An enigmatic new archosauriform from the Carnian-Norian, Upper Triassic, Ischigualasto Formation of northwestern Argentina

In this contribution we introduce a new Late Triassic archosaur, Incertovenator longicollum gen. et sp. nov., with an unusual combination of character states that are present in certain early avemetatarsalian and pseudosuchian archosaur clades. The holotype consists of a partial postcranial skeleton, preserving most of the axial skeleton and displaying a marked anteroposterior elongation in the cervical vertebrae. We include I. longicollum gen. et sp. nov. into one of the most comprehensive early archosaur phylogenetic data sets available, and recover it as either an early diverging avemetatarsalian, closely associated with the clade Aphanosauria and Ornithodira, or as an early diverging loricatan closely related to Mandasuchus tanyauchen in the most parsimonious trees. We further evaluate which alternative phylogenetic positions can I. longicollum gen. et sp. nov. take in the suboptimal trees, and determined which character states support those alternative positions in comparison with those of the unconstrained analysis. The analyses recover the new taxon in three main general phylogenetic placements within Archosauria, as well as one position outside this clade, highlighting widespread morphological evolutionary convergence towards neck elongation in several clades of Triassic archosauriforms.Fil: Yáñez, Imanol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Pol, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; ArgentinaFil: Leardi, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Alcober, Oscar A.. Universidad Nacional de San Juan; ArgentinaFil: Martínez, Ricardo Néstor. Universidad Nacional de San Juan; Argentin

Age constraints on the dispersal of dinosaurs in the Late Triassic from magnetochronology of the Los Colorados Formation (Argentina)

A measured magnetozone sequence defined by 24 sampling sites with normal polarity and 28 sites with reverse polarity characteristic magnetizations was established for the heretofore poorly age-constrained Los Colorados Formation and its dinosaur-bearing vertebrate fauna in the Ischigualasto–Villa Union continental rift basin of Argentina. The polarity pattern in this ∼600-m-thick red-bed section can be correlated to Chrons E7r to E15n of the Newark astrochronological polarity time scale. This represents a time interval from 227 to 213 Ma, indicating that the Los Colorados Formation is predominantly Norian in age, ending more than 11 My before the onset of the Jurassic. The magnetochronology confirms that the underlying Ischigualasto Formation and its vertebrate assemblages including some of the earliest known dinosaurs are of Carnian age. The oldest dated occurrences of vertebrate assemblages with dinosaurs in North America (Chinle Formation) are younger (Norian), and thus the rise of dinosaurs was diachronous across the Americas. Paleogeography of the Ischigualasto and Los Colorados Formations indicates prolonged residence in the austral temperate humid belt where a provincial vertebrate fauna with early dinosaurs may have incubated. Faunal dispersal across the Pangean supercontinent in the development of more cosmopolitan vertebrate assemblages later in the Norian may have been in response to reduced contrasts between climate zones and lowered barriers resulting from decreasing atmospheric pCO2 levels

Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina

Background: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.Methodology/Principal Findings: We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia (“stomach ribs”), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax.Conclusions/Significance: We present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds:(1) Phase I—Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic.(2) Phase II—Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation.(3) Phase III—Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic.(4) Phase IV—Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic.In addition, we conclude:(5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation.(6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.</p

¿Qué comía Exaeretodon Cabrera (Therapsida, Cynodontia)? Primera evidencia geoquímica de su dieta

El traversodóntido Exaeretodon es uno de los cinodontes más abundantes en las paleocomunidades de las formaciones triásicas Ischigualasto (Argentina) y Santa María (Brasil). Los numerosos restos hallados en ambas formaciones fosilíferas han permitido un detallado estudio de este género. Sin embargo, existen importantes controversias respecto a sus preferencias dietarias y consecuente rol paleoecológico. Algunos autores proponen que fue herbívoro basándose en las facetas de desgaste de los postcaninos. Otros justifican su omnivoría por sus postcaninos superiores transversalmente amplios con una cresta sectorial alta y aguda, o por considerar un modelo de la estructura trófica de la paleocomunidad de Ischigualasto. La dieta de un animal extinto y consecuentemente su posición en la cadena trófica, puede inferirse en base a la relación isotópica entre el carbono 13 y 12 (δ13C) preservada en el esmalte de los dientes. Cuando un herbívoro basa su dieta en plantas C3 (ciclo Calvin-Bensen, únicas en el Triásico), la señal isotópica δ13C preservada en sus dientes estará enriquecida 12‰ a 14‰ veces respecto a las plantas que consumía. Cuando un animal carnívoro se alimenta de un herbívoro, esta señal volverá a enriquecerse en aproximadamente 4‰ respecto al herbívoro y seguirá enriqueciéndose a medida que se sube en la cadena trófica. En el caso de un animal omnívoro, esta señal tendrá un valor intermedio entre el de un herbívoro y un carnívoro. Estudios isotópicos de cutículas vegetales de la Formación Ischigualasto arrojaron un valor promedio de -25,4‰ (rango -22,7 a -27,4). Por otro lado, análisis isotópicos realizados en un diente de Exaeretodon preservado en la porción basal de la misma formación, arrojaron valores de -12,6‰ y -11,3‰. La diferencia entre ambos valores (diente menos planta) es de 12,8 y 14,1. Estos valores corresponderían al esperado en un animal herbívoro, evidenciando la herbivoría de Exaeretodon.Sesiones libresFacultad de Ciencias Naturales y Muse

Los depósitos continentales triásicos

Las sedimentitas triásicas se encuentran representadas principalmente en dos regiones geográficas: la Región Patagónica, en donde se incluyen los afloramientos de El Tranquilo en el norte de la provincia de Santa Cruz y una serie de localidades ubicadas en el área del Macizo Nordpatagónico; y la Región Centro-oeste del país, donde se ubican los afloramientos de las provincias de Mendoza, San Luis, San Juan y La Rioja (Figuras 1 y 2). Además de estos grupos principales de afloramientos triásicos, se han identificado sedimentitas asignables a este período en el subsuelo de la cuenca Chacoparanense.Facultad de Ciencias Naturales y Muse

Evidencias preliminares de un bosque destruido por un evento volcaniclástico en el Triásico de Formación El Alcázar, Cuenca Cuyana, San Juan, Argentina

Fil: Drovandi, Juan Martín. Universidad Nacional de San Juan. Instituto y Museo de Ciencias Naturales; ArgentinaFil: Colombi, Carina Ester. Universidad Nacional de San Juan. Instituto y Museo de Ciencias Naturales; ArgentinaFil: Bodnar, Josefina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleobotánica; ArgentinaFil: Ejarque, Yanina. Universidad Nacional de San Juan. Instituto y Museo de Ciencias Naturales; ArgentinaFil: García, Gonzalo. Universidad Nacional de San Juan. Instituto y Museo de Ciencias Naturales; ArgentinaFil: Santi Malnis, Paula. Universidad Nacional de San Juan. Instituto y Museo de Ciencias Naturales; ArgentinaFil: Morel, Eduardo Manuel. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleobotánica; ArgentinaFil: Alcober, Oscar A.. Universidad Nacional de San Juan. Instituto y Museo de Ciencias Naturales; Argentin

A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), Northwestern Argentina

BACKGROUND: Argentinean basal sauropodomorphs are known by several specimens from different basins; Ischigualasto, El Tranquilo, and Mogna. The Argentinean record is diverse and includes some of the most primitive known sauropodomorphs such as Panphagia and Chromogisaurus, as well as more derived forms, including several massospondylids. Until now, the Massospondylidae were the group of basal sauropodomorphs most widely spread around Pangea with a record in almost all continents, mostly from the southern hemisphere, including the only record from Antarctica. METHODOLOGY/PRINCIPAL FINDING: We describe here a new basal sauropodomorph, Leyesaurus marayensis gen. et sp. nov., from the Quebrada del Barro Formation, an Upper Triassic-Lower Jurassic unit that crops out in northwestern Argentina. The new taxon is represented by a partial articulated skeleton that includes the skull, vertebral column, scapular and pelvic girdles, and hindlimb. Leyesaurus is diagnosed by a set of unique features, such as a sharply acute angle (50 degrees) formed by the ascending process of the maxilla and the alveolar margin, a straight ascending process of the maxilla with a longitudinal ridge on its lateral surface, noticeably bulging labial side of the maxillary teeth, greatly elongated cervical vertebrae, and proximal articular surface of metatarsal III that is shelf-like and medially deflected. Phylogenetic analysis recovers Leyesaurus as a basal sauropodomorph, sister taxon of Adeopapposaurus within the Massospondylidae. Moreover, the results suggest that massospondylids achieved a higher diversity than previously thought. CONCLUSIONS/SIGNIFICANCE: Our phylogenetic results differ with respect to previous analyses by rejecting the massospondylid affinities of some taxa from the northern hemisphere (e.g., Seitaad, Sarahsaurus). As a result, the new taxon Leyesaurus, coupled with other recent discoveries, suggests that the diversity of massospondylids in the southern hemisphere was higher than in other regions of Pangea. Finally, the close affinities of Leyesaurus with the Lower Jurassic Massospondylus suggest a younger age for the Quebrada del Barro Formation than previously postulated

Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina

Background: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence. Methodology/Principal Findings: We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia (‘‘stomach ribs’’), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax. Conclusions/Significance: We present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds: (1) Phase I—Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic. (2) Phase II—Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract wit

A Basal Sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the Early Evolution of Sauropodomorpha

BACKGROUND: The earliest dinosaurs are from the early Late Triassic (Carnian) of South America. By the Carnian the main clades Saurischia and Ornithischia were already established, and the presence of the most primitive known sauropodomorph Saturnalia suggests also that Saurischia had already diverged into Theropoda and Sauropodomorpha. Knowledge of Carnian sauropodomorphs has been restricted to this single species. METHODOLOGY/PRINCIPAL FINDINGS: We describe a new small sauropodomorph dinosaur from the Ischigualsto Formation (Carnian) in northwest Argentina, Panphagia protos gen. et sp. nov., on the basis of a partial skeleton. The genus and species are characterized by an anteroposteriorly elongated fossa on the base of the anteroventral process of the nasal; wide lateral flange on the quadrate with a large foramen; deep groove on the lateral surface of the lower jaw surrounded by prominent dorsal and ventral ridges; bifurcated posteroventral process of the dentary; long retroarticular process transversally wider than the articular area for the quadrate; oval scars on the lateral surface of the posterior border of the centra of cervical vertebrae; distinct prominences on the neural arc of the anterior cervical vertebra; distal end of the scapular blade nearly three times wider than the neck; scapular blade with an expanded posterodistal corner; and medial lamina of brevis fossa twice as wide as the iliac spine. CONCLUSIONS/SIGNIFICANCE: We regard Panphagia as the most basal sauropodomorph, which shares the following apomorphies with Saturnalia and more derived sauropodomorphs: basally constricted crowns; lanceolate crowns; teeth of the anterior quarter of the dentary higher than the others; and short posterolateral flange of distal tibia. The presence of Panphagia at the base of the early Carnian Ischigualasto Formation suggests an earlier origin of Sauropodomorpha during the Middle Triassic