El Molino Formation Research Articles

Diversity of dinosaur tracks and swim traces in a new site in the Upper Cretaceous El Molino Formation, Torotoro National Park, Bolivia

In January 2021, a new site containing dinosaur trackways was uncovered at kilometer 99 during the Anzaldo to Torotoro highway construction. The trackways were found on two beds of ooid and ostracod-bearing quartz arenites of about 160 m2, each separated by roughly 2 m of calcareous siltstone. In the lower layer, five theropod and five sauropod trackways were identified, three trackways of uncertain identity, and three trackways of didactyl tracks. Due to time constraints, only the upper layer containing a rich assemblage of theropod tracks and traces was thoroughly studied before road construction removed the bed. The upper bed contained 493 tracks in 88 trackways. Of those trackways, 21 consisted of a single, isolated track. In addition to tracks, 73 swim traces from 14 trackways were characterized. We distinguished five track morphotypes based on the morphology of the digits and pedal impression. Swim traces occurred in three distinct morphotypes. Invertebrate burrowing and sediment collapse, after the kick-off phase of track formation, partially modified most tracks. Before substrate stabilization, the water level rose, and dinosaurs swam in the area, leaving characteristic swim trackways with their feet scratching the bottom. This report records abundant theropod tracks and swim traces in a fortuitous exposure that is no longer accessible and comments on behavioral and paleoenvironmental implications. This location adds to the significance of the dinosaur track record of the Parque Nacional Torotoro (Torotoro National Park), Bolivia.

New ankylosaurian trackways (cf. Tetrapodosaurus) from an uppermost Cretaceous level of the El Molino Formation of Bolivia

Since the second half of the 20th Century, the study of fossil tracks in South America has steadily increased. A large number of tetrapod ichnogenera is currently known mainly from Argentina, Bolivia and Brazil. In this study, we present a new record consisting of several trackways that we refer to cf. Tetrapodosaurus, representing the first explicit mention of the ichnogenus in South America. These tracks come from the lacustrine to transitional El Molino Formation, deposited in Maastrichtian-Danian times, at the locality of Niñu-Mayu, near Sucre, Bolivia. These tracks preserve a quite similar manual morphology to that of Tetrapodosaurus borealis and minor differences in its pedal prints. Tetrapodosaurus is a typical ichnogenus of the northern hemisphere and commonly assigned to an ankylosaurian trackmaker. Tracks assigned to ankylosaurs were already reported from other sites of Bolivia, Brazil and tentatively Argentina; the new finding further improves our understanding of the ankylosaurian record from South America. A detailed morphological analysis allows us to make an accurate trackmaker identification and footprints are attributed to a member of the ankylosaurian family, the Nodosauridae. The trackways from Niñu-Mayu also have paleobiological implications. Manus prints are complete, pes prints generally lack the proximal region of the pes, the sole pad, expulsion rims are proximally placed in pes prints and the trackway parameters are highly variable, suggesting formation influenced by certain buoyancy of the trackmakers.

The Late Cretaceous dinosaur track record of Bolivia – Review and perspective

We present an update and a review of the Late Cretaceous dinosaur tracksites of Bolivia. The Puca Group (Coniacian – Late Maastrichtian) records the tracks and trackways of two different titanosaurid sauropods, ankylosaurs, hadrosaurs and different theropod groups from the Central Andean lacustrine back arc basin. We review the sites from the Maragua syncline (Chuquisaca) and present new data on the famous Toro Toro site (Potosi).Furthermore, the first complete map of the world's largest dinosaur tracksite, Cal Orck'o (El Molino Formation, Sucre) gives an insight into behavior and movement patterns. Parallel trackways of subadult ankylosaurs provide the first unequivocal evidence of social behavior amongst these dinosaurs worldwide. The El Molino Formation and the coeval deposits of Southern Peru and Northern Argentina form a megatracksite with a size of around 100,000 km2. The paleogeographic position of the main sites within the basin suggests that they are part of a seasonal migration route along the shoreline and deltas of an ancient lake system.

Astronomically forced hydrology of the Late Cretaceous sub-tropical Potosí Basin, Bolivia

AbstractPeriodic variations in Earth’s orbital parameters force climate on local and global scales, with global responses particularly sensitive to the presence of ice sheets and their associated feedbacks. Therefore, determining whether orbital forcings influenced sedimentary records of the past, and if so, which had such an effect, can shed light on Earth’s climate sensitivity and global ice volume. To this end, we present a field- and drone-based cyclostratigraphy of the predominantly lacustrine El Molino Formation of the Late Cretaceous–Early Paleogene Potosí Basin in present day Bolivia, which contains carbonate mud parasequences that record fluctuating hydrological conditions, including ephemeral marine connections, from 73 Ma to 64 Ma. We introduce a novel methodology for incorporating drone imagery into a quantitative, three-dimensional stratigraphic model that generates an upward-younging quantity comparable to stratigraphic height, and we find that our model outperforms our own field measurements of stratigraphic height. We project drone imagery at two sites into the stratigraphic model to construct time series of outcrop color, which vary systematically with facies and track basin water depth. Spectral analysis of these time series reveals sedimentary periodicities corresponding to short eccentricity, precession, and semi-precession, which are corroborated with measurements of magnetic susceptibility from mudstones. We generate independent age models at both study areas from four new U-Pb chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA–ID–TIMS) ages, which are consistent with an orbital interpretation for observed sedimentary periodicities. Importantly, we observe the presence of obliquity-scale periodicity in sedimentation during a period of marine connection, suggesting that sea level oscillations were driven by obliquity. This observation is consistent with previous claims about the presence of a small, orbitally forced Antarctic ice sheet during the latest Cretaceous.

Titanosaur trackways from the Late Cretaceous El Molino Formation of Bolivia (Cal Orck’o, Sucre)

The Cal Orck’o tracksite is exposed in a quarry wall, approximately 4.4 km NW of Sucre (Department Chuquisaca, Bolivia) in the Altiplano/Cordillera Oriental, in the El Molino Formation (Middle Maastrichtian). Fossiliferous oolitic limestones, associated with large, freshwater stromatolites and nine levels of dinosaur tracks in the El Molino Formation document an open lacustrine environment. The main track-bearing level is almost vertical with a surface area of ~ 65,000 m 2 . The high-resolution mapping of the site from 1998 to 2015 revealed a total of 12,092 individual dinosaur tracks in 465 trackways. Nine different morphotypes of dinosaur tracks have been documented. Amongst them are several trackways of theropods, ornithopods, ankylosaurs and sauropods, with the latter group accounting for 26% of the trackways. Two different types of sauropod trackways are present. One exhibits speech-bubble-shaped manus impressions that are rotated outwardly and located more outwards than pes prints, and oval to rounded pes imprints with few details, but with a characteristic oval track shape. The second morphotype has more rounded and axially compressed pes imprints and horseshoe-like manus impressions. The manus shows clear impressions of digits I and V. The first morphotype with the more rounded manus can be attributed to a derived titanosaur. The second is assigned to the new ichnogenus Calorckosauripus and was probably made by a basal titanosaur. Both sauropod morphotypes exhibit a narrow-gauge and a wide-gauge stance along the same trackway, and therefore the authors suggest that trackway width may not be correlated, or may not be correlated completely with the osteological characters of the trackmaker’s skeleton.

The relationships of Gasteroclupea branisai Signeux, 1964, a freshwater double-armored herring (Clupeomorpha, Ellimmichthyiformes) from the Late Cretaceous-Paleocene of South America

The clupeomorph fish Gasteroclupea branisai Signeux, 1964 from the Late Cretaceous-Paleocene of El Molino Formation, Cayara locality, Bolivia is redescribed in detail. This South American double-armored herring is the sole member of the family Gasteroclupeidae and exhibits a unique combination of features (skull roof ornamented with fine tubercles, beryciform foramen, endopterygoid teeth, about 16–18 supraneurals, a series of 35–38 predorsal and 40 ventral scutes, median fins small and containing 12–14 rays) that clearly supports its assignment to the extinct clupeomorph order Ellimmichthyiformes. G. branisai shares a number of synapomorphies with Sorbinichthys elusivo and S. africanus (five hypurals, second hypural autogenous, distal end of the second uroneural not reaching the distal end of the first uroneural) with which it forms a monophyletic assemblage recognized herein for the first time as the new suborder Sorbinichthyoidei. The peculiar morphology of Gasteroclupea that is characterized by having an extremely deep abdominal profile, hypertrophied coracoid, and elongated pectoral fins, resembles in many aspects the body plan of extant freshwater hatchetfishes of the characiform family Gasteropelecidae, suggesting that the morphological adaptations of G. branisai can be related, at least in part, to a similar lifestyle.

New characoids from the Upper Cretaceous and Paleocene of Bolivia and the Mio-Pliocene of Brazil: phylogenetic position and paleobiogeographic implications

ABSTRACT New genera of characoid fossil fishes are described on the basis of remains from the Maastrichtian El Molino Formation and the early late Paleocene Santa Lucía Formation of Bolivia, and the Mio-Pliocene Solimões Formation of Brazil. Comparisons with the Hepsetidae, Erythrinidae, Ctenoluciidae, Acestrorhynchidae, and the characid Hydrocynus allow the following conclusions to be made: the new Bolivian genus lacks some erythrinid synapomorphies but shows notable resemblance to the Acestrorhynchidae, particularly in the pattern of the replacement teeth. The Brazilian genus is included in the erythrinids.

Middle Maastrichtian vertebrates (fishes, amphibians, dinosaurs and other reptiles, mammals) from Pajcha Pata (Bolivia). Biostratigraphic, palaeoecologic and palaeobiogeographic implications

The Pajcha Pata fossil locality in south central Bolivia, in the upper part of the Lower Member of the El Molino Formation, is the first late Cretaceous fauna in South America which has yielded, in addition to some invertebrates and plants, all kinds of vertebrates except birds, but including dinosaurs and mammals. Its middle Maastrichtian age, indicated by geochronologic data, is consistent with the fauna, including the marine ichthyofauna. The vertebrate fossils reported here come from the main fossiliferous level which includes terrestrial, freshwater and marine taxa: vertebrates, Mammalia (both tribosphenic and non-tribosphenic therians), Theropoda (Coelurosauria and Sauropoda), Crocodylia, Squamata (Serpentes), Chelonia, Amphibia (Anura, Gymnophiona, Caudata) and fish (Dipnoi, Teleostei, Actinopteri, Cladistia, Chondrostei); invertebrates (Gastropoda, Bryozoa) and plants (charophytes). Amongst these taxa are the earliest records of some fish, Amphibia and tribosphenic Mammalia in South America and/or in the world. The fish concerned are: Polypteriformes (Latinopollia suarezi), Siluriformes of the family Andinichthyidae (Andinichthys) and two new families, Osteoglossiformes of the subfamily Heterotidinae (Osteoglossidae), Perciformes of the family Latidae, Dipnoi of the family Lepidosirenidae (Lepidosiren cf. paradoxa). The Amphibia concerned are: indeterminate Gymnophiona, Noterpetontidae (Noterpeton bolivianum). Pajcha Pata is the only known locality in South America with both non-tribosphenic and tribosphenic therian mammals. The depositional environment was probably estuarian or lagoonal as indicated by a mixed continental, freshwater, and marine fauna. Comparison of this local fauna with faunas of the same age at localities belonging to the same proximal part of the El Molino basin on one hand, and with others belonging to the distal part on the other hand, shows that the two continental areas seem to have their own endemic freshwater fish fauna (except the Characidae and the Lepisosteidae, known in all levels of Bolivia). However, these two areas have the same marine taxa. This implies some influence of the sea in the whole basin. Calculated temperatures of the marine waters range from 13 to 17° for a latitute of about 22°S, implying a southern Pacific upwelling. The El Molino Basin could have been also connected with the open sea through present-day Argentina and not only Venezuela as thought until now.

Palaeoenvironmental and diagenetic control of the mineralogy of Upper Cretaceous–Lower Tertiary deposits of the Central Palaeo–Andean basin of Bolivia (Potosi area)

Abstract A study, involving mainly X-ray diffraction, of the mineralogy of Upper Cretaceous and Lower Tertiary deposits (Aroifilla, Chaunaca, El Molino, Santa Lucia and Cayara Formations) of the Andean basin in the Bolivian Eastern Cordillera is presented. This work refines environmental reconstructions based on previous sedimentological studies in the Potosi Basin. The results including the clay mineralogy show that the sediments were deposited in a lacustrine system which suffered large variations of water level and groundwater influence. The siliciclastic sediments are characterized either by abundant feldspars or analcime, suggesting a perennial volcanoclastic influence. Tuff layers in the Santa Lucia Formation support this interpretation. The great diversity of clay minerals identified reflects both detrital influences and diagenetic overprinting. Although diagenetic changes are common in this sedimentary series, it is still possible to identify the nature of detrital supply. Illite and illite–smectite mixed-layer clays constitute the background clay sedimentation and reflect predominantly arid climate. This had already been deduced from sedimentogical and geochemical investigations. However, detrital kaolinite occurs in a 40 m-thick interval of the El Molino Formation which probably embraces the K/T boundary and reflects more humid conditions. Further work is necessary to locate more precisely this boundary in the absence of accurate biostratigraphical markers. Authigenic clays are also recognized: in the sandstones in the basal part of the Cayara Formation kaolinite developed authigenically; in the tuff layers of the Santa Lucia Formation well-crystallized authigenic smectite characterizes the clay fraction. In addition, chlorite replaces smectite in limestones beds of the El Molino Formation which were deposited in evaporitic environments.The clay assemblages including illite and chlorite at base of the stratigraphic column (Aroifilla, and Chaunaca Formations) probably results from the replacement of smectitic minerals either by chlorite or illite where depth of burial reached more than 2000 m.

Environmental controls on perennial and ephemeral carbonate lakes: the central palaeo-Andean Basin of Bolivia during Late Cretaceous to early Tertiary times

In the central palaeo-Andean Basin (Potosí Basin) of Bolivia, the up to 450-m-thick El Molino Formation (Campanian-Maastrichtian to early Tertiary) includes two main carbonate lacustrine episodes each of different extent and duration. These episodes are separated by an extensive development of alluvial facies (floodplain deposits) and limestones deposited in playa lakes or isolated ponds. The El Molino Formation has been investigated in six different areas of the Potosí Basin and affords the opportunity to document climatic and tectonic controls on the development of perennial and ephemeral carbonate lacustrine systems. The first lacustrine episode originated predominantly in perennial lakes with wave-dominated low-gradient ‘ramp’-type margins. Outer marginal lacustrine facies include winnowed oolitic grainstones, ostracod packstones and microbialite bioherms. More agitated areas were characterized by nearshore oolitic bars with associated thrombolite mounds. The fossil content, and the lack of significant precipitation of evaporites, indicate that the lake waters were of low salinity (probably oligohaline) during most of this period. After the first lacustrine episode, the widespread development of terrigenous alluvial facies (floodplain deposits), with interspersed playa lakes or isolated ponds in depressions on the floodplain, may indicate a change in the net water budget. The second lacustrine episode is dominated by dark micritic limestones and, to a lesser extent, microbialite bioherms which developed under semiarid climatic conditions. This episode includes the deposits of ephemeral saline, locally alkaline, shallow lakes which were characterized by low-energy, low-gradient ‘ramp’-type margins. The stable isotopic analysis of 163 carbonate samples covering the different facies and depositional settings displays a wide range of values ( −14.2 < δ 18 O < +2.8‰ and −12.9 < δ 13 C < +2.8‰ ) that is typical of nonmarine environments. The distribution of the values indicates that, during the deposition of the El Molino Formation, the basin was hydrologically closed and experienced no strong hydrogeographical changes, except for variations in the palaeolake level related to fluctuations in the regional P/E ratio. These are recorded by two main isotopic trends related to changes between perennial and ephemeral lacustrine conditions. Lacustrine sedimentation was controlled predominantly by climatically driven hydrological changes with repeated oscillations of the water level (expansion and contraction) and subsequent fluctuations in the width of lacustrine-facies belts.

Stratigraphy and chronology of Upper Cretaceous–lower Paleogene strata in Bolivia and northwest Argentina

Integration of sequence stratigraphy, magnetostratigraphy, Ar/Ar dating, and paleontology considerably advances knowledge of the Late Cretaceous–early Paleogene chronostratigraphy and tectonic evolution of Bolivia and adjacent areas. The partly restricted marine El Molino Formation spans the Maastrichtian and Danian (°73–60.0 Ma). Deposition of the alluvial to lacustrine Santa Lucia Formation occurred between 60.0 and 58.2 Ma. The widespread erosional unconformity at the base of the Cayara Formation is 58.2 Ma. This unconformity separates the Upper Puca and Corocoro supersequences in Bolivia, and is thus coeval with the Zuni-Tejas sequence boundary of North America. The thick overlying Potoco and Camargo formations represent a late Paleocene–Oligocene foreland fill. The onset of shortening along the Pacific margin at °89 Ma initially produced rifting in the distal foreland. Santonian–Campanian eastward-onlapping deposits indicate subsequent waning of tectonic activity along the margin. Significant tectonism and magmatism resumed along the margin at °73 Ma and produced an abrupt increase in subsidence rate and other related phenomena in the basin. Subsidence was maximum between °71 and °66 Ma. Due to the early Maastrichtian global sea-level high, marine waters ingressed from the northwest into this underfilled basin. Subsidence decreased during the Late Maastrichtian and was low during the Danian. It increased again in the latest Danian, for which a slight transgression is recorded, and peaked in the early Selandian. Tectonism between 59.5 and 58.2 Ma produced a variety of deformational and sedimentary effects in the basin and correlates with the end of emplacement of the Coastal batholith. The subsequent 58.2 Ma major unconformity marks the onset of continental foreland basin development, which extended into Andean Bolivia during the late Paleocene–Oligocene interval. This basin underwent internal deformation as early as Eocene time in the Altiplano and Cordillera Oriental. These early structures, previously assigned to the late Oligocene–early Miocene orogeny, probably accommodated observed tectonic rotations in the Eocene–Oligocene.

The central palaeo-Andean basin of Bolivia (Potosi area) during the late Cretaceous and early Tertiary: reconstruction of ancient saline lakes using sedimentological, paleoecological and stable isotope records

In the Bolivian Eastern Cordillera, continental evaporites occur in late Cretaceous and early Tertiary Formations (Aroifilla, Chaunaca, uppermost El Molino, Santa-Lucia). Studies carried out in the Potosi basin show that these formations were deposited within an almost continuous lacustrine system subjected to large variations in hydrology independent of any significant marine contribution. Thus, in addition to tectonic effects, the hydrology was mainly governed by changes in the evaporation/precipitation ratio. Major evaporitic phases took place during arid periods which caused the contraction of the lakes and induced the formation of sub-perennial to ephemeral residual brine ponds trapped in the deep part of the lacustrine system (upper Aroifilla, middle Chaunaca, Santa-Lucia Formations). The crystallization of evaporitic minerals occurred as subaqueous precipitation in brine sheets and as interstitial growth both in the dry peripheral mud flats and in the central area when the water table fell below the sediment surface. Although the evaporite mineral assemblage only includes calcium sulfate, it is likely that moresoluble salts may have crystallized and subsequently underwent a partial or total dissolution. The source ions were the catchment basin rocks with a probable contribution of reduced sulfur compounds of volcanic origin. Wide variations of water redox conditions are substantiated by the isotopic composition of the sulfates. During wetter periods (Chaunaca p.p., El Molino), the expansion of the lacustrine system induced perennial conditions with slightly saline to freshwater although episodic desiccations may have occurred. The sedimentation is therefore characterized by decreasing evaporitic influences, carbonate sedimentation (shell coquinas, oolite/oncolite deposits, stromatolitic and thrombolitic build-ups, organic-rich laminated carbonates, etc) and, the diversification of the fauna and flora in the lake waters and near the shorelines. Toward the top of the El Molino Formation, episodic prevalence of sodic alkaline waters induced the formation of analcime-rich laminites. The rise of the lake level was responsible for the sporadic development of seaward outflows by which marine organisms may have entered into the lacustrine system. This late Cretaceous-early Tertiary continental domain was located in the subtropical belt where aridity and sub-desertic conditions alternated with more humid periods.

La présence de fossiles marins dans le Crétacé terminal des Andes centrales et ses conséquences paléogéographiques

The Maastrichtian deposits (late Campanian? to early Danian?) of the central Andes comprise three transgressive-regressive sequences. In Bolivia (El Molino Formation) they have yielded diverse terrestrial, brackish-water or marine fossils, which make it possible to define the depositional environments at their exact stratigraphic position. Marine-influenced transgressive facies are by far the best developed in the first sequence. Among the vertebrates, five groups of fishes are restricted, with some rare exceptions, to marine environmentsl. Some other fish families, genera or species, are known to occur both in freshwater, brackish and marine environments and therefore provide no precise environmental indications. Among the invertebrates, echinoids, serpulids, foraminifera and some pelecypods and gastropods attest to a marine-influenced environment, which may however have experienced periodic salinity variations. The other pelecypods and gastropods generally indicate freshwater environments. The ostracods, often ubiquitous, only provide paleoecologic indications when they constitute oligospecific shell beds, suggesting abnormally low salinity values. Calcispheres and dinoflagellates indicate a stronger marine influence. Charophytes, especially when abundant, suggest a lacustrine environment. Because of their stratigraphic and paleogeographic positions, stromatolites may indicate intertidal to supratidal environments. The fossils most likely of marine generally occur in the transgressive lower parts of the three sequences, where marine oolites and glauconite are also observed. The often endemic nature of the marine assemblages, the common occurrence of dwarfism and the lack of true nektonic forms suggest that most part of the basin was permanently rather shallow and subjected to important, frequent and/or local, salinity variations. The freshwater fishes appear to be reworked and dissociated in the marine levels, but are better preserved in the mainly continental upper parts of the sequences. Marine fossils are rare in the upper sequence. These data contradict with interpretations which suggest that the central Andean Senonian deposits are exclusively terrestrial. Given other paleogeographic constraints, we propose that Maastrichtian sedimentation took place in a wide, elongated, subsident basin, forming the eastern foreland of the paleo-Andes and showing a “cul-de-sac” shape in the south. This restricted basin was periodically connected with the open sea through present-day Venezuela. The salinity of its southern part, situated far from the basin mouth, was shallow and affected by fresh water from inflowing rivers.

Nouveau remaniement de laganoïne chez un semionotidae du crétacé supérieur de Bolivie: Intérêt paléobiologique

Peculiar ganoid scales (thick, globulous, without articular process, with a smooth or an indented upper surface), from the Maastrichtian of the El Molino Formation (Central Bolivia), are considered as belonging to a new Holostean Semionotidae: Lepidotyle enigmatica gen. and sp. nov. The presence of an important remodelling of ganoine in most of these scales allows us to hypothesize physiological modification in relation to calcium, which can be related either to reproduction (with migration from a thalassoid to a freshwater environment), or to an imput of fresh water from the continent. Lepidotyle is considered to be a margino-littoral taxon, and confirms the presence, already demonstrated, of a Maastrichtian sea in Central Bolivia.

Tertiary dinosaurs in South America? A reply to some of Van Valen's assertions

The discussion of the age of some South American Late Cretaceous fossil vertebrate localities by Van Valen led this author to admit the possible persistence of Dinosaurs at the base of the Paleocene. Van Valen's arguments resting on the selachians are reviewed and it can be asserted that the selachian‐bearing localities of the El Molino Formation of Bolivia are Cretaceous and not Tertiary.

Late Cretaceous mammals ( Marsupialia) from Bolivia

A second Late Cretaceous (Maestrichtian Age)mammal fauna for South America was recovered from the El Molino Formation in southcentral Bolivia. Three species are referred to the marsupial super-family Didelphoidea. The most abundant species has marked bunodont dental specializations which are convergent with some early placental Condylarthra; it is named and is tentatively placed in the didelphid subfamily Caroloameghiniinae.

Late Cretaceous vertebrates, including mammals,from Tiupampa, Southcentral Bolivia

A taxonomically diverse fossil fauna with small and medium size vertebrates was recovered from the Late Cretaceous (Maestrichtian) age El Molino Formation at Tiupampa, southcentral Bolivia. Among the known taxa, many new to science, are selacians, actinopterygians, lungfish, amphibians, lizards, snakes, turtles, crocodiles, and several mammals. This finding provides a unique and previously unavailable opportunity to understand debated aspects of the phylogenetic and biogeographic histories of these groups.

ボリビアの白亜系について

In Bolivia the Cretaceous System is distribution widely in the Altiplano, Andes Oriental, Subandes, and eastern hill regions. It is underlain unconfermably by the Palaeozoic formations, lacking most of the Triassic and Jurassic sequence. The System is characterized by the predominance of reddish or brownish red rock facies, and is named by STEINMANN (1904) as the Puca Group. The name was derived from “puca” which means red in Quechus. The whole section of the System is distributed in the Altiplano and Andes Oriental regions, and the upper part of the System is in the Subandes and eastern hill regions.1) In the Andes Oriental region the System forms a large syncline named the Huarachani-Mocomoco syncline. The System is divided into the Huayrapata, Ococoya, Suches, Moho and Huancané Formations in decending order. The Huancané and Moho Formations are well exposed along the northeast coast of Titicaca Lake, but the Suches, Ococoya, and Huayrapata Formations are typically seen in the area upper course of the Suches River which flows from northeast into Titicaca Lake. The Moho Formation is a marine deposits, consisting of fine-to medium-grained sandstone, brownish red or black shale and dark grey massive limestone. There are thin fossil beds in several horizons. These fossils are mostly of echinoids and brachiopods which consist poor number of species. The Huayrapata Formation yields Viviparus, Melanoides and others. Judging from these fossils the formation is considered to be a non-marine deposit.2) The system in the Titicaca basin, consisting of the Muñane, Vilquechico, Cotacucho, Moho, and Huancané Formations, forms a large synclinorium with axes trending from NW to SE.3) In the Miraflores district, southern Bolivia, the System can be classified stratigraphically into six formations, as follows : El Molino, Chaunaca, Aroifilla, Miraflores, Tarapay, and La Puerta Formations in descending order. The Miraflores Formation consist chiefly of black or dark grey massive limestone, and contains pelecypods, brachiopods and ammonites. Based on these fossils the formation corresponds to the Moho Formation in Altiplano and Andes Oriental regions. It has been considered as Cenomanian in age. The formation is stratigraphically important in central Bolivia, because it is the most pronounced marine beds in the Cretaceous and can be used as the horizon marker. The El Molino Formation is another shallow marine deposits, yielding brachiopods, pelecypods and vertebrates. The formation is late Cretaceous in age.4) In the Altiplano region near Titicaca Lake, Subandes and eastern hill regions, the uppermost Cretaceous sediments are continous to the lower Tertiary formations which are composed of the remarkable reddish facies quite similar to the Cretaceous red beds. It is very difficult to define the boundary between the uppermost Cretaceous and the lower Tertiary sediments.

Sur quelques sélaciens nouveauxdu Crétacé supérieur de Bolivie: Amérique du Sud

The locality of Torotoro (Puca Group, Upper Cretaceous of Bolivia) has yielded a small shark-fauna including a new genus and five new species: Pucabatis hoffstetteri nov. gen., nov. sp., Ischyrhiza hartenbergeri nov. sp., Dasyatis branisai nov. sp., D. molinoensis nov. sp. et D. schaefferi nov. sp. The genus Pucapristis, previously described on rostral teeth, is represented by numerous oral teeth unknown until this day. The occurence of the genus Schizorhiza, already pointed out, allows to attribute the El Molino formation to maestrichtian.