Vertebral pneumatic structures in the Early Cretaceous sauropod dinosaur Pilmatueia faundezi from northwestern Patagonia,Argentina

One of the diagnostic characters of dicraeosaurid sauropods is a reduction of pneumatization of dorsal and caudal vertebrae relative to their Flagellicaudata sister taxon, Diplodocidae. Here, we analyse pneumatic structures in the dicraeosaurid sauropod Pilmatueia faundezi, compare them to those of diplodocoids and report the first record of camerate chambers in a dicraeosaurid. The pneumatic structures are in a posterior cervical centrum (MLL-Pv-002) and consist of lateral pneumatic fossae on the centrum that communicate internally with large camerae. By contrast, Pilmatueia's dorsal and caudal vertebrae (MLL-Pv-005-016) lack pneumatic fossae on the centra, which is consistent with the previously reported reduced pneumaticity in dicraeosaurids. Nevertheless, the base of the neural arch and possibly the base of the bifid neural spines of a posterior dorsal vertebra (MLL-Pv-005) show pneumatic internal chambers. The pneumatic features of the Pilmatueia cervical centrum and dorsal neural arch we describe indicate that the degree of pneumatization is variable within dicraeosaurids.     

Dentition and histology in titanosaurian dinosaur embryos from Upper Cretaceous of Patagonia,Argentina

Abstract: Exceptionally preserved sauropod embryos from the Late Cretaceous Anacleto Formation in Auca Mahuevo (Neuquén Province, Argentina) have provided fundamental information on titanosaurian ontogeny. This paper describes the dental composition, disposition and microstructure of the specimens. Embryonic teeth show size disparity, with lengths that vary from 1 to 3 mm and diameters ranging from 0.15 to 0.26 mm, with the most frequent length values between 2.5 and 3 mm. Apparently, a typical ‘pencil‐like’ tooth morphology and a dental formula of Pm 4, M 7–8/D10? remained constant during titanosaurian ontogeny, whereas the arrangement of teeth in the skull shows notable ontogenetic changes. Absence of wear facets on teeth suggests a lack of prenatal chewing movements. The enamel proportion is significantly higher in embryos than in mature titanosaurs, which suggests that this relationship varies during ontogeny. Embryonic bony tissue is composed of highly vascularized, cellular woven bone. The absence of osteonal tissue, the high degree of vascularization, the presence of numerous osteocytes and poor development of periosteal bone reveals that the Auca Mahuevo titanosaurs would have had a high early growth rate and that they were buried at a relatively advanced embryonic stage.     

Ultrastructural study of Arcellites humilis Villar de Seoane and Archangelsky, 2008, from the Cretaceous of Patagonia,Argentina

A scanning and transmission electron microscopy-based ultrastructural study of Arcellites humilis Villar de Seoane and Archangelsky, 2008, from the Kachaike Formation and Piedra Clavada Formation (Albian-Cenomanian) from several localities in Patagonia (Argentina), is presented in this paper. TEM-photographs of thin-sectioned specimens show a thick spore body wall composed of three layers: a thin and dense exine, an inner granular perine sublayer with irregularly disposed small channels and lacunae, and an outer alveolate perine sublayer with channels perpendicular to the external surface. Transverse sections of the A. humilis wall are compared with fossil and extant species of Marsileaceae. We show that the wall ultrastructure is similar in A. humilis, A. santacrucensis, A. disciformis, A. stellatus and Regnellidium upatoiensis. However, the body wall and acrolamella of A. humilis are more similar to those of R. diphyllum Lindman than to those of the Marsilea L. or Pilularia L. species. Water ferns such as members of the Marsileaceae played an important role in aquatic or semi-aquatic niches in Patagonian Cretaceous floras, suggesting that high humidity and temperature prevailed during the Albian-Cenomanian in this region of Argentina.     

An articulated titanosaur from Patagonia (Argentina): New evidence of neosauropod pedal evolution

Most titanosaur dinosaurs are represented by incomplete skeletal elements lacking articulated pes. An exceptionally preserved specimen from the Late Campanian–Early Maastrichtian strata of Patagonia (Argentina) provides new data on pedal morphology and the evolutionary trends of these huge dinosaurs. This finding is one of the few articulated titanosaur pes known in the world, and shows a phalangeal formula of 2-2-2-2-0. The first three digits possess sickle-shaped claws and the articular facets of ungual phalanges, suggesting mobility in horizontal and vertical planes. A comparative analysis of available record suggests that titanosaurs had a progressive reduction of size and number of pedal phalanges in digits III and IV during the Late Cretaceous.     

A New Marine Reptile (Sauropterygia) from New Zealand: Further Evidence for A Late Cretaceous Austral Radiation of Cryptoclidid Plesiosaurs

Kaiwhekea katiki gen. et sp. nov. represents the first described cryptoclidid plesiosaurian from New Zealand. It is one of the largest cryptoclidids known, at a length of over 6.5 m, and represents the third reported genus of austral Late Cretaceous cryptoclidids. Kaiwhekea katiki is from siltstones of the Katiki Formation, upper Haumurian Stage (Cenomanian–Maastrichtian; c. 69–70 Ma) of coastal Otago, South Island, New Zealand. In the Late Cretaceous, the locality lay close to the polar circle. The holotype and only known specimen is an articulated skeleton with skull, preserved mostly as natural molds, but which lacks the forelimbs and pectoral girdle. The skull is relatively large and possesses several distinct characters, including a substantial, deep, jugal. There are about 43 upper and 42 lower teeth in each jaw quadrant; all are homodont, slim, and slightly recurved, lacking prominent ornament. Kaiwhekea probably took single soft-bodied prey. Based on cranial structure, it clearly belongs with the Cryptoclididae, but is not certainly close to the southern Late Cretaceous cryptoclidids Morturneria (Seymour Island, Antarctica) and Aristonectes (Chile, Argentina).     

Palaeoecological and morphofunctional interpretation of bone mass increase: an example in Late Cretaceous shallow marine squamates

Bone mass increase (BMI; i.e. osteosclerosis with possible additional pachyostosis) is characteristically displayed by many Late Cretaceous squamates that adapted to shallow marine environments—plesiopelvic mosasauroids, stem‐ophidians and pachyophiids. A combined morphological and microanatomical analysis of vertebrae and, to a lesser extent, ribs of these fossil squamates provides new data about the distribution and variability of this osseous specialization in these taxa. Classical thin sections and third generation synchrotron microtomography and laminography were used for the microanatomical analysis. Following the explanation of the likely involvement of this specialization in the control of buoyancy, body trim and Carrier's constraint, new palaeoecological inferences and new hypotheses about the locomotor abilities and life environment of these organisms are produced. The taxa displaying BMI are considered to have undertaken long dives, hovering slowly and maintaining a horizontal trim, in shallow and protected water environments. Conversely, marine stem‐ophidians deprived of this specialization are regarded as slow surface swimmers able to live in more open marine environments. This study highlights the importance of microanatomical data for palaeoecological studies. It also discusses the significance of the use of this specialization as a character in phylogenetic studies.     

Neoselachians (Chondrichthyes,Elasmobranchii) from the Lower and lower Upper Cretaceous of north‐eastern Spain

Extensive sampling of several Barremian and Albian–Cenomanian levels across the Aguilón, Oliete and Aliaga subbasins of the Iberian Basin, north‐east Spain, yielded abundant material of new or so far poorly known neoselachians. The faunas consist of 16 different species, five of which represent new species and two new genera: Cantioscyllium brachyplicatum sp. nov. , Platypterix venustulus gen. et sp. nov. , Ptychotrygon pustulata sp. nov. , Ptychotrygon striata sp. nov. and Iberotrygon plagiolophus gen. et sp. nov. In addition, teeth of Heterodontus cf. H. carerens, Lamniformes indet., Pteroscyllium sp., Scyliorhinidae indet., Rhinobatos sp., Spathobatis sp., Belemnobatis sp., Ptychotrygon geyeri, Ptychotrygon sp. and Celtipristis herreroi are described. The new family Ptychotrygonidae is defined. The localities comprise palaeoenvironments ranging from lacustrine and shallow lake to open marine settings. Neoselachians are almost completely absent from continental settings in the Barremian, as a result of prevailing freshwater conditions, but became more abundant in marine strata. The Albian–Cenomanian selachian assemblage is the most profuse and diverse of the three assemblages studied. It is dominated by small, benthic and near‐coastal taxa, for instance Cantioscyllium and Ptychotrygon, and contains several new species, including an endemic batoid, Iberotrygon plagiolophus gen. et sp. nov. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 316–347.     

A new baurusuchid crocodyliform (Archosauria) from the Late Cretaceous of Patagonia (Argentina)

A new baurusuchid, Wargosuchus australis gen. et sp. nov., coming from the Bajo de La Carpa Formation, Neuquén Province (Argentina), is described. This new taxon is based on a fragment of snout and a portion of the cranial roof. Wargosuchus differs from other crocodyliforms by possessing a deep median groove on the frontals, a contact between nasals and frontals extremely reduced, a large depression for the olfactory bulbs, three large foramina surrounding the large, smooth perinarial depression, and a hypertrophied, conical last premaxillary tooth followed by a large paracanine fossa. The finding of Wargosuchus in Patagonia (Argentina), a taxon with a strong resemblance to Brazilian baurusuchids, reinforces the hypothesis of a similar biota between both regions by the Late Cretaceous. Wargosuchus and Cynodontosuchus represent the only Argentinian mesoeucrocodylians to be included within Baurusuchidae. This finding extends the number of crocodyliforms from the Bajo de la Carpa Formation, which, in turn, corresponds to the most taxonomically diverse one in Argentina.     

Patellogastropoda and Vetigastropoda (Mollusca,Gastropoda) from the marine Jurassic of Patagonia,Argentina

Gastropod faunas from the Early Jurassic (Late Pliensbachian–Early Toarcian) marine deposits of Chubut Province, Argentina, are described from Lomas Occidentales, Cerro La Trampa and Puesto Currumil localities, representing eight species, three of them new. These are Scurriopsis? sp., Chartronella gradata sp. nov., Calliotropis? sp., Pleurotomaria sp., Leptomaria sp., Hamusina? wahnishae sp. nov., Colpomphalus musacchioi sp. nov. and Jurassiphorus? cf. triadicus Haas. The gastropod assemblage reported here testifies paleobiogeographical connections with other coeval gastropod associations from the western Tethys. However, Chartronella, Hamusina and Jurassiphorus may represent survivors of Triassic associations, considering the ancient seaway from Peru as the most plausible hypothesis for biotic exchange of these faunas during the Late Triassic–Early Jurassic boundary. An abundant and diverse invertebrate fauna such as corals, echinoderms, cephalopods, brachiopods, bivalves and other gastropods found in association with the gastropods described here characterises a shallow marine environment for the gastropod-bearing rocks.http://www.zoobank.org/urn:lsid:zoobank.org:pub:7B8EAFC0-3AC0-4F91-97A5-22AAC6A19909     

Specialization of bone structure in Pachyvaranus crassispondylus Arambourg, 1952, an aquatic squamate from the Late Cretaceous of the southern Tethyan margin

The histological organization of the vertebrae of the Maastrichtian squamate Pachyvaranus crassispondylus Arambourg, 1952 , was compared to that of various extant squamates, in order to further document the causes and functional consequences of the so-called 'pachyostosis', frequently observed in Late Cretaceous squamates. The vertebrae of Pachyvaranus are composed of the same basic bone tissue types as those of extant lizards and snakes. In particular, periosteal cortices are made of a pseudolamellar (or 'parallel-fibred') tissue, with radial vascular canals, Sharpey's fibres and conspicuous cyclic growth marks that are strictly identical to that found in extant varanids. Conversely, the vertebrae of Pachyvaranus are extremely compact, whereas those of extant squamates are very cancellous and lightly built. This difference is due to the absence in Pachyvaranus of a broad internal resorption field that, in extant lizards and snakes, transforms compact cortices into loose spongy formations. This absence of inner bone resorption typically corresponds to an osteosclerotic process. In Pachyvaranus , cortical hyperplasy, or pachyostosis stricto sensu , was restricted to the walls of the neural spine. Extreme vertebral porosity is likely to be a primitive condition in squamates, because all lizards and snakes examined in this study display this feature. Therefore, the high vertebral compactness observed in Pachyvaranus would be a derived condition arising from the loss (or de-differentiation) of a morphogenetic process: the broad internal resorption of the vertebrae. Possible palaeoecological bearings of these results are discussed.     

Morphological abnormalities in Late Cretaceous and early Paleocene foraminifer tests (northern Patagonia, Argentina)

Morphological abnormalities are common in Late Cretaceous and early Paleocene foraminifer tests at two localities in northern Patagonia, Argentina. Protelphidium sp. in the Auca Mahuevo section (late Campanian–early Maastrichtian) exhibit abnormal size or shape of the later chambers, with the last chamber commonly larger than normal or inflated and variably extending onto one of the lateral sides of the test; modification of the coiling plane; protuberances near the proloculus or on one or more chambers; a double last chamber, and complex forms. Protelphidium hofkeri Haynes in the Cerro Azul section (Danian) exhibit abnormal size or shape of one or more chambers, producing peripheral irregularities. In addition, there are rare multiple tests in planktic species from the Cerro Azul section, probably teratological specimens. The sedimentology of the sections and the character of the accompanying faunas indicate that the abnormalities in the two benthic foraminiferal taxa were most probably caused by hypersalinity and/or fluctuations in salinity. The fossil occurrence of assemblages with abundant deformed specimens suggests that investigators should carefully look at many aspects of the environment before concluding that anthropogenic pollution is the only cause of deformations of living benthic foraminifera.     

Bone microstructure of Vegavis iaai (Aves,Anseriformes) from the Upper Cretaceous of Vega Island,Antarctic Peninsula

Vegavis iaai is a neornithine bird coming from the Late Cretaceous Sandwich Bluff Member of the López de Bertodano Formation (Maastrichtian), Antarctic Peninsula. Vegavis constitutes the only unquestionable Cretaceous neornithine bird, and is known by the holotype and specimen MACN-PV 19.748. The goal of this paper is to present a detailed osteohistological analysis of V. iaai. Vegavis shows a highly vascularized fibrolamellar matrix lacking lines of arrested growths, features widespread among modern birds. This is consistent with previous hypotheses indicating that modern birds were dominant at high latitudes. This is probably related to high-metabolic rates shared by modern birds, whereas archaic taxa as Enantiornithes are absent or form a minority part of High-Latitude bird assemblages. Vegavis was a diver, characterised by a certain degree of limb osteosclerosis, with an increase of bone inner compactness, and inhibition of secondary remodelling, with no effect on the external dimensions of the bone, a combination of characters related to diving lifestyle. Based on Relative Bone Thickness it is possible to infer that Vegavis was a foot-propelled diving bird, similar to some extant anseriforms. Occurrence of osteosclerotic limb bones in Vegavis and Polarornis may constitute a derived shared feature, sustaining the hypothesis that both taxa are phylogenetically related.     

Paleoazolla,a new heterosporous fern from the Upper Cretaceous of Argentina

Megaspore and microspore massulae of Paleoazolla patagonica gen. et sp. nov. are described from the Upper Cretaceous of La Colonia Formation, Chubut Province, Argentina. The new fern possesses megaspore complexes with three to four glochidiate floats attached directly to the megaspore; a columella-like structure appears to be absent. The megaspore wall consists of a two-layered exine that is smooth to irregularly perforate, a two-layered perine with a spongy, densely packed endoperine, and a loosely organized exoperine. Infrafilosum hairs cover the exoperine. Microspore massulae are irregular in size and shape and bear multibarbed glochidia that generally have anchor-shaped tips. A comparison with other azollaceous and salviniaceous genera, particularly Azolla, is provided, together with a discussion of some evolutionary trends within the family.     

Foliar cuticle of Ruflorinia orlandoi nov. sp. (Pteridospermophyta) from the Lower Cretaceous of Patagonia

Foliar cuticle of a new species of Ruflorinia, R. orlandoi Carrizo et Del Fueyo, from the Lower Cretaceous Springhill Formation in Santa Cruz province, Argentina, is herein described with light and electronic (scanning and transmission) microscopy. The fronds of R. orlandoi nov. sp. are bipinnate and imparipinnate with a conspicuous main rachis bearing alternate to sub-opposite pinnae. Cuticular striations and hairs are present in both epidermises whereas stomata are only on the abaxial cuticle. Stomata have several papillate subsidiary cells and the guard cells are sunken. Ultrastructurally the adaxial and abaxial cuticles are composed of three and two cuticular layers, respectively. The cuticular characters here described are interpreted as a response to a possible adaptation to a wet climate as well as to the fluctuating environment produced by the gradual transition from fluvial to an estuarine and marine setting that characterizes the Springhill Formation. The discovery of this new species allows expanding the previous knowledge of the paleofloristic composition of the Springhill Formation with the addition of the first pteridospermous megafossil described for this formation. Moreover, the record of Ruflorinia orlandoi nov. sp. in the Springhill Formation highlights the importance of the Caytoniales during the Cretaceous in Patagonia.     

Variations in the periphytic community structure and dynamics of Lake Nahuel Huapi (Patagonia,Argentina)

Little is known about periphyton community in Patagonia and the influence that urban development has on a particular water body. Lake Nahuel Huapi is located in a National Park with little industrial or agricultural activity in the basin, but it is influenced by urban discharges from San Carlos de Bariloche, a town of 80000 inhabitants located on its south shore. Variations in structure and dynamics of the periphyton community in Lake Nahuel Huapi were studied during 1 year, to examine the influence of urban discharges on this community. Periphyton samples were collected on the shoreline of the lake and evaluated for biomass (as chlorophyll a concentration) and cell density of the main algal groups, at sites with and without urban influence. Results indicated the major influence of pollution from urban sources on periphyton at the most impacted sites, as well as the effect of different local events at each site (degree of contamination, type of coast, wind exposure, etc.). Higher biomass and cell densities at contaminated sites were evident, but the variation of main algal groups through the year was similar in all the sites. Periphyton in Lake Nahuel Huapi proved to be an important bioindicator of urban impacts on this water body.     

Palaeolimnology of Lake Hess (Patagonia,Argentina): multi-proxy analyses of short sediment cores

In contrast with the extensive palaeolimnological studies carried out in North America and Europe, relatively few studies have described the anthropogenic and/or climate impacts in Patagonian lakes. We addressed these issues by analysing geochemistry, lithology, pigments and chironomid remains from sediment cores collected from Lake Hess (41°22′20″S, 71°44′0″W) located in the Nahuel Huapi National Park in northern Patagonia. The aim of this study is to provide a palaeoenvironmental and climate reconstruction of the past ca. three centuries for this cold oligotrophic, quasi-pristine lake which receives meltwaters from the Tronador ice cap. Chronology was based on ¹³⁷Cs and ²¹⁰Pb measurements of the upper sediments, and the inferred sedimentation rate of 23.2 mg cm⁻² y⁻¹ (0.15 cm y⁻¹) was consistent with both sets of measurements. The sediment from Lake Hess was rich in tephra deposits particularly evident in the lower part of the cores. Tephras are valuable to use for core correlation and can be traced through peaks in the magnetic susceptibility (MS) profiles. Results from the multiproxy analyses in the longest core (83 cm) identify three main phases of change. From the bottom up to 42 cm (ca. ad 1800), the sediment is composed of light-grey organically rich clays. Both pigments and chironomids suggest variable trends in productivity and precipitation regime. At the end of the Little Ice Age chronozone (ad 1770–1850), pigment concentrations were very low. From 42 cm to ca. 25 cm (ad 1800–1940), the sedimentary record is composed of alternating black and dark organic-matter rich mud with variable amounts of macrophyte remains. Pigment concentrations and chironomid head capsule counts were also very low. These facies are composed of very fine plastic sediments with some faintly laminated intervals and an organic matter composition gradually decreasing towards the top of the zone. A sharp change occurs at 25 cm (ca. ad 1940) showing a strong increase in organic matter content, algal nutrients and plant pigments together with a change in the chironomid assemblages. This might document a change in the trophic condition of the lake associated with changes in erosion/deposition rates. Although there are records of human impact in the area studied, involving the use of fires, most of the observed chemical and biological changes in Lake Hess sediment sequence were interpreted in terms of climate changes, especially to changes in moisture balance brought about by variations in the strength of the westerlies. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water