Metriorhynchidae (Crocodylomorpha: Thalattosuchia) del jurásico superior–cretácico inferior de la Cuenca Neuquina (Argentina), con comentarios sobre los moldes naturales del encéfalo

Los Metriorhynchidae fueron los únicos Crocodylomorpha con un estilo de vida marino pelágico. Relacionado con este estilo de vida, su peculiar plan corporal permite diferenciarlos claramente de los demás Crocodylomorpha. El registro fósil de los metriorrínquidos titonienses–berriasienses de la Formación Vaca Muerta (Cuenca Neuquina, Argentina) es excepcional, tanto en términos cuantitativos como cualitativos. Su diversidad taxonómica está compuesta por cuatro taxones: Cricosaurus araucanensis, Cricosaurus lithographicus, Dakosaurus andiniensis y Purranisaurus potens. Este registro fósil también se caracteriza por la preservación tridimensional de los materiales y por la preservación de numerosos moldes naturales de las cavidades del cráneo. En este trabajo se presenta una descripción de los moldes naturales del encéfalo de Cricosaurus araucanensis junto con una síntesis de los avances en el conocimiento realizados, en los últimos años, sobre estos cuatro taxones argentinos. La calidad de la información que aporta los moldes naturales, sumado a la cantidad de moldes recuperados, hacen del registro patagónico una pieza clave para la exploración y reconstrucción de la anatomía blanda de estos crocodilomorfos, y para la comprensión de los cambios fisiológicos que acompañaron los cambios estructurales del esqueleto. La comprensión de estos cambios permitirá delimitar las innovaciones evolutivas claves que le permitieron a los metriorrínquidos la conquista, sin paralelo entre los arcosaurios, del medio pelágico.Metriorhynchidae was the only Crocodylomorpha with a pelagic marine lifestyle. Related to this lifestyle, its peculiar body plan al- lows clearly differentiate them from others Crocodylomorpha. The fossil record of metriorhynchids from Tithonian–Berriasian levels of the Vaca Muerta Formation (Neuquén Basin, Argentina) is outstanding, in terms of quantitative and qualitative record. Its taxonomical diversity is composed by four taxa: Cricosaurus araucanensis, Cricosaurus lithographicus, Dakosaurus andiniensis, and Purranisaurus potens. This fossil record is also characterized by the tridimensional preservation of the materials and by the preservation of numerous natural endocasts of the skull cavities. Here, I made a description of the natural endocasts of the brain of Cricosaurus araucanensis together with a synthesis of the advances in the knowledge of these four taxa that were performed during the last years. The information that provides the endocasts, to- gether with the quantity of endocasts, make of the Patagonian fossil record of metriorhynchids a key to the exploration and reconstruction of soft anatomy of these crocodylomorphs, and for the understanding of the physiological changes that accompanied the structural changes of the skeleton. Understanding these changes will allow defining the key innovations that allowed to the metriorhynchids conquer the pelagic environment, unparalleled among archosaurs.Fil: Herrera, Laura Yanina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Metriorhynchidae (Crocodylomorpha: Thalattosuchia) del jurásico superior–cretácico inferior de la Cuenca Neuquina (Argentina), con comentarios sobre los moldes naturales del encéfalo

Metriorhynchidae was the only Crocodylomorpha with a pelagic marine lifestyle. Related to this lifestyle, its peculiar body plan al- lows clearly differentiate them from others Crocodylomorpha. The fossil record of metriorhynchids from Tithonian–Berriasian levels of the Vaca Muerta Formation (Neuquén Basin, Argentina) is outstanding, in terms of quantitative and qualitative record. Its taxonomical diversity is composed by four taxa: Cricosaurus araucanensis, Cricosaurus lithographicus, Dakosaurus andiniensis, and Purranisaurus potens. This fossil record is also characterized by the tridimensional preservation of the materials and by the preservation of numerous natural endocasts of the skull cavities. Here, I made a description of the natural endocasts of the brain of Cricosaurus araucanensis together with a synthesis of the advances in the knowledge of these four taxa that were performed during the last years. The information that provides the endocasts, to- gether with the quantity of endocasts, make of the Patagonian fossil record of metriorhynchids a key to the exploration and reconstruction of soft anatomy of these crocodylomorphs, and for the understanding of the physiological changes that accompanied the structural changes of the skeleton. Understanding these changes will allow defining the key innovations that allowed to the metriorhynchids conquer the pelagic environment, unparalleled among archosaurs.Los Metriorhynchidae fueron los únicos Crocodylomorpha con un estilo de vida marino pelágico. Relacionado con este estilo de vida, su peculiar plan corporal permite diferenciarlos claramente de los demás Crocodylomorpha. El registro fósil de los metriorrínquidos titonienses–berriasienses de la Formación Vaca Muerta (Cuenca Neuquina, Argentina) es excepcional, tanto en términos cuantitativos como cualitativos. Su diversidad taxonómica está compuesta por cuatro taxones: Cricosaurus araucanensis, Cricosaurus lithographicus, Dakosaurus andiniensis y Purranisaurus potens. Este registro fósil también se caracteriza por la preservación tridimensional de los materiales y por la preservación de numerosos moldes naturales de las cavidades del cráneo. En este trabajo se presenta una descripción de los moldes naturales del encéfalo de Cricosaurus araucanensis junto con una síntesis de los avances en el conocimiento realizados, en los últimos años, sobre estos cuatro taxones argentinos. La calidad de la información que aporta los moldes naturales, sumado a la cantidad de moldes recuperados, hacen del registro patagónico una pieza clave para la exploración y reconstrucción de la anatomía blanda de estos crocodilomorfos, y para la comprensión de los cambios fisiológicos que acompañaron los cambios estructurales del esqueleto. La comprensión de estos cambios permitirá delimitar las innovaciones evolutivas claves que le permitieron a los metriorrínquidos la conquista, sin paralelo entre los arcosaurios, del medio pelágico.Facultad de Ciencias Naturales y Muse

Metriorhynchidae (Crocodylomorpha: Thalattosuchia) del jurásico superior–cretácico inferior de la Cuenca Neuquina (Argentina), con comentarios sobre los moldes naturales del encéfalo

Metriorhynchidae was the only Crocodylomorpha with a pelagic marine lifestyle. Related to this lifestyle, its peculiar body plan al- lows clearly differentiate them from others Crocodylomorpha. The fossil record of metriorhynchids from Tithonian–Berriasian levels of the Vaca Muerta Formation (Neuquén Basin, Argentina) is outstanding, in terms of quantitative and qualitative record. Its taxonomical diversity is composed by four taxa: Cricosaurus araucanensis, Cricosaurus lithographicus, Dakosaurus andiniensis, and Purranisaurus potens. This fossil record is also characterized by the tridimensional preservation of the materials and by the preservation of numerous natural endocasts of the skull cavities. Here, I made a description of the natural endocasts of the brain of Cricosaurus araucanensis together with a synthesis of the advances in the knowledge of these four taxa that were performed during the last years. The information that provides the endocasts, to- gether with the quantity of endocasts, make of the Patagonian fossil record of metriorhynchids a key to the exploration and reconstruction of soft anatomy of these crocodylomorphs, and for the understanding of the physiological changes that accompanied the structural changes of the skeleton. Understanding these changes will allow defining the key innovations that allowed to the metriorhynchids conquer the pelagic environment, unparalleled among archosaurs.Los Metriorhynchidae fueron los únicos Crocodylomorpha con un estilo de vida marino pelágico. Relacionado con este estilo de vida, su peculiar plan corporal permite diferenciarlos claramente de los demás Crocodylomorpha. El registro fósil de los metriorrínquidos titonienses–berriasienses de la Formación Vaca Muerta (Cuenca Neuquina, Argentina) es excepcional, tanto en términos cuantitativos como cualitativos. Su diversidad taxonómica está compuesta por cuatro taxones: Cricosaurus araucanensis, Cricosaurus lithographicus, Dakosaurus andiniensis y Purranisaurus potens. Este registro fósil también se caracteriza por la preservación tridimensional de los materiales y por la preservación de numerosos moldes naturales de las cavidades del cráneo. En este trabajo se presenta una descripción de los moldes naturales del encéfalo de Cricosaurus araucanensis junto con una síntesis de los avances en el conocimiento realizados, en los últimos años, sobre estos cuatro taxones argentinos. La calidad de la información que aporta los moldes naturales, sumado a la cantidad de moldes recuperados, hacen del registro patagónico una pieza clave para la exploración y reconstrucción de la anatomía blanda de estos crocodilomorfos, y para la comprensión de los cambios fisiológicos que acompañaron los cambios estructurales del esqueleto. La comprensión de estos cambios permitirá delimitar las innovaciones evolutivas claves que le permitieron a los metriorrínquidos la conquista, sin paralelo entre los arcosaurios, del medio pelágico.Facultad de Ciencias Naturales y Muse

Cricosaurus (Thalattosuchia, Metriorhynchidae) survival across the J/K boundary in the High Andes (Mendoza Province, Argentina)

Metriorhynchidae is an extinct group of Jurassic–Cretaceous crocodylomorphs that developed a fully pelagic lifestyle. Its Jurassic record is outstanding (it includes around 40 nominal species), while the records that can be restricted to the Cretaceous are particularly sparse. Here we describe a partial skull of a new species of Cricosaurus, Cricosaurus puelchorum sp. nov., from the lower Berriasian of the Vaca Muerta Formation (Neuquén Basin, Argentina). The description of the specimen reveals a series of autapomorphies and a unique combination of characters that justify the creation of a new species. Phylogenetic analysis places Cricosaurus puelchorum sp. nov. closer to three upper Kimmeridgian–lower Tithonian species of southern Germany. The new taxon was recovered in connection with an accurate ammonoid-based biostratigraphic control and allows confirming the survival of Cricosaurus across the J/K boundary at the southeastern Pacific.Fil: Herrera, Laura Yanina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fernández, Marta S.. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Vennari, Verónica Vanesa. Universidad Tecnologica Nacional. Facultad Reg.san Rafael. Instituto de Evolucion, Ecologia Historica y Ambiente. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mendoza. Instituto de Evolucion, Ecologia Historica y Ambiente.; Argentin

Braincase and endocranial anatomy of two thalattosuchian crocodylomorphs and their relevance in understanding their adaptations to the marine environment

Thalattosuchians are a group of Mesozoic crocodylomorphs known from aquatic deposits of the Early Jurassic-Early Cretaceous that comprises two main lineages of almost exclusively marine forms, Teleosauridae and Metriorhynchoidea. Teleosaurids were found in shallow marine, brackish and freshwater deposits, and have been characterized as semiaquatic near-shore forms, whereas metriorhynchids are a lineage of fully pelagic forms, supported by a large set of morphological characters of the skull and postcranial anatomy. Recent contributions on Thalattosuchia have been focused on the study of the endocranial anatomy. This newly available information provides novel evidence to suggest adaptations on the neuroanatomy, senses organs, vasculature, and behavioral evolution of these crocodylomorphs. However, is still not clear if the major morphological differences between teleosaurids and metriorhynchids were also mirrored by changes in the braincase and endocranial anatomy. Based on X-ray CT scanning and digital endocast reconstructions we describe the braincase and endocranial anatomy of two well-preserved specimens of Thalattosuchia, the semiaquatic teleosaurid Steneosaurus bollensis and the pelagic metriorhynchid Cricosaurus araucanensis. We propose that some morphological traits, such as: an enlarged foramen for the internal carotid artery, a carotid foramen ventral to the occipital condyle, a single CN XII foramen, absence of brain flexures, well-developed cephalic vascular system, lack ofsubtympanic foramina and the reduction of the paratympanic sinus system, are distinctive features of Thalattosuchia. It has been previously suggested that the enlarged foramen for the internal carotid artery, the absence of brain flexures, and the hypertrophied cephalic vascular system were synapomorphies of Metriorhynchidae; however, new information revealed that all of these features were already established at the base of Thalattosuchia and might have been exapted later on their evolutionary history. Also, we recognized some differences within Thalattosuchia that previously have not been received attention or even were overlooked (e.g., circular/bilobate trigeminal foramen, single/double CN XII foramen, separation of the cranioquadrate canal from the external otic apertureFacultad de Ciencias Naturales y Muse

The study of the mesozoic marine reptiles at the Museo de La Plata

El estudio de los reptiles marinos en Argentina en general, y desde el Museo de La Plata en particular, comenzó con breves descripciones realizadas por investigadores europeos. A nivel nacional, los primeros estudios datan de fines del siglo XIX y principios del siglo XX. Durante la primera mitad del siglo XX, las contribuciones sobre reptiles marinos desde el Museo de La Plata fueron producto de hallazgos casuales durante prospecciones geológicas y no de exploraciones paleontológicas sistemáticas. En la década de los setenta, esta situación se revirtió a través de un programa de investigación liderado por Zulma Brandoni de Gasparini y desarrollado en el Museo de La Plata, el cual continúa hoy a través de algunos de sus discípulos. A lo largo de los años, en el marco de este programa se prospectaron formaciones marinas mesozoicas en varias provincias de la Argentina y en la Península Antártica. También se formaron recursos humanos, que en la actualidad desarrollan sus investigaciones sobre reptiles marinos mesozoicos tanto en el Museo de La Plata como en otras renombradas instituciones nacionales.The study of marine reptiles in Argentina in general, and in the Museo de La Plata in particular, began with some brief descriptions by European researchers. The first local contributions date from the end of the 19th century and the beginning of the 20th century. During the latter period, contributions on marine reptiles from this institution were the result of fortuitous findings from geological surveys and not from specific paleontological fieldwork. In the 1970s, the situation changed when Zulma Brandoni de Gasparini started a research program at the Museo de La Plata, which is currently continued by some of her students. Since then and within the framework of this program, Mesozoic marine formations were prospected in several provinces of Argentina and in the Antarctic Peninsula as well. Also, numerous students were trained, many of whom are currently developing their research on Mesozoic marine reptiles at the Museo de La Plata and other renowned national scientific institutions.Fil: Herrera, Laura Yanina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Fernández, Marta Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentin

Occurrence of Torvoneustes (Crocodylomorpha, Metriorhynchidae) in marine jurassic deposits of Oaxaca, Mexico

IGM 9026 is a singular fossil collected at the beginning of the 20th century in an improperly documented site within the Tlaxiaco Basin, near to Tlaxiaco town, Oaxaca, Mexico. The age of the site was suggested as being early Cretaceous. This specimen is the holotype of Plesiosaurus (Polypticodon) mexicanus, which later was identified as a possible late Jurassic marine crocodylomorph of the family Metriorhynchidae, and consequently it was referred as ?Cricosaurus mexicanus. The present study provides a re-description of this fossil based on a microscopic analysis and the use of white and UV lights; these analyses led to the discovery of peculiar dental characters diagnostic of the genus Torvoneustes. This finding supports the re-classification of IGM 9026 under a new nominal combination as Torvoneustes mexicanus. Along the Tlaxiaco Basin, the fossil preservation mode and lithological composition observed in IGM 9026 only occur in the marine vertebrates recently discovered in Yosobé, a Kimmeridgian shale outcrop characterized by clay calcareous nodules that belong to the Sabinal Formation, near Tlaxiaco town. This peculiarity suggests that T. mexicanus could represent an additional element of the Kimmeridgian vertebrate assemblage recovered in this geological unit. The two nominal species of Torvoneustes were collected in Kimmeridgian marine deposits of England; hence, this finding expands the geographical distribution of Torvoneustes all along the Tethys Sea, from its Eastern/European to western/Caribbean domains.Facultad de Ciencias Naturales y Muse

Occurrence of Torvoneustes (Crocodylomorpha, Metriorhynchidae) in marine jurassic deposits of Oaxaca, Mexico

IGM 9026 is a singular fossil collected at the beginning of the 20th century in an improperly documented site within the Tlaxiaco Basin, near to Tlaxiaco town, Oaxaca, Mexico. The age of the site was suggested as being early Cretaceous. This specimen is the holotype of Plesiosaurus (Polypticodon) mexicanus, which later was identified as a possible late Jurassic marine crocodylomorph of the family Metriorhynchidae, and consequently it was referred as ?Cricosaurus mexicanus. The present study provides a re-description of this fossil based on a microscopic analysis and the use of white and UV lights; these analyses led to the discovery of peculiar dental characters diagnostic of the genus Torvoneustes. This finding supports the re-classification of IGM 9026 under a new nominal combination as Torvoneustes mexicanus. Along the Tlaxiaco Basin, the fossil preservation mode and lithological composition observed in IGM 9026 only occur in the marine vertebrates recently discovered in Yosobé, a Kimmeridgian shale outcrop characterized by clay calcareous nodules that belong to the Sabinal Formation, near Tlaxiaco town. This peculiarity suggests that T. mexicanus could represent an additional element of the Kimmeridgian vertebrate assemblage recovered in this geological unit. The two nominal species of Torvoneustes were collected in Kimmeridgian marine deposits of England; hence, this finding expands the geographical distribution of Torvoneustes all along the Tethys Sea, from its Eastern/European to western/Caribbean domains.Facultad de Ciencias Naturales y Muse

Morphology of the sacral region and reproductive strategies of Metriorhynchidae: a counter-inductive approach

Morphological and physiological features indicate Metriorhynchidae as the only group of crocodylomorphs with a pelagic lifestyle. Some of these features have evolved convergently in several clades of tetrapods secondarily adapted to aquatic life. One striking feature of metriorhynchids as compared to other crocodylomorphs is the morphology of the pelvic region (i.e., ventrally deflected sacral ribs and reduced pelvic girdle), which increases significantly the depth of this region. This morphology, as a whole, resembles that of other viviparous Mesozoic marine reptiles not phylogenetically related to metriorhynchids. We tested two alternative hypotheses of reproductive strategies in this clade: oviparity vs. viviparity. Given the lack of direct evidence supporting one or the other, we explored the use of evidence that may disconfirm either of these hypotheses. Using this counter-inductive approach, we found no cases contradicting viviparity in metriorhynchids, except for their phylogenetic position as archosaurs. A survey of reproductive modes amongst amniotes depicts the evolutionary plasticity of the transition to viviparity, and a widespread occurrence among tetrapods secondarily adapted to a marine life. Assuming oviparity for metriorhynchids implies egg-laying out of the water. However, their postcranial morphology (i.e., features of fore and hind limbs, pelvic girdle, and tail) contradicts this possibility. In this context, we rejected oviparity for metriorhynchids.Facultad de Ciencias Naturales y Muse

Occurrence of Torvoneustes (Crocodylomorpha, Metriorhynchidae) in marine jurassic deposits of Oaxaca, Mexico

IGM 9026 is a singular fossil collected at the beginning of the 20th century in an improperly documented site within the Tlaxiaco Basin, near to Tlaxiaco town, Oaxaca, Mexico. The age of the site was suggested as being early Cretaceous. This specimen is the holotype of Plesiosaurus (Polypticodon) mexicanus, which later was identified as a possible late Jurassic marine crocodylomorph of the family Metriorhynchidae, and consequently it was referred as ?Cricosaurus mexicanus. The present study provides a re-description of this fossil based on a microscopic analysis and the use of white and UV lights; these analyses led to the discovery of peculiar dental characters diagnostic of the genus Torvoneustes. This finding supports the re-classification of IGM 9026 under a new nominal combination as Torvoneustes mexicanus. Along the Tlaxiaco Basin, the fossil preservation mode and lithological composition observed in IGM 9026 only occur in the marine vertebrates recently discovered in Yosobé, a Kimmeridgian shale outcrop characterized by clay calcareous nodules that belong to the Sabinal Formation, near Tlaxiaco town. This peculiarity suggests that T. mexicanus could represent an additional element of the Kimmeridgian vertebrate assemblage recovered in this geological unit. The two nominal species of Torvoneustes were collected in Kimmeridgian marine deposits of England; hence, this finding expands the geographical distribution of Torvoneustes all along the Tethys Sea, from its Eastern/European to western/Caribbean domains.Facultad de Ciencias Naturales y Muse