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A new Miocene vertebrate assemblage from the Río Yuca Formation (Venezuela) and the northernmost record of typical Miocene mammals of high latitude (Patagonian) affinities in South America
Abstract
Geological explorations of the basal beds of the Río Yuca Formation (Tucupido region, Portuguesa State, western Venezuela) resulted in the recognition of a new vertebrate assemblage that includes eight taxa: the toxodont cf. Adinotherium, a Peltephilidae armadillo, the freshwaters fishes Platysilurus and Phractocephalus, the caiman Purussaurus, an indeterminate dolphin, turtles, and the previously recognized sloth Pseudoprepotherium venezuelanum. When compared with the higher latitudes faunas of Argentina and Chile, the presence of cf. Adinotherium and peltephilids in the Rio Yuca Formation is consistent, but not conclusive, with a Santacrucian to Frisian SALMA age. The associated fauna, as well recent apatite fission track analysis, indicates that the Río Yuca assemblage is more likely younger in age, specifically middle to late Miocene. So far the Miocene localities of the northern part of South America have provided a less prolific fossil record compared to the southern part of the continent (e.g., Santacrucian and Friasian faunas of Patagonia), but the present work documents the surprising occurrence of two taxa (Peltephilidae and Nesodontinae) common in southern high latitude faunas of South America, implying the persistence of the Santacrucian-Friasian genus Adinotherium in younger strata from northern South America, and that peltephilids were much more widespread during the Miocene than previously recognized. The presence of these common Patagonian taxa (Peltephilidae and Nesodontinae) in Río Yuca also supports the hypothesis presented by prior researchers for the presence of biogeographical connections between the northern and southern portions of South America during the late Oligocene or early Miocene, which facilitated faunal interchange between the two regions. Finally, the biogeographical affinities of the freshwater fishes and the giant caiman (Purussaurus) indicate close relationships of the Tucupido region with the ancestral distribution of the Orinocoan-Amazonian drainage system.
... This genus is also common during the Santacrucian, with several records in Argentina and Chile (Bostelmann et al., 2013;Croft et al., 2004;Fernández and Muñoz, 2019;Flynn et al., 2002b). However, it has also been mentioned in younger ages (e.g., "Friasian") in Argentina and Chile (Bostelmann et al., 2012;Marshall, 1990) and tentatively in the middle to late Miocene of Venezuela (Rincón et al., 2016). ...
... Comments. The fragment of osteoderm shows diagnostic features of peltephilids, like a small overlap area with other osteoderms, a rough outer surface, one very conspicuous piliferous pit on the outer surface, and absence of figures on the outer surface (Fig. 5e) (Croft et al., 2007;González-Ruiz et al., 2012, 2013Montoya-Sanhueza et al., 2017;Rincón et al., 2016). Nonetheless, given the scarce and fragmentary available material, a more specific identification of this specimen is unfeasible. ...
... Nonetheless, given the scarce and fragmentary available material, a more specific identification of this specimen is unfeasible. Peltephilids range from the early Eocene to late Miocene; however, most of the recognized species in the family are restricted to the late Oligocene to early Miocene of the southern and central South America (Croft et al., 2007;González-Ruiz et al., 2012, 2013Kramarz et al., 2010;Montoya-Sanhueza et al., 2017;Rincón et al., 2016). ...
Despite recent efforts, the diversity of Neogene mammals in Chile remains poorly known, with several presumed new taxa awaiting description. For example, previous studies have suggested that the early to late Miocene mammalian assemblages from the Laguna del Laja fossiliferous locality (Cura-Mallín and Trapa-Trapa formations), in the Andean Cordillera of south-central Chile (∼37°), comprise dozens of undescribed taxa. Therefore, a better understanding of the Laguna del Laja faunal taxonomic affinities is needed, especially because the region holds one of the few known localities spanning from early to late Miocene in Chile. Dozens of mammal specimens recently recovered in late early Miocene beds of the Cura-Mallín Formation at Laguna del Laja are described and illustrated, and a discussion of their biogeographical and paleoenvironmental significance is provided. We recognize the presence of at least 17 taxa, including some potential new ones (e.g., Maruchito sp. nov.?) and others recognized in Chile for the first time (e.g., Galileomys). Geochronological (17.7–16.4 Ma) and biostratigraphical data indicate that this fauna correlates well with the Santacrucian SALMA, contributing to filling the gap in the taxonomic composition of Santacrucian mammalian assemblages in Chile and southwestern of South America. However, it is noteworthy that Laguna del Laja has documented some taxa previously found only in older (Colhuehuapian) and younger (Colloncuran) ages. Finally, the faunal assemblage supports a paleoenvironmental reconstruction of mixed forested and open habitats, likely with the predominance of the former, in the region during the late early Miocene and a widely distributed Santacrucian fauna throughout southern South America in both intra-arc and foreland basins.
... Interestingly, like Pseudoprepotherium, this taxon was also originally included in the Prepotheriinae but is now also recognized as a mylodont. Other groups for which new sloth taxa have been described beside the mylodonts (Carlini, Scillato-Yané & Sánchez et al., 2006a;Rincón, McDonald, Solórzano, Núñez & Ruiz-Ramoni, 2015a, 2015bRincón, Solorzano, Macsotay, McDonald & Núñez-Flores, 2016a;Rincón, Solorzano, McDonald & Nuñez-Flores, 2016b;) are megatheres (Carlini, Brandoni & Sanchez, 2006b and megalonychids (Rincón, Solórzano, McDonald & Montellano-Ballesteros, 2019). ...
... Based on these characters (Rodriguez Garcia, and Nuñez Tello, 1999;Marquínez and Velandia, 2001); D, Type locality of Magdalenabradys kolossiaia in Urumaco Formation, Falcón State (Rincón, et al., 2019).; E, relative position of locality of Rio Yuca type locality of Pseudoprepotherium venezuelanum, in Portuguesa State (Rincón, et al., 2016a). 4 Revista Geológica de América Central RGAC, 2020, 63, 1-20, doi: 10.15517/rgac.v62i0.41278 ...
... The locality today is apparently under water resulting from the creation of the Virgen de Coromoto reservoir. Recently, a new vertebrate locality with multiple taxa close to the original locality of Pseudoprepotherium venezuelanum was described (Rincón et al., 2016a). The small fauna consists of at least seven taxa and includes a toxodont cf. ...
We present a review of the Miocene mylodont sloths described from the Urumaco Formation, Venezuela, and the Villa-vieja Formation, Colombia, and reexamine their phylogenetic relationships to the holotype of Pseudoprepotherium from the Río Yuca Formation, Venezuela. Based on our analysis we propose a number of taxonomic changes and consider Pseudoprepotherium confusum to be sufficiently different from the type of Pseudoprepotherium venezuelanum, that it merits a distinct genus, Magdale-nabradys. We include in this new genus post-cranial material formerly assigned to Bolivatherium urumaquensis as a new species, Magdalenabradys kolossiaia. Comparison of Mirandabradys, first described from the late Miocene, Urumaco Formation of Vene-zuela, and its included species with the holotype of Pseudoprepotherium indicates they are the same genus, and Mirandabradys is considered a junior synonym. Three species of Pseudoprepotherium are recognized: the genotypic species, P. venezuelanum from the Río Yuca Formation, P. socorrensis from the Socorro Formation and P. urumaquensis, from the Urumaco Formation. We propose that based on the poor preservation and incompleteness of the type material that Mirandabradys zabasi is not a valid species and should be considered a nomen dubium. Resumen: Presentamos una revisión de los perezosos mylodontidos descritos de la Formación Urumaco, Venezuela, y la Formación Villavieja de Colombia, y reexaminamos sus relaciones filogenéticas con Pseudoprepotherium de la Formación Río Yuca, Venezuela. Con base en nuestro análisis, proponemos una serie de cambios taxonómicos y consideramos que Pseudoprepotherium confusum es lo suficientemente diferente del tipo de Pseudoprepotherium venezuelanum, por lo que merece ser asignado a un género distinto, Magdalenabradys gen. et sp. nov. Incluimos en este nuevo género material post-craneal anteriormente asignado a Bolivatherium uru-maquensis como una nueva especie, Magdalenabradys kolossiaia sp. nov. La comparación de Mirandabradys, descrita por primera vez a partir del Mioceno tardío, la Formación Urumaco de Venezuela, y sus especies incluidas con el holotipo de Pseudoprepothe-rium indica que son del mismo género, por lo que Mirandabradys se considera un sinónimo junior de Pseudoprepotherium. Se reco-nocen tres especies de Pseudoprepotherium, el genotipo P. venezuelanum de la Formación Río Yuca, P. socorrensis de la Formación Socorro y P. urumaquensis, de la Formación Urumaco. Proponemos que, con base en lo incompleto y pobre preservación del material tipo de Mirandabradys zabasi, es una especie no valida, y debería ser considerada como nomen dubium.
... ;Salas-Gismondi et al. 2015;Antoine et al. 2016;Moreno-Bernal et al. 2016;Rincón et al. 2016b). Although the earliest Purussaurus species, P. neivensis, is of middle Miocene age, indeterminate Purussaurus records have been recently reported from late Oligocene to early Miocene of eastern Peru), the lower Miocene Barzaloza Formation of Colombia (Moreno-Bernal 2006), the lower to middle Miocene Castilletes Formation of Colombia (16.7-14.2 ...
... Ma;Hastings et al. 2013). The fossil record of Purussaurus in Venezuela is also rather continuous during the early to late Miocene(Scheyer et al. 2013;Rincón et al. 2016b). With a constrained age of ...
Crocodyliform diversity was particularly high during the middle and late Miocene of South America, with up to 12 species recovered from a single geological unit. Nonetheless, the early Miocene fossil record of low-latitude vertebrates is scarce; hence, crocodylians remain poorly known in the region. The Castillo Formation, located in the northwest of Venezuela, preserves an interesting vertebrate fauna with a well-constrained late early Miocene age. Previous work dealing with crocodylians of this formation only recorded three taxa: the gavialoid Siquisiquesuchus venezuelensis and Gryposuchus sp. and indeterminate alligatoroid remains. New cranial and mandibular material recently recovered from the Castillo Formation allows us to document four previously unrecognised alligatoroid forms: Purussaurus sp., Caiman sp., an indeterminate caimanine and an indeterminate alligatoroid. With six taxa, the crocodylian assemblage reveals a previously undocumented relatively high taxonomic diversity in the early Miocene. The Castillo crocodylians show a broad range of morphological disparity and body sizes ranging from small (2.5 m–62 kg) to large (7.5 m–1600 kg) taxa. Thus, crocodylian niche partition, as well as the abundance and variety of resources and environmental heterogeneity of aquatic ecosystems in South America, were already established by at least the early Miocene. The presence of Caiman in ~ 18 Ma strata represents the unequivocally earliest record of the taxon in South America and allows us to propose that the origin of the jacareans is more likely to have occurred during or before the early Miocene, challenging previous molecular hypotheses.
... Topologies inferred from DNA and protein sequences found Bradypus (the extant three-fingered sloths) nested within Megatherioidea (the clade including Megatherium), while Choloepus (the extant two-fingered sloths) was identified as a member of Mylodontoidea (the clade including Mylodon; Delsuc et al. 2019;Presslee et al. 2019). In contrast, virtually all morphological phylogenies placed the entire fossil sloth diversity more closely related to Choloepus than to Bradypus, with Bradypus as the sister taxon to all other sloths and Choloepus closely related to recently extinct Caribbean sloths (e.g., Gaudin 2004;Rincón et al. 2016;Varela et al. 2019;Casali et al. 2022). The consistency of morphology-based topologies, regardless of the methodology used (e.g., maximum parsimony or Bayesian inference), is rather unsurprising since for the last 2 decades morphological phylogenies have been mostly based on variations of the same matrix of craniodental characters (i.e., Gaudin 2004). ...
Combining morphological and molecular characters through Bayesian total-evidence dating allows inferring the phylogenetic and timescale framework of both extant and fossil taxa, while accounting for the stochasticity and incompleteness of the fossil record. Such an integrative approach is particularly needed when dealing with clades such as sloths (Mammalia: Folivora), for which developmental and biomechanical studies have shown high levels of morphological convergence whereas molecular data can only account for a limited percentage of their total species richness. Here, we propose an alternative hypothesis of sloth evolution that emphasizes the pervasiveness of morphological convergence and the importance of considering the fossil record and an adequate taxon sampling in both phylogenetic and biogeographic inferences. Regardless of different clock models and morphological datasets, the extant sloth Bradypus is consistently recovered as a megatherioid, and Choloepus as a mylodontoid, in agreement with molecular-only analyses. The recently extinct Caribbean sloths (Megalocnoidea) are found to be a monophyletic sister-clade of Megatherioidea, in contrast to previous phylogenetic hypotheses. Our results contradict previous morphological analyses and further support the polyphyly of “Megalonychidae”, whose members were found in five different clades. Regardless of taxon sampling and clock models, the Caribbean colonization of sloths is compatible with the exhumation of islands along Aves Ridge and its geological time frame. Overall, our total-evidence analysis illustrates the difficulty of positioning highly incomplete fossils, although a robust phylogenetic framework was recovered by an a posteriori removal of taxa with high percentages of missing characters. Elimination of these taxa improved topological resolution by reducing polytomies and increasing node support. However, it introduced a systematic and geographic bias because most of these incomplete specimens are from northern South America. This is evident in biogeographic reconstructions, which suggest Patagonia as the area of origin of many clades when taxa are underrepresented, but Amazonia and/or Central and Southern Andes when all taxa are included. More generally, our analyses demonstrate the instability of topology and divergence time estimates when using different morphological datasets and clock models, and thus caution against making macroevolutionary inferences when node support is weak or when uncertainties in the fossil record are not considered.
... Additionally, recent analysis demonstrated the presence of material identified as cf. Adinotherium in a vertebrate assemblage from the middle to late Miocene of Venezuela, probably being the first record of an early diverging toxodontid in northern South America (Rincón et al., 2016). Therefore, Adinotherium may range into the middle Miocene, coinciding with the time span of Llastaya yesera but not so in geographical terms, since they were found, until now, in Patagonia and northern South America. ...
We analyze fossil footprints and trackways from the middle to late Miocene Vinchina Formation of La Rioja Province, northwestern Argentina. Ichnofossils are preserved in floodplain deposits of anastomosing and meandering fluvial systems and in ephemeral lake facies deposited under arid and semi-arid conditions. The tridactyl ungulate tracks are assigned to the novel ichnotaxa, Macrauchenichnus troyana and Llastaya yesera. Based on comparisons with phylogenetic character states observable on the postcrania of functionally tridactyl ungulates, the trackmaker of M. troyana was a litoptern macraucheniid whereas early toxodontids produced L. yesera. Based on the isometric relationship of footprint area and body mass in modern unguligrade mammals, we propose body mass estimate for these extinct ungulates. Facies analysis of this fossil footprint assemblage reveals that this previously undocumented fauna inhabited mixed grassland-woodland ecosystems developed under warm and seasonal climates in mid-palaeolatitudes. Findings support the idea of a faunal link between high and low latitude ecosystems of South America during the middle to late Miocene.
Peltephilidae (Xenarthra, Cingulata) is an ancient lineage of medium-large-sized 'armadillos' from South America, characterized by chisel-shaped molariforms, a U-shaped dental arcade, and cephalic osteoderms modified into hornlike structures. Although the biochron of the group extends from the early Eocene to the Late Miocene, the most abundant and complete records come from the Early Mio-cene of Patagonia. Remains from the Late Miocene are very scarce, and the last records of the group are from the Chas-icoan Stage (Tortonian). The only taxon known from this interval is Epipeltephilus kanti from the Arroyo Chasic o Formation (9.23 AE 0.09 Ma; Buenos Aires Province, Argentina), a species previously represented only by a few isolated osteo-derms. Here we report new remains assigned to E. kanti from the Late Miocene of Loma de Las Tapias Formation (c. 9.0-7.8 Ma; San Juan Province, Argentina), including a hemimandible and several fixed and mobile osteoderms. These new specimens constitute the youngest record of Pel-tephilidae. The inclusion of E. kanti within Epipeltephilus and the monophyly of the genera Peltephilus and Epipeltephi-lus are corroborated for the first time through a cladistic analysis. The decline and eventual disappearance of this 'armadillo' group in the Late Miocene is chronologically coincident with the replacement of subtropical/tropical environments by more open and arid ones and with the proliferation of other large armadillos such as Vetelia, Macrochorobates, and Macroeuphractus.
Freshwater fossil fish faunas have long been used to infer past drainage connections, given that they are bounded by physical freshwater barriers. Here we study a middle Miocene (15.0–15.5 Ma) freshwater fish fossil fauna (Makaraipao) from the Castilletes Formation in northern Colombia, nowadays west of the Andes. We record the presence of lungfishes (Lepidosiren), pacus (Mylossoma and Piaractus), armoured catfishes (Callichthyidae), and red-tail catfishes (Phractocephalus). Extant members of all those groups (except the Callichthyidae, due to lack of taxonomic resolution) are found in Amazonian faunas east of the Andes and are absent from faunas west of the Andes, indicating that the riverine systems of the Guajira Peninsula were connected to Amazonia during the middle Miocene. The similarity of La Venta (west of the Andes) and Rio Acre (east of the Andes) fish faunas during the late Miocene further indicates that the northern Andean uplift was not a complete barrier at least until c. 11 Ma. However, there is a continental-wide structuring of the Miocene fish faunas that is also found in the extant faunas, suggesting that other factors such as ecological conditions, in addition to the uplift of the Andes, have shaped the biogeographic evolution of South American fish faunas.
The intrageneric relationships of the pampatheriid genus Scirrotherium and its affinities with supposedly related genera Kraglievichia and Holmesina are revised through new comparative morphological descriptions and parsimony phylogenetic analyses. Unpublished material of pampatheriids (numerous osteoderms, one partial skull and a few postcranial bones) from Neogene formations of Colombia was analyzed. Results show that Scirrotherium is paraphyletic when including all its referred species, i.e., Scirrotherium hondaensis, S. carinatum, and S. antelucanus. The species S. carinatum appears closer to Kraglievichia paranensis than to S. hondaensis or S. antelucanus, therefore the new combination Kraglievichia carinatum is proposed. The relationship between S. hondaensis and S. antelucanus could not be resolved, so these species should be designated in aphyly. In spite of failing to recover S. hondaensis and S. antelucanus as one single clade, it is preferred to maintain the generic name Scirrotherium for both species based on diagnostic evidence. New emended diagnoses for Scirrotherium, S. hondaensis and Kraglievichia are provided. The genus Holmesina was found to be monophyletic and positioned as the sister clade of Scirrotherium + Kraglievichia. The evolutionary and biogeographic implications of the taxonomic re-arrangements and the new phylogeny are discussed. A possible geographic origin of the family Pampatheriidae and Scirrotherium in low latitudes of South America as early as the early Miocene is claimed. The immediate South American sister taxon of Holmesina is predicted to be morphologically more similar to Scirrotherium than to Kraglievichia.
A new genus and species of megalonychid sloth, Zacatzontli tecolotlanensis n. gen. n. sp., is described from the late Hemphillian of Jalisco, Mexico. Comparison and analysis of the type specimen, a mandible, with other megalonychid sloths shows a closer relationship to South American taxa than those from North America or the Caribbean. This suggests that during the early stages of the Great American Biotic Interchange there were two separate dispersal events of megalonychid sloths—an earlier one represented by Pliometanastes and the later one by Zacatzontli n. gen. While the morphology of the spout of Zacatzontli more closely resembles that of Megalonyx , based on the current record, Zacatzontli does does not enter North America until after the evolution of Megalonyx from Pliometanastes . The role of the northern neotropics in South America as a staging area for South American taxa that entered North America is discussed.
We report a new genus and species of sloth, based on a partial mandible and associated femur, from the early Miocene of Venezuela. Baraguatherium takumara, gen. et sp. nov., represents the earliest member of the Mylodontoidea recognized from northern South America. Phylogenetically and morphologically, Baraguatherium possesses some plesiomorphic characters: a vasodentine layer in the core of the tooth similar to Octodontotherium, Paroctodontotherium, and Orophodon; molariforms parallel to the long axis of the toothrow; teeth with a very thin layer of cementum; mf1-mf3 series of similar size and bilobate; mf3 conspicuously piriform; and occlusal surface of tooth beveled, which places it at the base of the Mylodontidae clade. Baraguatherium was found in continental deposits that also preserve abundant wood and leaves associated with a near shore marine complex, indicating that Baraguatherium lived in a coastal tropical forest in the early Miocene in northern South America. The presence of a vasodentine layer in the core of the tooth is quite similar to Octodontotherium, Paroctodontotherium, and Orophodon and allows assignment of this new taxon to the Mylodontoidea.
The La Guajira Peninsula, Colombia, has a continuous vertebrate fossil record that includes both the late early–early middle Miocene and the Pliocene. Crocodilians from the early to early middle Miocene Jimol and Castilletes formations include gavialoids, recovered from both coastal and shallow marine deposits, and caimanines representing early records of the specialized caimanine taxa Purussaurus and Mourasuchus. Crocodyloid specimens from the Pliocene Ware Formation are assigned to Crocodylus and represent one of the oldest occurrences of the genus in the New World. Records from the La Guajira Peninsula suggest that diverse crocodilian assemblages were already established by the late early Miocene, including several widely distributed lineages that persisted for several million years. Crocodylus is a recent immigrant to South America that occupied habitats left vacant by the extinction of several crocodilian lineages.Citation for this article: Moreno-Bernal, J. W., J. Head, and C. A. Jaramillo. 2016. Fossil crocodilians from the High Guajira Peninsula of Colombia: Neogene faunal change in northernmost South America. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1110586.
Various Structured Light (SL) methods are used to capture 3D range images, where a number of binary or continuous light patterns are sequentially projected onto a scene of interest, while a digital camera captures images of the illuminated scene. All existing SL methods require the projector and camera to be hardware or software synchronized, with one image captured per projected pattern. A 3D range image is computed from the captured images. The two synchronization methods have disadvantages, which limit the use of SL methods to niche industrial and low quality consumer applications. Unsynchronized Structured Light (USL) is a novel SL method which does not require synchronization of pattern projection and image capture. The light patterns are projected and the images are captured independently, at constant, but possibly different, frame rates. USL synthesizes new binary images as would be decoded from the images captured by a camera synchronized to the projector, reducing the subsequent computation to standard SL. USL works both with global and rolling shutter cameras. USL enables most burst-mode-capable cameras, such as modern smartphones, tablets, DSLRs, and point-and-shoots, to function as high quality 3D snapshot cameras. Beyond the software, which can run in the devices, a separate SL Flash, able to project the sequence of patterns cyclically, during the acquisition time, is needed to enable the functionality.
In his 1940 "Review of the mammal-bearing Tertiary of South America," G. G. Simpson summarized the scanty record of Venezuela (703-704): "Few as discoveries are, they are important because they show unquestionable affinities with fossil mammals of Argentina and none with those of North America. In view of the fact that no South American mammals had reached North America in the Miocene or earliest Pliocene, even this small budget of evidence is enough to prove that South America was then a unified continent with its northern and southern parts united by land and that the northern part, as well as the southern, was then separated from North America by a marine barrier." What little was known about northern neotropical vertebrate paleontology in 1940 was already important in addressing some large issues about biogeography and the past history of the American continent. Vertebrate paleontology in Venezuela is still in a descriptive phase, but the number of discoveries has increased exponentially in the last few years, and contributions in this volume exemplify how some of them are being used to address fundamental issues about evolution in the tropics and major events in vertebrate evolution, such as the Great American Biotic Interchange in both terrestrial and marine habitats. Here we present a chronological review of Venezuelan formations and sites with reported fossil vertebrates. Many of the sites and their fossils are also discussed specifically in different chapters of this book. Paleogene vertebrates from Venezuela are almost unknown. Several aspects on paleoenvironments and palynology of the Paleocene and Eocene of Venezuela were discussed by Rull (2000). There are several Neogene fossil sites, but most are poorly known localities with only one or a few taxa or remains reported. By far the most important section with vertebrates in the Cenozoic of Venezuela is that of the Urumaco sequence, the geology of which is treated in a separate chapter (Quiroz and Jaramillo this volume). Most vertebrate faunas from the Neogene show very low diversity, with the sole exception of the Urumaco sequence and the Cerro La Cruz site. Faunas with vertebrates are found in the Guárico sub-basin, Barinas basin, and Falcón basin. Pleistocene and Holocene deposits are becoming better known, and as discussed below the recently discovered tar pits in Zulia state and the archeological sites in Falcón state are the most significant sites. Many of the fossils mentioned below are in collections in Europe and the USA. In Venezuela, vertebrate fossils are reposited principally in the following institutions: Collección Urumaco Rodolfo Sánchez Alcaldía, Estado Falcón (AMU-CURS); Centro de Historia de la Ciudad de Trujillo, Colección de Geología y Paleontología (CH-V); Centro de Investigaciones Antropológicas, Arqueológicas, y Paleontológicas, Coro (CIAAP); Museo de Biología de la Universidad del Zulia, Paleontología (MBLUZ-P); Museo de Ciencias Naturales de Caracas (MCNC); Universidad Nacional Experimental Francisco de Miranda, Coro (UNEFM); Universidad Nacional Experimental Francisco de Miranda, Coro / Centro de Investigaciones Antropológicas, Arqueológicas y Paleontológicas, Coro (UNEFM-CIAAP); Universidad Simón Bolívar, Laboratorio de Paleobiología (USB-PB).
A multidisciplinary approach, combining sediment petrographic, palynological and thermochronological techniques, has been used to study the Miocene-Pliocene sedimentary record of the evolution of the Venezuelan Andes. Samples from the Maracaibo (pro-wedge) and Barinas (retro-wedge) foreland basins, proximal to this doubly vergent mountain belt, indicate that fluvial and alluvial-fan sediments of similar composition were shed to both sides of the Venezuelan Andes. Granitic and gneissic detritus was derived from the core of the mountain belt, while sedimentary cover rocks and uplifted foreland basin sediments were recycled on its flanks.Palynological evidence from the Maracaibo and Barinas basins constrains depositional ages of the studied sections from Late Miocene to Pliocene. The pollen assemblages from the Maracaibo Basin are indicative of mountain vegetation, implying surface elevations of up to 3500-4000 m in the Venezuelan Andes at this time. Detrital apatite fission-track (AFT) data were obtained from both stratigraphic sections. In samples from the Maracaibo basin, the youngest AFT grain-age population has relatively static minimum ages of 5±2 Ma, while for the Barinas basin samples AFT minimum ages are 7±2 Ma. With exception of two samples collected from the Eocene Pagüey Formation and from the very base of the Miocene Parángula Formation, no evidence for resetting and track annealing in apatite due to burial heating in the basins was found. This is supported by rock-eval analyses on organic matter and thermal modeling results. Therefore, for all other samples the detrital AFT ages reflect source area cooling and impose minimum age constraints on sediment deposition.The main phase of surface uplift, topography and relief generation, and erosional exhumation in the Venezuelan Andes occurred during the Late Miocene to Pliocene. The Neogene evolution of the Venezuelan Andes bears certain similarities with the evolution of the Eastern Cordillera in Colombia, although they are not driven by exactly the same underlying geodynamic processes. The progressive development of the two mountain belts is seen in the context of collision of the Panama arc with northwestern South America and the closure of the Panama seaway in Miocene times, as well as contemporaneous movement of the Caribbean plate to the east and clock-wise rotation of the Maracaibo block.This article is protected by copyright. All rights reserved.
This dissertation presents the results and observations of an investigation on the long-term (Miocene to present) exhumation history of the Venezuelan Andes, and the relationships between inherited structures and development of topography in response to tectonic and surface processes. The Venezuelan Andes are ideal for understanding the relationships between these processes, because they have involved through inversion and reactivation of pre-existing structures, they are associated with a major climatic gradient due to the orograpic effect of the belt and extensive data is available concerning their recent tectonic evolution. This mountain belt is the result of transpression caused by oblique convergence of the continental Maracaibo block and the South America Plate, controlled, on a larger scale, by the triple junction between the South American, Caribbean and Nazca plates. The complex kinematics of triple plate interaction and the continuous evolution of related structures coupled with surface processes have profoundly affected the evolution of the Venezuelan Andes. An extensive low-temperature thermochronometer database composed of 47 new apatite fission-track (AFT) ages: 24 bedrock samples, 15 samples from synorogenic detrital sediments and 8 samples from modern rivers sediments is presented in this dissertation. The dataset is supplemented with 27 previously unpublished AFT bedrock ages and 10 revised AFT ages provided by B.P. Kohn. The AFT ages are converted into long-term exhumation rates using thermal modeling. Analyses of in-situ AFT data from seven tectonically delineated areas reveal variable exhumation patterns across the Venezuelan Andes. The Caparo and Valera blocks, which were separated by dextral movement along the Boconó strike-slip fault system, respectively have AFT ages ranging from 7 to 27 Ma, and 11 to 145 Ma, representing areas of relatively slow exhumation. In the central part of the Venezuelan Andes, AFT ages in the Sierra La Culata (5-8 Ma), El Carmen (2-3 Ma) and Sierra Nevada (5-8 Ma) blocks, record major recent exhumation in response to transpression and erosion along the Boconó fault system. To both sides of the chain, AFT ages in the Escalante block (5-6 Ma) on the far northern flank, and the Cerro Azul thrust block (5-8 Ma AFT age) on the southern flank provide evidence of significant compression, which produced the doubly vergent structure of the Venezuelan Andes during Late Miocene times. Fission-track analysis of detrital apatite from modern river samples permit a) verification and extrapolation of the bedrock cooling age patterns across the Venezuelan Andes, b) determination of sediment provenance, and c) analysis of relationships between exhumation rates and potential controlling factors. The results imply a strong correlation between relief and long-term exhumation rate but a lack of correlation between long-term exhumation rate and present-day precipitation or seismic energy release (measured during the last 20 years), indicating that the control of tectonic and/or climatic processes on exhumation cannot be discerned in a straightforward manner. Fission-track data from synorogenic sediments in the Maracaibo and Barinas foreland basins permit tracing the present-day exhumation patterns back to the Late Miocene. Rock-Eval analyses of sediments sampled show that Mio-Pliocene sediments in these basins have not been buried deeper than the AFT partial annealing zone in the studied sections. Young AFT ages in samples from the Parángula Formation on the south flank imply that this formation is probably of Tortonian age, significantly younger than previously suggested. The AFT data, together with pollen analyses, imply that the Pliocene Betijoque Formation to the north corresponds in age to the upper part of the Río Yuca Formation to the south of the Venezuelan Andes.
Las faunas miocénicas de Suramérica intertropical proporcionan asociaciones bien conocidas de Crocodylia fósiles. Estas asociaciones son ricas en especies, ocupando un espectro ecológico muy amplio. Varios restos de cocodrilos fueron recuperados en campañas dirigidas por INGEOMINAS en Pubenza, Cundinamarca. La asociación incluye restos de tortugas dulceacuícolas y piezas de mamíferos, entre las que destacan molares bunodontos posiblemente pertenecientes a un Megadolodinae. Los elementos aparecen impregnados de gipsita, lo que dificulta su preparación y observación. Con base en particularidades craneales y dentales se reconocen formas pertenecientes a las familias Alligatoridae y Gavialidae. Un cráneo de gran tamaño presenta características (extrema longitud rostral, festoneado lateral del rostro, orbitas y fenestras supratemporales de tamaño similar) que indican afinidades con Ikanogavialis, mientras que un fragmento de maxilar y varios dientes de gran tamaño sugieren la posible presencia de Purussaurus. También han sido recuperadas varias vértebras pertenecientes a cocodrilos de gran tamaño. La Formación Barzalosa, de donde proceden estos restos, ha sido datada tentativamente como Mioceno Inferior en base a polen. De confirmarse, estos restos corresponderían a los registros más antiguos para estos géneros. La persistencia de formas similares de Crocodylia a lo largo del Mioceno indicaría así un periodo prolongado de estabilidad ambiental.
Recent studies show Xenarthra to be even more isolated systematically from other placental mammals than traditionally thought. The group not only represents 1 of 4 primary placental clades, but proposed links to other fossorial mammal taxa (e.g., Pholidota, Palaeanodonta) have been contradicted. No unambiguous Paleocene fossil xenarthran remains are known, and Eocene remains consist almost exclusively of isolated cingulate osteoderms and isolated postcrania of uncertain systematic provenance. Cingulate skulls are unknown until the late middle Eocene, and the oldest sloth and anteater skulls are early Oligocene and early Miocene age, respectively; there are no nearly complete xenarthran skeletons until the early Miocene. Ecological reconstructions of early xenarthrans based on extant species and the paleobiology of extinct Neogene taxa suggest the group's progenitors were myrmecophagous with digging and perhaps some climbing adaptations. The earliest cingulates were terrestrial diggers and likely myrmecophagous but soon diverged into numerous omnivorous lineages. Early sloths were herbivores with a preference for forested habitats, exhibiting both digging and climbing adaptations. We attribute the rarity of early xenarthran remains to low population densities associated with myrmecophagy, lack of durable, enamel-covered teeth, and general scarcity of fossil localities from tropical latitudes of South America. The derivation of numerous omnivorous and herbivorous lineages from a myrmecophagous ancestor is a curious and unique feature of xenarthran history and may be due to the peculiar ecology of the native South American mammal fauna. Further progress in understanding early xenarthran evolution may depend on locating new Paleogene fossil sites in northern South America.
In an effort to document the diversity and distribution of Neogene neotropical fishes in time and space, in this chapter we summarize and analyze previous records in the Venezuela sedimentary basin and include additional unpublished fossil records. The investigation has identified ~ 209 taxa (56 elasmobranchs and 153 teleosts), ranging in age from Late Oligocene to Pleistocene. Venezuelan Caribbean and Orinocoan Neogene fishes are examined in the context of the Caribbean and Tropical South American fossil assemblage. Detailed reviews of the fossil record of Caribbean Neogene teleostean fish are available for: Panama (Gillette 1984), Panama and Costa Rica (Aguilera and Rodrigues de Aguilera 1999; Collins et al. 1999; Laurito 1999), Trinidad (Nolf 1976), Venezuela (Nolf and Aguilera 1998; Aguilera and Rodrigues de Aguilera 2001, 2004a, b, c; Aguilera 2004), the Dominican Republic (Nolf and Stringer 1992), Cuba (Iturralde- Vinent, Hubbell, and Rojas 1996; Iturralde-Vinent et al. 1998), Puerto Rico (Nieves-Rivera 1999), and Jamaica (Stringer 1998; Donovan and Gunter 2001). Systematic reviews of Caribbean Neogene elasmobranchs have not been attempted since Sánchez-Roig (1920), Leriche (1938), Casier (1958), Gillette (1984), Kruckow and Thies (1990), Iturralde-Vinent, Hubbell, and Rojas (1996), Laurito (1999), and Aguilera (2004). However, these previous compilations reveal the scarce and scattered records of fossil selachians from the Caribbean. Additional detailed reviews of the fossil record of Orinocoan/Amazonian freshwater Neogene fish are available for: Brazil (Richter 1984, 1989; Silva-Santos 1987; Monsch 1998; Aguilera et al. 2008b; Bocquentin Villanueva and Souza Mello 2001; Gayet et al. 2003), Colombia (Lundberg, Machado-Allison, and Kay 1986; Lundberg and Chernoff 1992; Lundberg 2005; Monsch 1998), Peru (Monsch 1998), and Venezuela (Lundberg et al. 1988, 2010; Lundberg and Aguilera 2003; Aguilera 2004; Dahdul 2004; Sabaj, Aguilera, and Lundberg 2007). Because fossil assemblages of fishes represent only a small fraction of the richness of the Recent fish fauna, we suggest that a large fraction of fossil taxa from the Venezuelan sedimentary basins still remain uncollected.
The Neogene sedimentary fill of the Cocinetas Basin in northern Colombia preserves a rich record of marine invertebrates and can be analyzed in the context of a high-resolution stratigraphy and excellent chronostratigraphy. Molluscan fossils are highly diverse and often well preserved, offering a window into the rapidly changing paleoenvironments and biogeography of northern South America during parts of the Early to Middle Miocene and latest Pliocene to Pleistocene. Before the evolutionary and biogeographic implications of these fossils can be understood, however, their associated depositional environments and geologic ages must be determined. Here, we present preliminary results from paleoenvironmental, biostratigraphic, and strontium isotope chronostratigraphic analyses of sediments and fossils from the Uitpa, Jimol, Castilletes, and Ware formations found in Cocinetas Basin. The basal unit in the Neogene succession, the Uitpa Formation, comprises mudstones redeposited sandstones and molluscs typical of bathyal to outer shelf environments at its base. It is a shallowing-up sequence and is conformable with the overlying Jimol Formation, which comprises coarse-grained lithic calcarenite, coquina, and mudstone that represent a regressive-transgressive-regressive sequence. This sequence includes foreshore and transition zone through lower inner shelf environments, but generally poorly preserved invertebrate assemblages. The conformably overlying Castilletes Formation contains a varied suite of depositional environments with better-developed shell beds and thicker successions of intervening siltstone. A significant unconformity exists between the Castilletes Formation and the overlying Ware Formation, which represents a deltaic to coastal shoreface deposition environment, rich in shallow marine molluscs from a variety of ecotopes. Biostratigraphic assessment and strontium isotopic results from the Jimol and Castilletes formations indicate that these units contain fossils of latest Early Miocene through Middle Miocene age, while those of the Ware are approximately Late Pliocene in age. These results help to place the shallow marine assemblages of Cocinetas Basin into a wider geologic context that aids our understanding of how these faunas relate to the broader evolutionary and biogeographic history of the southern Caribbean during the Neogene. Additionally, the isotope dating and paleoecology of this fauna help to place co-occurring terrestrial and aquatic vertebrate assemblages into a local paleoenvironmental and chronostratigraphic framework.
Three orders of South American extinct native ungulates are recorded from the Santa Cruz Formation along the Atlantic coast of Patagonia: Notoungulata (Adinotherium Ameghino, Nesodon Owen, Interatherium Ameghino, Protypotherium Ameghino, Hegetotherium Ameghino, and Pachyrukhos Ameghino), Litopterna (Theosodon Ameghino, Anisolophus Burmeister, Tetramerorhinus Ameghino, Diadiaphorus Ameghino, and Thoatheriurn Ameghino), and Astrapotheria (Astrapotherium Burmeister). An ecomorphological study based on geometric morphometries of the masticatory apparatus was performed. The reference sample included 618 extant specimens of the orders Artiodactyla, Perissodactyla, Hyracoidea, and Diprotodontia. Thirty six cranial and 27 mandibular three-dimensional landmarks were digitized. Allometric scaling, principal component analyses, and phylogenetic generalized estimating equations on the cranium and mandible were preformed. Analyses of cranial shape show strong phylogenetic constraints, whereas the mandibular analyses show a functional pattern related to habitat/ diet and hypsodonty. The extant brachydont ungulates from closed habitats show a more elongated and narrower mandibular symphysis with a lower mandibular corpus, than hypsodont, open habitat species. The latter have short symphyses with a high, curved mandibular corpus. This morphological pattern was also present among Santacrucian ungulates, allowing characterization of notoungulates mainly as open habitats dwellers, with some taxa foraging on grass (Protypotherium, Interatherium), and others on grass and leaves {Hegetotherium, Pachyrukhos, and Adinotheriurn), depending on the availability. Nesodon may have dwelled in mixed habitats and had a mixed feeding behavior, while small proterotheriids {Anisolophus and Thoatheriurn) may have fed predominantly on dicotyledonous plants. The remaining litopterns {Tetramerorhinus, Diadiaphorus, and Theosodon) and Astrapotherium may have foraged in closed habitats and fed on dicotyledonous plants.
The Cocinetas Basin of Colombia provides a valuable window into the geological and paleontological history of northern South America during the Neogene. Two major findings provide new insights into the Neogene history of this Cocinetas Basin: (1) a formal re-description of the Jimol and Castilletes formations, including a revised contact; and (2) the description of a new lithostratigraphic unit, the Ware Formation (Late Pliocene). We conducted extensive fieldwork to develop a basin-scale stratigraphy, made exhaustive paleontological collections, and performed 87Sr/86Sr geochronology to document the transition from the fully marine environment of the Jimol Formation (ca. 17.9–16.7 Ma) to the fluvio-deltaic environment of the Castilletes (ca. 16.7–14.2 Ma) and Ware (ca. 3.5–2.8 Ma) formations. We also describe evidence for short-term periodic changes in depositional environments in the Jimol and Castilletes formations. The marine invertebrate fauna of the Jimol and Castilletes formations are among the richest yet recorded from Colombia during the Neogene. The Castilletes and Ware formations have also yielded diverse and biogeographically significant fossil vertebrate assemblages. The revised lithostratigraphy and chronostratigraphy presented here provides the necessary background information to explore the complete evolutionary and biogeographic significance of the excellent fossil record of the Cocinetas Basin.
Amazonia contains one of the world's richest biotas, but origins of this diversity remain obscure. Onset of the Amazon River drainage at approximately 10.5 Ma represented a major shift in Neotropical ecosystems, and proto-Amazonian biotas just prior to this pivotal episode are integral to understanding origins of Amazonian biodiversity, yet vertebrate fossil evidence is extraordinarily rare. Two new species-rich bonebeds from late Middle Miocene proto-Amazonian deposits of northeastern Peru document the same hyperdiverse assemblage of seven co-occurring crocodylian species. Besides the large-bodied Purussaurus and Mourasuchus, all other crocodylians are new taxa, including a stem caiman-Gnatusuchus pebasensis-bearing a massive shovel-shaped mandible, procumbent anterior and globular posterior teeth, and a mammal-like diastema. This unusual species is an extreme exemplar of a radiation of small caimans with crushing dentitions recording peculiar feeding strategies correlated with a peak in proto-Amazonian molluscan diversity and abundance. These faunas evolved within dysoxic marshes and swamps of the long-lived Pebas Mega-Wetland System and declined with inception of the transcontinental Amazon drainage, favouring diversification of longirostrine crocodylians and more modern generalist-feeding caimans. The rise and demise of distinctive, highly productive aquatic ecosystems substantially influenced evolution of Amazonian biodiversity hotspots of crocodylians and other organisms throughout the Neogene.
© 2015 The Author(s) Published by the Royal Society. All rights reserved.
A new genus and species of sloth (Eionaletherium tanycnemius gen. et sp. nov.) recently collected from the Late Miocene Urumaco Formation, Venezuela (northern South America) is herein described based on a partial skeleton including associated femora and tibiae. In order to make a preliminary analysis of the phylogenetic affinities of this new sloth we performed a discriminate analysis based on several characters of the femur and tibia of selected Mylodontoidea and Megatherioidea sloths. The consensus tree produced indicates that the new sloth, E. tanycnemius, is a member of the Mylodontoidea. Surprisingly, the new taxon shows some enigmatic features among Neogene mylodontoid sloths, e.g. femur with a robust lesser trochanter that projects medially and the straight distinctly elongated tibia. The discovery of E. tanycnemius increases the diversity of sloths present in the Urumaco sequence to ten taxa. This taxon supports previous studies of the sloth assemblage from the Urumaco sequence as it further indicates that there are several sloth lineages present that are unknown from the better sampled areas of southern South America.
Purussaurus brasiliensis thrived in the northwestern portion of South America during the Late Miocene. Although substantial material has been recovered since its early discovery, this fossil crocodilian can still be considered as very poorly understood. In the present work, we used regression equations based on modern crocodilians to present novel details about the morphometry, bite-force and paleobiology of this species. According to our results, an adult Purussaurus brasiliensis was estimated to reach around 12.5 m in length, weighing around 8.4 metric tons, with a mean daily food intake of 40.6 kg. It was capable of generating sustained bite forces of 69,000 N (around 7 metric tons-force). The extreme size and strength reached by this animal seems to have allowed it to include a wide range of prey in its diet, making it a top predator in its ecosystem. As an adult, it would have preyed upon large to very large vertebrates, and, being unmatched by any other carnivore, it avoided competition. The evolution of a large body size granted P. brasiliensis many advantages, but it may also have led to its vulnerability. The constantly changing environment on a large geological scale may have reduced its long-term survival, favoring smaller species more resilient to ecological shifts.
Purussaurus brasiliensis thrived in the northwestern portion of South America during the Late Miocene. Although substantial material has been recovered since its early discovery, this fossil crocodilian can still be considered as very poorly understood. In the present work, we used regression equations based on modern crocodilians to present novel details about the morphometry, bite-force and paleobiology of this species. According to our results, an adult Purussaurus brasiliensis was estimated to reach around 12.5 m in length, weighing around 8.4 metric tons, with a mean daily food intake of 40.6 kg. It was capable of generating sustained bite forces of 69,000 N (around 7 metric tons-force). The extreme size and strength reached by this animal seems to have allowed it to include a wide range of prey in its diet, making it a top predator in its ecosystem. As an adult, it would have preyed upon large to very large vertebrates, and, being unmatched by any other carnivore, it avoided competition. The evolution of a large body size granted P. brasiliensis many advantages, but it may also have led to its vulnerability. The constantly changing environment on a large geological scale may have reduced its long-term survival, favoring smaller species more resilient to ecological shifts.
A new species of Peltephilidae (Mammalia, Xenarthra, Cingulata) (early Eocene–late Miocene) is described here. The new taxon is based on three specimens collected from the margins of Arroyo Chasicó, Buenos Aires Province, (Argenti-na), which correspond to the Arroyo Chasicó Formation (late Miocene, Chasicoan SALMA). The new species is charac-terized by osteoderms with a very rough exposed surface showing high longitudinal and well developed crests (two lateral and one central) with deep and ample valleys among them. The new taxon is the only " relictual " xenarthran cingulate of the Santacrucian Age (late early Miocene) to be registered for the last time in the Chasicoan SALMA (late Miocene), and represents the youngest record of the family Peltephilidae.
Armadillos, sloths and anteaters represent a small fragment of a much more diverse fossil assemblage of xenarthrans that includes bizarre forms such as the armored glyptodonts and the giant ground sloths. We reconstruct extinct xenarthrans as living animals, describing their basic biology, behaviors and ecological roles. In this contribution we provide two examples of the ecological diversity of xenarthrans in the geological past that largely surpass the one we know today. One is the Santacrucian fauna that developed in southern Patagonia during the Middle Miocene Climatic Optimum (17 to 15 Ma). The richness of Santacrucian xenarthrans recorded in a single locality comprises 21 genera in seven families, exceeding the present total diversity in the continent as a whole (14 genera within five families). The other is the Lujanian fauna that inhabited the Pampean Region during the late Quaternary (0.130 to 0.07 Ma). The total large mammal (above 100 kg) and megamammal (above a ton) richness during Lujanian times may have been as high as 83 species distributed in 48 genera. Most megaherbivores were xenarthrans, which constituted about 80% of the mammals above 500 kg: at least four genera of glyptodonts (Glyptodontidae) and five genera of ground sloths (Mylodontidae and Megatheriidae). There was also a giant armadillo-like herbivore that must have reached 200 kg (Pampatheriidae). This ancient diversity is lost forever, and we therefore urge that autochthony and past taxonomic richness and ecologic diversity be recognized as values for establishing conservation priorities and policies.
The Middle Miocene has been identified as a time of great diversification in modern lineages now distrib-uted in tropical South America, and when basic archetypal traits defining Amazonia appear, including climatic humid conditions, basic floral physiognomy and phylogenetic com-position of modern rainforests. Nonetheless, Middle Miocene localities in South America are poorly known, especially at low latitudes where only one species-rich locality, La Venta in Colombia, has been extensively studied. The present con-tribution describes the mammal fauna of Fitzcarrald, a new Middle Miocene local fauna from western Amazonia in Peru. Fitzcarrald is correlated with the Laventan South American Land Mammal Age based on the presence of taxa defining the 'Miocochilius assemblage zone' in La Venta. The mamma-lian fauna of Fitzcarrald comprises 24 taxa among cingulates, folivores, astrapotheres, notoungulates, litopterns, rodents, odontocetes and a possible marsupial. At this time, tropical South America was characterized by the presence of the Pebas megawetland, a huge lacustrine complex that provided unique ecological and environmental conditions most likely isolating northern South America from southern South America. These isolating conditions might have come to an end with its disappearance in the Late Miocene and the establishment of the subsequent Acre system, the predecessor fluvial system of modern Amazonia. Results of faunistic simi-larity between Fitzcarrald and other Miocene faunas through-out South America support these scenarios. The Fitzcarrald mammal fauna exhibits first appearance datums and last appearance datums of various taxa, showing that tropical South America has played a crucial role in the evolutionary history and biogeography of major clades, and revealing a more complex biological history than previously proposed, based on the record from the southern cone of the continent.
We describe a new toxodontid species, Nesodon taweretus sp. nov., from the Aisol Formation in Mendoza Province, central-west Argentina. Nesodon is a frequently found Toxodontidae, member of the Notoungulata, an extinct endemic group of Cenozoic South American mammals that are ecologically similar to current hoofed ungulates. The holotype of N. taweretus sp. nov. is a skull, and we tentatively assign some mandibular fragments and postcranial bones. N. taweretus sp. nov. differs from the other Nesodon species in several cranial and dental features, and close comparisons were made with the Patagonian Nesodon imbricatus, common in the Santa Cruz Formation (Santacrucian Age, Early Miocene). The material is of a similar size to N.imbricatus, with a body mass estimation of about 550 kg. The phylogenetic analysis groups N. taweretus sp. nov. with other species of Nesodon. The absolute age of the Aisol Formation has been established at ca 19.480 ± 0.025 Ma (Burdigalian; Early Miocene) by means of U–Pb zircon dating. The vertebrate association is encompassed by the Santacrucian Age. Latitudinal separation between Mendoza and Patagonia in the south would have favored taxonomic differences, as reflected in the species of Nesodon.
The paleoenviroment and paleoecology of the Santa Cnruz Formation (SCF) is summarized. combining the data fromthe chapters of this book and new examination of the community structure of the venebrate fauna using modem analogs. Emphas is is placed on the SCF outcrops along the coastal Atlantic between about 50.30 and 51.60 S and their faunas (-17.9 to 16.2 Ma; Santacrucian SALMA). New data on the sedimentology. the ichnology, and the flora and fauna of the SCF is particularly strong for the lower paris of the SCF south of the Rio Coyle (FL 1-7). FL 1-7 (-17.4 to 17.5 Ma) is analogous to a single modem fauna of limited geographic and temporal scope. As paleolatitude during Santacrucian limes was the same as that of loday, FL 1-7 was exlralropical and had highly seasonal day lengths. The
Andes had nol risen to a sufficient ailitude to block westerly winds and moisture from reaching the Atlantic coast. New dales for FL 1-7 indicate lhat the mid-Miocene global
climatic cool ing had not yet begun. Several taxa recovered at FL 1-7 or in nearby penecontemporaneous levels (e.g. palm trees, the frog Calyptocephalella, the lizard
Tupinambis. the anteater Protamandua, and the primate Homunculus) strongly indicate that Ihe climate of FL 1-7 was much warmer and weller than today. 1lle overall mammalian
species richness and niche composi tion. expressed as percentages of arboreal or scansorial, frugivorous. and grazing, suggest that overall rainfall wns in the range of 1000 to 1500 mm per annum. Occurrence of trees and forest-dwelling birds and mammals (porcupines, spiny rats, sloths, scansorial marsupials. and monkeys) supports this conclusion. The occurrence of calcareous root casts in paleosols indicates high seasona lity in rainfall with cool wet winters and dry wann summers. Grasses were also present , and a number of vertebrate taxa (giant terrestrial birds. many notoungulate. glyplodonts, and armadilos) appear to have been adapted to open environments. Consideration of sedimentologic, ichnologic, floral, and
faunal elements taken together suggests a landscape for FL 1-7 consisting of a mosaic of open temperate humid and semi-arid forests with ponds in some areas and seasonal flooding in others. no doubt promoting the formation of marshlands with a mixture of grasses and forbes.
Coastal exposures of the Santa Cruz Formation in southern Patagonia have been a fertile ground for recovery of Early Miocene vertebrates for more than 100 years. This volume presents a comprehensive compilation of important mammalian groups which continue to thrive today. It includes the most recent fossil finds as well as important new interpretations based on 10 years of fieldwork by the authors. A key focus is placed on the paleoclimate and paleoenvironment during the time of deposition in the Middle Miocene Climatic Optimum (MMCO) between 20 and 15 million years ago. The authors present the first reconstruction of what climatic conditions were like and present important new evidence of the geochronological age, habits and community structures of fossil bird and mammal species. Academic researchers and graduate students in paleontology, paleobiology, paleoecology, stratigraphy, climatology and geochronology will find this a valuable source of information about this fascinating geological formation.
This paper deals with an Oligocene section that is stratigraphically homogeneous from both a lithological and palynological point of view. It has been impossible to subdivide it into discrete units, using either taxon‐range analysis or assemblage‐zone approach based on the relative abundance of palynomorphs. Furthermore, the common multivariate numerical methods used so far with success in the region (Cluster Analysis, Principal Components Analysis, etc.) gave no useful results in this case. The search for cyclicity using palynocycles and ecologs has been also unsuccessful. Instead of considering the section of low interest, an alternative, high‐resolution ecological approach was attempted to extract the information contained in these sediments. Paleoecologi‐cal trends were deduced from statistical methods commonly used in modern and Quaternary ecology, mainly TWINSPAN and gradient analysis, combined with diversity analysis. As a result, the fine‐scale stratigraphic variability of the data could be successfully explained in terms of paleoecological succession taking place in upper delta environments, characterised by a complex mosaic vegetation including morichales, herbaceous fern swamps, and gallery forests. The succession could be reconstructed in detail, and would be of indirect stratigraphic value for high‐resolution correlation. This is an example of how the search for narrow or biased objectives can hidden significant information. It is more fruitful to have a wider perspective, and to be open to any information that sediments can provide us, without a priori limitations.
Catfish bones from Tortonian (Miocene) freshwater beds of central Argentina are here identified as pertaining to a new species of the tropical pimelodid genus Phractocephalus. The new species differs from the other recent and fossil species of the genus in skull, pectoral girdle and spine characters. The material was found in different localities near the city of Paraná, Entre Ríos Province. The bearing horizon is the so-called “Conglomerado osífero” which constitutes the lowermost beds of the fluvial Ituzaingó Formation. The aquatic vertebrate fauna occurring in the bearing bed shows a similar generic composition to several northern South American Miocene units where Phractocephalus remains were found. This report extends the range of Phractocephalus more than 2000 km to the South. The record is in agreement with higher global temperatures and putative ample hydrographic connections of the river basins in the Paraná area with the Amazon basin until at least the early late Miocene.
The evolution of high-crowned teeth, hypsodonty, is a defining characteristic of many terrestrial herbivores. To date, the most prominent focus in the study of the teeth of grazing herbivores has been co-evolution with grasses and grasslands. This book develops the idea further and looks at the myriad ways that soil can enter the diet. Madden then expands this analysis to examine the earth surface processes that mobilize sediment in the environment. The text delivers a global perspective on tooth wear and soil erosion, with examples from the islands of New Zealand to the South American Andes, highlighting how similar geological processes worldwide result in convergent evolution. The final chapter includes a review of elodonty in the fossil record and its environmental consequences. Offering new insights into geomorphology and adaptive and evolutionary morphology, this text will be of value to any researcher interested in the evolution of tooth size and shape.
Coastal exposures of the Santa Cruz Formation in southern Patagonia have been a fertile ground for recovery of Early Miocene vertebrates for more than 100 years. This volume presents a comprehensive compilation of important mammalian groups which continue to thrive today. It includes the most recent fossil finds as well as important new interpretations based on 10 years of fieldwork by the authors. A key focus is placed on the paleoclimate and paleoenvironment during the time of deposition in the Middle Miocene Climatic Optimum (MMCO) between 20 and 15 million years ago. The authors present the first reconstruction of what climatic conditions were like and present important new evidence of the geochronological age, habits and community structures of fossil bird and mammal species. Academic researchers and graduate students in paleontology, paleobiology, paleoecology, stratigraphy, climatology and geochronology will find this a valuable source of information about this fascinating geological formation.
The radiation of a diverse array of endemic marsupials, edentates, primates, rodents and "ungulates' has been exceedingly useful for developing a detailed biochronological sequence of about 20 South American Land Mammal Ages (SALMAs), covering much of Cenozoic time. Best estimates for the approximate durations of the SALMAs are: Lujanian, 10 000-800 000 years ago; Ensenadan, 0.8-1.2 Ma; Uquian, 1.5-3.0 Ma; Chapadmalalan, 3.4-4.0 Ma; Montehermosan, 4.0-6.8 Ma; Huayquerian, 6.8-9.0 Ma; Chasicoan, 9.0-10.0(?) Ma; Mayoan, (?) 10.0-11.8 Ma; Laventan, 11.8-13.8 Ma; Colloncuran, 14.0-15.5 Ma; Friasian, uncertain; Santacrucian, 16.3-17.5 Ma; Colhuehuapian, (?)19-21(?) Ma; Deseadan, 24.5-29 Ma; New SALMA ("Tinguirirican'), 31.5-36 Ma; Divisaderan, (?)40-42(?) Ma; Mustersan, (?)45-48(?) Ma; Casamayoran, (?)51-54(?) Ma; Riochican 55.5-57 Ma; Itaboraian, 57.5-59 Ma; Peligran, 61-62.5 Ma; and Tiupampan, 63-64.5 Ma. The South American faunal and floral record can be combined with available geochronologic information to evaluate timing and pattern of major biotic and environmental changes and events. It is clear that Cenozoic terrestrial biotas responded to both global and regional, physical and biotic, changes and events, including major plate tectonic reorganizations and associated biogeographic events, global Eocene-Oligocene boundary events, phases of Andean uplift, Pliocene-Pleistocene Epoch glaciation/climatic changes, etc. -from Authors
We provide a synopsis of ~60 million years of life history in Neotropical lowlands, based on a comprehensive survey of the Cenozoic deposits along the Quebra da Cachiyacu near Contamana in Peruvian Amazonia. The 34 fossil-bearing localities identified have yielded a diversity of fossil remains, including vertebrates, mollusks, arthropods, plant fossils, and microorganisms, ranging from the early Paleocene up to the late Miocene–?Pliocene (>20 successive levels). This Cenozoic series includes the base of the Huchpayacu Formation (Fm.; early Paleocene; lacustrine/fluvial environments; charophyte-dominated assemblage), the Pozo Fm. (middle + ?late Eocene; marine then freshwater environments; most diversified biomes), and complete sections for the Chambira Fm. (late Oligocene–late early Miocene; freshwater environments; vertebrate-dominated faunas), the Pebas Fm. (late early to early late Miocene; freshwater environments with an increasing marine influence; excellent fossil record), and Ipururo Fm. (late Miocene–?Pliocene; fully fluvial environments; virtually no fossils preserved). At least 485 fossil species are recognized in the Contamana area (~250 ‘plants’, ~212 animals, and 23 foraminifera). Based on taxonomic lists from each stratigraphic interval, high-level taxonomic diversity remained fairly constant throughout the middle Eocene-Miocene interval (8–12 classes), ordinal diversity fluctuated to a greater degree, and family/species diversity generally declined, with a drastic drop in the early Miocene. The Paleocene–?Pliocene fossil assemblages from Contamana attest at least to four biogeographic histories inherited from (i) Mesozoic Gondwanan times, (ii) the Panamerican realm prior to (iii) the time of South America’s Cenozoic “splendid isolation”, and (iv) Neotropical ecosystems in the Americas. No direct evidence of any North American terrestrial immigrant has yet been recognized in the Miocene record at Contamana.
Between c. 23 and 8 Ma, western Amazonia was occupied by the vast Pebas long-lived lake/wetland system. The Pebas system had a variety of influences over the evolution of Miocene and modern Amazonian biota; it formed a barrier for the exchange of terrestrial biota, a pathway for the transition of marine biota into freshwater Amazonian environments, and formed the stage of remarkable radiations of endemic molluscs and ostracods. The lithological variation of the Pebas Formation has furthermore enhanced edaphic heterogeneity in western Amazonia, sustaining present-day high terrestrial diversity in the region.
This article presents a morphofunctional analysis of the hind limb of Santacrucian (Early Miocene) sloths from southernmost Patagonia (Argentina). These fossil sloths were mid sized to large animals, ranging from 40 to 120 kg, and their postcranial skeleton was markedly different in shape compared with that of extant tree sloths, which vary from 2 to 10 kg. The functional anatomy of the hind limb of Santacrucian sloths was compared with that of living xenarthrans (tree sloths, anteaters, and armadillos), which involved reconstruction of the hind limb musculature and comparative and qualitative morphofunctional analyses, and hypotheses on the biological role of the hind limb in terms of preferences in substrate, posture, and strategies of locomotion were formulated. The hind limb of Santacrucian sloths bears strong resemblances to that of living South American anteaters in stoutness of skeletal elements, form of the characteristics related to muscular and ligamentous attachments, and conservative, pentadactylous strong-clawed pes. The musculature was very well developed, allowing powerful forces, principally in entire limb adduction, crus flexion and extension, pes extension, and toe prehension. These functional features, together with those of the forelimb, are congruent with climbing behavior, and support the hypothesis that Santacrucian sloths were good but slow climbing mammals. However, their climbing strategies were limited, owing principally to their comparatively large body size, and they relied to a large extent on their powerful musculature and curved manual and pedal unguals for both moving and standing on the arboreal supports.
In general the geology of paleontological sites in Venezuela is poorly
known. With the purpose of improve this knowledge we described the geology of Castillo
Formation (Late Oligocene to Early Miocene) at Cerro La Cruz locality, in Lara state,
Venezuela, that contain several records of vertebrate and invertebrate fauna.
Lithologically, Cerro La Cruz sequence is composed by alternating packages of
siliciclastic and carbonate sediments, with predominance of mudstone. The
paleoenvironment was inferred as a mainly near–shore marine complex that could be
associated to regressive and trangressive phases. Nevertheless, into the middle part of the
Cerro La Cruz outcrops were find two levels containing at least six mammal remains,
conforming the early continental mammal assemblage of Venezuela. The continental
vertebrate assemblage who includes Xenarthra, Notoungulata and Litopterna mammals,
fresh water fishes, the turtle Chelus, wood and leaves, allows us to interpret the
paleoenvironment of the continental episodes of this locality as a mosaic composed of a
humid forest and lowland savanna. Four isotopic dates using Strontium (87Sr/86Sr), from
the Cerro La Cruz locality were obtain, which places an age limit of the sediments to
between 17.21 to 19.27 Ma, confirming an Early Miocene age for this locality.
Biochronologically, the mammalian assemblage so far recovered does not permit us to
assign this fauna to any of the recognized South American Land Mammal Ages, however
the isotopic ages suggest affinities with a Pansantacrucian mammalian sub–cycle. Our
interpretation of the geology at Cerro La Cruz shows no evidence for the presence of a
major river system crossing over that zone during the Early Miocene, does not support the
hypothesis of the possible draining of a “Proto–Orinoco” river into Maracaibo or Falcón
Basin during the Early Miocene.