Paleontología virtual: un viaje tridimensional al pasado de los cocodrilos

Los fósiles de vertebrados han sido estudiados históricamente por los paleontólogos de manera directa y preparados por ellos y los técnicos para su estudio superficial. Sin embargo, la aplicación de metodologías modernas como por ejemplo la tomografía, han permitido avances impensados como reconstruir sus partes blandas y responder preguntas sobre sus modos de vida. Así, conocemos un poco más a los ancestros de los cocodrilos cuando los continentes estaban juntos formando la Pangea.Fundación Museo de La Plat

The higher-level phylogeny of Archosauria (Tetrapoda:Diapsida)

Crown group Archosauria, which includes birds, dinosaurs, crocodylomorphs, and several extinct Mesozoic groups, is a primary division of the vertebrate tree of life. However, the higher-level phylogenetic relationships within Archosauria are poorly resolved and controversial, despite years of study. The phylogeny of crocodile-line archosaurs (Crurotarsi) is particularly contentious, and has been plagued by problematic taxon and character sampling. Recent discoveries and renewed focus on archosaur anatomy enable the compilation of a new dataset, which assimilates and standardizes character data pertinent to higher-level archosaur phylogeny, and is scored across the largest group of taxa yet analysed. This dataset includes 47 new characters (25% of total) and eight taxa that have yet to be included in an analysis, and total taxonomic sampling is more than twice that of any previous study. This analysis produces a well-resolved phylogeny, which recovers mostly traditional relationships within Avemetatarsalia, places Phytosauria as a basal crurotarsan clade, finds a close relationship between Aetosauria and Crocodylomorpha, and recovers a monophyletic Rauisuchia comprised of two major subclades. Support values are low, suggesting rampant homoplasy and missing data within Archosauria, but the phylogeny is highly congruent with stratigraphy. Comparison with alternative analyses identifies numerous scoring differences, but indicates that character sampling is the main source of incongruence. The phylogeny implies major missing lineages in the Early Triassic and may support a Carnian-Norian extinction event.Marshall Scholarship for study in the United KingdomJurassic FoundationUniversity of BristolPaleontological Societ

The evolution of dermal shield vascularization in Testudinata and Pseudosuchia: phylogenetic constraints versus ecophysiological adaptations

Studies on living turtles have demonstrated that shells are involved in the resistance to hypoxia during apnea via bone acidosis buffering; a process which is complemented with cutaneous respiration, transpharyngeal and cloacal gas exchanges in the soft-shell turtles. Bone acidosis buffering during apnea has also been identified in crocodylian osteoderms, which are also known to employ heat transfer when basking. Although diverse, many of these functions rely on one common trait: the vascularization of the dermal shield. Here, we test whether the above ecophysiological functions played an adaptive role in the evolutionary transitions between land and aquatic environments in both Pseudosuchia and Testudinata. To do so, we measured the bone porosity as a proxy for vascular density in a set of dermal plates before performing phylogenetic comparative analyses. For both lineages, the dermal plate porosity obviously varies depending on the animal lifestyle, but these variations prove to be highly driven by phylogenetic relationships. We argue that the complexity of multi-functional roles of the post-cranial dermal skeleton in both Pseudosuchia and Testudinata probably is the reason for a lack of obvious physiological signal, and we discuss the role of the dermal shield vascularization in the evolution of these groups. This article is part of the theme issue ‘Vertebrate palaeophysiology’

The osteoderm microstructure in doswelliids and proterochampsids and its implications for palaeobiology of stem archosaurs

Osteoderms are common in most archosauriform lineages, including basal forms, such as doswelliids and proterochampsids. In this survey, osteoderms of the doswelliids Doswellia kaltenbachi and Vancleavea campi, and proterochampsid Chanaresuchus bonapartei are examined to infer their palaeobiology, such as histogenesis, age estimation at death, development of external sculpturing, and palaeoecology. Doswelliid osteoderms have a trilaminar structure: two cortices of compact bone (external and basal) that enclose an internal core of cancellous bone. In contrast, Chanaresuchus bonapartei osteoderms are composed of entirely compact bone. The external ornamentation of Doswellia kaltenbachi is primarily formed and maintained by preferential bone growth. Conversely, a complex pattern of resorption and redeposition process is inferred in Archeopelta arborensis and Tarjadia ruthae. Vancleavea campi exhibits the highest degree of variation among doswelliids in its histogenesis (metaplasia), density and arrangement of vascularization and lack of sculpturing. The relatively high degree of compactness in the osteoderms of all the examined taxa is congruent with an aquatic or semi-aquatic lifestyle. In general, the osteoderm histology of doswelliids more closely resembles that of phytosaurs and pseudosuchians than that of proterochampsids

Palaeobiological inferences of "rauisuchians" Fasolasuchus tenax (Los Colorados Fm., Argentina) and Prestosuchus chiniquensis (Santa Maria Super sequence, Brazil) from the Middle-Upper Triassic of South America based on microstructural analyses

“Rauisuchia” is a non-monophyletic group of quadrupedal and carnivorous pseudosuchians that inhabited the entire world during the Middle–Upper Triassic period (Anisian/Ladinian–Rhaetian). In South America, “rauisuchians” reached the largest sizes among continental carnivores. Despite their important ecological role, some aspects of their palaeobiology have been poorly examined. Here, we study appendicular bones, dorsal ribs and osteoderms of two genera, the Argentinean Fasolasuchus tenax (PVL 3850, holotype) and the Brazilian Prestosuchus chiniquensis (SNSB-BSPG AS XXV) respectively. The femur of F. tenax is formed by laminar fibrolamellar bone, which is composed of non-fully monorefringent woven-fibred matrix and primary osteons; the dorsal rib has a Haversian bone composition with an external fundamental system recorded and the osteoderm is formed by well-organised parallel-fibred bone. The femur, humerus and fibula of P. chiniquensis are mostly composed of strongly arranged parallel-fibred bone and a laminar vascularisation. The minimal ages obtained correspond to 9 years for F. tenax (based on the maximum number of growth mark in the osteoderm) and 4 years for P. chiniquensis (obtained from the highest count of growth marks in the femur and in the humerus). F. tenax attained somatic and skeletal maturity, while P. chiniquensis was near to reaching skeletal and sexual maturity, but it was somatically immature. The overall rapid growth rate and the high and uniform vascularisation seems to imply that these features are common in most of “rauisuchians”, except in P. chiniquensis. K E Y W O R D S bone histology, fibrolamellar complex, growth rate, Loricata, Paracrocodylomorph

The evolution of dermal shield vascularization in Testudinata and Pseudosuchia : phylogenetic constraints versus ecophysiological adaptations

Studies on living turtles have demonstrated that shells are involved in the resistance to hypoxia during apnea via bone acidosis buffering; a process which is complemented with cutaneous respiration, transpharyngeal and cloacal gas exchanges in the soft-shell turtles. Bone acidosis buffering during apnea has also been identified in crocodylian osteoderms, which are also known to employ heat transfer when basking. Although diverse, many of these functions rely on one common trait: the vascularization of the dermal shield. Here, we test whether the above ecophysiological functions played an adaptive role in the evolutionary transitions between land and aquatic environments in both Pseudosuchia and Testudinata. To do so, we measured the bone porosity as a proxy for vascular density in a set of dermal plates before performing phylogenetic comparative analyses. For both lineages, the dermal plate porosity obviously varies depending on the animal lifestyle, but these variations prove to be highly driven by phylogenetic relationships. We argue that the complexity of multi-functional roles of the post-cranial dermal skeleton in both Pseudosuchia and Testudinata probably is the reason for a lack of obvious physiological signal, and we discuss the role of the dermal shield vascularization in the evolution of these groups. This article is part of the theme issue 'Vertebrate palaeophysiology'

Aetosauria: a clade of armoured pseudosuchians from the Upper Triassic continental beds

Aetosauria is a clade of obligately quadrupedal, heavily armoured pseudosuchians known from Upper Triassic (late Carnian?Rhaetian) strata on every modern continent except Australia and Antarctica. As many as 22 genera and 26 species ranging from 1 to 6 m in length, and with a body mass ranging from less than 10 to more than 500 kg, are known. Aetosauroides scagliai was recently recovered as the most basal aetosaur, placed outside of Stagonolepididae (the last common ancestor of Desmatosuchus and Aetosaurus). Interrelationships among the basal aetosaurs are not well understood but two clades with relatively apomorphic armour ? the spinose Desmatosuchinae and the generally wide-bodied Typothoracisinae ? are consistently recognized. Paramedian and lateral osteoderms are often distinctive at the generic level but variation within the carapace is not well understood in many taxa, warranting caution in assigning isolated osteoderms to specific taxa. The aetosaur skull and dentition varies across taxa, and there is increasing evidence that at least some aetosaurs relied on invertebrates and/or small vertebrates as a food source. Histological evidence indicates that, after an initial period of rapid growth, lines of arrested growth (LAGs) are common and later growth was relatively slow. The common and widespread Late Triassic ichnogenus Brachychirotherium probably represents the track of an aetosaur.Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Heckert, Andrew B.. Appalachian State University; Estados UnidosFil: Martz, Jeffrey W.. Denver Museum of Nature and Science; Estados UnidosFil: Parker, William G.. University of Texas; Estados UnidosFil: Schoch, Rainer. Staatliches Museum für Naturkunde; AlemaniaFil: Small, Bryan J.. Museum of Texas Tech University; Estados UnidosFil: Sulej, Tomasz. Instytut Paleobiologii; Poloni