Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The deposits of the Chorrillo Formation (Maastrichtian) were accumulated during a ‘continental window’ that occurred during the Late Cretaceous in the Austral-Magallanes foreland basin, southern Patagonia, Argentina. The aim of the present contribution is to describe the depositional conditions as well as new vertebrate and plant fossils from this unit. The analysis of these deposits resulted in the definition of five architectural elements: Complex sandy narrow sheets channels (SS), Complex gravelly narrow sheets channels (GS), Sandstone lobes (SL), Thick fine-grained deposits (GF) and Thin dark fine-grained deposits (DF). These were separated into channelized and non-channelized units and represent the accumulation in a fine-grained dominated, fossil rich fluvial depositional system. Vertebrates fossil records include two species of frogs of the genus Calypteocephalella (representing the southernmost record of Pipoidea), snakes belonging to Madtsoiidae and Anilioidea (the latter ones being the first records for the basin), chelid turtles similar to Yaminuechelys-Hydromedusa, meiolaniiform turtles, titanosaur sauropods, megaraptoran theropods, new remains of the elasmarian Isasicursor santacrucensis (including the first cranial remains available for this species), hadrosaur ornithischians, enantiornithine birds. Sharks and elasmosaurs are also recorded and may possibly derive from the overlying marine Calafate Formation. These new taxa, together with previous findings from the Chorrillo Formation, are included into a stratigraphic column, thus providing valuable information that sheds new light on faunistic composition and paleobiogeography of high-latitude biotas of Gondwana.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Recent explorations on the Maastrichtian Chorrillo Formation at La Anita farm, far 30 km. from the Calafate city, at Santa Cruz province, yielded a high number of microvertebrates Chimento et al. 2020Chimento et al. , 2021Rozadilla et al. 2021;Moyano-Paz et al. 2022;Aranciaga Rolando et al. 2022). Among fossils recovered from those beds, lepidosaurs were represented up to the date by isolated and incomplete vertebrae of snakes referable to indeterminate snakes, madtsoiids, and 'anilioids' Moyano-Paz et al. 2022). ...
... Recent explorations on the Maastrichtian Chorrillo Formation at La Anita farm, far 30 km. from the Calafate city, at Santa Cruz province, yielded a high number of microvertebrates Chimento et al. 2020Chimento et al. , 2021Rozadilla et al. 2021;Moyano-Paz et al. 2022;Aranciaga Rolando et al. 2022). Among fossils recovered from those beds, lepidosaurs were represented up to the date by isolated and incomplete vertebrae of snakes referable to indeterminate snakes, madtsoiids, and 'anilioids' Moyano-Paz et al. 2022). These constitute the only evidence of fossil lepidosaurs from high latitudes in Patagonia. ...
... The specimens were collected at upper levels of the Chorrillo Formation (Maastrichtian), close to the transition with the overlying Calafate Formation (Nullo et al. 2006;Moyano-Paz et al. 2022). The specimens here reported were discovered at 'La Anita' farm, located approximately 30 km SW from El Calafate City, Santa Cruz Province, Argentina. ...
... Previous uppermost Cretaceous report from insects in the region consisted of coleopteran elytra imprints presumably from the lowermost levels of the Dorotea Formation in southern Chile 12,13 . The Chorrillo Formation has yielded a rich and variegated fossil content 14 including titanosaurids, hadrosaurids, ankylosaurids 15 , non-avian theropods 16 , enantiornithine birds 17,18 , gondwanatherian and monotreme mammals [19][20][21] , turtle, frogs, and fishes 14,17 , terrestrial mollusks 14 , and conifer woods, pollen and spores of different plant groups 14,17,22,23 . The entomofauna currently recognized is composed by members of Chironomidae, Ephemeroptera, and Lepidoptera. ...
... Previous uppermost Cretaceous report from insects in the region consisted of coleopteran elytra imprints presumably from the lowermost levels of the Dorotea Formation in southern Chile 12,13 . The Chorrillo Formation has yielded a rich and variegated fossil content 14 including titanosaurids, hadrosaurids, ankylosaurids 15 , non-avian theropods 16 , enantiornithine birds 17,18 , gondwanatherian and monotreme mammals [19][20][21] , turtle, frogs, and fishes 14,17 , terrestrial mollusks 14 , and conifer woods, pollen and spores of different plant groups 14,17,22,23 . The entomofauna currently recognized is composed by members of Chironomidae, Ephemeroptera, and Lepidoptera. ...
... Previous uppermost Cretaceous report from insects in the region consisted of coleopteran elytra imprints presumably from the lowermost levels of the Dorotea Formation in southern Chile 12,13 . The Chorrillo Formation has yielded a rich and variegated fossil content 14 including titanosaurids, hadrosaurids, ankylosaurids 15 , non-avian theropods 16 , enantiornithine birds 17,18 , gondwanatherian and monotreme mammals [19][20][21] , turtle, frogs, and fishes 14,17 , terrestrial mollusks 14 , and conifer woods, pollen and spores of different plant groups 14,17,22,23 . The entomofauna currently recognized is composed by members of Chironomidae, Ephemeroptera, and Lepidoptera. ...
Article
Full-text available
Insect faunas from the latest Cretaceous are poorly known worldwide. Particularly, in the Southern Hemisphere, there is a gap regarding insect assemblages in the Campanian-Maastrichtian interval. Here we present an insect assemblage from the Maastrichtian Chorrillo Formation, southern Argentina, represented by well-preserved and non-deformed, chitinous microscopic remains including head capsules, wings and scales. Identified clades include Chironomidae dipterans, Coelolepida lepidopterans, and Ephemeroptera. The assemblage taxonomically resembles those of Cenozoic age, rather than other Mesozoic assemblages, in being composed by diverse chironomids and lepidopterans. To the best of our knowledge, present discovery constitutes the first insect body fossils for the Maastrichtian in the Southern Hemisphere, thus filling the gap between well-known Early Cretaceous entomofaunas and those of Paleogene age. The presented evidence shows that modern clades of chironomids were already dominant and diversified by the end of the Cretaceous, in concert with the parallel radiation of aquatic angiosperms which became dominant in freshwater habitats. This exceptional finding encourages the active search of microscopic remains of fossil arthropods in other geological units, which could provide a unique way of enhancing our knowledge on the past diversity of the clade.
... The Chorrillo Formation (Maastrichtian, Austral-Magallanes Basin at the Lago Argentino area, southern Argentina; Fig. 1) is an important dinosaur-bearing unit of Patagonia (Feruglio, 1945). The sedimentological aspects of this important dinosaur-bearing unit of Patagonia were newly addressed by Moyano-Paz et al. (2022a), in which a detailed characterization of the channelized fluvial deposits of the unit was conducted. However, up to now no detailed studies were carried out the non-channelized and pedogenically modified fine-grained deposits of the Chorrillo Formation, which represent more than the 60% of the unit, and consequently, environmental and climatic conditions of this unit still remained unstudied. ...
... At the Lago Argentino region (49 40 0 to 50 37 0 S), southwest of the Santa Cruz province, the onset of the foreland basin is characterized by a thick record of deep marine to coastal strata (e.g., Malkowski et al., 2017;Moyano Paz et al., 2020, 2022b, 2022cDobbs et al., 2022). During the late Campanian through Maastrichtian, this region of the basin underwent a complete continentalization (Ghiglione et al., 2021) and exhibits thick fluvial successions assigned to the Cerro Fortaleza, La Irene and Chorrillo formations (Sickmann et al., 2018;Tettamanti et al., 2018;Moyano-Paz et al., 2022a). ...
... The Chorrillo Formation (Maastrichtian) was initially named as 'dinosaur-bearing strata' because of its abundance in fossil vertebrate remains (Feruglio, 1945;Bonaparte, 1996). However, it was in the last of years that there has been a boom in studies focused on the palaeontological content of the unit (Novas et al., 2019;Chimento et al., 2020Chimento et al., , 2021Rozadilla et al., 2021;Aranciaga Rolando et al., 2022;Vera et al., 2022;Moyano-Paz et al., 2022a). This formation is the youngest lithostratigraphic unit that accumulated during the continental expansion of the Austral-Magallanes Basin and crops out to the south of the Lago Argentino ( Fig. 1B-C) (Moyano-Paz et al., 2022a). ...
Article
The Maastrichtian dinosaur-bearing Chorrillo Formation in southern Patagonia (⁓50° S, Austral-Magallanes Basin, Argentina) is a pedogenically modified fluvial succession, which records sediment deposition at mid-high paleolatitudes in the Southern Hemisphere. In order to reconstruct the paleoenvironment and paleoclimates for the Chorrillo Formation, we performed a paleopedological study (abiotic components) of the unit within a well-defined sedimentological-paleontological context, and considering new paleobotanical data of the unit. Using detailed macro and micromorphological features and clay mineralogy of the paleosols, we show that the Chorrillo Formation paleosols are overall smectite-rich soils with vertic and redoximorphic features (i.e., moderately developed hydromorphic Vertisol-, calcic Vertisol-, poorly developed hydromorphic Vertisol-, Histosol-, and argillic Vertisol-like paleosols). The small-scale or high-frequency stacking of such paleosols indicates that they developed under different hydrologic conditions, and subtle differences in grain-size (parent material) and topographic relief on a distal floodplain. Conversely, the large-scale or small-frequency vertical stacking of different paleosols is linked to avulsion processes. Paleobotanical remains through the Chorrillo succession demonstrates different ecological requirements for the inhabited part of the fluvial floodplain. Abiotic and biotic climate proxies suggest that these paleosols formed under a broadly temperate-warm and seasonally humid climate. Overall, these combined data record environmental and climatic conditions during the uppermost Cretaceous, and preserve a record of Maastrichtian terrestrial conditions in the Southern Hemisphere.
... The articular surface of the process is rounded in contour, slightly concave and ventrolaterally facing. The process shows a rugose anterior surface that probably constitutes the insertion of the ligaments that attach the rib to the vertebra 39 . Posteriorly, the transverse process shows at least three pneumatic foramina closer to its tip. ...
... MPM-PV-22864 and MPM-PV-22865 are almost identical in morphology differing, as expected, in those traits that vary within the anterior and posterior parts of the jaw (such as the symmetry or not of the tooth crowns). Conversely, one tooth (MACN-Pv 19,066) differs from the rest in having a high density of distal denticles (5 per mm vs 3 per mm in all other megaraptorids 3,39 ). It should be noted that MACN-Pv 19,066 was collected in the area in 1980 but lacks specific stratigraphic and geographic provenances 3 . ...
... In sum, Maip macrothorax is the first megaraptorid taxon to be named for the Maastrichtian of southern Patagonia, representing the biggest among currently known megaraptorids (Lamanna et al. 20 and Supplementary Information II), and one of the youngest records (alongside with those from Lago Colhué Huapi Formation) for the entire clade 39 . ...
Article
Full-text available
Megaraptora is a theropod clade known from former Gondwana landmasses and Asia. Most members of the clade are known from the Early to Late Cretaceous (Barremian–Santonian), with Maastrichtian megaraptorans known only from isolated and poorly informative remains. The aim of the present contribution is to describe a partial skeleton of a megaraptorid from Maastrichtian beds in Santa Cruz Province, Argentina. This new specimen is the most informative megaraptoran known from Maastrichtian age, and is herein described as a new taxon. Phylogenetic analysis nested the new taxon together with other South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built.
... The ulna bears a poorly projected olecranon, which resembles those of other Elasmaria, such as Anabisetia, Notohypsilophodon, and Isasicursor (Coria & Calvo, 2002;Ibiricu et al., 2014;Moyano-Paz et al., 2022), although not as reduced as in Mahuidacursor (Cruzado-Caballero et al., 2019). The ulna of Chakisaurus differs from Anabisetia, Notohypsilophodon, Mahuidacursor, Isasicursor, and Gasparinisaura in having a transversely compressed proximal end and a deeper radial facet delimited by prominent lateral and medial processes. ...
... The ulna of Chakisaurus differs from Anabisetia, Notohypsilophodon, Mahuidacursor, Isasicursor, and Gasparinisaura in having a transversely compressed proximal end and a deeper radial facet delimited by prominent lateral and medial processes. The ulna of these taxa has a wider subtriangular outline in proximal view and a shallower radial facet (Cambiaso, 2007;Cruzado-Caballero et al., 2019;Moyano-Paz et al., 2022). The distal end of the radius of Chakisaurus is transversely narrow and sub-triangular in contour, not as transversely expanded as Sektensaurus, and differs from Anabisetia which shows a sub-rectangular distal end in distal view (Cambiaso, 2007;Ibiricu et al., 2019;Rozadilla et al., 2019). ...
... Despite recent advances, the fossil record of Cretaceous lepidosaurs (Reptilia: Diapsida) in South America is very patchy, and mainly rests on information coming from Argentina (particularly Patagonia) and Brazil (Albino, 2011;Apesteguía and Jones, 2012;Albino and Brizuela, 2014;Novas et al., 2019;Martinelli et al., 2021;Moyano-Paz et al., 2022). In Patagonia, the record is dominated by abundant snakes including stem-taxa, madtsoiids, and anilioids ranging from Cenomanian to Maastrichtian times (Zaher et al., 2009;Albino, 2011;Scanferla, 2016;Gómez, 2016;Gómez et al., 2019). ...
... These differences between sphenodontian assemblages of northern and southern Patagonia are in agreement with proposals based on other fossil vertebrates suggesting important faunistic distinction between both regions of Patagonia (Crisci et al., 1991;Novas et al., 2013Novas et al., , 2019Moyano-Paz et al., 2022). This hypothesis contrasts with some recent works suggesting that Maastrichtian faunas from southern Chilean and Argentinian Patagonia were "Allenian" in nature (Alarcón-Muñoz et al., 2020;Suazo-Lara and Gómez, 2022). ...
... The molar was collected from levels of the Chorrillo Formation (Upper Cretaceous, Early Maastrichtian 7 ), cropping out in SW Santa Cruz province, Patagonia, Argentina. It was found in association with both terrestrial and aquatic mollusks, calyptocephalellid anurans, chelid turtles, snakes, ornithopod, sauropod, and non-avian and avian theropod remains 7,8 . As far as mammals is concerned, the same fossil spot yielded a molar of the gondwanatherian Magallanodon baikashkenke 9 and isolated caudal vertebrae regarded as Mammalia incertae sedis 8 . ...
... The material reported in this publication was collected from the Chorrillo Formation (Upper Cretaceous, lower Maastrichtian 7 ) cropping out in La Anita fossil site, SW Santa Cruz Province, Patagonia, Argentina. The specimen was found in association with both terrestrial and aquatic mollusks, calyptocephalellid anurans, chelid turtles, snakes, ornithopods, sauropods, and non-avian and avian theropod remains 7,8 . With regard to mammals, the same outcrop yielded remains of the gondwanatherian Magallanodon baikashkenke and isolated caudal vertebrae of yet unidentified mammals 8,9,13 . ...
Article
Full-text available
Monotremata is a clade of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands. Occurrence of basal monotremes in the Early Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America. Here we report on the discovery of a Late Cretaceous monotreme from southern Argentina, demonstrating that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.
... This The La Anita Formation (Bianchi, 1967) . The upper unit of the La Anita Formation is overlain by the terrestrial deposits of the UCCD (Fig. 1D) (Tettamanti et al., 2018, 2022b. ...
... shallowing-upward succession in the Lago Argentino region ended with the deposition of the uppermost Cretaceous continental deposits (UCCD), an interval that includes several terrestrial lithostratigraphic units, such as the Cerro Fortaleza, La Irene and Chorrillo formations(Fig. 1B, D)(Tettamanti et al., 2018; Ghiglione et al., 2021;Moyano-Paz et al., 2022b). ...
Article
Aggradational deltaic successions are uncommon in the stratigraphic record since deltas are progradational by nature. However, deltaic coastlines fed by multiple small distributaries rather than by a well-defined trunk fluvial distributary system might result in aggradational successions if the sediment is effectively redistributed from river mouths by active basinal processes (e.g., tides, fairweather waves, and/or storm waves). The wave-dominated deltaic succession in the lower part of the La Anita Formation accumulated during the foreland stage of the Austral-Magallanes Basin (Argentina). Through a sedimentological and ichnological study of the interval, we evaluate and discuss the potential controls on the evolution of aggradational wave-dominated deltaic successions. The studied stratigraphic interval is up to 150 m thick and includes facies deposited in wave-dominated prodelta, wave-dominated distal delta-front, wave-influenced mouth bar, terminal channel, and distributary channel settings. These facies associations stack vertically, forming clear thick aggradational sets. Fairweather wave processes largely dominate the delta-front and prodelta deposits, although discrete beds point to the periodic importance of linked storm-wave and river-flood processes. Owing to the alternation of beds generated during fairweather shoaling waves with those of coupled storm-wave and river-flood cycles, it is proposed that the overall aggradational stacking pattern of the delta is the response to the sediment balance. Clastic material supplied by the distributary channels of the delta was easily transported alongshore during fairweather conditions by longshore currents and basinward via storm-generated waves, and/or hyperpycnal currents and hypopycnal plumes generated by river floods. The alternation of these depositional processes strongly affected the benthic faunal communities, which is well expressed by the resulting ichnological suites. Storm-wave and river-flood events led to the widespread defaunation of tracemaking organisms, leading to generation of unburrowed beds. Between these events, short-lived colonization windows appeared locally, allowing sparse, facies-crossing dwelling and detritus-feeding burrows to be constructed by the recovering benthic communities. By contrast, during prolonged periods of fairweather shoaling, river-induced physico-chemical stresses were greatly reduced, and the resulting beds display elevated bioturbation intensities with greater numbers of burrows that record a wide range of behaviors.
... The onset of the foreland regime is recorded by flexural deeping of the foredeep main depozone from 100-500 m to 1000-2000 m (Natland et al., 1974). The AMB foreland system is characterized by a thick marine infill followed by continental deposits, representing an evolution from an underfilled to overfilled stage (Malkowski et al., 2015;Tettamanti et al., 2018;Moyano-Paz et al., 2018, 2022Varela et al., 2019;Ghiglione et al., 2021, Fig. 2). Sediment accumulation in the foredeep starts with the deep-marine, siliciclastic, turbiditic deposits of the Cerro Toro Formation (Albian-Cenomanian; Wilson, 1991;Fildani and Hessler, 2005;Malkowski et al., 2015Malkowski et al., , 2017, which are covered by the siliciclastic fine-grained, prograding slope to outer-shelf deposits of the Alta Vista/Tres Pasos Formation (Hubbard et al., 2010;Daniels et al., 2018Daniels et al., , 2019. ...
... This deep-marine sedimentation is capped on top by the Santonian-Maastrichtian siliciclastic coastal deposits of the La Anita Formation or by its equivalent in Chile, the Dorotea Formation (Macellari et al., 1989;Moyano-Paz et al., 2018Santamarina et al., 2020;Ghiglione et al., 2021). Finally, this marine succession is overlain by the uppermost Cretaceous continental deposits, which include several lithostratigraphic units such as the Cerro Fortaleza, La Irene and Chorrillo formations (Fig. 2;Tettamanti et al., 2018;Ghiglione et al., 2021;Moyano-Paz et al., 2022). ...
Article
Wave-, tidal-, and fluvial-dominated deltas are important hydrocarbon reservoirs worldwide, and it is well known that depositional facies types, detrital composition and diagenetic products are key aspects when evaluating potential reservoir properties. Moreover, detrital composition and diagenetic products are controlled by external forces such as tectonism, climate, and depositional conditions. The Upper Cretaceous La Anita Formation (Austral-Magallanes Basin, Argentina) is a deltaic succession that shows a clear vertical variation in the relative role of wave, tidal and fluvial processes. The formation was accumulated during the foreland stage of the basin under relatively warm climate conditions. A detailed compositional and diagenetic analysis for these deposits is provided to evaluate the role of the controlling factors on the detrital and authigenic composition, and the impact on reservoir properties. Samples were analyzed by conventional petrography, X-ray diffraction and scanning electron microscopy to obtain a full spectrum of its detrital, authigenic and diagenetic composition. The analyzed sandstones were classified as lithic arenites which come from the fold-thrust belt region and from the magmatic arc located toward the westward. The clay mineral composition is characterized by variable proportions of illite, smectite, kaolinite and mixed-layer illite-smectite with the sporadic presence of chlorite. Stratigraphic variations in the abundance of authigenic kaolinite and smectite indicate a change in the climatic conditions during the de-positions of the unit evolving from tropical to more temperate conditions. Diagenetic processes affecting the porosity are considered as controlled mainly by the lithological nature of the deposits and depositional facies type. Sandstone porosity is mainly primary in origin, moderate to good in abundance and show micropore to mesopore as the main pore-sizes. This work enhances that the diagenetic products are heavily controlled by the dominant depositional process. The presence of diagenetic products as quartz overgrowth and calcite and hematite cement reduces pore spaces and affects the reservoir properties. The development of these types of cement is conditioned by the relative dominance of wave and river processes. Under wave-dominated conditions, quartz tends to develop thick overgrowths. Conversely, under river-dominated conditions quartz overgrowths are thinner and calcite and hematite cementation patches are developed.
... Interestingly, we identified in the fossils from the Los Alamitos Formation some diagnostic (autapomorphic) traits of Kuruleufenia xenopoides (G omez, 2016) in the sphenethmoid (transverse constriction just posterior to the level of the orbitonasal foramina; frontoparietal fenestra extending anteriorly through a tapering embayment) and the humeri (medial epicondyle ending in a sharp distal point and separated from the humeral ball by a shallow groove; fine medial crest), confirming that this species is also part of the assemblage from the Los Alamitos Formation. In addition, the pipid frog from the Dorotea Formation, which represents the first pipid from Chile and the southernmost record of pipids worldwide, as well as the recently reported pipoid from the Chorrillo Formation (Moyano-Paz et al., 2022), are here interpreted as an indeterminate species of Kuruleufenia based on the abovementioned diagnostic features of the humerus. To summarize, all currently-known pipid frogs from the upper Campanianelower Maastrichtian of Patagonia belong to Kuruleufenia. ...
... These anurans are limited to this Patagonian assemblage and have not yet been reported elsewhere in South America (B aez et al., 2012a; G omez, 2016; B aez and G omez, 2018), nor they occur in older or younger Patagonian assemblages, in which known pipoids and calyptocephalellids represent different forms G omez, 2016;Muzzopappa et al., 2020), thus reinforcing their reliability as Allenian diagnostic taxa. Furthermore, the frog records from the Dorotea Formation described herein, coupled with the already known tetrapod taxa from this Chilean unit (Manríquez et al., 2019;Alarc on-Muñoz et al., 2020;Goin et al., 2020;Martinelli et al., 2021) and the partially equivalent Chorrillo Formation in Argentina (Novas et al., 2019;Chimento et al., 2021;Moyano-Paz et al., 2022), indicate that the Allenian tetrapod assemblage reached southernmost Patagonia. The Allenian tetrapod assemblage can be recognized all across Patagonia, including its southernmost region, by the joint occurrence of Calyptocephalella-like calyptocephalellids and Kuruleufenia frogs, gondwanathere mammals, chelid turtles, madtsoiid snakes, hadrosaurid and ankylosaurian ornithischians, large titanosaurs, abelisauroid theropods, and ornithothoracine birds. ...
Article
Frogs (Anura) are nowadays common and abundant constituents of terrestrial and freshwater ecosystems near globally and their fossil record shows that they were already important during Cretaceous times. However, their fossils are often very incomplete, challenging their identification, which, coupled to historical reasons, has led to their marginalization in studies of Cretaceous tetrapod assemblages. We here report on the identities of frogs from three upper Campanian–lower Maastrichtian assemblages from Chilean (Dorotea Formation) and Argentinean (Allen and Los Alamitos formations) Patagonia, with focus on humeral morphology. Records from the Dorotea Formation represent the first described Mesozoic frogs from Chile and include the southernmost record of pipids worldwide. In the three assemblages we have identified humeri of the pipid Kuruleufenia and of calyptocephalellid frogs, proving humeral morphology valuable in diagnosing and identifying Cretaceous frogs from Patagonia. These frogs are diagnostic components of the South American Allenian tetrapod assemblage that was widespread across Patagonia near the end of the Cretaceous.
... Only a few species are recorded from the Early and Late Cretaceous: Arariphrynus placidoi (Leal et al., 2007;Báez et al., 2009), Eurycephalella alcinae , Cratia gracilis , Primaevorana cratensis (Moura et al., 2021), Kururubatrachus gondwanicus (Agnolin et al., 2020), Baurubatrachus pricei (Báez & Perí, 1989;Báez & Gómez, 2018) and Uberabatrachus carvalhoi (Báez et al., 2012) from Brazil; Hungarobatrachus szukacsi from Hungary (Szentesi & Venczel, 2010;Venczel et al., 2021); Indobatrachus pusillus from India (Noble, 1930;Špinar & Hodrová, 1985); and Beelzebufo ampinga from Madagascar (Evans et al., 2008). Additional Cretaceous neobatrachian records come from Chile and Argentina (calyptocephalellid neobatrachians, Báez, 1987;Martinelli & Forasiepi, 2004;Agnolin, 2012;Novas et al., 2019;Sterli et al., 2021;Moyano-Paz et al., 2022;Suazo-Lara & Gómez, 2022), from Sudan (neobatrachian indet., Báez & Werner, 1996) and Niger (neobatrachian indet., de Broin et al., 1974). It is noteworthy that the systematic position of the aforementioned extinct species remains blurred despite attempts to include them in phylogenetic studies. ...
Article
In the present paper, we report new anuran remains recovered from strata referred to the Adamantina Formation (Upper Cretaceous) cropping out near Catanduva city, São Paulo, Brazil. The remains represent two individuals, one of which bears a set of peculiar characteristics, both cranial and postcranial, that allows us to assign them to the already known genus Baurubatrachus. To date, the genus was only represented by the holotype of Baurubatrachus pricei, recovered from the Upper Cretaceous Serra da Galga Formation (which is younger than the Adamantina Formation), near Peirópolis (Minas Gerais, Brazil), 200 km north of Catanduva City. The lesser ossification as well as the slender configuration of the scapula and ilia of the new remains, relative to B. pricei, points to the identification of a new species, Baurubatrachus santosdoroi sp. nov. The detailed study of the peculiar anatomy of these specimens provides new osteological features for the genus, such as the presence of a subtympanic foramen, as well as new character states for other traits to be considered in future systematic studies. El presente trabajo reporta nuevos restos de anuros hallados en estratos referidos a la Formación Adamantina (Cretácico Superior) aflorantes en las proximidades de la ciudad de Catanduva, San Pablo, Brasil. Los restos representan dos individuos, uno de ellos portador de una cantidad de características particulares, cranianas y postcranianas que permite asignarlo al género ya conocido Baurubatrachus. Hasta la fecha, el género estaba únicamente representado por el holotipo de Baurubatrachus pricei, recuperado de la Formación Serra da Galga del Cretácico Superior (que es más joven que la Formación Adamantina), cerca de la ciudad de Peirópolis (Minas Gerais, Brasil), 200 km al norte de la ciudad de Catanduva. La menor osificación, así como la condición más esbelta de las cinturas pectoral y pélvica de estos restos respecto de B. pricei, indica la presencia de una especie diferente, Baurubatrachus santosdoroi sp. nov. El estudio detallado de la anatomía particular de estos especímenes permitió identificar nuevos caracteres como la presencia de un foramen subtimpánico y, a su vez, nuevos estados de carácter para otras características, las cuales son plausibles de ser utilizadas en futuros estudios sistemáticos.
Article
Agnolín et al. (2024) (Hereafter A24) report on a Late Cretaceous lepidosaur assemblage from southern Patagonia. The fossils described by A24 are noteworthy as they extend the record of lepidosaurs from southern Patagonia and as such deserve a detailed study. However, we find several issues in the descriptions and consider most of their taxonomic assignments to be unsupported by the data, which in turn makes their faunistic interpretations to be seriously flawed. Here, we would like to comment on some of the major inconsistencies and misstatements that we have found in the work of A24 in order to prevent wrong faunal lists and biogeographic considerations.
Article
Dryolestoid mammals are classical members of the Jurassic faunas of Laurasia but mostly absent during the Cretaceous. The reverse is true in Gondwana in general and South America in particular, where meridiolestid dryolestoids are dominant in the Late Cretaceous. We describe here 21 new mammalian specimens from the Upper Cretaceous locality Cerro Tortuga (Allen Formation, Patagonia, Argentina) collected via screenwashing, which we identify as meridiolestid dryolestoids. We recognize a new species of meridiolestid and reassign a previously described specimen to the new taxon. The morphology of these new remains represents a new morphotype in the spectrum of meridiolestid diversity, recording a broadening of trophic adaptations from the ancestral insectivory to the more derived herbivory observed among the later and more derived members of the group. The novel dental morphology helps bridge the anatomy of the plesiomorphic sharp-toothed meridiolestidans with that of the more derived and bunodont mesungulatoids. The new taxon suggests that development of both broad cingulids and complex crown morphology precede the development of the wide compressed roots, bunodonty, and thickened enamel characteristic of derived mesungulatids. Other specimens from the collection are referable to taxa previously known from the same locality. These provide new information about tooth positioning, dental formula, and overall dental morphology. The new material suggests that Groebertherium, previously regarded as a dryolestid taxon, is in fact a likely member of Meridiolestida.
Article
The Cretaceous/Paleogene boundary (K/Pg) event, associated with a meteorite impact at Chicxulub, Mexico, is globally recognized as one of the largest mass extinctions in natural history, marking the end of the Mesozoic Era. However, most of the outcrops with records and geochemical evidence of this boundary are distributed in the Northern Hemisphere and at mid-latitudes. Here, aiming to contribute to the knowledge of this event at high southern latitudes, we characterize a single iridium anomaly correlated with the K/Pg boundary, present within a carbonaceous mudstone level in a continental depositional environment in the Río de las Chinas Valley, Chilean Patagonia. High-resolution geochemical and palynofacies analyses were performed on a stratigraphic section from the top of the Dorotea Formation. Results showed that the iridium enrichment coincides with an anomaly of other platinum group elements. In addition, the palynofacies analysis showed a disturbance in the depositional environment, marked by an abrupt change from non-degraded phytoclasts (e.g., cuticles) to pseudoamorphous and degraded cuticles, and by an increase in the abundance of spores at the same level. The Río de las Chinas Valley locality provides new evidence for the comprehensive study of the end-Cretaceous event, from the poorly represented continental environments of high southern latitudes.
Article
Full-text available
Theria represent an extant clade that comprises placental and marsupial mammals. Here we report on the discovery of a new Late Cretaceous mammal from southern Patagonia, Patagomaia chainko gen. et sp. nov., represented by hindlimb and pelvic elements with unambiguous therian features. We estimate Patagomaia chainko attained a body mass of 14 kg, which is considerably greater than the 5 kg maximum body mass of coeval Laurasian therians. This new discovery demonstrates that Gondwanan therian mammals acquired large body size by the Late Cretaceous, preceding their Laurasian relatives, which remained small-bodied until the beginning of the Cenozoic. Patagomaia supports the view that the Southern Hemisphere was a cradle for the evolution of modern mammalian clades, alongside non-therian extinct groups such as meridiolestidans, gondwanatherians and monotremes.
Article
The Adamantina Formation is the most extensive and taxonomically rich unity within the Bauru Group (Upper Cretaceous). This unity is considered one of the complete fossil records of vertebrate continental communities during the Cretaceous Gondwanan landmasses. However, this important fossil record is mainly based on large and articulated remains, and few works attempted to better understand its microvertebrate assemblages. This study reports a diverse microvertebrate assemblage from a new site in the Adamantina Formation in São Paulo, Brazil. The geological context in which the fossils were collected was analyzed, and all fossils were recovered in channel facies of the outcrop. The fossil assemblage described here includes elements commonly found in previous works in the Adamantina Formation, such as lepisosteiforms, amiids, dinosaurs, and crocodyliforms. But in this assemblage were also identified elements rarely recovered from Adamantina Formation, such as siluriforms, anurans, and a putative mammal. Furthermore, the taxa identified here indicate a humid environment, contributing to recognizing a diversity of paleoenvironments in the Adamantina Formation and highlighting the importance of microvertebrate assemblages to understanding the palaeoecological aspects of fossil communities.
Article
The end Cretaceous mass extinction was marked by a dramatic change in biodiversity, and the extinction of all non-avian dinosaurs. To understand the diversity of dinosaur clades prior to this event, as well as recovery by avian dinosaurs (birds), we need a better understanding of the global fossil record. However, the fossil record from southern localities, particularly southernmost (>60°S) South America, has only recently begun to be described. Discoveries from Patagonia are important to accurately assess global trends in dinosaur diversity, particularly during the latest Cretaceous before the Cretaceous/Paleogene (K/Pg) mass extinction event. Here we describe new theropod dinosaur specimens, representing both associated material and isolated elements, from Upper Cretaceous (Campanian-Maastrichtian) deposits of the Río de las Chinas Valley, Magallanes-Austral Basin, Chile. These discoveries include the southern-most known occurrences of several theropod clades outside of Antarctica, including megaraptorids, unenlagiines, enantiornithines and ornithurines. Notably, these remains provide much needed time-constrained records of smaller theropods, including birds, which are less often recovered from Upper Cretaceous deposits. While fragmentary, these fossils are the first records of theropods from Chilean Patagonia, and provide insight into the distribution of avian and non-avian theropods in southern high latitude ecosystems prior to the K/Pg mass extinction event. Sampling from this region is still sparse, and more fossils from age-controlled sections are needed to accurately assess global extinction dynamics through the end Cretaceous.
Article
Enantiornithes were the dominant avialan clade in the Mesozoic. However, their record for the Upper Cretaceous is scarce. In this study, we present and describe Yatenavis ieujensis gen. et sp. nov., one of the youngest occurrence of an enantiornithine bird. The specimen, the distal half of a right humerus, was found in Chorrillo Formation, southern Santa Cruz Province of Argentina, making it also the australmost enantiornithine specimen recorded to date. Yatenavis is unique among enantiornithines for its combination of characters, including a crest on the medial side of the shaft which bears a muscular scar cranially; the presence of a dorsal supracondylar process proximal to the dorsal epicondyle; equally distally projected dorsal and ventral condyles; and a rod-like caudal extension of the ventral condyle bearing a distal sulcus scapulotricipitalis. Several of these features are shared with an unnamed enantiornithine recovered from Upper Cretaceous beds in another fossil site in Patagonia.
Article
Full-text available
The fossil record of Cretaceous turtles in Santa Cruz Province is scarce. Turtles have been reported from the Mata Amarilla Formation (Cenomanian), the Cerro Fortaleza Formation (Campanian–Maastrichtian), and the Chorrillo Formation (early Maastrichtian). In this contribution, we examined all the turtle remains recovered from six localities in the Mata Amarilla Formation, nearby Mata Amarilla farm (Santa Cruz Province, Argentina). These fossils are housed at the “Padre Molina” Museum in Río Gallegos, Santa Cruz. Most of the carapace and plastral remains are conferred to an indeterminate small species of cf. Prochelidella sp., while the remaining fragments are attributed to a mid-sized species of an indeterminate Chelidae. Prochelidella spp. is a group of turtles distributed in Chubut, Río Negro, Neuquén, and Mendoza provinces, ranging fromthe Aptian to the Maastrichtian, with two main gaps (late Albian and Coniacian–Santonian). The recognition of cf. Prochelidella sp. in the Austral-Magallanes Basin extends the geographic range of this group more than 500 km south to the previously known southernmost record ofProchelidella, Pr. argentinae, from the Golfo San Jorge Basin (Chubut, Argentina).
Article
Calyptocephalella is nowadays only represented by the emblematic Chilean Helmeted Water Toad C. gayi, restricted to water bodies of Central Chile. Numerous fossil remains from latest Cretaceous to Miocene sedimentary rocks at the east of Los Andes have been attributed to this genus and several extinct Calyptocephalella species were erected. The relationships of these taxa, including the monophyly of the genus and the validity of some species, are however still unresolved. Here, we described a fossil anuran from the late Miocene of the northern Argentine Patagonia, which we attributed to a new extinct species of Calyptocephalella after analyzing the osteology and shared characters of all presumed species of the genus. These characters, whose co-occurrence seems to be exclusive of Calyptocephalella, include ornamented skull, extensive nasal processes contacting maxillae, broad nasal-frontoparietal contact, occipital artery enclosed by bone, maxilla contributing to the orbital margin and contacting squamosal, squamosal zygomatic and otic rami forming a continuous plate, scapula with a well-developed anterior lamina, and high iliac dorsal crest. The new species is differentiable in the proportion of the maxillary partes, triangular maxillary postorbital process, narrow maxillary contribution to the orbital margin; an oblique frontoparietal-squamosal suture. We also analyzed the putative morphological and ecological diversity of Calyptocephalella along the geological record, from which this fossil is nowadays the youngest and northernmost record east of Los Andes. We concluded that Calyptocephalella would be a successful lineage that inhabited Patagonia since, probably, the latest Cretaceous and during most of the Cenozoic, whose diversification might be related with the environmental changes that took place in southern South America during the these times, and from which C. gayi is only a vestigial representative.
Article
Few latest Cretaceous fossil floras are known for South America, and in particular for the Austral-Magallanes Basin. Recent studies carried out in the Chorrillo Formation (Maastrichtian) revealed a diverse array of fossil elements, including continental invertebrates, vertebrates, palynomorphs, fossil woods and leaf impressions. In this work, we describe the megafloristic elements identified in the unit from two fossiliferous levels, along with a palynological sample obtained from one such level. The first Mesozoic Nymphaeaceae (water lilies) remains for Argentina are reported, consisting of fragmentary leaves and seeds of a minute Nuphar-grade plant. Several leaf impressions referred to dicotiledonean and monocotiledonean morphotypes are also described. Additionally, microscopic remains reveal a diverse palynological assemblage containing terrestrial and aquatic ferns, conifers and angiosperms. A community that inhabited low energy, probably paludal, freshwater environments was identified, based on the sedimentology of the bearing strata such as the presence of hydromorphic paleosols and poorly decomposed organic matter suggesting poor drainage and eventual reducing and anoxic conditions, as well as the presence of Salviniaceae (water ferns), Marsileaceae (water-clovers), Nymphaeaceae and Zygnemataceae (freshwater conjugate algaes). Palynological elements suggest similarities with Campanian to Paleocene Patagonian units, mostly located in the Austral-Magallanes, Cañadón Asfalto and Golfo the San Jorge basins. Finally, aquatic communities from other Maastrichtian units (e.g. La Colonia and Lago Colhué Huapi formations) are compared with the Chorrillo Formation presented herein, suggesting similarities in functional groups even though taxa involved differ partially
Article
The Oligocene–early Miocene Tranquitas Formation in the southern Chaco foreland basin records the onset of Central Andean shortening. The aims of this contribution are to: (1) provide original data of the depositional conditions of the Tranquitas Formation, (2) to determine the role of tectonic and climate influence on the depositional conditions and on the composition of these deposits and (3) propose an evolutionary model of accumulation based on a sequence stratigraphic approach. The detailed analysis of these deposits resulted in the definition of six facies associations, including: complex sandy narrow sheets (FA1), sandy narrow sheets with lateral accretion surfaces (FA2), sandstone ribbons (FA3), tabular muddy-sandstone deposits (FA4), sandstone lobes (FA5), and fine-grained deposits (FA6). Based on the spatial distribution and the vertical stacking of these associations, the Tranquitas Formation was divided into two major intervals. Interval 1 (lower section) is characterized by braided fluvial deposits and represents low accommodation conditions with a high proportion of channel deposits. Interval 2 (upper section) tends to an increase in the accommodation space characterized by the better preservation of floodplain deposits in moderate to high sinuosity meandering fluvial systems. The integration of paleocurrent, petrography, and clay mineralogy analyses indicates that detrital components come from the orogenic region located to the west, in an overfilled stage of the foreland basin. Clay mineral assemblage analysis suggests a long-term climate change from drier to more humid conditions and reflects the climate effect on the depositional paleoenvironments developed in the distal position of the basin. In addition, the resultant vertical and lateral stacking of sedimentary sequences representing different paleoenvironments of the Tranquitas Formation could be correlated with the Oligocene–early Miocene Petaca and lower-Yecua formations located in the center and north of the Chaco foreland basin.
Article
Full-text available
Anurans, along with urodeles and caecilians are the extant representatives of the clade Lissamphibia. Nowadays, lissamphibians are widely distributed in all continents, except Antarctica, but are particularly diversified in South America, where almost 3,000 species are found. This huge biodiversity is directly related to the complex geologic history of South America, which includes key events like the Gondwanan breakup, its isolation during parts of Mesozoic and Cenozoic, the Andean uplift, and the formation of the Panamá isthmus. Here, we present the most comprehensive bibliographic review of fossil lissamphibians from South America to date, covering unpublished (e.g. theses and dissertations) and published data (i.e. peer-reviewed scientific papers, book chapters, monographs, and conferences abstracts). We used a mixed approach, both qualitative (with brief comments on each material) and quantitative (including scientometric parameters). Compared to the latest published reviews with similar scope, our results indicate that approximately 85.4% of the records correspond to specimens new to science or older ones that have been revisited. These materials come from 164 different fossil-bearing localities, spread over eight of the twelve South American countries, and range from the Early Jurassic to the Quaternary. In total, we compiled 273 records, mostly anurans (~97.6%), followed by indeterminate caecilians (~1.4%) and urodeles (~1%). Additionally, we discussed issues directly related to those fossil occurrences, such as their temporal and geographic range, as well as the presence of putative biological and taphonomic biases. Finally, we also provided calibration constraints for several anuran taxa.
Preprint
Full-text available
Megaraptorans are a theropod clade distributed in former Gondwana landmasses and Asia. Most members of the clade are known from early Cretaceous to Turonian times whereas Maastrichtian megaraptorans are known just from isolated and poorly informative remains. The aim of present contribution is to describe a partial skeleton of a megaraptorid coming from Maastrichtian beds at Santa Cruz province, Argentina. This new taxon constitutes the most informative megaraptoran from post-Turonian beds. Phylogenetic analysis nested the new taxon together with South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built. It is possible that the Cenomanian-Turonian extinction of carcharodontosaurids was allowed to megaraptorans to occupy the niche of top predators in South America.
Article
Studies on the environmental dynamics of high energy beach systems have to deal with factors as diverse as wave energy, coastal currents and tidal amplitude. Their interaction produces complex and often poorly understood sedimentary architectures. As a rule, the results achieved do not allow us to understand the depositional architectures associated with each of these processes. In this article, we analyze a high-energy beach system describing geometries, textures, paleocurrents, ichnological associations and taphonomic aspects seeking to define the associated environmental parameters. Detailed analyses of sedimentary facies, and analyses of paleocurrents, ichnological and taphonomic associations were performed in a high resolution sequence stratigraphy. The integrated analyses demonstrate the evolution of a high-energy beach system with a general north-south direction in a meso- to macrotidal regime, built by waves from the northwest, generating longshore currents to the south. A subordinate pattern, with waves coming from the southeast, generating longshore currents to the north, was also interpreted. Due to the high wave energy, evidence of tide action is sporadic, but the wide dominance of upper shoreface deposits with low angle dips, indicating an extension in the continent-offshore section, are compatible with a meso- to macrotidal setting. Taphonomic analysis shows that skeletons of marine invertebrates and vertebrates were significantly reworked and redistributed by strong wave action and longshore currents marking high energy events related to scour surfaces. Changes in the pattern of ichnofauna and bioturbation intensity are associated with variations in environmental energy and probably in salinity. The ichnological data helps to indicate progressive environmental stress towards the Cretaceous/Paleogene (K/Pg) boundary. Paleocurrent data, measured in trough cross-bedding of the upper shoreface deposits, suggest a complex atmospheric circulation pattern and water circulation of an inland sea. The resultant climatic pattern is compatible with modern atmospheric circulation at a similar latitude. The excellent exposure and abundant fossil records at K-Pg interval make this region an important source for studies of environmental dynamics and their interaction with biota at middle-high latitudes.
Article
Full-text available
A key event in the paleogeographic evolution of the Austral-Magallanes foreland basin was the Santonian-Maastrichtian continentalization, marked by the appearence of deltaic, fluvial and wetland sequences stacked on top of deep marine deposits. The expanding ecological niche was exploited by theropods and influenced the evolutionary history of dinosaurs. We present new detrital zircon U-Pb geochronological data across this littoral to continetnal depocenter, in order to provide insights of its age, geographical extension, source regions and geodynamic setting. Littoral sandstones from La Anita Formation yield Maximum Depositional Ages (MDA) between ~86-80 Ma (weighted mean ages), and ~79-78 Ma youngest zircons. Our results are in accordance with Santonian-Campanian depositional age. The sequence continues with badlands and fluvial systems (Cerro Fortaleza and La Irene Formations), followed by meandering fluvial and lacustrine deposits (Chorrillo Formation). Transgressive marine facies topping the sequence (Calafate Formation) yield a preferred Maastrichtian 69 ± 2 Ma MDA from the youngest zirzon. The provenance and tectonic analyses indicate that basin shallowing during Santonian-Campanian times was driven by advance of the orogenic front, which produced the shift from foredeep setting to a wedge-top depozone. The unroofing of progressively deeper structural levels is registered in the basin fill, which suggests exhumation in the Basement domain during the Santonian-Maastrichtian.
Article
Full-text available
In the last decades, several discoveries have uncovered the complexity of mammalian evolution during the Mesozoic Era, including important Gondwanan lineages: the australosphenidans, gondwanatherians, and meridiolestidans (Dryolestoidea). Most often, their presence and diversity is documented by isolated teeth and jaws. Here, we describe a new meridiolestidan mammal, Orretherium tzen gen. et sp. nov., from the Late Cretaceous of southern Chile, based on a partial jaw with five cheek teeth in locis and an isolated upper premolar. Phylogenetic analysis places Orretherium as the earliest divergence within Mesungulatidae, before other forms such as the Late Cretaceous Mesungulatum and Coloniatherium , and the early Paleocene Peligrotherium . The in loco tooth sequence (last two premolars and three molars) is the first recovered for a Cretaceous taxon in this family and suggests that reconstructed tooth sequences for other Mesozoic mesungulatids may include more than one species. Tooth eruption and replacement show that molar eruption in mesungulatids is heterochronically delayed with regard to basal dryolestoids, with therian-like simultaneous eruption of the last premolar and last molar. Meridiolestidans seem endemic to Patagonia, but given their diversity and abundance, and the similarity of vertebrate faunas in other regions of Gondwana, they may yet be discovered in other continents.
Article
Full-text available
Over the last 25 years, researchers, mostly paleontologists, have developed a system of rank-free, phylogenetically defined names for the primary clades of turtles. As these names are not considered established by the PhyloCode, the newly created nomenclatural system that governs the naming of clades, we take the opportunity to convert the vast majority of previously defined clade names for extinct and extant turtles into this new nomenclatural framework. Some previously defined names are converted with minor adjustments. We also define a number of new clade names to close apparent nomenclatural gaps. In total, we establish 113 clade names, of which 79 had already received phylogenetic definitions and 34 are new. ZooBank LSID: urn:lsid:zoobank.org:pub:43B418C2-BE9A-4BD5-91B7-8A9E0C8CB79D.
Article
Full-text available
Gondwanatheria is an enigmatic mammaliaform clade distributed in the Cretaceous and Paleogene of South America, Africa, Madagascar, India and Antarctica. The Mesozoic record in South America is restricted to the Latest Cretaceous of Río Negro and Chubut provinces, Argentina and Magallanes Region of southern Chile. The aim of the present contribution is to describe a new specimen of gondwanatherian mammaliaforms from beds belonging to the Maastrichtian Chorrillo Formation, cropping out 30 km SW of El Calafate, Santa Cruz Province, Argentina. It is represented by a single molariform referable to the species Magallanodon baikashkenke with which it shares a unique combination of characters. Analysis of the unique combination of characters exhibited by Magallanodon shed doubts on the monophyly of Ferugliotheriidae and suggest that South American taxa may be closely related to each other. The wide geographical distribution and occurrence of gondwanatherians on geological units of diverse origins suggest that they were capable of facing disparate environmental conditions.
Conference Paper
Full-text available
En el presente trabajo se dan a conocer nuevos fósiles de anuros colectados durante el presente año en la campaña paleontológica realizada en la localidad del Valle de Las Chinas, región de Magallanes, provenientes de rocas de la Formación Dorotea (Cretácico Superior). Los restos recuperados indican que existió una diversidad de anfibios en asociación con una fauna de microvertebrados. Localidad y Marco Geológico El área de estudio se sitúa en la localidad de Valle de Las Chinas, que cuenta hasta ahora con los únicos registros fósiles de anuros del Cretácico Superior en Chile (Suazo et al 2017). Esta se ubica en el sector NE de la Provincia de Última Esperanza, región de Magallanes, y presenta afloramientos de la Formación Dorotea (Campaniano superior-Maastrichtiano). El nivel portador se ubica en la sección inferior-media de la formación, y la litología asociada al nivel fosilífero corresponde a un estrato de 1 m de potencia de areniscas fangosas de color verde en roca fresca y pardo en roca alterada, con nódulos fosfáticos anaranjados. Hacia techo, se observan fangolitas grises con laminación paralela fina que infrayacen a areniscas de grano medio a grueso con estratificación cruzada, donde el contacto entre ambas está deformado por huellas de carga. El ambiente de depositación corresponde a un sistema fluvial meandriforme, específicamente a la llanura de inundación donde predomina la depositación por suspensión de los sedimentos finos (areniscas finas y pelitos en acreción vertical) que favorece la preservación de material de vertebrados de menor tamaño, entre ellos los anuros. Dataciones radiométricas en circones detríticos permiten asignar un rango de edad de 74,9±2,1 Ma – 71,7±1,2 Ma (Gutiérrez et al. 2017) para el nivel portador, ubicándolo en el límite Campaniano superior – Maastrichtiano inferior. 345 Materiales y Métodos Los materiales fueron colectados usando la técnica de picking y tamizado de sedimento con contenido fosilífero. La identificación fue realizada mediante la comparación con elementos óseos de anuros actuales y con fósiles depositados en la colección del Área de Paleontología del Museo Nacional de Historia Natural de Chile (MNHN, acrónimo SGO.PV.), colección osteológica de anfibios del Laboratorio de Zoología de Vertebrados de la Facultad de Ciencias de la Universidad de Chile (UCHZV), Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN-PV) y de la Fundación “Félix de Azara” de la Universidad Maimónides (CFA-AN). Resultados Los fósiles corresponden a restos desarticulados e incompletos correspondientes a fragmentos de húmeros y unas posibles radioulna y tibiofíbula. Húmero: Se colectaron cuatro epífisis distales, que pueden ser reconocidas debido a la presencia de una bola humeral (eminentia capitata), un cóndilo ulnar (entepicóndilo) y un cóndilo radial (ectepicóndilo). En tres de estas epífisis, el cóndilo ulnar posee un mayor desarrollo que el cóndilo radial y ambos no alcanzan el límite inferior de la bola humeral. Estos cóndilos no están expandidos lateral y medialmente, como sí ocurre en los materiales colectados el año 2017 asignados a la familia Calyptocephalellidae, el diámetro de la bola humeral supera el ancho distal de la epífisis. El estado de la cuarta epífisis es más fragmentario, Sin embargo, es posible observar rastros de la cicatriz de la posición de los cóndilos ulnar y radial. No es posible hacer una descripción más precisa de tal material. Tibiofíbula?: Fue colectada una diáfisis fragmentada que posee en uno de sus extremos rasgos de la acanaladura típica de este elemento en los anuros, sin embargo, se observa una estructura que se interpreta como un foramen nutricio, el que solamente aparece en la región media de la diáfisis de la tibiofíbula lo que permitiría su identificación anatómica, el material tiene un diámetro 2,63 mm, y aparentemente presenta un grado de osificación avanzado Radioulna?: Fue colectada otra diáfisis muy fragmentada que posee una marcada acanaladura en vista dorsal y ventral, sin embargo, tal acanaladura puede estar presente también en la tibiofíbula. Debido a lo anterior, el elemento se identifica preliminarmente como una radioulna. Discusión Hasta la fecha para el límite Campaniano-Maastrichtiano en el sur de Gondwana aparte de la localidad descrita en el presente trabajo, solo se conocen registros de anuros fósiles en la Fm. Allen (Martinelli & Forasiepi, 2004) y en la Fm. Los Alamitos (Baez, 1987) en Río Negro, Argentina, donde han sido descritos distintos elementos asignables a Calyptocephalellidae y Pipidae, sin embargo, la comparación anatómica con estos fósiles no permite asignar los elementos del Valle de Las Chinas a tales familias. Por otra parte, la comparación con esqueletos juveniles de Calyptocephalella gayi sugieren que la variación en la morfología de los cóndilos humerales no se debe a algún estadio más juvenil. En C. gayi en estadios muy tempranos del desarrollo ya es posible observar un desarrollo lateral y medial de los epicóndilos radial y ulnar, así mismo, la escasa osificación de la bola humeral genera que en 346 individuos preparados en esqueleto seco, tome una forma ovalada, no esférica como la que se observa en individuos subadultos o adultos. Conclusiones Los nuevos hallazgos, si bien sólo pueden ser referidos a un nivel taxonómico inclusivo, indican que en el Cretácico Superior del Valle de Las Chinas existieron al menos 2 taxa de anuros, planteando la necesidad de realizar nuevas campañas paleontológicas en la zona para buscar materiales más diagnósticos que permitan una asignación taxonómica más precisa. Agradecimientos Proyecto Fondecyt N°1151389, Proyecto Anillo N°172099. Referencias Báez, A. M., 1987. "The Late Cretaceous fauna of Los Alamitos, Patagonia, Argentina. Part III Anurans." Revista de Museo Argentino de Ciencas Naturales “Bernardino Rivadavia” - Paleontología 3(3): 121-130. Gutiérrez, N.M., Le Roux, J.P., Vásquez, A., Carreño, C., Pedroza, V., Araos, J., Oyarzún, J.L., Pino, J.P., Rivera, H.A. and Hinojosa, L.F., 2017. Tectonic events reflected by palaeocurrents, zircon geochronology, and palaeobotany in the Sierra Baguales of Chilean Patagonia. Tectonophysics, 695, pp.76-99. Martinelli, A. & Forasiepi, A.M., 2004. Late Cretaceous vertebrates from Bajo de Santa Rosa (Allen Formation), Rio Negro province, Argentina, with the description of a new sauropod (Titanosauridae). Rev. Mus. Argentino Cienc. Nat., n.s. 6(2): 257-305. Suazo Lara, F., Fernández-Jiménez, R., Soto-Acuña, S., Manríquez, L., Alarcón-Muñoz, J., Aravena, B., Vargas, A.O., Leppe, M. 2017. Primer registro de Calyptocephalellidae (Anura, Australobatrachia) en el Cretácico Superior de Chile. I Reunión de Paleontología de Vertebrados de Chile, Santiago, pp. 17.
Article
Full-text available
Abstract: Here we describe the spore and pollen assemblages recovered from the La Anita Formation, Late Cretaceous, Austral-Magallanes Basin (~50°S). This unit shows a high diversity of spores, with subordinate gymnosperms (mainly represented by Podocarpaceae) and angiosperms (mainly represented by Proteaceae and Arecaceae). The abundance of these groups varies between the two fertile studied levels, being one dominated by ferns (mainly Cyathidites minor and Laevigatosporites ovatus) and the other by gymnosperms (Podocarpidites spp.). The presence of aquatic ferns (Azollopsis), diverse Podocarpaceae and key angiosperm taxa (such as Arecipites, Clavatipollenites, Dichastopollenites, and Spinizonocolpites) is indicative of warm and hyper-humid conditions. The great abundance of Arecaceae and the presence of some key taxa (e.g. Azollopsis sp., Ericipites scabratus, Peninsulapollis gillii, Proteacidites spp.) support a probable Maastrichtian age for the uppermost strata of the La Anita Formation. The multivariate statistical analysis here conducted showed that the La Anita Formation has its greatest similarity with the La Irene Formation (Maastrichtian from the Austral-Magallanes Basin). Both formations are also related with other coeval palynofloras from Patagonia and Antarctica
Article
Full-text available
Temporary storage of sediment between source and sink can hinder reconstruction of climate and/or tectonic signals from stratigraphy by mixing of sediment tracers with diagnostic geochemical or geochronological signatures. Constraining the occurrence and timing of intrabasinal sediment recycling has been challenging because widely used detrital geothermochronology applications do not record shallow burial and subsequent reworking. Here, we apply strontium isotope stratigraphy techniques to recycled marine shell material in slope deposits of the Upper Cretaceous Tres Pasos Formation, Magallanes Basin, Chile. Detrital 87Sr/86Sr ages from 94 samples show that the majority (>85%) of the shells are >1–12 m.y. older than independently constrained depositional ages. We interpret the gap between mineralization age (87Sr/86Sr age) and depositional age of host strata to represent the intrabasinal residence time of sediment storage at the million-year time scale. We also use specimen type to infer relative position of intrabasinal source material along the depositional profile, where oysters represent shallow-water (i.e., proximal) sources and inoceramids represent deeper-water (i.e., distal) sources. The combined use of detrital strontium isotope ages and specimen types from linked depositional segments provides an opportunity to identify and quantify sediment storage and recycling in ancient source-to-sink systems.
Article
Full-text available
We describe Magallanodon baikashkenke gen. et. sp. nov., a new gondwanatherian mammal from the Late Cretaceous of the Magallanes Region in southern Chile (Río de Las Chinas Valley, Estancia Cerro Guido, north of Puerto Natales city, Última Esperanza Province). The mammal-bearing layer is placed within the Late Campanian-Early Maastrichtian levels of the Dorotea Formation (Magallanes/Austral Basin). The new remains constitute the southernmost record of a Mesozoic gondwanatherian mammal, as well as the frst Mesozoic mammal from Chile. This taxon is comparable in size to the hypsodont-toothed Gondwanatherium (Late Cretaceous) and Sudamerica (Early Paleocene) but with noticeably brachyodont molariforms supported by four to fve roots. As in other gondwanatherians, it has at least one hypertrophied, rodent-like incisor in the upper jaw. The new taxon is here diagnosed and described, and is regarded as a possible ferugliotheriid (?Ferugliotheriidae). If confrmed, it would represent the largest known taxon for this family. Its molariform occlusal crown pattern, after wear, resembles that of other gondwanatherians, particularly ferugliotheriids and that of the sudamericid Gondwanatherium. This adds new evidence on the phylogenetic proximity of ferugliotheriid and sudamericid gondwanatherians. An analysis of the enamel microstructure of the upper incisor of Magallanodon was performed demonstrating several crucial similarities with the pattern shown by Gondwanatherium (Sudamericidae). We discuss the signifcance of Magallanodon for understanding the acquisition, within gondwanatherians, of a lophed molariform pattern. Finally, we discuss the signifcance of the new fnding in the context of southern biotas, including those of Patagonia and Antarctica.
Article
Full-text available
Cenozoic ectothermic continental tetrapods (amphibians and reptiles) have not been documented previously from Antarctica, in contrast to all other continents. Here we report a fossil ilium and an ornamented skull bone that can be attributed to the Recent, South American, anuran family Calyptocephalellidae or helmeted frogs, representing the first modern amphibian found in Antarctica. The two bone fragments were recovered in Eocene, approximately 40 million years old, sediments on Seymour Island, Antarctic Peninsula. The record of hyperossified calyptocephalellid frogs outside South America supports Gondwanan cosmopolitanism of the anuran clade Australobatrachia. Our results demonstrate that eocene freshwater ecosystems in Antarctica provided habitats favourable for ectothermic vertebrates (with mean annual precipitation ≥900 mm, coldest month mean temperature ≥3.75 °C, and warmest month mean temperature ≥13.79 °C), at a time when there were at least ephemeral ice sheets existing on the highlands within the interior of the continent.
Article
Full-text available
The Austral-Magallanes is an oil-producing basin located in southern Argentina and Chile, containing a siliciclastic stratigraphic record ranging from the Late Jurassic to late Cenozoic. This short paper finalize the two special volumes of the Latin American Journal of Sedimentology and Basin Analysis dedicated to the basin, and aims to provide a comprehensive synthesis based on the current knowledge about the chronology of deposition, stratigraphy, and tectonic events that shaped this basin. During the breakup of Gondwana in the Jurassic, an extensional phase was responsible for the beginning of accumulation of volcaniclastic material within grabens, which subsequently were covered by widespread Lower Cretaceous shallow and deep marine deposits that conforms the main hydrocarbon system. From Late Cretaceous onward, the subduction-related compressive regime associated to Andean uplift and fold and thrust belt migration was responsible for the onset of the foreland stage. During the Late Cretaceous, the foredeep zone accumulated a thick pile of deep marine deposits that graded upward to shallow marine and terrestrial deposits. During the Cenozoic, the foredeep was less marked and shallow marine and terrestrial sediments accumulated in wide areas, punctuated by important unconformities associated to foreland uplift. Future developments should focus on: i) improving the age-controlled stratigraphy; ii) joining the information provided by subsurface and outcrop studies; and iii) developing source to sink models to address the Andean impact in the sedimentation of the basin. ARTICLE INFO Article history
Article
Full-text available
Pan-Chelidae (Testudines, Pleurodira) is a group of side-necked turtles with a currently disjointed distribution in South America and Australasia and characterized by two morphotypes: the long-necked and the short-necked chelids. Both geographic groups include both morphotypes, but different phylogenetic signals are obtained from morphological and molecular data, suggesting the monophyly of the long-necked chelids or the independent evolution of this trait in both groups. In this paper, we addressed this conflict by compiling and editing available molecular and morphological data for Pan-Chelidae, and performing phylogenetic and dating analyses over the individual and the combined datasets. Our total-evidence phylogenetic analysis recovered the clade Chelidae as monophyletic and as sister group of a clade of South American extinct chelids; furthermore Chelidae retained inside the classical molecular structure with the addition of extinct taxa in both the Australasian and the South American clades. Our dating results suggest a Middle Jurassic origin for the total clade Pan-Chelidae, an Early Cretaceous origin for Chelidae, a Late Cretaceous basal diversification of both geographic clades with the emergence of long-necked lineages, and an Eocene diversification at genera level, with the emergence of some species before the final breakup of Southern Gondwana and the remaining species after this event.
Article
Full-text available
The first fossil remains of vertebrates, invertebrates, plants and palynomorphs of the Chorrillo Formation (Austral Basin), about 30km to the SW of the town of El Calafate (Province of Santa Cruz), are described. Fossils include the elasmarian (basal Iguanodontia) Isasicursor santacrucensis gen. et sp. nov., the large titanosaur Nullotitan glaciaris gen. et sp. nov., both large and small Megaraptoridae indet., and fragments of sauropod and theropod eggshells. The list of vertebrates is also composed by the Neognathae Kookne yeutensis gen. et sp. nov., two isolated caudal vertebrae of Mammalia indet., and isolated teeth of a large mosasaur. Remains of fishes, anurans, turtles, and snakes are represented by fragmentary material of low taxonomical value, with the exception of remains belonging to Calyptocephalellidae. On the other hand, a remarkable diversity of terrestrial and freshwater gastropods has been documented, as well as fossil woods and palinological assemblages. The Chorrillo Formation continues south, in the Las Chinas River valley, southern Chile, where it is called Dorotea Formation. Both units share in their lower two thirds abundant materials of titanosaurs, whose remains cease to appear in the upper third, registering only elasmarians (Chorrillo Formation) and hadrosaurs (Dorotea Formation). Above both units there are levels with remains of invertebrates and marine reptiles. It is striking that the dinosaurs of the lower two thirds of the Chorrillo and Dorotea formations are represented by large basal titanosaurs and Megaraptoridae coelurosaurs, being the Saltasaurinae and Aeolosaurinae sauropods and Abelisauridae theropods totally absent. In contrast, these taxa are dominant components in sedimentary units of central and northern Patagonia (e.g., Allen, Los Alamitos, La Colonia formations). Such differences could reflect, in part, a greater antiquity (i.e., late Campanian-early Maastrichtian) for the Chorrillo fossils, or, more probably, different environmental conditions. Thus, knowledge of the biota of the southern tip of Patagonia is expanded, particularly those temporarily close to the K-Pg boundary.
Article
Full-text available
The Maastrichtian shallow marine deposits exposed at the south margin of the Lago Argentino within the Austral-Magallanes Basin are known as the Calafate Formation. In order to interpret the depositional systems and reconstruct the sequence stratigraphic architecture for this unit at its type locality (Cerro Calafate), we acquire new data from seven stratigraphic sections. We recognized six facies associations (FA-1 to FA-6) corresponding to shallow marine deposits, which are organized vertically displaying a transition from shallower to deeper conditions, representing a ~90 m thick transgressive succession. The Calafate Formation deposits are differentiated into a lower wave-dominated coast (FA1, FA2 and FA3) and an upper tide-dominated coast (FA4, FA5 and FA6), each marked by the dominance of wave and tidal sedimentary processes, respectively. The Calafate Formation overlies the fluvial deposits of the Chorrillo Formation by a transgressive surface (TS), which is overlaid by a transgressive marine succession characterized by a retrogradational stacking pattern. The latter is finally covered by offshore transition marine deposits marking a progressive deepening of the depositional system that culminates with the maximum flooding surface (MFS). From here, an aggradational stacking pattern dominates the upper sandstones of the unit representing the highstand systems tract (HST), which is interpreted to be the cause of short-term periods when the accommodation space rate was nearly equaled to the sediment supply rate during the Maastrichtian.
Article
Full-text available
The sedimentary infill of the Austral-Magallanes Basin since the onset of its foreland stage in the Lago Argentino region is dominated by deep-marine and coastal deposits. However, during the Late Cretaceous the basin accumulated a thick and poorly known continental sedimentary succession, which has received different lithostratigraphic names. The aim of this work is to characterize the here defined Uppermost Cretaceous Continental Deposits (UCCD) from a detailed facies and architectural analysis, as well as the resulting stacking pattern. Seven Facies Associations (FAs) were discriminated in order to define the sedimentary paleoenvironments: FA1, gravelly sheet bodies; FA2, tabular bodies of conglomerates with mud rip-up clasts; FA3, complex tabular sandy bodies; FA4, simple tabular sandy bodies; FA5, tabular bodies of structureless sandstones; FA6, heterolithic deposits; and FA7, fine-grained deposits. Three different fluvial styles were recognized: meandering systems dominated by avulsion and meander abandonment processes (fluvial style a), braided systems (fluvial style b), and meandering systems dominated by overbank flood processes (fluvial style c). The stacking pattern of the FAs allowed to divide the UCCD into two major depositional stages related to the accommodation space vs sediment supply (A/S) ratio. Stage I is characterized by the alternation of fluvial styles a and b, while the Stage II is represented by the alternation of fluvial styles c and b, and the Stage III is characterized entirely by fluvial style c deposits. Although the UCCD are considered as a whole within a framework of low A/S ratio, several high frequency variations were recognized. The Stage I records seven high frequency intervals of which four are characterized by high A/S ratio interrupted by three events of low A/S. While the stage II is represented by six high frequency periods of low A/S ratio and other five high frequency events of high A/S ratio. The Stage II is considered as deposited in a relative higher A/S context in comparison with the Stage I, based on the behavior of the moderate to high sinuosity meander fluvial systems. Finally, the Stage III is represented entirely by a high frequency low A/S ratio event.
Article
Full-text available
The aim of the present contribution is to describe a new genus and species of Pipoidea from the Huitrera Formation (Eocene) from Patagonia, Argentina. The new genus shows a unique combination of characters indicating that it is a valid taxon different from other pipimorphs, including the coeval Llankibatrachus truebae. The phylogenetic analysis resulted in the nesting of the new taxon within a previously unrecognized endemic clade of South American aglossans. This new clade turns out to be the sister-group of crown-group Pipidae. This phylogenetic proposal reinforces the hypothesis sustaining the dispersal of pipids between Africa and South America through an island chain or a continental bridge across the Atlantic Ocean by Early Tertiary times.
Conference Paper
Full-text available
Se presentan los resultados del estudio de improntas foliares fósiles provenientes de las Formaciones Tres Pasos y Dorotea (Cretácico superior). Se incorporan detalles de la determinación taxonómica, tales como los caracteres morfológicos y patrones de venación diagnósticos. Las comparaciones permiten asignar estas improntas al género Brachychiton. Este hallazgo representa el registro más antiguo (Campaniano superior y Maastrichtiano inferior) del género a nivel global y el primer registro para Sudamérica.
Article
Full-text available
Talenkauen santacrucensis represents one of the most complete South American ornithopods yet discovered. This dinosaur comes from the Mata Amarilla Formation (Turonian) of Santa Cruz Province, Argentina. The aim of this contribution is to present a detailed description of Talenkauen santacrucensis. Features of the cervical series of Talenkauen, which are shared with other elasmarians, indicate that these dinosaurs have a proportionally longer neck than other ornithopods. These traits were convergently acquired by several saurischian clades. Additionally, some features, including an ornamented labial surface of the mandibular teeth and a sigmoidal greater trochanter of femur, are traits shared by most elasmarians, and may prove to be synapomorphies of this clade. A phylogenetic analysis recovers most Cretaceous Gondwanan ornithopods in the clade Elasmaria. This analysis indicates that Elasmaria was distributed more widely geographically and temporally than previously thought.
Article
Full-text available
Coastal depositional systems are commonly classified in terms of the relative interaction of wave, tide and fluvial processes. The La Anita Formation represents the opportunity to study and better understand coastal sedimentary systems. It is a poorly studied prograding siliciclastic deltaic-coastal wedge accumulated in the Campanian during the foreland stage of the Austral-Magallanes Basin. A detailed depositional process-based facies analysis have allowed the definition of 13 sedimentary facies and 9 facies associations for the La Anita Formation, ranging from prodelta to interdistributary delta-channel deposits. According to the spatial distribution of these facies associations, the La Anita Formation was divided into two informal units bounded by a regional erosion surface. The lower unit shows abundant hummocky cross-bedded and bioturbated sandstones, coarsening-upward trends and mainly aggradational to progradational vertical stacking pattern, and it was interpreted as a wave-dominated fluvial-influenced delta. The upper unit is characterized by unidirectional dune cross-bedding, coarsening-upward trend and a progradational vertical stacking pattern, and was interpreted as a fluvio-dominated delta with no evidence of tide or wave influence. These two units represent two genetically unrelated depositional sequences bounded by a regional erosion surface, which is interpreted as a sequence boundary triggered by a relative sea-level fall. The lower unit is part of a progradational highstand systems tract which involves the underlying deep-marine Alta Vista Formation. The upper unit contain deposits that reflect a complete relative sea-level cycle which includes an undifferentiated lowstand and transgressive systems tracts deposits and, toward the top, highstand systems tract deposits.
Article
Full-text available
The fossil record of Late Cretaceous–Paleogene modern birds in the Southern Hemisphere includes the Maastrichtian Neogaeornis wetzeli from Chile, Polarornis gregorii and Vegavis iaai from Antarctica, and Australornis lovei from the Paleogene of New Zealand. The recent finding of a new and nearly complete Vegavis skeleton constitutes the most informative source for anatomical comparisons among Australornis, Polarornis, and Vegavis. The present contribution includes, for the first time, Vegavis, Polarornis, and Australornis in a comprehensive phylogenetic analysis. This analysis resulted in the recognition of these taxa as a clade of basal Anseriformes that we call Vegaviidae. Vegaviids share a combination of characters related to diving adaptations, including compact and thickened cortex of hindlimb bones, femur with anteroposteriorly compressed and bowed shaft, deep and wide popliteal fossa delimited by a medial ridge, tibiotarsus showing notably proximally expanded cnemial crests, expanded fibular crest, anteroposterior compression of the tibial shaft, and a tarsometatarsus with a strong transverse compression of the shaft. Isolated bones coming from the Cretaceous and Paleogene of South America, Antarctica, and New Zealand are also referred to here to Vegaviidae and support the view that these basal anseriforms were abundant and diverse at high southern latitudes. Moreover, vegaviids represent the first avian lineage to have definitely crossed the K–Pg boundary, supporting the idea that some avian clades were not affected by the end Mesozoic mass extinction event, countering previous interpretations. Recognition of Vegaviidae indicates that modern birds were diversified in southern continents by the Cretaceous and reinforces the hypothesis indicating the important role of Gondwana for the evolutionary history of Anseriformes and Neornithes as a whole.
Article
Full-text available
Deciphering depositional age from deposits that accumulate in deep-water slope settings can enhance understanding of shelf-margin evolutionary timing, as well as controlling mechanisms in ancient systems worldwide. Basin analysis has long employed biostratigraphy and/or tephrochronology to temporally constrain ancient environments. However, due to poor preservation of index fossils and volcanic ash beds in many deep-water systems, deducing the timing of slope evolution has proven challenging. Here, we present >6600 new U-Pb zircon ages with stratigraphic information from an ∼100-km-long by ∼2.5-km-thick outcrop belt to elucidate evolutionary timing for a Campanian−Maastrichtian slope succession in the Magallanes Basin, Chile. Results show that the succession consists of four stratigraphic intervals, which characterize four evolutionary phases of the slope system. Overall, the succession records 9.9 ± 1.4 m.y. (80.5 ± 0.3 Ma to 70.6 ± 1.5 Ma) of graded clinoform development punctuated by out-of-grade periods distinguished by enhanced coarse-grained sediment bypass downslope. Synthesis of our results with geochronologic, structural, and stratigraphic data from the basin suggests that slope evolution was largely controlled by an overall decline in basin subsidence from 82 to 74 Ma. In addition to providing insight into slope evolution, our results show that the reliability of zircon-derived depositional duration estimates for ancient sedimentary systems is controlled by: (1) the proportion of syndepositionally formed zircon in a stratigraphic interval; (2) the magnitude of the uncertainty on interval-bounding depositional ages relative to the length of time evaluated; and (3) the geologic time (i.e., period/era) over which the system was active.
Article
Full-text available
Finer-grained components of fluvial sediments are usually deposited in overbank environments, and their preservation in the rock record is generally subordinate to that of the coarser-grained channel fills. However, though the fossil record and lithological characteristics of the Late Triassic Maleri Formation, Gondwana Supergroup of the Pranhita-Godavari continental rift basin, India, indicate that it is a fluvial deposit, the formation is characterized by thin sandstone bodies vertically separated by thicker fine-grained sediments. With the help of petrographic and sedimentological features, this study characterizes the fluvial system that produced a deposit dominated by fines. These syn-rift sediments provide valuable clues towards understanding the spectrum of fluvial processes operating in continental rift-basins. We observe that the formation is dominated by stratified siltstone (mudrocks) rather than massive mudstones. These mudrocks contain a large quantity of silt to fine-sand-size pedogenic mud aggregates, and the preserved primary structures indicate transportation by traction currents. The internal organization of the mudrock units reveals that an admixture of pedogenic mud aggregates along with other sand-grade siliciclastic grains were transported through the channelized and unconfined reaches of a network of discontinuous ephemeral streams constituting the axial drainage of the rift basin. However, evidence for accumulation of fines in swamp-like environments is preserved in a few pedogenically modified mudstones that occur in between much thicker intervals of stratified mudrocks. On the other hand, the small bodies of cross-bedded carbonate grainstones and laminated marls indicate that the conditions suitable for precipitation of freshwater carbonates prevailed in some of these swampy areas. The sedimentary features of the thinner sheet-sandstone bodies associated with the mudrocks suggest that though the overall character of the fluvial system remained unchanged the sandstones were deposited during the phases of higher discharge. We suggest that the basin was persistently fed with a sediment load rich in mud aggregate produced in the vertic soils forming on the shales and limestones in the source area under a warm climate and seasonal rainfall.
Article
The fossil record of gondwanatherian mammaliaforms from Patagonia is represented by several species known on the basis of isolated teeth, with the single exception of a partial dentary with two molariforms of the Paleocene species Sudamerica ameghinoi. The aim of the present contribution is to describe both a fragmentary dentary (with the base of the lower incisive) and a partial upper incisor coming from the Campanian–Maastrichtian Chorrillo Formation, at the La Anita Farm, SW Santa Cruz province, Argentina. The specimens are referred to Magallanodon baikashkenke, a species previously known by isolated teeth from the Dorotea (Chile) and Chorrillo (Argentina) beds. The present discovery expands our knowledge of this mammaliaform clade.
Article
The changes in the geometry, density and distribution of the fluvial reservoir sand-bodies have been modelled both in the laboratory and from outcrop analogues. On the other hand, fine-grained floodplain deposits, often called “background” sedimentation, have not been in the spotlight. However, they provide a very important database for fluvial architecture reconstruction and therefore constitute a key tool in characterizing, correlating and modelling heterogeneous fluvial reservoirs. The methodology used in this work combines classical sedimentological and palaeopedological data. Palaeosols were identified in outcrops of the Cretaceous of Patagonia and Triassic red beds of Spain based on the main pedofeatures such as colour, soil structures, mottles, nodules, clay illuviation cutans, slickensides and rhizoliths. Palaeosol horizons, thickness and types of contact were described. The palaeosols classification was made through the comparison with the Soil Taxonomy. For the characterization of lateral palaeosols variability, several palaeopedological logs were constructed following the same stratigraphic level at both margins of the main channels. Small-scale or high-frequency palaeosol variations, identified in both fluvial succession are represented by the lateral and vertical superimposition of Inceptisols/Entisols, Vertisols and hydromorphic Vertisols/swamp deposits. We recognized a decrease in the drainage conditions within the palaeosols catena moving away from the main channel bodies. The most waterlogged palaeosol is located at 200 to 300 m from the main channels. Lateral changes of palaeosols are interpreted as the result of intrinsic factors to the depositional systems, such as the relative position within the floodplain and the distance from the main channels, that condition the particle size of parent material, the sedimentation rate and the palaeotopographic position which state the drainage conditions of palaeosols. Vertical stacking of different palaeosols is linked to avulsion processes and the relatively abrupt change in the distance to main channels as the system aggraded. The study of these two environmentally similar examples (low-gradient meandering fluvial systems subjected to a high rate of aggradation), although located in different tectonic and chronostratigraphic contexts, shows that the type of fluvial system acted as the main control of sedimentary and pedogenic processes; as well as the scale at which they occur. Thus, when choosing an outcrop fluvial reservoir analogue, the type of fluvial system and climate should be more important than the age or the tectonic framework of the succession to be studied.
Article
The fossil record of ornithischians in South America is sparse, and they are clearly underrepresented when compared with sauropod dinosaurs. However, recent discoveries indicate that ornithischians were more diversified than thought. The aim of the present contribution is to describe isolated remains belonging to ankylosaurs, and ornithopods, including basal euiguanodontians and hadrosaurs coming from the Chorrillo Formation (upper Campanian–lower Maastrichtian), Santa Cruz province, southern Argentina. The fossil remains of ankylosaurs reported here are the southernmost recorded for the continent. They show a unique combination of plesiomorphic features, indicating that they may belong to a basal ankylosaur. Ankylosaurs and hadrosaurids are thought to have arrived in South America during the latest Cretaceous through Central America. However, a detailed overview of the fossil record of Gondwana indicates that both clades were present and probably diversified along southern continents. This indicates that their presence in South America may be alternatively interpreted as the result of migration from other landmasses, including Africa and Europe, or may even be the result of Jurassic–Early Cretaceous vicariance from their northern counterparts.
Article
Fluvial sandstones deposited by high-sinuosity fluvial systems are one of the most complex reservoirs to predict and model with confidence, a reflection of both the geometries and complex distribution of the component geobodies. By integrating both analogue outcrop data and associated subsurface data, as well as new technical advances in the reconstruction of the outcrop in 3D (Digital Outcrop Models, DOM), the geostatistical parameters, which condition the modelling of these reservoirs, can be better determined. In addition, DOMs also allow us to easily extract the necessary georeferenced input data (digitized outcrop interpretations, geometrical parameters, as well as key surfaces) and so create geocellular outcrop models (GOM); a useful tool with which to contrast the results obtained from geostatistical simulations, as well as to quantify the uncertainty associated with the results. In this study, classical field data, digital data derived from outcrop models and subsurface data were combined in order to carry out a geostatistical modelling of a Channel – Crevasse-splay complex outcrop analogue, located in the Triassic Red Beds of Iberian Meseta (TIBEM). Geostatistical modelling results were obtained by combining Object-based (OBM) and MultiPoint Statistics-based (MPS) modelling techniques. A critical element in this study was the design of appropriate modelling workflows with Petrel® which would best reproduce the distribution of heterogeneities at macroscale. The designed modelling workflow was used to construct a 3D Training Image (TI) of a fluvial reservoir comprising both a meandering channel system and its associated overbank sandstone deposits. The resulting TI represents all geobodies described in the studied outcrop example and is exportable to similar fluvial reservoirs. This TI was then used in MPS simulations, in order to establish how it could assist in the prediction of the reservoir geobodies, as well as confirming to what extent this prediction matched the outcrop.
Article
A fossil gastric pellet from the Danian 'Banco Negro Inferior' of the Salamanca Formation at Punta Peli-gro Locality (Chubut, Argentina) and its 3D preserved fossil content is studied herein. The structure of the pellet and the condition of the enclosed bones suggest that it was produced by a bird of prey, although birds of any kind are as yet unknown from osteological remains in the Banco Negro ecosystem. The content of the pellet originated from a single anuran individual, representing a new species of the genus Calyptocephalella, is described herein as C. sabrosa sp. nov. The new find highlights the broad temporal, geographical and taxonomic diversity of this frog genus in Patagonia's geological past.
Article
We describe remains of freshwater turtles from the Upper Cretaceous of Chilean Patagonia. The fossils, which comprise isolated shell fragments and incomplete appendicular bones, were recovered from meandering fluvial deposits of the Dorotea Formation (upper Campanian–Danian), in the Río de Las Chinas Valley, Magallanes region. These remains represent the first records of Upper Cretaceous pan-chelid pleurodiran turtles in the Magallanes-Austral Basin. The shell fragments show a strong ornamentation of irregular polygons distributed over their entire dorsal surface, and one of the peripheral plates is narrow and elongated. These features are consistent with traits described in Yaminuechelys, a chelid genus from the Upper Cretaceous and Paleogene of Argentinian Patagonia. In addition, the suprapygal plate presents sulci that mark the limits of the vertebral scute 5 and the marginal scutes 12 as in Yaminuechelys sulcipeculiaris. This finding represents the southernmost record of a species conferred to Yaminuechelys, extending the distribution of this genus to the Magallanes-Austral basin during the Campanian–Maastrichtian.
Article
Exploration and production from formations deposited in low‐gradient fluvial systems is typically associated with a high degree of uncertainty; a reflection of the inherent characteristics of these environments, notably the dominance of non‐reservoir floodplain fines, rapid lateral facies variations and associated heterogeneities at different scales. However, for a field development to be successful it becomes crucial to know the location, geometry, dimensions and connectivity of the most permeable facies, related to the main channel and the associated proximal overbank deposits (crevasse‐splay complexes). With the aim of addressing this problem, a multi‐disciplinary study is presented, combining outcrop data, high‐resolution sedimentological descriptions and advanced visualization techniques based on Digital Outcrop Models. This is compared with subsurface data from behind the outcrop (core, gamma ray and borehole images logs). The Mudstone–Sandstone Unit of the Triassic Red Beds of Iberian Meseta formation in south‐central Spain was selected for the present study. The unit is characterized by the lateral and vertical stacking of four architectural elements: (i) channelized sandstone bodies; (ii) asymmetrical sigmoidal‐shaped sandstone bodies; (iii) lobe‐shaped to sheet‐like sandstone bodies; and (iv) sheet‐like mudstones. These elements represent meandering channel, crevasse‐channel‐splay and floodplain sub‐environments, comprising a distal, low‐gradient meandering fluvial system. Together with well‐documented outcrop and core facies, calibrated log responses are also presented for the channel bodies (bell‐shape Gamma Ray profile, random azimuths and low to high dip angles), the crevasse‐splay bodies (funnel‐shape Gamma Ray profile, unidirectional azimuths and low dip angles) and the floodplain deposits (serrated Gamma Ray profile, unidirectional azimuths and very low dip angles). The full integration of outcrop and subsurface datasets has enabled generation of a robust conceptual model with predictive potential when establishing the three‐dimensional stacking of facies, distribution of heterogeneities and the connectivity between reservoir rock geobodies of primary (channel) and secondary (crevasse complex) interest in this type of fluvial reservoir.
Article
The Maastrichtian-Danian transgression was one of the most extensive Atlantic-derived marine incursions in Patagonia. This study examines its stratigraphic record and origin in the Magallanes-Austral Basin, revealing an interplay of sedimentation, tectonism, and base-level changes, which contribute to our understanding of foreland basin dynamics. We present a multidisciplinary approach from a relatively poorly documented sector (51°38’-53°50’S) of the basin. This approach includes facies and provenance analysis, palynology, sequence stratigraphy, and U-Pb geochronology. These techniques enable us to evaluate the role of climate, tectonics, and eustasy on the transgression, as well as providing insight into the growth of the Southern Patagonian Andes. A first shallowing-upward cycle (late Campanian to late Maastrichtian) is represented by the transition from outer shelf and upper slope deposits (Fuentes and Tres Pasos formations) to shoreface and deltaic environments (Rocallosa and Dorotea formations), favoured by high erosion rates in the fold-thrust belt and eustatic sea-level drop. A subsequent deepening-upward cycle (late Maastrichtian to Paleocene) records the Atlantic transgression, manifested by estuarine deposits in an incised valley (uppermost Dorotea Formation) and deep-water turbidites (Chorrillo Chico Formation and Cabo Naríz beds). Palynological results suggest a temperate palaeoclimate (~6-17°C) during the Maastrichtian-Danian, which agrees with significant cooling of the South Atlantic Ocean at this time. Therefore, relative climatic optima are not a driver of marine ingression. The stratigraphic and tectonic evolution of the succession studied suggests that flexural and dynamic subsidence promoted marine incursion into the Magallanes-Austral Basin. Provenance data indicate sediment input to the basin from the Southern Patagonian Batholith, Rocas Verdes Basin remnants, Tobífera Formation, and metamorphic terranes exposed in the hinterland of the Southern Patagonian Andes during the early Maastrichtian. However, by the Paleocene, sediments derived from the hinterland had been structurally dammed during basinward propagation of the fold-thrust belt.
Article
The holotype of the elasmosaurid Aphrosaurus furlongi from the Maastrichtian levels of the Moreno Formation is redescribed and considered a valid species based on one autapomorphy, a deep trough in the ventral surface of vertebral centra of the posterior cervicals, and the following combination of features: wide and short clavicle-interclavicle complex with concave anterior border and without posterior medial process or medial ventral keel, humerus with anterior depression, and posterior limb with accessory element on the posterior margin. The phylogenetic analysis recovered A. furlongi as an elasmosaurid within Weddellonectia. The phylogenetic analysis generated a new topology of Elasmosauridae. A new clade, Euelasmosaurida, is recovered, including all post-Cenomanian elasmosaurids other than Zarafasaura oceanis. Euelasmosaurida is composed of two main clades: Elasmosaurinae and Weddellonectia. The latter includes mostly Weddellian elasmosaurids, including Aristonectinae. Based on the new phylogenetic results, the evolution of key cranial and postcranial characters is discussed. Two key intervals of elasmosaurid evolutionary history are recognized: the Cenomanian, with the appearance of Euelasmosaurida, and the Santonian, with the differentiation of Weddellonectia and Elasmosaurinae.
Article
In terminal fluvial‐fan systems, characteristic proximal to distal variations in sedimentary architectures are recognized to arise from progressive downstream loss of water discharge related to both infiltration and evaporation. This work aims to elucidate downstream trends in facies and architecture across the medial and distal zones of terminal‐fan systems, which record transitions from deposits of channel elements to lobe‐like and sheet‐like elements. This is achieved via a detailed characterization of ancient ephemeral fluvial deposits of the well‐exposed Kimmeridgian Tordillo Formation (Neuquén Basin, Argentina). The fine sand‐prone and silt‐prone succession associated with the medial to distal sectors of the system has been studied to understand relationships between depositional processes and resulting architectures. Facies and architectural‐element analyses, and quantification of resulting sedimentological data at multiple scales, have been undertaken to characterize sedimentary facies, facies transitions, bed types, architectural elements and larger‐scale architectural styles. Eight bed types with distinct internal facies transitions are defined and interpreted in terms of different types of flood events. Channelized and non‐channelized architectural elements are defined based on their constituent bed types and their external geometry. The most common elements are terminal lobes, which are composite bodies within which largely unconfined sandy deposits are stacked in a compensational manner; a hierarchical arrangement of internal components is recognized. Proximal feeder‐channel avulsion events likely controlled the evolution of terminal‐lobe elements and their spatiotemporal shifts. Stratigraphic relations between architectural elements record system‐wide trends, whereby a proximal sector dominated by channel elements passes downstream via a gradational transition to a medial sector dominated by sandy terminal‐lobe elements, which in turn passes further downstream to a distal sector dominated by silty terminal lobe‐margin and fringing deposits. This work enhances current understanding of the stratigraphic record of terminal fluvial systems at multiple scales, and provides insight that can be applied to predict the facies and architectural complexity of terminal fluvial successions.
Article
The Magallanes-Austral retroarc foreland basin of southernmost South America presents an excellent setting in which to examine interpretive methods for large detrital zircon data sets. The source regions for retroarc foreland basins generally, and the Magallanes-Austral Basin specifically, can be broadly divided into (1) the magmatic arc, (2) the fold-and-thrust belt, and (3) sources around the periphery of foreland flexural subsidence. In this study, we used an extensive detrital zircon data set (30 new, 87 previously published samples) that is complemented by a large modal provenance data set of 183 sandstone petrography samples (32 new, 151 previously published) and rare earth element geochemical analyses (130 previously published samples) to compare the results of empirical (multidimensional scaling) and interpretive (age binning based on source regions) treatments of detrital zircon data, ultimately to interpret the detailed evolution of sediment dispersal patterns and their tectonic controls in the Magallanes-Austral Basin. Detrital zircon sample groupings based on both a priori age binning and multidimensional scaling are required to maximize the potential of the Magallanes-Austral Basin data set. Multidimensional scaling results are sensitive to differences in major unimodal arc-related U-Pb detrital zircon ages and less sensitive to differences in multimodal, thrust belt–related age peaks. These sensitivities complicate basin-scale interpretations when data from poorly understood, less densely sampled sectors are compared to data from better-understood, more densely sampled sectors. Source region age binning alleviates these biases and compares well with multidimensional scaling results when samples from the less well-understood southern basin sector are excluded. Sample groupings generated by both multidimensional scaling and interpretive methods are also compatible with compositional provenance data. Together, this integration of provenance data and methods facilitates a detailed interpretation of sediment dispersal patterns and their tectonic controls for the Late Cretaceous to Eocene fill of the Magallanes-Austral retroarc foreland basin. We interpret that provenance signatures and dispersal patterns during the retroarc foreland phase were fundamentally controlled by conditions set by a predecessor extensional basin phase, including (1) variable magnitude of extension with latitude, (2) the composition of lithologies emplaced on the antecedent western flank, and (3) long-lasting structural discontinuities associated with early rifting that may have partitioned dispersal systems or controlled the location of long-lived drainage networks.
Article
The Magallanes-Austral foreland basin preserves an important record of orogenesis and landscape evolution in the Patagonian Andes of Chile and Argentina. Throughout the retroarc foreland basin, a regional disconformity with little to no angular discordance separates Upper Cretaceous–lower Paleocene strata from overlying deposits of diachronous Eocene to Miocene age. Here we report detrital zircon U-Pb geochronological results for 11 sandstone samples, and vitrinite reflectance data for 6 samples of organic matter from a fossiliferous dinosaur-bearing marine and nonmarine clastic succession in the Río de las Chinas valley (50–51°S) of central-southern Patagonia to: (1) determine the timing and duration of the unconformity using U-Pb maximum depositional age constraints, (2) reconstruct sediment provenance and dispersal patterns, (3) assess possible temporal variations in arc magmatism, (4) evaluate the amount of sedimentary overburden removed during unconformity development, and (5) confirm the presence of a fossiliferous southern hemisphere Cretaceous–Paleogene (K/Pg) boundary site. Samples from the Dorotea Formation yield maximum depositional ages spanning Maastrichtian to Danian time (with ages as young as ∼65–63 Ma), confirming preservation of the K/Pg boundary in a section with recently discovered fossils of dinosaurs, other terrestrial vertebrates, and plants. Samples from directly above the unconformity in the Man Aike Formation, yield middle Eocene maximum depositional ages (with a prominent 45–40 Ma age cluster), indicating a long-lived ∼20 Myr hiatus representative of nondeposition or erosion. Analyses of organic matter preserved in multiple coal horizons of the uppermost Dorotea Formation show consistently low vitrinite reflectance values, requiring limited sedimentary burial, consistent with nondeposition or sediment bypass rather than deposition and later erosional removal of a previously proposed thick package of Paleocene to middle Eocene clastic material. On the basis of regional trends in the age and geometry of the unconformity, timing of arc magmatism, and temporal variations in sediment provenance, we consider a range of potential mechanisms for unconformity genesis, including (1) shortening-related uplift of the frontal fold-thrust belt, (2) cratonward advance of a flexural forebulge, (3) accommodation changes driven by regional or eustatic variations in sea level, (4) ridge collision and slab-window genesis, (5) isostatic rebound during tectonic quiescence (or minor extension), or (6) regional foreland uplift during flat-slab subduction.
Article
The stratigraphic architecture and environmental evolution of the Cerro Guido-Rio de las Chinas Valley Complex contains the upper Cretaceous to Eocene record of the Magallanes/Austral Basin, located in southernmost Chile. This retroarc foreland basin contains a significant record of early Cretaceous to Miocene biogeographic and environmental changes that occurred in high paleolatitudes after the break-up of Gondwana. Using 37 stratigraphic sections, we generated a 1390 m thick stratigraphic column, which was used to developed sedimentary facies and an analysis of sequence stratigraphy. Results show, in general, aggradation composed of six third-order depositional sequences each delimited by an erosive surface. A lowstand systems tract developed above each surface, represented by alluvial environments similar to braided fluvial systems, and coastal plain environments, with the development of meandering fluvial and lacustrine systems. Above the lowstand tract, the transgressive systems tract is composed of a shallow marine environment with foreshore, shoreface, and offshore systems. A highstand systems tract was observed in one sequence, and is represented by shallow marine facies. The extensive outcrop in the studied area contains a diverse and voluminous fossil record, containing fossilized invertebrates (bivalves, gastropods, bryozoans, and brachiopods), vertebrates (hadrosaurs, ornithischians, sauropods, theropods, birds, mammals, frogs, turtles, plesiosaurs, mosasaurs, and sharks), and plants (wood, leaves impressions, flowers, pollen, and spores). Thus, this study broadens the understanding of the South American-Antarctic connection during the late Cretaceous-Paleogene, through a diverse fossil record and study of the paleoenvironmental evolution of this high-latitude basin.
Article
Peligrochelys walshae is a meiolaniform turtle originally described based on four specimens represented by cranial remains found in the classic locality of Punta Peligro (Chubut, Argentina) in outcrops of the Salamanca Formation (Danian). Recent field work in the vicinity of Punta Peligro resulted in the discovery of almost 30 new specimens, represented by cranial and postcranial remains that can be assigned to P . walshae . In this contribution, we provide a detailed anatomical description of the new specimens, provide an emended diagnosis for the species, and explore its phylogenetic relationships based on all anatomical data available for the species. The new specimens bring valuable information about the anatomy of the skull and postcranium of P . walshae as well as for meiolaniforms in general. The 3D preservation of the skull bones allows us to provide a 3D reconstruction using novel techniques. The updated phylogenetic analysis confirms that P . walshae is part of the clade Meiolaniformes, which spans from the Early Cretaceous until the Holocene and contains the giant, horned turtles (Meiolaniidae). This phylogenetic analysis reinforces the previous hypothesis that the clade Meiolaniformes is dominated by Gondwanan taxa, but also includes some Laurasian representatives. Alternate phylogenetic positions of taxa included in Meiolaniformes in this analysis were tested using the Templeton test. The lineage leading to Peligrochelys walshae is the only meiolaniform non-meiolaniid lineage to have survived the K-Pg mass extinction; its study provides valuable information to evaluate the effects of the K-Pg extinction in turtles.
Article
Pipimorpha is a clade of tongueless anurans with a wide fossil record. Furthermore, the oldest South American fossils come from the Late Cretaceous (Cenomanian) of Patagonia, Argentina. The aim of the present contribution is to describe a new genus and species of Pipimorpha from the Crato Formation (Aptian, Early Cretaceous), Araripe Basin, Brazil. The new specimen consists of a nearly complete skeleton that shows several anatomical similarities with other fossils from South America. Phylogenetic analysis resulted in the nesting of the new taxon within a previously unrecognized endemic South American clade. Further, some traditional groupings within Pipimorpha were not recognized. The new phylogenetic analysis reinforces previous biogeographical hypotheses sustaining dispersal of pipimorph between Africa and South America through an island chain or continental bridge across the Atlantic Ocean.
Article
Recent advances in the fossil record, anatomy, and evolutionary history of South American turtles allow a thorough analysis of their changes in diversity, as well as to identify several major extinction events. The history of turtles in South America starts with stem turtles surviving in the southwestern margin of the Pangea. With the onset of the breakup of Pangea in the Middle Jurassic, turtles begin to diversify, giving rise to the main South American turtle clades, some of which survive until present. The first peak of diversity was achieved in the Early Cretaceous, given by basal members of Pelomedusoides, Pan-Chelidae, and Meiolaniformes. A first extinction event is recognized in the end of the Early Cretaceous, affecting mainly the pelomedusoids in northern latitudes and coinciding with the final separation of South America from Africa. Although a general trend of diversification was obtained for most of the Mesozoic, pan-chelids registered extintion events during the middle to Late Cretaceous, and posteriorly the clade is only represented by its crown group members. The K?Pg boundary mass extinction affected the thriving turtle communities deeply in South America by reducing their diversity in half. The effect of this extinction is noted in all clades and latitudes, although turtles with their distributions more extended towards the north (e.g., Pelomedusoides) were more affected. Reduction of diversity continued on the aftermath of the K?Pg extinction, roughly until the middle Eocene and the final isolation of South America from Antarctica. In this ?new? continent, the surviving turtles continued to decrease on their diversity, up to an injection of biodiversity from Africa, with the arrival of tortoises, which helped to recover the diversity levels to higher values. The Andean uplift in Late Oligocene?Early Miocene and the associated climate and habitat changes posed new problems for the turtles and tortoises of the continent, but they continued to rise and expand. New injections of biodiversity took place at the end of the Neogene with the Great American Biotic Interchange, as novel clades reached South America from the North. The modern biodiversity of South American turtles took its final shape only during the last million years.
Article
The north-south trending, Late Cretaceous to modern Magallanes-Austral foreland basin of southernmost Patagonia lacks a unified, radiometric age-controlled stratigraphic framework. By simplifying the sedimentary fill of the basin to deep-marine, shallow-marine and terrestrial deposits and combining thirteen new U-Pb detrital zircon maximum depositional ages (DZ MDAs) with published DZ MDAs and U-Pb ash ages, we provide the first attempt at a unified, longitudinal stratigraphic framework constrained by radiometric age controls. We divide the foreland basin history into two phases including (1) an initial Late Cretaceous shoaling upward phase and (2) a Cenozoic phase that overlies a Paleogene unconformity. New DZ samples from the shallow marine La Anita Formation, the terrestrial Cerro Fortaleza Formation, and several previously unrecognized Cenozoic units provide necessary radiometric age controls for the end of the Late Cretaceous foreland phase and the magnitude of the Paleogene unconformity in the Austral sector of the basin. These samples show that the La Anita and Cerro Fortaleza Formations have Campanian DZ MDAs and that overlying Cenozoic strata have Eocene to Miocene DZ MDAs. By filling this data gap, we are able to provide a first attempt at constructing a basin wide, age controlled, stratigraphic framework for the Magallanes-Austral foreland basin. Results show southward progradation of shallow-marine and terrestrial environments from the Santonian through the Maastrichtian, as well as a northward increase in the magnitude of the Paleogene unconformity. Furthermore, our new age data significantly impact the chronology of fossil flora and dinosaur faunas in Patagonia. This article is protected by copyright. All rights reserved.
Article
We describe isolated shark teeth collected from levels of the Calafate Formation at the SE coast of the Argentino Lake, Calafate city, Santa Cruz province, Argentina (Atlantic Ocean), and from the Algarrobo coast at the Valparaíso Region in central Chile (Pacific Ocean). The teeth belong to a new species of the echinorhiniform genus Echinorhinus. Echinorhinus maremagnum n. sp. was a taxon distributed in both the southwestern Atlantic and the southeastern Pacific. This new taxon constitutes the oldest record of echinorhiniforms from South America and one of the few Mesozoic records at a worldwide scale.
Article
Two Jurassic–Cretaceous anurans are described based on well-preserved specimens from the lower part of the Yixian Formation, western Liaoning Province, northeastern China. One specimen, from the Heitizigou site, documents a new genus and species, and the second, from the Sihetun site, is the holotype and only known specimen for the recently named Callobatrachus sanyanensis. Phylogenetic relationships of the major archaeobatrachian anuran clades are investigated with incorporation into the analysis of selected (well-established) early fossil taxa. The new taxon named and described in this paper is placed as the representative of a distinct archaic anuran clade, and Callobatrachus is considered to be an ingroup member of the Discoglossidae, constituting the earliest record of the family from Asia. The oldest known fossil anuran, Prosalirus from the Early Jurassic of Arizona, is grouped with Notobatrachus as sister taxa, and the two together form the most basal clade of Anura. Contradicting the widely accepted Leiopelmatidae–Discoglossidae sistergroup relationship, new evidence places the Leiopelmatidae as the most basal extant familial group and the sister group to other archaeobatrachian clades. The relationships and classification of the major archaic anuran clades are discussed, based on the phylogenetic results of this study.