SALMA Research Articles

Beyond extinction: Uncovering morphological aspects of the last typotherid population (Mesotherium cristatum) and the unexpected body mass decrease

We present a detailed analysis of the craniomandibular and dental remains of Mesotherium cristatum, the quaternary mesotheriid typotherid notoungulate, from Corralito, Santa María Department, Cordoba Province. This population represents the final lineage of Typotheria during middle Pleistocene, Post-Ensenadan Age (>220 ± 13 ka). We compared these new craniomandibular and postcranial samples from Corralito with those from Toscas del Río de La Plata, as well as other localities in the province of Buenos Aires dating to the Ensenadan Age 1.98–0.4 Ma). Our investigation reveals a substantial decline in the size and body mass of the last known population of M. cristatum during the Bonaeran Age period, before its extinction. This occurrence, hitherto unrecorded in any prior South American Land Mammal Age leading up to extinction, might be attributed to the climatic and abiotic changes of the Pleistocene. These changes notably caused a marked reduction in the paleobiogeographical distribution area ofM. cristatum during the Middle Pleistocene. This size and body mass reduction, possibly an outcome of compelled reproductive isolation, is situated against the context of global cooling and heightened predatory pressures. Moreover, our analysis unveiled distinctive taxonomic attributes specific to this taxon, we compare dental size and find a preliminary evidence of an accelerated tooth replacement pattern. Furthermore, we have effectively updated the faunal composition information of the Corralito deposit, elucidating previous biostratigraphic inferences that had led to the belief of Corralito being an Ensenadan Age site. This adjustment impacts the first appearance datum (FAD) of the Neolicaphrium recens proterotheriid litoptern, younger than previously estimated and revised Bonaerian-Lujanian. Finally, this study provides insights into the biological analysis of the iconic species M. cristatum, prevalent in the South American quaternary of the Pampean region. It unreveils new faunal features specific to the Pampean region, shedding light particularly on the lesser-explored western area. These findinngs provide crucial insight into the ever-evolving ecosystem dynamics during the Middle Pleistocene.

Systematic revision of the species of Protypotherium (Notoungulata: Interatheriidae) from the Santa Cruz Formation (Early–Middle Miocene), Argentinian Patagonia: a new phylogenetic hypothesis for the Interatheriidae

Abstract Protypotherium is one of the main genera of the Interatheriidae due to its species richness, abundance, and wide distribution from southern to middle latitudes of Argentina, Bolivia, Uruguay, and Chile. This genus is better known from the species founded by Florentino Ameghino during late 19th century from the prolific Santa Cruz Formation (Santacrucian South American Land Mammal Age (SALMA); Burdigalian–Early Langhian), Santa Cruz Province (Argentina). This contribution provides the taxonomic revision of the Santacrucian species of Protypotherium and the species erected by Florentino within this genus. We conclude that among the initial 21 species, Protypotherium antiquum, Protypotherium australe, Protypotherium praerutilum, Protypotherium compressidens, and Protypotherium claudum are valid, whereas Protypotherium obstructum is a Hegetotheriidae indet. We present a phylogenetic analysis that does not recover Protypotherium as a clade, due to the nesting of Juchuysillu and Caenophilus, and this assemblage appears as the sister taxon of the clade Progaleopithecus plus Archaeophylus. Finally, the interatheriines from the Santa Cruz Formation do not allow a subdivision of this unit, due to their wide geographic and temporal distribution, thus rejecting the biozones preliminary proposed by other authors. The Atlantic coast (east) and Río Santa Cruz (central) regions are similar in their interatheriine content, but both differ from the western area.

Caviomorphs (Rodentia, Hystricognathi) from Pampa Castillo, Chile: new octodontoid records and biochronological implications

AbstractCaviomorph rodents have been diverse and abundant components of South American mammal communities since the late Eocene. We describe herein the octodontoids of Pampa Castillo, a Lower Miocene site in southern Chile (Aysén Region). Six genera and seven species of octodontoids are present, two of which are new: Dudumus berggreni sp. nov. and Caviocricetus guenekko sp. nov. The octodontoids from Pampa Castillo support assignment of this fauna to the Santacrucian South American Land Mammal Age (SALMA), which is consistent with previous studies. We conducted similarity analyses on 11 Early–Middle Miocene Patagonian rodent faunas using hierarchical clustering. Faunas generally fell into the three SALMAs to which they were traditionally assigned: Colhuehuapian, Santacrucian and ‘post‐Santacrucian’. The ‘Pinturan’ is a proposed biochronological interval between the Colhuehuapian and Santacrucian. At the genus level, Pampa Castillo clustered with ‘Pinturan’ faunas, while at the species level it clustered with the ‘typical’ faunas on which the Santacrucian SALMA is based (from outcrops of the Santa Cruz Formation along the Atlantic coast and Río Santa Cruz). The Pampa Castillo rodent fauna resembles both ‘Pinturan’ and ‘typical’ Santacrucian faunas in taxon distributions, reflecting complex temporal and palaeoenvironmental influences. Geochronological data indicate that some ‘Pinturan’ sites overlap temporally with Pampa Castillo and the upper Pinturas Formation, which both clustered with ‘typical’ Santacrucian faunas. These results indicate that the ‘Pinturan’ does not represent a distinct biochronological interval, but that the differences between it and ‘typical’ Santacrucian faunas are attributable to geographic or palaeoenvironmental differences.

Resolution of the long-standing controversy over the type species of the genus Pseudotypotherium (Notoungulata, Typotheria, Mesotheriidae)

Mesotheres (Notoungulata: Typotheria) are among the most common mammals found in upper Miocene to Pliocene deposits of central Argentina, including the classic type Monte Hermoso locality, which defines the Montehermosan South American Land Mammal “Age”. Nevertheless, the correct name for the mesothere species from this site has been shrouded in uncertainty for well over a century due to questions of taxonomic priority, specimen provenance, and ontogenetic changes in dental formula. Since the mesotheres from Monte Hermoso were named, three distinct species have been formally considered as the type species of the genus: (1) Pseudotypotherium bravardi; (2) “Pseudotypotherium” maendrum; and (3) Pseudotypotherium exiguum. However, none of these species is a nominal species of the Pseudotypotherium genus; all three were originally referred to Typotherium. Article 67.2 of the International Code of Zoological Nomenclature (ICZN, 1999) indicates that only species considered as nominal species are eligible to set the type; in the case of Pseudotypotherium, these include: P. pulchrum, P. carlesi, P. hystatum, and P. carhuense. We conclude that Pseudotypotherium pulchrumF. Ameghino, 1904 (holotype MACN A 10299, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Ameghino Collection), is the type species of the mesotheriid notoungulate genus from Monte Hermoso. According to Article 68.2, F. Ameghino fixed the type by original designation in 1904 when he described P. pulchrum and included “n. g., n. sp.”. Two of the other species previously considered species P. (= T.) bravardi and P. (= T.) exiguum are invalid as type species according to Article 70.2, since their designations overlooked the previous type fixation. The third species (M. (= T.) maendrum) represents a different mesothere genus (Mesotherium) that only occurs in younger (Pleistocene) deposits. Our analysis puts an end to a historical debate that has been ongoing for more than a century regarding the identity of this well-represented late Miocene–Pliocene mesotheriine genus (Pseudotypotherium). This study provides a solid taxonomic foundation for future studies on intraspecific and ontogenetic variation of Pseudotypotherium pulchrum.

A new proterotheriid (Mammalia, Litopterna) from the Salla Beds of Bolivia (upper Oligocene): phylogeny and litoptern patellar pit knee locks

ABSTRACT The Salla Beds of Bolivia reveal a rich, late Oligocene (Deseadan, South American Land Mammal “Age”) fauna composed of at least 50 mammalian species. Many taxa (e.g., rodents and typotherian notoungulates) are represented by dozens to hundreds of specimens. Litopterns are much less common but are represented by one macraucheniid and two adianthid species. Until now, only fragmentary postcrania of proterotheriids have been described from Salla. The recent discovery of a maxillary fragment with two molars, examination of previously recovered mandibular fragments, and a phylogenetic analysis, allow us to recognize Promylophis cifellii gen. et sp. nov. It is characterized by small size, absence of a metaconule on M1–2, and lower molars with a short “paracristid” and reduced or absent “paraconid.” Postcranial elements referred to cf. P. cifellii resemble geologically younger (e.g., Miocene) proterotheriids by way of anatomically tridactyl, but functionally monodactyl pes, and distal femora with a supra-trochlear fossa that forms a “patellar pit” that appears to function as a passive stay apparatus for the knee joint. Such a mechanical means of diverting forces from muscle to bone and sinew could save biologically significant amounts of metabolic energy in long-standing animals.

Late middle Miocene Metatheria (Mammalia: Didelphimorphia and Paucituberculata) from Juan Guerra, San Martín Department, Peruvian Amazonia

Currently, marsupials (modern members of the Metatheria clade) are widely distributed in tropical and subtropical areas of South America, but poorly represented in the fossil record of these regions. Except for the species-rich fossiliferous localities of La Venta in Colombia, additional Miocene metatherians from tropical, equatorial South America are sparsely reported in Bolivia, Brazil, Peru, and Venezuela. Here, we introduce new metatherian remains recovered from the late middle Miocene locality of TAR-31, San Martín Department, Peru, which has been assigned to the Laventan South American Land Mammal Age (∼13 Ma) by mammalian biostratigraphy. Three metatherian taxa are recognized at TAR-31: the didelphid didelphimorph ‘Thylamys’ cf. ‘T.’ colombianus, and the paucituberculatans aff. Palaeothentes and Pitheculites ipururensis sp. nov. This assemblage and the presence of a cebid primate at TAR-31 suggests predominantly humid and warm tropical conditions, with the occurrence of both forests and drier habitats in the surroundings. Comparisons with other Miocene metatherian assemblages at low and mid latitudes of South America clearly confirm close relationships between TAR-31 and La Venta (agreeing with observations based on monkeys and rodents), as well as, to a lesser extent, with Acre River local faunas and Madre de Dios (MD-67) in Brazil and Peru, respectively. The current results support the hypothesis that Western Amazonia was a single and consistent biogeographical region for land mammals over middle Miocene times, at the western edge of the Pebas Mega-Wetland System, and highlight the role of the Amazonian region concerning marsupial Neogene radiation. U–Pb analysis made on detrital zircon grains from TAR-31 gave a maximum depositional age of 17.4 ± 0.12 Ma (i.e., 4 Ma older than the biostratigraphical age), with a mixed detrital source likely comprising Precambrian (Western Amazon Craton), Neoproterozoic (Neoproterozoic mobile belts), and Phanerozoic rocks (Andes).

Cavioids, Chinchilloids, and Erethizontoids (Hystricognathi, Rodentia, Mammalia) of the Early Miocene Pampa Castillo Fauna, Chile

Caviomorph rodents became important components of South American faunas after their Eocene arrival from Africa. Here we describe the cavioid, chinchilloid, and erethizontoid caviomorphs of the early Miocene Pampa Castillo fauna of southern Chile. This fauna's age and location make it key for resolving outstanding biostratigraphic questions concerning early Miocene Patagonian fossiliferous strata. Each of the four major caviomorph clades (“superfamilies”) is represented in the Pampa Castillo fauna, three whose members are detailed here: cavioids (3 genera; 3 species), chinchilloids (3 genera; 6 species), and erethizontoids (2 genera; 2 species). Abundantly represented taxa, e.g., Neoreomys australis, Perimys erutus, and Prolagostomus pusillus, corroborate previous work assigning the Pampa Castillo fauna to the Santacrucian South American Land Mammal “Age” (SALMA; inclusive of the “Pinturan”). Several taxa, including Eosteiromys, Perimys intermedius, and Perimys sp. nov.?, are also found in the lower and middle Pinturas Formation (lmPF) but not “core” Santacrucian faunas (from the Santa Cruz Formation [SCF] along the Río Santa Cruz and Atlantic coast), suggesting a distinctive resemblance between lmPF and Pampa Castillo rodents. Some authors consider the fauna from the lmPF to form the basis of a “Pinturan” SALMA or subage, considered to slightly predate core Santacrucian faunas, but which has yet to be formally recognized. The taxonomic composition of rodent fauna from Pampa Castillo, as well as relative abundance data, indicated a paleoenvironment intermediate between the closed forests of the lmPF and the mosaic of open and closed habitats of the core Santacrucian faunas from the SCF.

The distribution and conservation status of Tapirus terrestris in the South American Atlantic Forest

Tapirus terrestris is the largest South American land mammal, with an extensive historical distribution and capable of occupying diverse habitats, and yet its populations have declined across its range. In order to provide baseline data on the conservation status of tapirs in the Atlantic Forest, we conducted a long-term study in one landscape, visited 93 forests, and received 217 expert reports over the 15-year study. We estimate that 2,665–15,992 tapirs remain in 48 confirmed populations, occupying 26,654 km2 of forest or 1.78% of its original range in the biome. Historically, hunting and deforestation were the main causes of decline, but today population isolation is the principal long-term threat. Vortex models indicate that 31.3–68.8% and 70.8–93.8% of the populations are demographically and genetically non-viable over the next 100 years, respectively, and that only 3–14 populations are viable when considering both variables. Habitat use data indicate that tapirs are adaptable to disturbed and secondary forests and will use diverse tree plantations and agricultural lands but hunting and highways keep populations isolated. Reserve staff report tapirs as common/abundant at 62.2% of the sites, and populations as stable and growing in 60% and 36% of the sites, respectively, and there is ample habitat in the biome for a population expansion, but overcoming the causes of isolation will be necessary for this to occur. Lack of adequate funding for protecting reserves is a chronic threat throughout the biome, especially in federal and state/provincial reserves, and increased funding will be necessary to implement effective conservation plans.

EL REGISTRO DEL TIPOTERIO PACHYRUKHOS (MAMMALIA, NOTOUNGULATA) Y EL CHINCHÍLLIDO PROLAGOSTOMUS (MAMMALIA, RODENTIA) EN LA FORMACIÓN SANTA CRUZ (MIOCENO TEMPRANO–MEDIO) AL SUR DEL RÍO COYLE, PATAGONIA, ARGENTINA

The continental early–middle Miocene Santa Cruz Formation (SCF) from Patagonia is one of the most important stratigraphic units of southern South America in terms of the terrestrial Neogene record. Its fossil content was pivotal for establishing the succession of Cenozoic faunas from Patagonia and formed the basis of the Santacrucian South American Land Mammal Age. Despite the updated knowledge recently achieved, the stratigraphic distribution of many taxa within the SCF remains to be clarified. That is the case with the typothere notoungulate Pachyrukhos and the chinchillid rodent Prolagostomus. New information on the stratigraphy of the SCF along the north bank of the Río Gallegos and Cabo Buen Tiempo (Santa Cruz Province), together with a detailed analysis of the provenance information of the specimens in the principal old museum collections, sheds light on the record of these taxa south to Río Coyle. Our results show that the first recorded occurrence of both taxa in the area was between ~17 Ma and 17.41 Ma, restricted to the upper part of the SCF, including the upper part of the Estancia La Costa Member at Cañadón Las Totoras-Monte Tigre, and the superimposed Estancia La Angelina Member along the Río Gallegos and Cabo Buen Tiempo. Their presence suggests a trend to aridification in the upper part of the SCF south to the Río Coyle. These results are consistent with recent information obtained from other locations of the SCF north to the Río Coyle.

Changes in rainfall seasonality inferred from weathering and pedogenic trends in mid-Miocene paleosols of La Tatacoa, Colombia

The authigenic clay mineral assemblage of paleosol profiles and trends in their bulk geochemical evolution provide insight into the intensity of past chemical weathering regimes. These climate-sensitive weathering products can be used to interpret regional changes of the soil moisture regime, which in turn reflects upon the nature of rainfall seasonality (e.g., unimodal vs. bimodal). A conspicuous color change in the overbank deposits and paleosols of the mid-Miocene Honda Group of La Tatacoa, Colombia, is suggestive of a climatic transition which affected the fauna of La Venta - a mid-Miocene fossiliferous site and significant component of the South American Land Mammal Age (SALMA) classification. This study aims to determine how the paleopedology of this region records the climatic transition that modified the annual patterns of rainfall and soil moisture, forcing a change from the gray-colored paleosols hosted by the La Victoria Formation (~13.6 to ~13.1 Myr) to the red-beds of the Villavieja Formation (~13.1 to 12.0 Myr). In the La Victoria profile, the pedogenic fraction of the clay assemblage indicates that vermiculite, chlorite/HIV mixed-layered clays and high concentrations of base cations (Ca2+, Mg2+, Na+) developed in a poorly drained paleosol under reducing (low Eh) and above-neutral pH conditions. By contrast, the presence of kaolinite, goethite and hematite in the red-beds paleosols implies more oxidizing conditions (high Eh), whereas pedogenic vermiculite and smectite suggest a pH close to or mildly below neutral. A common detrital source (parent material) is inferred for both sets of paleosols. However, more intense chemical weathering towards aluminium rich clay in the Villavieja red-bed fossil soils indicates a change in soil humidity from a poorly drained soil environment of a seasonally flooded wetland system to an alternating regime of humidity and drought on a better drained floodplain. The variation in soil moisture is consistent with a change in seasonality from a unimodal rainfall regime in the case of the La Victoria paleosols to bimodal conditions in the case of the paleosols of the Villavieja Fm. After the establishment of a fully glaciated Antarctica and the global climate transition into the Mi-4 glacial stage at ~13.1 Ma, an increased rate of continental weathering along the paleotropical fringe could have been caused by a stronger temperature gradient between the equator and South Pole, shifting the Intertropical Convergence Zone northward and the rainfall patterns with it.

Cingulata (Mammalia, Xenarthra) from the Type Fauna of the “Friasian” South American Land-Mammal Age, Alto Río Cisnes (Río Frías Formation, Langhian, Miocene), Chile

Cingulata (Mammalia, Xenarthra) from the Type Fauna of the “Friasian” South American Land-Mammal Age, Alto Río Cisnes (Río Frías Formation, Langhian, Miocene), Chile

Late middle Miocene caviomorph rodents from Tarapoto, Peruvian Amazonia

Miocene deposits of South America have yielded several species-rich assemblages of caviomorph rodents. They are mostly situated at high and mid- latitudes of the continent, except for the exceptional Honda Group of La Venta, Colombia, the faunal composition of which allowed to describe the late middle Miocene Laventan South American Land Mammal Age (SALMA). In this paper, we describe a new caviomorph assemblage from TAR-31 locality, recently discovered near Tarapoto in Peruvian Amazonia (San Martín Department). Based on mammalian biostratigraphy, this single-phased locality is unambiguously considered to fall within the Laventan SALMA. TAR-31 yielded rodent species found in La Venta, such as the octodontoid Ricardomys longidens Walton, 1990 (nom. nud.), the chinchilloids Microscleromys paradoxalis Walton, 1990 (nom. nud.) and M. cribriphilus Walton, 1990 (nom. nud.), or closely-related taxa. Given these strong taxonomic affinities, we further seize the opportunity to review the rodent dental material from La Venta described in the Ph.D. volume of Walton in 1990 but referred to as nomina nuda. Here we validate the recognition of these former taxa and provide their formal description. TAR-31 documents nine distinct rodent species documenting the four extant superfamilies of Caviomorpha, including a new erethizontoid: Nuyuyomys chinqaska gen. et sp. nov. These fossils document the most diverse caviomorph fauna for the middle Miocene interval of Peruvian Amazonia to date. This rodent discovery from Peru extends the geographical ranges of Ricardomys longidens, Microscleromys paradoxalis, and M. cribriphilus, 1,100 km to the south. Only one postcranial element of rodent was unearthed in TAR-31 (astragalus). This tiny tarsal bone most likely documents one of the two species of Microscleromys and its morphology indicates terrestrial generalist adaptations for this minute chinchilloid.

The late Oligocene xenarthran fauna of Quebrada Fiera (Mendoza, Argentina) and its implications for sloth origins and the diversity of Palaeogene cingulates

AbstractThe late Oligocene mammalian fauna of Quebrada Fiera is one of the most diverse of the Deseadan SALMA (South American Land Mammal Age). We describe its endemic xenarthran assemblage, represented by 13 species, consisting of 2 stem sloths and 11 armoured cingulates. The rare folivoran material confirms the presence of Octodontotherium, one of the early known mylodontids, and suggests the existence of a new, small, non‐megalonychid megatherioid, Similhapalops nivis. The lumbar vertebrae of Octodontotherium sp. provide the oldest evidence of xenarthry for the order. The presence at the knee joint of an ossified meniscus and cyamo‐fabella strongly suggests a plantigrade ancestral condition in Mylodontidae. Armoured xenarthrans are represented by the armadillos Eutatini (Meteutatus sp., M. lagenaformis, and Stenotatus ornatus), an undetermined Euphractinii, the ‘horned’ peltephilids Peltephilus sp. and P. undulatus, and the palaeopeltid Palaeopeltis inornatus; an undetermined Glyptodontidae, the glyptatelines Glyptatelus cf. tatusinus and Clypeotherium sp., and an undetermined propalaehoplophorine. The xenarthrans represent one‐third of the mammals of the Quebrada Fiera fauna, one of the most varied at the end of the Palaeogene in South America. This vertebrate fauna is represented by a mix of endemic taxa and other species of high latitude (Patagonian) origin, but few from low latitude faunas. A detailed study of this mammalian assemblage, complemented by detailed geological and petrographical studies, suggests the existence of strong volcanic activity, and the presence of braided rivers and lagoonal environments in open habitats under a temperate or hot climate, with savannas and/or grasslands and isolated forests during the late Oligocene at the foot of the proto‐Andes.

New late Oligocene caviomorph rodents from Mendoza Province, central-western Argentina

ABSTRACT Late Oligocene caviomorphs represent one of the most important early adaptive radiations of this group of rodents. They show a high taxonomic diversity and a wide geographic distribution, with those found in the upper Oligocene of Salla (Bolivia) and Patagonia (Argentina) being particularly diverse. However, caviomorphs from the Deseadan South American Land Mammal Age in other latitudes are still scarcely known. In this contribution, we describe new caviomorph rodents from the Deseadan levels of Quebrada Fiera locality (Mendoza Province; central-western Argentina) and evaluate their systematic and paleobiogeographic significance. The taxonomic composition of the caviomorphs from Quebrada Fiera reveals a complex biogeographic history, as we recognize one endemic Cavioidea (Asteromys puelche sp. nov.) and two Chinchilloidea: one with Patagonian affinities (Cephalomys sp.) and another with a wide distribution in South America (Incamys bolivianus). Asteromys puelche sp. nov., shows closer phylogenetic affinities with the Bolivian A. bolivianus than with the Patagonian A. punctus. These rodents, in common with the whole mammalian association from Quebrada Fiera, show a mix of endemic taxa and others shared with higher and lower latitudes.

A singular Hegetotheriinae (Notoungulata, Typotheria) from the late Oligocene-Early Miocene of the Subandean Region of Bolivia

Abstract Geological studies in the northern sector of the Chaco foreland Basin, Bolivia, yielded new fossils coming from late Oligocene-late Miocene of the Petaca Formation. Few fossil mammals were known from the Subandean Region of Bolivia. We report a partially complete mandible of a hegetotheriid Hegetotheriinae (Notoungulata, Typotheria) from Abapo (Rio Grande River). The specimen (YPFB-LIT-PAL-005) is very close in size and dental morphology to the late Oligocene (Deseadan South American Land Mammal Age, SALMA) — Santacrucian (early Miocene) Prohegetotherium schiaffinoi (Kraglievich 1932) from Fray Bentos (Uruguay and Argentina), Salla (Bolivia), Divisadero Largo-Potrerillos and Quebrada Fiera (Argentina). However, mandibular characteristics, as the shape with a marked change in height along its length, increasing towards the back, a prominent masseteric crest, a deep mandibular groove, and a remarkable thickening of the ventral rim of the mandible, indicate differences between this specimen and Prohegetotherium schiaffinoi and the other Hegetotheriinae. The affinity of YPFB-LIT-PAL-005 with P. schiaffinoi suggests a late Oligocene to early Miocene for the upper bearing horizon of the Petaca Formation (in Abapo), an older age than previously assigned to the top of this unit (late Miocene), and confirms the taxon distribution between ∼ 36 ° to ∼ 17 ° south latitude.

New middle Miocene (Langhian - Serravallian) vertebrate localities in northwestern Patagonia, Argentina: A contribution to high latitude south american land mammal ages sequence

The Miocene represents a key moment in the South American evolution, since meaningful geographic and climatic processes occurred, promoting the development of several biologic changes. The isolation of South America together with major global and regional climatic changes resulted in an enormous variety of biomes and endemic diversity of flora and fauna, especially of mammals diversity. Most of the best-known continental vertebrate fossil-bearing deposits correspond to the early and late Miocene, existing a deficient knowledge for the middle Miocene, which is poorly understood at high latitudes. This work examines four new middle Miocene fossiliferous localities from a North Patagonian foreland succession, through a multidisciplinary approach that combines stratigraphic and preliminary paleontological analyses within a previously defined high-resolution temporal scheme. Two localities are referred to the lower section of Collón Cura Formation, and were constrained to a range of 14.6–12.75 Ma, whereas the other two localities correspond to the upper section of Collón Cura Formation and were constrained to 12.75–12.05 Ma. A large variety of fossil vertebrates were recognized in the lower section, belonging to Teleostei, Testudinidae, Teiidae, Anura and Mammalia; whereas Teleostei, Testudinidae and Mammalia vertebrates were documented in the upper section. Our results indicate a Colloncuran and younger (e.g., Mayoan) South American Mammals Ages (SALMAs) for the lower and upper sections of Collón Cura Formation, respectively. However, data from this work support the idea of a continuum on the SALMAs sequence for the middle Miocene where overlap, at least partially, both in absolute dates and in the faunal assemblages.

New record of Neosaimiri (Cebidae, Platyrrhini) from the late Middle Miocene of Peruvian Amazonia

The Honda Group of La Venta, Colombia, has yielded a wide array of crown platyrrhine primates, documenting the late Middle Miocene epoch (ca. 13.1–12.6 Ma, Laventan South American Land Mammal Age). Although exceptional, this record represents only a snapshot of the evolutionary history of New World monkeys because virtually none of the primate taxa recorded at La Venta had so far been found elsewhere. We describe here few dental remains of a cebine platyrrhine discovered from Laventan deposits in the San Martín Department of Peru (Peruvian Amazonia). The primate dental specimens from that new fossil-bearing locality (TAR-31) are strongly reminiscent morphologically of the teeth of Neosaimiri fieldsi from La Venta. However, given that several aspects of the dental variability from TAR-31 are unknown, we prefer to provide an assignment with open nomenclature (i.e., N. cf. fieldsi), instead of formally referring these remains to N. fieldsi, pending the discovery of additional specimens. The occurrence of Neosaimiri in Peru, in coeval deposits of La Venta, thus represents a second and southernmost record of that low-latitude genus in the Neotropics, thereby demonstrating its wide distribution along the northwestern edge of the Pebas Mega-Wetland System, in tropical western South America.

New insights into the Kibenikhoria and Ernestokokenia faunas and the implications for the early Eocene of Patagonia, Argentina

ABSTRACT The Kibenikhoria and Ernestokokenia local faunas were described in the 1930s by George G. Simpson, who defined them as two chronologically consecutive faunas based on a comparison with the Casamayoran South American Land Mammal Age (SALMA). Later, in the 1980s, the two faunas were respectively the basis of the Itaboraian and Riochican SALMAs, a scheme broadly accepted for more than eight decades. However, a systematic revision of their native ungulates is still lacking. In this contribution, we studied several collections performed in the classical localities of Cañadón Hondo and Bajo Palangana (southeastern South America) and discuss the systematic status of the mammals listed in their faunas. Our results allow us to (1) assert that the beds containing the mammal associations in Cañadón Hondo and Bajo Palangana are located in the upper Las Flores Formation and are essentially contemporaneous; (2) improve the knowledge for Kibenikhoria get and Henricosbornia lophodonta; (3) propose H. waitehor and ?Peripantostylops orehor to be synonymous with H. lophodonta; and (4) recognize Shecenia ctirneru, Seudenius cteronc, and ?Postpithecus as Trigonostylopidae aff. Trigonostylops. The Kibenikhoria and Ernestokokenia faunas have six genera in common; five of them are shared with the lower levels of the Sarmiento Formation. Kibenikhoria get, Isotemnus ctalego, Pliodolops winecage, and Gasternia ctalehor are exclusive taxa of the Kibenikhoria fauna. Here, the Riochican sensu stricto from Marshall is used to include both local faunas, which represents a distinct and more derived fauna than that from the Itaboraí Formation, but with a less advanced evolutionary stage than the lower Sarmiento Formation.

ANALYSIS OF THE EARLY- MIDDLE MIOCENE MAMMAL ASSOCIATIONS AT THE RÍO SANTA CRUZ (PATAGONIA, ARGENTINA)

The Santa Cruz Formation (SCF) records high latitude terrestrial paleoecosystems in the Southern Hemisphere during Burdigalian– early Langhian times (Early–Middle Miocene). Mammalian fossils from Río Santa Cruz (RSC) localities were first collected in the late 19th century, forming the basis for the Santacrucian South American Land Mammal Age. New collections permitt an update of the SCF mammalian species along the RSC. The total taxonomic richness is 95 mammalian species. Many species considered by Ameghino as exclusive for the older Notohippidian stage at similar latitude in the west, are not in fact so. The taxonomic richness in three localities along the RSC is substantially different: 47 species from Barrancas Blancas (BB), 60 from Segundas Barrancas Blancas (SBB) and nine from Yaten Huageno. The faunal composition between BB and SBB is also different: they share 31 species, of which six are present only at BB and 20 only at SBB. More than 85 % of all RSC species are also found at Atlantic coastal exposures of the SCF. In spite of BB (~17.04–16.49 Ma) being closer in age to coastal exposures, and SBB fossils (~16.46–15.63 Ma) being younger than the coastal localities (~17.80–16.30 Ma), the greatest similarity is between SBB and the coast. Faunal differences among the localities may be accounted for local variation in climatic and environmental factors. Previously proposed Santacrucian biozones should be set aside. The exposures of the SCF along the RSC should be considered as the type area of this unit and the Santacrucian fauna.

CINGULATES (MAMMALIA, XENARTHRA) OF THE SANTA CRUZ FORMATION (EARLY-MIDDLE MIOCENE) FROM THE RÍO SANTA CRUZ, ARGENTINE PATAGONIA

In 1887 Carlos Ameghino carried out the earliest extensive exploration of the fossiliferous localities along the Río Santa Cruz (Patagonia). His brother Florentino erected more than 100 vertebrate species based on the remains that Carlos recovered. The faunal assemblage eventually came to be recognized as the Santacrucian South American Land Mammal Age (Early–Middle Miocene). Over the past several years, an interdisciplinary group from the Museo de La Plata, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (Argentina), and Duke University (USA) revisited the Río Santa Cruz localities, including Barrancas Blancas, Segundas Barrancas Blancas, and Yaten Huageno. This contribution presents a taxonomic list of cingulates based on the abundant material recovered during these expeditions. In Barrancas Blancas, we recorded the armadillos Peltephilus pumilus Ameghino, Stenotatus patagonicus Ameghino, Proeutatus oenophorus Ameghino, Prozaedyus proximus Ameghino, and Stegotherium tessellatum Ameghino, and the glyptodonts Cochlops muricatus Ameghino and Eucinepeltus sp. Ameghino. We did not record St. tessellatum in Segundas Barrancas Blancas and St. tessellatum, P. pumilus and Eucinepeltus sp. in Yaten Huageno. The comparative analysis between the faunal composition of the Santa Cruz Formation in the Río Santa Cruz and other areas to the west and the east reveals minor differences that, preliminarily, suggest environmental differences between the analyzed regions.