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The early Miocene Santa Cruz Formation (SCF) in southern Patagonia hosts the Santacrucian South American Land Mammal Age (SALMA), whose age is known mainly from exposures along the Atlantic coast. Zircon U-Pb ages were obtained from intercalated tuffs from four inland sections of the SCF: 17.36 ± 0.63 Ma for the westernmost Río Bote locality, and 17.04 ± 0.55 Ma–16.32 ± 0.62 Ma for central Río Santa Cruz localities. All ages agree with the bounding age of underlying marine units and with equivalent strata in coastal exposures. New ages and available sedimentation rates imply time spans for each section of ∼18.2 to 17.36 Ma for Río Bote and 17.45–15.63 Ma for central Río Santa Cruz (Burdigalian). These estimates support the view that deposition of the SCF began at western localities ∼1 Ma earlier than at eastern localities, and that the central Río Santa Cruz localities expose the youngest SCF in southern Santa Cruz Province. Associated vertebrate faunas are consistent with our geochronologic synthesis, showing older (Notohippidian) taxa in western localities and younger (Santacrucian) taxa in central localities. The Notohippidian fauna (19.0–18.0 Ma) of the western localities is synchronous with Pinturan faunas (19.0–18.0 Ma), but older than Santacrucian faunas of the Río Santa Cruz (17.2–15.6 Ma) and coastal localities (18.0–16.2 Ma). The Santacrucian faunas of the central Río Santa Cruz localities temporally overlap Colloncuran (15.7 Ma), Friasian (16.5 Ma), and eastern Santacrucian faunas. [ABSTRACT FROM AUTHOR]

Between January and September of 1887 Carlos Ameghino carried out his first geologic and paleontological expedition to the Río Santa Cruz, Patagonia. Based on the fossils and geologic information compiled, in 1887 and 1889, Florentino Ameghino named more than 120 new species of extinct mammals and his Formación Santacruceña and Piso Santacruceño (Santacrucian stage). Data published by both brothers state that the specimens were collected in outcrops by the Río Santa Cruz, between 90 and 200 km west of its mouth. However, information in the posthumously published letters and Travel Diary of C. Ameghino allows us to recognize a fourth locality, Río Bote, at about 50 km further southwest. In 1900, 1902, F. Ameghino divided the Piso Santacruceño in a younger étage Santacruzienne and older étage Notohippidéen, restricting the geographical distribution of the latter to Kar Aiken locality, northeast of Lago Argentino. However, 15 of the 54 species that F. Ameghino listed as exclusively Notohippidian stage already had been named on specimens collected South to the Río Santa Cruz in 1887, two year prior to C. Ameghino's first visit to Kar Aiken. Based on historical information and several expeditions to the Río Santa Cruz and its environs, in this contribution we establish the geographical locations of the 1887 localities, formalize their names, evaluate the stratigraphic position of the fossil-bearing levels, and analyze the geographic extension of the Notohippidian, inferring that Río Bote is where C. Ameghino first collected species that came to define the Notohippidian. [ABSTRACT FROM AUTHOR]

In the Eocene deposits of Northwestern Argentina, the order Cingulata was recognized in the sedimentary levels of the upper and lower sections of the Lumbrera (Salta Province), Geste (Catamarca and Salta provinces), Quebrada de Los Colorados (Salta Province), and Casa Grande (Jujuy Province) formations. The traditional biochronological scheme associated the Geste Formation to the Mustersan SALMA (37.3–35.4 Ma; Priabonian), the lower section of the Lumbrera Formation to the Vacan Subage (44–46 Ma; Lutetian) of the Casamayoran SALMA, and the fossiliferous levels of the remaining units to the Barrancan Subage (39–42 Ma; Bartonian) of the Casamayoran SALMA. Nevertheless, recent dating obtained for the top of the lower section of the Lumbrera Formation supports a new geochronological framework for Northwestern Argentina, which changes the temporal assignation of the taxa that have been collected in this section, going from the Vacan Subage to the Itaboraian SALMA, affecting also the biochronology of the Quebrada de Los Colorados and the upper section of the Lumbrera formations, which are now constrained between 46 and 40 Ma (Lutetian). In this contribution, we present a new cingulate assemblage based on osteoderms collected in the basal levels of the Quebrada de Los Colorados Formation at Los Cardones National Park, Calchaquí Valley (Salta, Northwestern Argentina), which is constituted by a new taxon plus Pucatherium parvum and Parutaetus punaensis. In addition, we discuss all the Eocene cingulate associations reported for Northwestern Argentina taking into consideration the new geochronological framework. [Display omitted] • New cingulate assemblage from the middle Eocene Quebrada de Los Colorados Fm (Los Cardones National Park, Salta, Argentina). • The assemblage is composed by the new taxa Saltatherium rosaurae plus Pucatherium parvum and Parutaetus punaensis. • An updated biochronology for the middle Eocene of Northwestern Argentina is presented. • The mammalian fauna of the QLCF is constrained between the late Vacan and the Barrancan subages of the Casamayoran SALMA. [ABSTRACT FROM AUTHOR]

Abstract: Two new fossil vertebrate localities are described from the Santa Cruz Formation (late early – early middle Miocene) of coastal Patagonia. They are noteworthy because they are the lowest stratigraphically of any precisely recorded in coastal Santa Cruz Province and they contain a rich fauna including many partially articulated skeletons undisturbed by collecting. Thus, they offer the potential for taphonomic analysis and paleocommunity reconstruction. The latter is particularly intriguing because the fauna document the Miocene Climatic Optimum at >51° South latitude. Together with several previously documented sites in this region, it offers a potential window into the nature of mammalian communities farther south than any other in the world during this time and documents the farthest south distribution of primates. [Copyright &y& Elsevier]

In this contribution, we report the discovery of Archaeogaia macachaae gen. et sp. nov., one of the oldest notoungulate recovered from the upper section of Mealla Formation in the Tonco Valley (Northwestern Argentina, Salta Province). The new material consists on a left mandibular fragment with damaged m1 and complete m2-3. Archaeogaia macachaae is characterized by the following combination of features: m1 slightly shorter than m2 and both larger than m3; brachydont molars; talonid mesio-distally shorter than trigonid; metaconid slightly taller than protoconid and distally placed; reduced paraconid in m2; metalophid straight in m2–3, but it runs mesially forming a slightly obtuse angle in the labial edge in m2, whereas it is more transverse in m3; transverse entolophid; mesial cingulid extending from the middle to the lingual face of molars; and distal cingulid connecting the hypoconulid with the mesial face of the entoconid on m2–3. We perform a phylogenetic analysis based on a data matrix composed of 147 craniodental characters and 70 taxa. The analysis yields 6104 most parsimonious trees of 423 steps each. In the strict consensus previously well-supported clades collapse into a polytomy; and Archaeogaia is positioned within the order Notoungulata based on two synapomorphies: a) presence of a transverse entolophid, and b) lower cheek teeth with short mesio-distal protolophid, transverse metalophid and mesio-distal hypolophid slightly convex labially. The former character was recovered as a synapomorphy for Notoungulata in several previous studies. According to the reduced consensus, Archaeogaia occupies different positions within the order; these fluctuating locations could be the result of the presence of plesiomorphic features in the holotype, and the absence of the structures that define the notoungulate clades in which the new taxon is located. The paleomagnetic data indicates that the Mealla Formation was deposited during Chron 27r to the base of Chron 26r (latest Danian-earliest Selandian). In this context, we discuss the finding of Archaeogaia , and the age of Mealla Formation in the South American biochronology. • A new genus and species (Archaeogaia macachaae) of South American Native Ungulate (Notoungulata) is described.. • This new taxon comes from the late Danian-early Selandian Mealla Formation Northwestern Argentina.. • Together with Simpsonotus spp., this finding constitutes the most ancient record for the order Notoungulata. • These finding reinforces the necessity of new paleontological prospections in the Paleocene of the Northwestern Argentina. [ABSTRACT FROM AUTHOR]