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Early Miocene astrapotheres (mammalia) from northern South America
Abstract
Astrapotheriid postcranial elements are described from the early Miocene locality Cerro La Cruz in northwestern Venezuela. This skeletal material provides new insights into the structure and lifestyle of this enigmatic group of extinct South American mammals that lack any living analogues. A newly observed pedal character, the dorsoventral curvature of the astragalar head, is shown to distinguish the Venezuelan astrapotheres (Xenastrapo- therium christi and the Cerro La Cruz form) from the Patagonian genus Parastrapotherium. Two tibial specimens possess twisted shafts with obliquely oriented distal articular extremities, this feature appearing to characterise all known astrapothere tibiae. A cervical vertebral specimen exceeds in size any previously known specimens and brings into question the function of the astrapothere's extraordinarily thick neck and comparatively small slender limbs. The astrapotheriid postcranial elements from Cerro La Cruz indicate the presence of two coeval species of astrapothere that can be assigned to the subfamily Astrapotheriinae.
... Palabras clave: Mioceno temprano, Pansantacrucense, Formación Castillo, Evolución del 'Proto-Orinoco', Venezuela. studies by several authors (Sánchez-Villagra et al., 2000;Dahdul, 2004;Aguilera and Rodríguez de Aguilera, 2004a y b;Sánchez-Villagra et al., 2004;Brochu and Rincón, 2004;Weston et al., 2004;O'Leary, 2004) have reported more or less thirty new faunal records for this formation, seven of which are mammals, but only two of these are terrestrial mammals. Most of these taxa are from a locality named Cerro La Cruz, Lara state. ...
... The third terrestrial mammal, from the Quiamare Formation (Early to Late Miocene), Boreostemma venezolensis was reported by Simpson (1947). More recently Weston et al., 2004;O'Leary, 2004) reported another Early Miocene locality in the Castillo Formation with fossil mammals. ...
... These authors report a fauna composed of one turtle, one crocodile, two whales (Odontoceti), three sharks, along with a palm fruit, 20 molluscan species, and one crab. Subsequent studies carried out at the Cerro La Cruz locality (Sánchez-Villagra et al., 2001;Dahdul, 2004;Aguilera and Rodríguez de Aguilera, 2004a and b;Sánchez-Villagra et al., 2004;Weston et al., 2004;O'Leary, 2004;Brochu and Rincón, 2004;Aguilera and Lundberg, 2010;Sánchez-Villagra et al., 2010;Rincón et al., 2010a and b;Aguilera et al., 2013) resulted in the recognition of a diverse vertebrate assemblage. ...
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.
... 1937; Riggs, 1935;Croft, 1999Croft, , 2016Koenigswald, 2011Koenigswald, , 2018Cassini et al., 2012). The postcranial skeleton of Astrapotherium was equally peculiar; among other features, it included a relatively long neck that was mobile but also quite robust, apparently gracile limbs relative to body size, and small but very unusual feet (Scott, 1937;Weston et al., 2004). According to Scott (1937:337), who described the only articulated astrapothere skeleton yet known, "[a]nyone who has looked through the foregoing osteological description will be prepared to agree that the Astrapotheria comprise some of the strangest and most grotesque mammals of which we have any knowledge." ...
... Discoveries of Neogene astrapothere remains in recent decades are generally compatible with the taphonomic observations of Riggs (1935) and support a preference among astrapotheres for riverine habitats. For example, astrapotheres are among the few terrestrial vertebrates recovered from the early Miocene Castillo Formation of northern Venezuela, a near-shore marine sequence that mainly preserves remains of invertebrates, fishes, turtles, and crocodiles Weston et al., 2004;Rincón et al., 2014). Astrapothere remains have been found associated with fluviolacustrine intervals and fully aquatic species at several sites in Colombia including the Honda Group at La Venta , the Castilletes Formation of the Guajira Peninsula Carrillo et al., 2018), and outcrops that may pertain to the Real Group at Ciénaga de Zapatosa (Pardo-Jaramillo, 2018). ...
Astrapotheres were a clade of unusual early to middle Cenozoic herbivorous mammals endemic to South America. Neogene astrapotheres were large, tusked mammals that probably had a short proboscis and may have preferred mesic lowland habitats; they were widespread during the early Miocene, became restricted to the tropics during the middle Miocene, and apparently did not persist into the late
Miocene. The geologically youngest astrapotheres pertain to the subfamily Uruguaytheriinae, and in this report, we describe a partial uruguaytheriine astrapothere cranium with well-preserved postcanine dentition that we identify as Granastrapotherium cf. snorki. This specimen was collected from fluviolacustrine strata in the Tumbes Region of extreme northwestern Peru that likely pertain to the Zorritos Formation. At present, the temporal range of Granastrapotherium snorki is restricted to the late middle Miocene (Serravallian Age; ca. 13.6–12.8 Ma), which suggests a similar age for the fossil-bearing sediments of the upper Zorritos Formation. The fossil locality, which is ca. 25 km southwest of the city of Tumbes, is ca. 1,000 km distant from other sites in Peru and Colombia where G. snorki has been recorded and extends the geographic range of the species westward more than 550 km. We estimate the body mass of G. snorki at 1,800-2,500 kg based on head-body length of 3.75 m; this is lower than dentition-based body mass estimates but still suggests G. snorki was the largest terrestrial mammal in South America at the time. Key words: Astrapothere, Body mass, Fossil, Granastrapotherium, Laventan, Megafauna, Paleobiology, Teeth.
... Like the Indian rhino, Parastrapotherium and Astrapotherium might be graviportal taxa frequently occupying aquatic environments. Weston et al. (2004) considered that the taphonomy associated with astrapotheres bones was more relevant than their morphology itself to suggest an amphibious way of life. Indeed, though the astrapothere limbs are slender, they are relatively short in comparison to their long trunk (Weston et al. 2004), which suggests that they are not as gracile as previously thought and that astrapotheres were not, as previously hypothesized, obligatorily aquatic in order to support their heavy body. ...
... Weston et al. (2004) considered that the taphonomy associated with astrapotheres bones was more relevant than their morphology itself to suggest an amphibious way of life. Indeed, though the astrapothere limbs are slender, they are relatively short in comparison to their long trunk (Weston et al. 2004), which suggests that they are not as gracile as previously thought and that astrapotheres were not, as previously hypothesized, obligatorily aquatic in order to support their heavy body. Moreover, Cassini et al. (2012b: 271) pointed out that the forelimb of some astrapotheres (i.e., Astrapotherium) Bwas capable of withstanding high mechanical loads, even more than its own body mass,^thereby echoing some previous workers mentioning adaptation to graviportality in astrapotheres (Osborn 1929;Cifelli 1985). ...
Adaptation to aquatic or semi-aquatic habits has been demonstrated in several distantly related mammalian clades worldwide during the Cenozoic, but curiously none has been conclusively evidenced inland for South America although a few South American native ungulates (SANU) have been proposed as possible subaquatic taxa. These taxa mostly correspond to large-sized herbivorous forms among astrapotheres, pyrotheres, and some toxodontid notoungulates, found at the end of the Paleogene and/or beginning of the Neogene. As no clear argument was provided for these ecological hypotheses, an analysis of the microanatomical features of long bones of some of these taxa in a comparative context was conducted in order to address the question of the paleoecology of these organisms. Our study highlights a variety of osseous specializations in the stylopod bones of SANU, and notably that Parastrapotherium, Pyrotherium, and Nesodon are affected by bone mass increase. If the microanatomical features of Parastrapotherium and Nesodon evoke what is observed in some terrestrial or semi-aquatic graviportal taxa, the very high compactness of Pyrotherium suggests extreme functional requirements in this taxon such as a graviportal hyperspecialization. This study thus evidences the occurrence of several convergent adaptations to graviportality and/or subaquatic habits within SANU and contributes to an important step towards a better integration of South American endemic mammals in large-scaled paleoecological studies.
... Astrapotheria, a lineage of South American extinct herbivores, is recorded from late Paleocene-early Eocene Itaboraian South American Land Mammal Age (SALMA; Oliveira and Goin, 2011) to middle Miocene Laventan SALMA (Paula Couto, 1952;Simpson, 1967;Johnson, 1984;Cifelli, 1985Cifelli, , 1993Johnson and Madden, 1997;Weston et al., 2004;Goillot et al., 2011). The group attained great size variation, with body mass estimates ranging from 60.28 kg in some primitive genera (Vizca ıno et al., 2012) to 4120 kg in more derived genera . ...
... Granastrapotherium is known from the middle Miocene of La Venta, Colombia (Honda Group; Johnson and Madden, 1997), and the Fiztcarrald Arch of the Peruvian Amazonia (late middle Miocene, »13 Ma; Goillot et al., 2011). There are also reports of indeterminate Uruguaytheriinae fragments from Quebrada Honda, Bolivia (middle Miocene, Laventan SALMA; Goillot et al., 2011), and postcranial remains from Venezuela (Castillo Formation, early Miocene) that cannot be unequivocally assigned to Uruguaytheriinae but are different from Patagonian taxa (Weston et al., 2004). ...
Astrapotheria is an order of extinct South American herbivores recorded throughout the continent, from the late Paleocene to middle Miocene. Here we describe Hilarcotherium castanedaii, gen. et sp. nov., an Uruguaytheriinae astrapothere from sediments of La Victoria Formation (middle Miocene) in the Tolima Department, Upper Magdalena Valley, Colombia. H. castanedaii, represented by a partial skull, mandible, and some postcranial remains, is characterized by (1) unique dental formula, with 0/3i, 1/1c, 1/1p, and 3/3 m; and (2) lower canines with subtriangular transverse section at the base. Hilarcotherium differs from the equatorial Uruguaytheriinae genera Xenastrapotherium and Granastrapotherium in (1) having three lower incisors; (2) the diagonal implantation of the lower canines; (3) lower molars with lingual cingulid; (4) the presence of the hypocone in the third upper molar; and (5) the presence of an anterolingual pocket in the fourth upper premolar. Our phylogenetic analysis supports the monophyly of the subfamilies Astrapotheriinae and Uruguaytheriinae. Within the latter, we confirm the monophyly of the neotropical clade (Hilarcotherium, Xenastrapotherium, and Granastrapotherium). H. castanedaii shows some plesiomorphic features such as the aforementioned presence of the i3 and the developed hypocone in the last upper molar. Its estimated body mass (1303 kg) is intermediate among Astrapotheriidae.
... A specimen of Astrapotherium magnum from the early Miocene of Santa Cruz, Argentina, is the most complete astrapothere skeleton known and displays a strange combination of features including a relatively long but robust neck, unusual limb proportions, a twisted tibial shaft, and gracile hindquarters compared to the rest of its body (Scott 1937, Weston et al. 2004, Croft & Guder 2014. Combined with large tusks and a proboscis, Astrapotherium and similar species were certainly among the most distinctive SANUs (Figure 1). ...
A remarkable diversity of plant-eating mammals known as South American native ungulates (SANUs) flourished in South America for most of the Cenozoic. Although some of these species likely filled ecological niches similar to those of modern hoofed mammals, others differed substantially from extant artiodactyls and perissodactyls in their skull and limb anatomy and probably also in their ecology. Notoungulates and litopterns were the longest-lived and most diverse SANU clades and survived into the Quaternary; astrapotheres went extinct in the late Miocene, whereas other SANU groups were restricted to the Paleogene. Neogene notoungulates were quite specialized in craniodental structure, but many were rather unspecialized postcranially; in contrast, litopterns evolved limb specializations early in their history while maintaining more conservative dentitions. In this article, we review the current understanding of SANU evolutionary relationships and paleoecology, provide an updated compilation of genus temporal ranges, and discuss possible directions for future research. ▪ South American native ungulates (SANUs) were a diverse, long-lived, and independent radiation of mammals into varied terrestrial plant-eater niches. ▪ We review origins, evolution, and paleoecology the major SANU clades: Notoungulata, Litopterna, Astrapotheria, Xenungulata, and Pyrotheria. ▪ At their peak, during the Eocene and Oligocene, more than 40 genera of native ungulates inhabited South America at any one time. ▪ SANUs ranged from <1 kg to several tons and evolved many combinations of diet and locomotor adaptations not seen in living ungulates.
Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 48 is May 29, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Astrapotheres (or at least astrapotheriids) are also generally regarded as semiaquatic (e.g., Scott, 1937; and indicative of permanent bodies of water. This interpretation is mainly based on taphonomic evidence, since astrapothere remains are frequently found in river channel or lake deposits (Riggs, 1935;Marshall, et al., 1990;Cladera et al., 2004), sometimes alongside remains of other semiaquatic or fully aquatic vertebrates (e.g., Weston et al., 2004;Moreno-Bernal et al., 2012;Moreno et al., 2015). Paleobiological studies of diet and locomotion in Astrapotherium magnum are compatible with semiaquatic habits for astrapotheres (Avilla and Vizca ıno, 2005;Cassini et al., 2012;Perez et al., 2013). ...
We provide new and revised identifications of mammals from the early middle Miocene (Langhian age, Colloncuran South American Land Mammal Age [SALMA]) of Cerdas, Bolivia. We also formally name a new typothere notoungulate, Hegetotherium cerdasensis, sp. nov., that can be distinguished by the absence of an external talonid sulcus on m3 and its small size (15–25% smaller than Hegetotherium mirabile). We refer several typothere specimens from Nazareno, Bolivia, to H. cerdasensis, which suggests that the two sites are of similar age. We report the first sparassodont and astrapothere remains from Cerdas. Sparassodont remains include an associated basicranium and mostly complete mandible; the species appears to represent a new, small-bodied borhyaenoid. Astrapothere remains consist of many tooth fragments from a new species of the subfamily Uruguaytheriinae. A partial sloth dentary from Cerdas likely pertains to the subfamily Megatheriinae and is the first report of the family Megatheriidae from the site. A newly discovered peltephilid armadillo specimen includes a partial articulated carapace that supports recognition of the Cerdas taxon as a new species. The two dasypodids of Cerdas (one Euphractini, one Eutatini) represent two new species closely related to undescribed species from the late middle Miocene (Serravallian age, Laventan SALMA) of Quebrada Honda, Bolivia. The mammals of Cerdas indicate that (1) the middle latitudes (southern tropics) contributed significantly to the diversity of Miocene mammal communities in South America; and (2) the Middle Miocene Climatic Optimum was a key factor in the differentiation of South American mammal assemblages. Citation for this article: Croft, D. A., A. A. Carlini, M. R. Ciancio, D. Brandoni, N. E. Drew, R. K. Engelman, and F. Anaya. 2016. New mammal faunal data from Cerdas, Bolivia, a middle-latitude Neotropical site that chronicles the end of the Middle Miocene Climatic Optimum in South America. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1163574.
... Despite achieving a remarkable diversity, the endemic South American ungulates are not represented in modern faunas. In general, these animals mirrored the ungulate diversity we are familiar with today around the world, having evolved their own analogous forms of hippos, rhinos, horses, camels, and elephants (Cifelli 1985;Elissamburu 2004;Weston et al. 2004;Shockey et al. 2007;Kramarz and Bond 2009), combinations of these (Owen 1837(Owen , 1840, or completely singular forms (Scott 1937). ...
A developmental model, based upon murine rodents, has been proposed by Kavanagh et al. (2007) to explain lower molar proportions in mammals. We produce a clade-wide macroevolutionary test of the model using the dental evolutionary trends in a unique radiation of extinct mammals endemic to South America ("Meridiungulata") that comprise a diverse array of molar morphologies. All of the South American ungulate groups examined follow the inhibitory cascade model with the exception of two groups: Interatheriidae (Notoungulata) and Astrapotheria. For most taxa studied, ratios between lower molar areas are greater than 1.0, indicating a weak inhibition by ml on the subsequent molars in the tooth row, and a trend to greater absolute size of the posterior molars. Comparisons of mean ratios between clades indicate that a significant phylogenetic signal can be detected, particularly between the two groups within Notoungulata—Typotheria and Toxodontia. Body mass estimates were found to be significantly correlated with both m3/m1 and m2/m1 ratios, suggesting that the larger body size achieved the weaker inhibition between the lower molars. Molar ratio patterns are examined and discussed in relation to the independent and numerous acquisitions of hypsodonty that are characteristic of dental evolution in "Meridiungulata."
... A" and "Astrapotheriidae indet. B"; Sánchez-Villagra et al. 2004;Weston et al. 2004). ...
Five mandibular and dental specimens referred to the extinct South American ungulate clade Astrapotheria are described. They originate from late middle Miocene deposits of the Ipururo Formation in the Río Inuya-Río Mapuya area, Peruvian Amazonia. The first Peruvian astrapothere remains unearthed in a controlled stratigraphical context reveal the co-occurrence of the uruguaytheriine astrapotheriids Xenastrapotherium sp. and Granastrapotherium cf. snorki. Bispecific uruguaytheriine assemblages were so far restricted to the early Miocene of Venezuela and the late middle Miocene of Colombia. The Fitzcarrald local fauna, including the uruguay theriines described here, recalls unequivocally the Xenastrapotherium kraglievichi Cabrera, 1929-Granastrapotherium snorki assemblage, which characterizes the 13.6-12.76 Ma interval in the Honda Group of La Venta area, Colombia. The spatio-temporal distribution of low-latitude astrapotheriids (< 30°S) is then reviewed, illustrated, and further detailed in both stratigraphical and taxonomic points of view. The group appears in the fossil record during the Oligocene or the earliest Miocene (Uruguaytherium Kraglievich, 1928 and Xenastrapotherium Kraglievich, 1928 in Uruguay and Venezuela, respectively). Uruguaytheriinae are conspicuous elements of middle Miocene mammal assemblages of northern South America (Colombia, Brazil, Bolivia, and now Peru). Astrapotheria probably become extinct during the late Miocene (Huayquerian South American Land Mammal Age), but the youngest specimens are of uncertain taxonomic affi nities and/or might be reworked (Astrapotheriidae indet. in Urumaco Formation of Venezuela;? Astrapotheria in Rio Acre local fauna of Brazil). © Publications Scientifiques du Muséum national d'Histoire naturelle, Paris.
The mammalian fauna of Cenozoic South America is known from the scientific literature to be mainly composed of a series of different aggregate waves of migrants, which originally were recognized and characterized by Simpson (1950) as the first to the third "strata." The living mammal fauna of South America still retains members of the three "strata," but during the Cenozoic the orders of endemic ungulates pertaining to the first stratum became extinct. The living South American ungulates are all northern immigrants from the third stratum. The zenith of the South American endemic or native ungulates can be traced back to the Paleogene. In the Casamayoran South American Land Mammal Age (SALMA) (Eocene) they are represented, conservatively, by five "orders"and more than forty genera. During later times in the Cenozoic there was a significant diminution in the taxonomic diversity, though a reduction in abundance of specimens has not been observed. This was a consequence of worldwide environmental changes that affected the biota during the Eocene and Oligocene transitions. During these transitions the decrease of worldwide temperature (Zachos et al. 2001, 2003) led to the modern "Icehouse-World." As a consequence mammalian communities underwent several changes in their lineages. This global climatic change led to several faunal changes, such as the "Grande Coupure"in Europe. In South America the end of the Eocene was associated with several geological events. Among them, sea-level fluctuation and the rise of the Andes mountain range accentuated climatic changes in South America. So during the Early Neogene (fig. 13.1), for example in the Santacruzian SALMA (Early Miocene), endemic ungulates were reduced from five to three orders (Astrapotheria, Litopterna, and Notoungulata) and nearly 50% of the genera, and holdover lineages became specialized and distinctive, almost "stereotyped"within each group. The evolutionary history of the native ungulates, as well as that of many other South American mammals, is based mainly on the Cenozoic fossil record from Argentina, with a considerable latitudinal range of fossiliferous sites. Hence this history is biased, when we consider all of South America, especially due to the scattered and sometimes scarce fossil record of the more tropical areas. In these outcrops scientific research has been not so extensive as it has been in Argentina, in part due to dif- ficulties in the field (rare preservation and limited access to outcrops; e.g., large fluvial basins subjected to extensive inundation). Considering the Venezuelan fossil record, the oldest mammal is supposed to come from Eocene rocks of Trujillo state. It was described by Patterson (1977) as Proticia venezuelensis and interpreted as a representative of the Pyrotheria, a bilophodont order of South American native ungulates. But its stratigraphic provenance and phylogenetic affinities were questioned by Sánchez-Villagra et al. (2000). Proticia venezuelensis is represented by a jaw fragment with p3-m1. The fossil was collected in 1964 by a second person, several years before Patterson visited the supposed locality in 1970. As related by Patterson (1977), the fossil was reported to be found in a spot along the Quebrada de Agua Viva, which is located about 13 km west of the Cerro La Cruz locality. As described by Sánchez-Villagra et al. (2000), in 1995 Rich Kay, Roberto Lozsan, Rick Madden, and Marcelo R. Sánchez-Villagra visited the purported collection spot of Proticia venezuelensis (Patterson 1977), with the help of Don Guillermo, a local resident who accompanied Patterson in 1970 to the locality. They found no traces of any vertebrate fossil in the area and, based on this observation (also experienced by Patterson 1977, 400), suggested that the provenance of P. venezuelensis should be put into question. P. venezuelensis is more likely to have come from the rocks of the Castillo Formation. Its dental anatomy places the phylogenetic position of this taxon in question. A cuspate tooth form (lack of bilophodonty) and the presence of thick enamel make the possibility of sirenian affinities worth testing (Sánchez-Villagra et al. 2000). This would correspond well with the kind of environment in which Sánchez-Villagra et al. (2000) suggested this fossil was found. Another important outcrop in Venezuela is the Urumaco Sequence in Falcón state (Quiróz and Jaramillo, this volume), which represents one of the few glimpses in the Tertiary of the northern areas. Its fossil mammals indicate a probable Huayquerian SALMA (upper Miocene) for this fauna (Linares 2004), although descriptions of the fossils on which this assessment was based have not yet been published, and correlations between tropical areas and high latitudes are problematic. In tropical areas the La Ventan fauna (Middle Miocene) from Colombia is well known as an early counterpart to the Urumaco fauna of Venezuela. There are also some scattered finds of probable Middle Miocene La Ventan age in Acre, Brazil (Cozzuol 2006), and a recently described La Ventan fauna for Peru is very similar to that of Colombia (Antoine et al. 2007). In Argentina, the Chasicoan and Huayquerian SALMA (fig. 13.1) are chronologically near the Urumaco fauna and represent extra-Patagonian faunas. The Colloncuran SALMA is more or less well known and reflects the changing pattern of the mammalian faunas, specially the native ungulates, in southern latitudes of the continent. The poorly known Mayoan SALMA fauna, Middle Miocene? (fig. 13.1) probably will be of special interest in the future for comparison of one of the last Patagonian faunas before the shift of the mammalian record to more northern areas in Argentina. But to date the Mayoan mammals are not understood well enough, nor are other new records of potential Middle Miocene faunas in Patagonia, to serve as useful antecedents to compare with earlier tropical faunas older than Urumaco. Therefore, given these limitations in knowledge of the Middle Miocene, the Colloncuran SALMA in Argentina and the La Ventan SALMA (fig. 13.1) of Venezuela and Colombia allow us to consider with some accuracy the differences between a southern fauna, probably mainly denizens of open areas, and a tropical one, that probably inhabited more forested and closed regions. In this work we examine what we know about the record of the native ungulates representing the three surviving orders in the Middle Miocene: Astrapotheria, Litopterna and Notoungulata, emphasizing the Urumaco Formation ungulates.
Turtles probably constitute the most readily recognizable group of all vertebrates, with their characteristic shell consisting of two parts, a dorsal carapace and a ventral plastron. Both parts are connected through a bridge, which completes the encasing of organs and even the shoulder girdle, the latter a unique feature among living vertebrates (present only in at least some placodonts among extinct clades, Rieppel 2002). This basic "grundplan" has existed in the group since at least the Late Triassic (ca. 210 Ma), the time from which the oldest stem-turtles are known (Rougier, de la Fuente, and Arcucci 1995). This general conservatism does not imply lack of variation in turtles. In fact, the Urumaco turtle fauna alone, the main subject of this chapter, is a good example of the variation in size, shape, and form that characterizes the turtle shell. Cranial variation also exists in turtles and is relevant at all taxonomic levels. This is evident in the Urumaco turtles discovered so far for a particular genus, for which several species have been recently described. There are two major clades of turtles existing today, distinguished by two distinct neck-retraction mechanisms. Cryptodires ("hidden necked" turtles) retract the head by bending the neck in a vertical plane, whereas pleurodires ("side necked" turtles) bend the neck in a horizontal plane. Living cryptodires are taxonomically and ecologically the more diverse group of the two, and have a worldwide distribution. Living pleurodires are restricted to freshwater environment in the Southern Hemisphere. However, ancient pleurodires were much more diverse ecologically and taxonomically than they are today (Gaffney, Tong, and Meylan 2006), as illustrated by the turtle fauna from the Urumaco sequence. Cryptodires are less abundant in Urumaco, but some occurrences are of singular biogeographic and ecological significance. A total of about eight turtle species are known from the Urumaco fauna. Since the Harvard expeditions of the early 1970s (Sánchez-Villagra this volume), the abundance of fossil turtles in Urumaco has been apparent. Subsequent collections have confirmed the abundance and singularity of this fauna. Other localities that have yielded an abundance of fossil turtles, such as the Miocene Castillo and La Venta formations of Colombia, as well as the Acre vertebrate fauna of Brazil, will be compared with the Urumaco sequence (Quiróz and Jaramillo this volume).
A diverse near-shore marine fauna existed during the early Miocene in what is today an arid inland region about 90 km south of the Caribbean coast of northern Venezuela, a poorly known area geologically and paleontologically. The fossil locality consists of more than 100 m of section exposed in an area of about 1 km2. We report the discovery of 20 molluscan species, one crab (Portunus oblongus), at least three sharks (Hemipristis serra and Carcharhinus spp.), one turtle (“Podocnemis” venezuelensis), one crocodile (Crocodylidae), two whales (Odontoceti) and a three dimensional cast of the mesocarp or endocarp of a palm fruit. Several taxa are reported for the first time in Venezuela or in northern South America. The fauna indicates, or at least is consistent with, an early Miocene age for the locality, and a near-shore and shallow water marine depositional environment. We suggest that the earliest mammal previously reported from Venezuela, the pyrothere Proticia venezuelensis, was collected in Miocene rocks of the Castillo Formation instead of Eocene rocks of the Trujillo Formation.