineages now distributed in tropical South America, and when basic archetypal traits defining Amazonia appear, including climatic humid conditions, basic floral physiognomy and phylogenetic composition of modern rainforests. Nonetheless, Middle Miocene localities in South America are poorly known, especially at low latitudes where only one species-rich locality, La Venta in Colombia, has been extensively studied. The present contribution describes the mammal fauna of Fitzcarrald, a new Middle Miocene local fauna from western Amazonia in Peru. Fitzcarrald is correlated with the Laventan South American Land Mammal Age based on the presence of taxa defining the ' Miocochilius assemblage zone' in La Venta. The mammalian fauna of Fitzcarrald comprises 24 taxa among cingulates, folivores, astrapotheres, notoungulates, litopterns, rodents, odontocetes and a possible marsupial. At this time, tropical South America was characterized by the presence of the Pebas megawetland, a huge lacustrine complex that provided unique ecological and environmental conditions most likely isolating northern South America from southern South America. These isolating conditions might have come to an end with its disappearance in the Late Miocene and the establishment of the subsequent Acre system, the predecessor fluvial system of modern Amazonia. Results of faunistic similarity between Fitzcarrald and other Miocene faunas throughout South America support these scenarios. The Fitzcarrald mammal fauna exhibits first appearance datums and last appearance datums of various taxa, showing that tropical South America has played a crucial role in the evolutionary history and biogeography of major clades, and revealing a more complex biological history than previously proposed, based on the record from the southern cone of the continent. [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]

Over the past three decades Ordovician pteraspidomorphs (armoured jawless fish) have been recorded from the fringes of the Gondwana palaeocontinent, in particular Australia and South America. These occurrences are dominated by arandaspid agnathans, the oldest known group of vertebrates with extensive biomineralisation of the dermoskeleton. Here we describe specimens of arandaspid agnathans, referable to the genus Sacabambaspis Gagnier, Blieck and Rodrigo, from the Ordovician of Oman, which represent the earliest record of pteraspidomorphs from the Arabian margin of Gondwana. These are among the oldest arandaspids known, and greatly extend the palaeogeographical distribution of the clade around the periGondwanan margin. Their occurrence within a very narrow, nearshore ecological niche suggests that similar Middle Ordovician palaeoenvironmental settings should be targeted for further sampling. [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]

Fossil woods are described and assigned to Cuyoxylon multipunctatus gen. et sp. nov. The woods were deposited in shales from an interglacial period, and are the first to be described in detail from the Carboniferous glaciation of western Gondwana. They have the primitive characters of Early Carboniferous woods, such as mesarch protoxylem and numerous contiguous pits in an alternate arrangement. They are the oldest fossil woods to have been described from South America. The growth ring characteristics are consistent with a seasonal cool climate. [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]

A new South American Early Triassic stereospondyl is described and considered to represent a new taxon, Cabralia lavinai gen. et sp. nov. The material consists of two well-preserved skull fragments. According to recent phylogenetic analyses of rhytidosteids and related taxa, the new taxon is referred to the Rhytidosteidae based on the presence of orbits that are located close to the skull margins, an otic notch that is reduced to an embayment, tabular horns that are reduced and broad based, a straight posterior margin of the palate, skull sculpture with nodules and pustules, and a ‘twisted’ quadrate ramus of the pterygoid. The presence of a prominent lacrimal bone suggests a basal position within Rhytidosteidae for C. lavinai, and possibly a close relationship with the Indian Indobrachyops, because all other known rhytidosteids exhibit the derived condition of an absence of the lacrimal. The presence of a basal rhytidosteid in the Paraná Basin of South America strongly supports previous hypotheses of a Gondwanan origin and radiation of stereospondyl temnospondyls during the Early Triassic, but leaves unresolved the question of where exactly they arose within that region. [ABSTRACT FROM AUTHOR]

Two Santacrucian borhyaenoids, Borhyaena tuberata and Prothylacinus patagonicus, are analyzed from a functional-adaptive perspective. Seven extant placental and marsupial models are examined in order to interpret the locomotor adaptations of the two fossils. These carnivorous models are characterized by various hunting types and locomotor habits, and the association of their skeletal adaptive features with diet, substrate preference, and locomotor performance permits a functional interpretation of the postcranium of Borhyaena and Prothylacinus. The analysis shows that the forelimb of Prothylacinus is modified to provide strength and flexibility for controlled climbing. This taxon exhibits semiplantigrade fore- and hind feet. Its vertebral column was flexible, and the hindlimb suggests an active predatory mode of hunting. The tail was muscular, heavy, and was probably used as a balancing organ. By comparison, the forelimb of Borhyaena indicates a more terrestrial mode of life, with a digitigrade forefoot, and more parasagittal movements. The tail was lighter and less muscular than in Prothylacinus. Both fossils are characterized by a powerful neck musculature related to predatory habits. [ABSTRACT FROM AUTHOR]