A temnospondyl trackway from the early mesozoic of Western gondwana and its implications for Basal tetrapod locomotion

BACKGROUND: Temnospondyls are one of the earliest radiations of limbed vertebrates. Skeletal remains of more than 190 genera have been identified from late Paleozoic and early Mesozoic rocks. Paleozoic temnospondyls comprise mainly small to medium sized forms of diverse habits ranging from fully aquatic to fully terrestrial. Accordingly, their ichnological record includes tracks described from many Laurasian localities. Mesozoic temnospondyls, in contrast, include mostly medium to large aquatic or semi-aquatic forms. Exceedingly few fossil tracks or trackways have been attributed to Mesozoic temnospondyls, and as a consequence very little is known of their locomotor capabilities on land. METHODOLOGY/PRINCIPAL FINDINGS: We report a ca. 200 Ma trackway, Episcopopus ventrosus , from Lesotho, southern Africa that was made by a 3.5 m-long animal. This relatively long trackway records the trackmaker dragging its body along a wet substrate using only the tips of its digits, which in the manus left characteristic drag marks. Based on detailed mapping, casting, and laser scanning of the best-preserved part of the trackway, we identified synapomorphies (e.g., tetradactyl manus, pentadactyl pes) and symplesiomorphies (e.g., absence of claws) in the Episcopopus trackway that indicate a temnospondyl trackmaker. Conclusions/Significance Our analysis shows that the Episcopopus trackmaker progressed with a sprawling posture, using a lateral-sequence walk. Its forelimbs were the major propulsive elements and there was little lateral bending of the trunk. We suggest this locomotor style, which differs dramatically from the hindlimb-driven locomotion of salamanders and other extant terrestrial tetrapods can be explained by the forwardly shifted center of mass resulting from the relatively large heads and heavily pectoral girdles of temnospondyls

Léxico Estratigráfico de la Argentina. Volúmen VIII. Triásico

Fil: Stipanicic, P.N. Comité Argentino de Estratigrafía. Subcomisión del Triásico; Argentina.Fil: Marsicano, C.A. Comité Argentino de Estratigrafía. Subcomisión del Triásico; Argentina.Se escaneó la portada y las primeras páginas de este trabajo, adjuntándolas al trabajo digital, ya que las mismas estaban faltantes.Este trabajo fue publicado por la Asociación Geológica Argentina, y forma parte de una de sus colecciones. Desde el repositorio institucional del SEGEMAR tan solo se le da difusión y acceso, respetando la autoría del trabajo.El Léxico Estratigráfico de la Argentina debió formar parte del Léxico Estratigráfico Internacional, obra que comenzó a publicar la Comisión Internacional de Estratigrafía a partir de la década del 50. Causas de diversa índole impidieron concretar tal participación, pero el material que se reunió comenzó a ser editado en el año 1976 por el Servicio Geológico Nacional, en una publicación especial que se tituló "Léxico Estratigráfico de la República Argentina", que incluyó unidades estratigráficas ordenadas alfabéticamente desde la "A" a la "Ch". A posteriori, el Comité Argentino de Estratigrafía decidió que resultaba de fundamental interés el concretar la totalidad de la obra, a los efectos de tender a normalizar la compleja nomenclatura existente en el país, por lo general no regida por códigos ad hoc. Para su organización, se siguió un criterio estratigráfico, más adecuado a la estructura del Comité y de más fácil utilización tanto por los especialistas como por los geólogos y paleontólogos que se vinculan a estos temas. De _acuerdo a dicho criterio, el Léxico Estratigráfico de la Argéntina debería incluir los siguientes volúmenes: I. Precámbrico, II. Cámbrico, III. Ordovícico, IV. Silúrico, V. Devónico, VI. Carbonífero, VII. Pérmico, VIII. Triásico, IX. Jurásico, X. Cretácico, XI. Paleógeno, XII. Neógeno, XIII. Cuaternario. Al igual que en el Léxico Estratigráfico Internacional el orden de publicación del Léxico Estratigráfico de la Argentina no necesariamente será el expuesto, pues las diferentes partes se publicarán a medida que se completen. En 1993 se editó la primera entrega, correspondiente al Volumen IX. JURÁSICO, de la programación citada. A la fecha, se da a conocer otra entrega de tal Léxico, correspondiente al Sistema TRIÁSICO. El esquema que se adoptó para la presentación del Léxico Estratigráfico de la Argentina se adecuó a las normas que se emplearon en el Léxico Estratigráfico Internacional. Las Escalas del Tiempo Geológico se irán actualizando de acuerdo a las que recomienden sucesivamente la Unión Internacional de Ciencias Geológicas, aunque para el caso local, a veces deba procederse a ciertas adecuaciones, de acuerdo con parámetros y datos que se registran en el territorio argentino

The role of tetrapod trace fossils in continental ichnofacies models

The ichnofacies model provides the main framework to understand the paleoenvironmental significance of trace fossils. Traditionally focused on invertebrate trace fossil, the ichnofacies model has only recently expanded to include tetrapod footprints. The purpose of this work is to discuss the role of tetrapod footprints in the development of continental ichnofacies models, as well as in the reconstruction of sedimentary paleoenvironments. An integrative perspective was employed to tackle this problem, taking into account depositional environments, as well as tetrapod and invertebrate trace-fossil data. The case studies that constitute the empiric base of this research project are based on trace-fossil associations studied in different lithostratigraphic units of Argentina, complemented with other ichnologic associations reported elsewhere. Proposed models on tetrapod ichnofacies have established a relationship between fossil footprint associations and sedimentary paleoenvironments, but no insight on the controlling environmental parameters has been provided. However, available data suggest that the distribution of tetrapod footprints and invertebrate trace fossils are not controlled by the same paleoenvironmental factors. Contrary to local environmental parameters involved in the distribution of invertebrate trace fossils, the distribution of tetrapod trace fossils in terrestrial environments seems to be more related to key environmental regional-scale parameters, such as climate and resource availability.Simposio IV: Icnología: su aporte en interpretaciones paleoecológicas y paleobiológicasFacultad de Ciencias Naturales y Muse

Paleoenvironmental framework of dinosaur tracksites and other ichnofossils in Early Cretaceous mixed siliciclastic-carbonate deposits in the Neuquén Basin, northern Patagonia (Argentina)

Fil: Pazos, Pablo J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. IDEAN. Buenos Aires, Argentina.Fil: Lazo, Dario G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. IDEAN. Buenos Aires, Argentina.Fil: Tunik, Maisa A. Universidad Nacional de Río Negro. Departamento de Geología. Río Negro, Argentina.Fil: Marsicano, Claudia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. IDEAN. Buenos Aires, Argentina.Fil: Fernández, Diana E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. IDEAN. Buenos Aires, Argentina.Fil: Aguirre Urreta, Beatriz. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. IDEAN. Buenos Aires, Argentina.Fil: Pazos, Pablo J. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Buenos Aires, ArgentinaFil: Lazo, Dario G. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Buenos Aires, ArgentinaFil: Tunik, Maisa A. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Buenos Aires, ArgentinaFil: Marsicano, Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Buenos Aires, ArgentinaFil: Fernández, Diana E. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Buenos Aires, ArgentinaFil: Aguirre Urreta, Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Buenos Aires, ArgentinaThe study of the uppermost section of the Early Cretaceous Agrio Formation in northern Patagonia (Neuquén Basin) where dinosaur tracks assigned to cf. Therangospodus pandemicus are exposed (tracksites I and II) evidence mixed marginal marine siliciclastic-carbonate deposits. The succession was divided in two intervals. A lower one containing theropod tracks, recorded on top of subtidal oolithic limestones with tiny wave ripples suggesting shoreline fluctuations and subaerial exposure. Tidal influence is recognised by fining upward and prograding cycles starting with subtidal carbonates and ending with fine-grained siliciclastic deposits at the top, or rarely laminites. Dolomitization affects subtidal deposits generated in an alkaline media stressful for tracemakers. Intertidal facies include abundant heterolithic deposits, coquinas composed of gastropods encrusted by multilayered bryozoans and muddy levels with incipient mud cracking. Invertebrate ichnofossils recognized from tidally dominated deposits include Arenicolites, Kouphichnium, and Rhizocorallium. The upper interval is a transgressive–regressive cycle that starts with dark shales, deficiently oxygenated, and covered by prograding sandstones and finally sand flat deposits. This interval contains Gyrochorte, Hillichnus, and Ophiomorpha documented in wave-influenced sandstones. Dinosaur tracks as well as Hillichnus, attributed to tellinoid bivalves, and Kouphichnium assigned to xiphosurans, imply the activity of producers rarely recorded previously as body fossils in marginal marine deposits of southern South America. Previous paleogeographic schemes are questioned by our analysis, which shows evidence of extremely shallow and tide-controlled sedimentation, sometimes with subaerial exposure, with high cyclicity related to a marginal marine depositional setting and lack of significant erosion by the overlying unit, as traditionally was suggested

Captorhinid reptiles from the lower Permian Pedra de Fogo Formation, Piauí, Brazil: the earliest herbivorous tetrapods in Gondwana

The Pedra de Fogo Formation in the Parnaíba Basin of northeastern Brazil hosts a recently discovered lacustrine fauna and provides the only known record of the Captorhinidae in South America. Here, new captorhinid remains from this unit are described. Two partial mandibles, including one formerly ascribed to the genus Captorhinus, are here referred to Captorhinikos sp. a genus previously described from North America. The natural mould of a large mandible probably represents a new taxon within the captorhinid subclade Moradisaurinae, and a small skull roof is regarded as Captorhinidae indet. Captorhinids are generally considered to have been herbivores or omnivores. The Pedra de Fogo captorhinids likely played an important ecological role as primary consumers in the palaeoenvironment of this geological unit, which is also known for its extensive record of petrified forests. The new finds reinforce the close relationships between the continental faunas of palaeotropical western Gondwana and palaeoequatorial North America during the Cisuralian

Dynamic Locomotor Capabilities Revealed by Early Dinosaur Trackmakers from Southern Africa

BACKGROUND: A new investigation of the sedimentology and ichnology of the Early Jurassic Moyeni tracksite in Lesotho, southern Africa has yielded new insights into the behavior and locomotor dynamics of early dinosaurs. METHODOLOGY/PRINCIPAL FINDINGS: The tracksite is an ancient point bar preserving a heterogeneous substrate of varied consistency and inclination that includes a ripple-marked riverbed, a bar slope, and a stable algal-matted bar top surface. Several basal ornithischian dinosaurs and a single theropod dinosaur crossed its surface within days or perhaps weeks of one another, but responded to substrate heterogeneity differently. Whereas the theropod trackmaker accommodated sloping and slippery surfaces by gripping the substrate with its pedal claws, the basal ornithischian trackmakers adjusted to the terrain by changing between quadrupedal and bipedal stance, wide and narrow gauge limb support (abduction range = 31 degrees ), and plantigrade and digitigrade foot posture. CONCLUSIONS/SIGNIFICANCE: The locomotor adjustments coincide with changes in substrate consistency along the trackway and appear to reflect 'real time' responses to a complex terrain. It is proposed that these responses foreshadow important locomotor transformations characterizing the later evolution of the two main dinosaur lineages. Ornithischians, which shifted from bipedal to quadrupedal posture at least three times in their evolutionary history, are shown to have been capable of adopting both postures early in their evolutionary history. The substrate-gripping behavior demonstrated by the early theropod, in turn, is consistent with the hypothesized function of pedal claws in bird ancestors

US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference