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Loricatan pseudosuchians (known as “rauisuchians”) typically consist of poorly understood fragmentary remains known worldwide from the Middle Triassic to the end of the Triassic Period. Renewed interest and the discovery of more complete specimens recently revolutionized our understanding of the relationships of archosaurs, the origin of Crocodylomorpha, and the paleobiology of these animals. However, there are still few loricatans known from the Middle to early portion of the Late Triassic and the forms that occur during this time are largely known from southern Pangea or Europe.Heptasuchus clarkiwas the first formally recognized North American “rauisuchian” and was collected from a poorly sampled and disparately fossiliferous sequence of Triassic strata in North America. Exposed along the trend of the Casper Arch flanking the southeastern Big Horn Mountains, the type locality ofHeptasuchus clarkioccurs within a sequence of red beds above the Alcova Limestone and Crow Mountain formations within the Chugwater Group. The age of the type locality is poorly constrained to the Middle—early Late Triassic and is likely similar to or just older than that of the Popo Agie Formation assemblage from the western portion of Wyoming. The holotype consists of associated cranial elements found in situ, and the referred specimens consist of crania and postcrania. Thus, about 30% of the osteology of the taxon is preserved. All of the pseudosuchian elements collected at the locality appear to belong toHeptasuchus clarkiand the taxon is not a chimera as previously hypothesized.Heptasuchus clarkiis distinct from all other archosaurs by the presence of large, posteriorly directed flanges on the parabasisphenoid and a distinct, orbit-overhanging postfrontal. Our phylogenetic hypothesis posits a sister-taxon relationship betweenHeptasuchus clarkiand the Ladinian-agedBatrachotomus kupferzellensisfrom current-day Germany within Loricata. These two taxa share a number of apomorphies from across the skull and their phylogenetic position further supports ‘rauisuchian’ paraphyly. A minimum of three individuals ofHeptasuchusare present at the type locality suggesting that a group of individuals died together, similar to other aggregations of loricatans (e.g.,Heptasuchus,Batrachotomus,Decuriasuchus,Postosuchus).

Most Notosuchia were active terrestrial predators. A few were semi-aquatic, or were insectivorous, omnivorous or herbivorous. A question relative to their thermometabolism remains to be answered: were Notosuchia warm-blooded? Here we use quantitative bone palaeohistology to answer this question. Two variables were used as proxies to infer thermometabolism: resting metabolic rate and red blood cell dimensions. Resting metabolic rate was inferred using relative primary osteon area and osteocyte size, shape and density. Blood cell dimensions were inferred using harmonic mean canal diameter and minimum canal diameter. All inferences were performed using phylogenetic eigenvector maps. Both sets of analyses suggest that the seven species of Notosuchia sampled in this study were ectotherms. Given that extant Neosuchia (their sister group) are also ectotherms, and that archosaurs were primitively endotherms, parsimony suggests that endothermy may have been lost at the node Metasuchia (Notosuchia–Neosuchia) by the Early Jurassic. Semi-aquatic taxa such as Pepesuchus may have had thermoregulatory strategies similar to those of recent crocodylians, whereas the terrestrial taxa (Araripesuchus, Armadillosuchus, Iberosuchus, Mariliasuchus, Stratiotosuchus) may have been thermoregulators similar to active predatory varanids. Thermal inertia may have contributed to maintaining a stable temperature in large notosuchians such as Baurusuchus.

Gracilisuchus stipanicicorum is a basal suchian from the Late Triassic Chañares Formation (Argentina), nested in the recently erected Gracilisuchidae, along with Turfanosuchus dabanensis and Yonghesuchus sangbiensis from China. The six known Gracilisuchus specimens preserve most of the skeleton, lacking most of the scapular girdle and forelimb. Our latest fieldworks have unearthed two specimens preserving previously unknown elements, including the humerus, radius, and ulna, as well as the femur, presacral vertebrae, and paramedian osteoderms. The femur and osteoderms were histologically sectioned, a study never undertaken in Gracilisuchidae. The anatomical analysis revealed characters in the new elements that improve the understanding of the anatomy of Gracilisuchus and its identification. Bone histology revealed that the specimen CRILAR PV 490 died before reaching somatic maturity and that growth was relatively slow compared to other pseudosuchians. This study deepens the knowledge of the anatomy of Gracilisuchus and constitutes a further step towards a broader understanding of Gracilisuchidae and basal suchian clades. Gracilisuchus stipanicicorum Romer, 1972 est un suchien souche de la Formation Chañares du Trias supérieur (Argentine), inclus dans les Gracilisuchidae, un groupe récemment créé avec Turfanosuchus dabanensis Young, 1973 et Yonghesuchus sangbiensis Wu et al., 2001 de Chine. Les six spécimens connus de Gracilisuchus Romer, 1972 conservent la majorité du squelette, à l’exception de la plupart de la ceinture scapulaire et du membre antérieur. Nos derniers travaux sur le terrain, ont exhumé deux spécimens qui préservent des éléments non encore connus, tels que l’humérus, le radius et l’ulna, ainsi qu’un fémur, des vertèbres et ostéodermes. Le fémur et les ostéodermes paramédiaux ont été sectionnés en vue d’une histologie, encore jamais abordée chez les Gracilisuchidae. L’analyse anatomique a révélé, dans les nouveaux éléments, des caracréristiques qui améliorent notre compréhension de l’anatomie de Gracilisuchus. L’histologie osseuse, elle, a révélé que l’individu CRILAR PV 490 était mort avant atteindre sa taille adulte et que sa croissance était relativement lente comparée à celle d’autres pseudosuchiens. Cette étude approfondit la connaissance de Gracilisuchus et constitue un pas supplémentaire vers une meilleure compréhension de Gracilisuchidae et des clades de suchiens souches. Fil: Lecuona, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina. Universidad Nacional de Río Negro; Argentina Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. División Paleontología Vertebrados, Facultad de Ciencias Naturales y Museo; Argentina Fil: Cerda, Ignacio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Negro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina

Ornithosuchidae is one of the most enigmatic clades of Triassic pseudosuchians. The group is composed by three carnivorous species that were excavated from Upper Triassic beds of Scotland and Argentina. We describe the first ornithosuchid from the Upper Triassic sediments of Brazil and explore its phylogenetic affinities and implications for the evolution of the group. Dynamosuchus collisensis gen. et sp. nov. was found as the sister taxon of the Argentinean form Venaticosuchus rusconii. These relationships reject a potential endemic radiation of ornithosuchids from the Ischigualasto-Villa Unión Basin and would better support multiple diversification events. Our findings with ornithosuchids is consistent with the pattern reported for proterochampsid and erpetosuchid archosauriforms from Ischigualasto-Villa Unión and the Paraná basins. In addition, the presence of an ornithosuchid in the Late Triassic of Brazil suggests that ornithosuchids were more widespread than previously thought in the southern hemisphere. The new ornithosuchid further demonstrates a faunistic link between the Argentinean and Brazilian basins during the Carnian. Finally, the discovery of the new species provides the first clue of a putative necrophagous vertebrate from the oldest dinosaur-bearing beds and expands our knowledge regarding the trophic structure of the Late Triassic of Brazil. Fil: Müller, Rodrigo. Universidade Federal de Santa Maria; Brasil Fil: Von Baczko, Belen. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Desojo, Julia Brenda. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Nesbitt, Sterling. Virginia Tech University; Estados Unidos

A review of the type and referred material of von Huene shows that Prestosuchus is a valid taxon represented by, at least, three different species: the lectotype and para-lectotype of Prestosuchus chiniquensis, an unnamed species from Brazil (UFRGS-PV-0152-T), and the new combination Prestosuchus nyassicus (=Stagonosuchus nyassi-cus). Several more recently referred specimens are also included within the genus Prestosuchus based on the absence of a vertical crest dorsal to the supracetabular rim; dorsal margin of postacetabular part of ilium concave; marked angle between pubic peduncle/obturator plate and ischial shaft; and elongate posteromedial depression on the distal fibula, making it one of the best known rauisuchian taxa. The phylogenetic analysis recovered a monophyletic Prestosuchidae including Saurosuchus galilei, Luperosuchus fractus, Prestosuchus chiniquensis, Prestosuchus nyassicus, and several specimens referred to the genus Prestosuchus. This clade is supported by the presence of a ridge on the ventral process of the squamosal; anteroventral process of the squamosal perforates the lower temporal fenestra; palpebral bones extensively sutured to each other and to the lateral margin of the frontals; robust, knob-shaped attachment for the musculus iliofibularis on the fibula; and anterior portion of nasals elevated above the skull roof. The identification of this natural group evidenced a remarkable diversity and abundance of basal loricatans in the Middle-Late Triassic continental ecosystems of southern Gondwana. Fil: Desojo, Julia Brenda. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Von Baczko, Belen. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Rauhut, Oliver Walter Mischa. Bayerische Staatssammlung für Paläontologie und Geologie; Alemania. Ludwig Maximilians Universitat; Alemania

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. Fil: Clarac, François. Uppsala Universitet; Suecia Fil: Scheyer, Torsten M.. Universitat Zurich; Suiza Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Cerda, Ignacio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina Fil: Sanchez, Sophie. Uppsala Universitet; Suecia. European Synchrotron Radiation Facility; Francia

In the present contribution, we aim to present the osteology of ‘ULBRA-PVT-281’, which comprises the best-preserved skeleton of Prestosuchus chiniquensis ever found. ULBRA-PVT-281 combines the morp...

The evolution of the braincase and brain of early pseudosuchians through to the earliest crocodylomorphs is poorly understood given the paucity of specimens, lack of well-preserved material, and lack of consensus on the phylogenetic relationships of the major clades of Pseudosuchia. Here, we describe three differently sized braincases diagnosable as belonging to the archosaur Parringtonia gracilis from the Middle Triassic Manda Beds of Tanzania. One of them, a nearly complete and exceptionally preserved braincase, possesses a complex set of character states typically present in early-diverging Pseudosuchia, but it also possesses nearly all of the character states previously hypothesized to represent synapomorphies exclusive to aetosaurs and crocodylomorphs. Details of the internal anatomy and a reconstructed endocast were obtained through high-resolution computed tomographic data and show a high degree of conservation of brain architecture across Pseudosuchia, in stark contrast to the extensive shifts observed within Theropoda to crown Aves. Integrating cranial and postcranial data into a phylogenetic analysis, we find Parringtonia gracilis to be closely related to a Revueltosaurus-Aetosauria clade at the base of Suchia and distantly related to crocodylomorphs. No matter which pseudosuchian clade is the most closely related to crocodylomorphs, we deduce that homoplasy in the braincase appears to be common across Pseudosuchia.

Vascularization in the core of crocodylian osteoderms, and in their superficial pits has been hypothesized to be a key feature involved in physiological thermoregulation and/or acidosis buffering during anoxia (apnea). However, up to now, there have been no quantitative data showing that the inner, or superficial, blood supply of the osteoderms is greater than that occurring in neighboring dermal tissues. We provide such data: our results clearly indicate that the vascular networks in both the osteoderms and the pits forming their superficial ornamentation are denser than in the overlying dermis. These results support previous physiological assumptions and indicate that vascularization in pseudosuchian (crocodylians and close relatives) ornamented osteoderms could be part of a broad eco-physiological adaptation towards ectothermy and aquatic ambush predation acquired by the crocodylomorphs during their post-Triassic evolution. Moreover, regressions demonstrate that the number of enclosed vessels is correlated with the sectional area of the cavities housing them (superficial pits and inner cavities). These regressions can be used to infer the degree of vascularization on dry and fossilized osteoderms and thus document the evolution of the putative function of the osteoderms in the Pseudosuchia. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:175-183, 2018. © 2017 Wiley Periodicals, Inc.

Our understanding of Typothorax coccinarum is primarily based on postcranial material, along with a few isolated cranial elements. Here we describe the first complete articulated skull of Typothora...

Acaenasuchus geoffreyi is a diminutive armored archosaur from the Upper Triassic Chinle Formation of northern Arizona, U.S.A., with uncertain evolutionary relationships and skeletal maturity. Known only from osteoderms, the taxon has been considered a valid taxon of aetosaur, juvenile specimens synonymous with the aetosaur Desmatosuchus spurensis, or a non-aetosaurian pseudosuchian archosaur. Here, we describe new fossils of Acaenasuchus geoffreyi that represent cranial, vertebral, and appendicular elements as well as previously unknown variations in the dorsal carapace and ventral shield. The skull bones are ornamented with the same anastomosing complex of ridges and grooves found on the paramedian and lateral osteoderms, and the appendicular skeleton resembles that of Revueltosaurus callenderi, Euscolosuchus olseni, aetosaurs, and other armored archosaurs such as erpetosuchids. Histology of osteoderms from the hypodigm of Acaenasuchus geoffreyi shows multiple growth lines, laminar tissue, and low vascularity, evidence that the individuals were close to skeletal maturity and not young juveniles. A revised phylogenetic analysis of early archosaurs recovers Acaenasuchus geoffreyi and Euscolosuchus olsenias sister taxa and members of a new clade that is the sister taxon of Aetosauria. This new phylogeny depicts a broader distribution of osteoderm character states previously thought to only occur in aetosaurs, demonstrating the danger of using only armor character states in aetosaur taxonomy and phylogeny. Acaenasuchus geoffreyi is also a good example of how new fossils can stabilize 'wild card' taxa in phylogenetic analyses and contributes to our understanding of the evolution of the aetosaur carapace. Petrified Forest Museum Association; Friends of Petrified Forest National Park We thank D. and J. Gillette (MNA), P. Holroyd (UCMP), and C. Levitt-Bussian (UMNH) for providing collections and archive access, and for facilitating loans from their institutions. M. Polcyn (SMU) graciously sent us locality information and photographs of SMU 75403. H.-D. Sues provided photographs of and helpful comments on Euscolosuchus olseni, and J. Strotman facilitated the molding, casting, and transfer of casts of USNM 448587 and USNM 448582. P. Holroyd (UCMP) graciously provided permission to histologically section two osteoderms, and A. Lee (Midwestern University) kindly assisted with sectioning. K. Ritterbush (University of Utah) generously provided access to her petrographic microscope imaging system, and the histological slides were imaged by N. Ong. R. Long's field notes are on file in the archives at PEFO and the UCMP and those of Charles Camp are available at the UCMP. Thanks to T. Olson for finding MDM specimens at PFV 211. We thank J. Kirkland and D. DeBlieux (Utah Geological Survey) for permission to include in this study material they collected. The collection and preparation of the specimens from PEFO was funded by the Petrified Forest Museum Association and Friends of Petrified Forest National Park. Silhouettes from phylopic.org in Figure 9 were created by S. Hartman, D. Bogdanov, and Smokeybjb and reused under the Creative Commons Attribution 3.0 Unported license (creativecommons.org/licenses/by/3.0). Thanks to V. Paes Neto and D. Gillette for constructive comments and discussion on aetosaur and glyptodont anatomy, and to A. Turner for help in constraining tree topology in TNT. Comments and suggestions made by M. B. von Baczko and I. Cerda improved the manuscript. This is Petrified Forest National Park Contribution No. 61. The conclusions presented here are those of the authors and do not represent the views of the United States Government.

Despite strong evidence for sexual selection in various display traits and other exaggerated structures in large extinct reptiles, such as dinosaurs, detecting sexual dimorphism in them remains difficult. Their relatively small sample sizes, long growth periods, and difficulties distinguishing the sexes of fossil specimens mean that there are little compelling data on dimorphism in these animals. The extant gharial (Gavialis gangeticus) is a large and endangered crocodylian that is sexually dimorphic in size, but males also possesses a sexually selected structure, the ghara, which has an osteological correlate in the presence of a fossa associated with the nares. This makes the species a unique model for potentially assessing dimorphism in fossil lineages, such as dinosaurs and pterosaurs, because it is a large, slow-growing, egg-laying archosaur. Here we assess the dimorphism of G. gangeticus across 106 specimens and show that the presence of a narial fossa diagnoses adult male gharials. Males are larger than females, but the level of size dimorphism, and that of other cranial features, is low and difficult to detect without a priori knowledge of the sexes, even with this large dataset. By extension, dimorphism in extinct reptiles is very difficult to detect in the absence of sex specific characters, such as the narial fossa.

During the Triassic period, pseudosuchians presented a broader variety of feeding habits than those seen nowadays, including herbivorous and omnivorous as well as carnivorous diets. Based on their general anatomy, ornithosuchids have been historically proposed to be either hunters or scavengers. The rediscovered cranial materials of the ornithosuchid Venaticosuchus herein described in detail enabled the reconstruction of its jaw musculature and a geometric biomechanical analysis to study the possible feeding habits of ornithosuchids. The muscles were reconstructed based on inferences of their osteological correlates seen in their closest living relatives, such as Caiman, Alligator, and Iguana. Consequently, the jaws were considered a third-class lever system and the moment arms were calculated for the adductor and depressor musculature. The study of the three species of ornithosuchids (Ornithosuchus, Venaticosuchus and Riojasuchus) revealed greater similarities between ornithosuchids and aetosaurs, in spite of their different feeding habits, than between ornithosuchids and crocodylians. The relative bite force of Venaticosuchus resulted higher than that of other ornithosuchids, aetosaurs and Alligator. The elevated bite force identified for ornithosuchids together with their low bite speed and the morphology of their constricted snouts, suggest features more compatible with scavenging feeding habits. Ornithosuchids were not the apex predators of the Late Triassic continental communities but were more likely regarded to have scavenged or preyed on small animals such as procolophonids, sphenodontians, juvenile aetosaurs, erpetosuchids, cinodonts, and dicynodonts that did not exceed them in size. Durante el período Triásico, los pseudosuquios presentaron una variedad más amplia de hábitos alimenticios que los que se ven hoy en día, incluidas las dietas herbívoras y omnívoras, así como las carnívoras. Basado en su anatomía general, los ornitosucidos han sido históricamente propuestos como cazadores o carroñeros. Los materiales craneales redescubiertos del ornitosuchid Venaticosuchus aquí descrito en detalle permitieron la reconstrucción de su musculatura mandibular y un análisis biomecánico geométrico para estudiar los posibles hábitos alimenticios de los ornitosuchids. Los músculos se reconstruyeron en base a las inferencias de sus correlatos osteológicos vistos en sus parientes vivos más cercanos, como Caiman , Alligator e Iguana.. En consecuencia, las mandíbulas se consideraron un sistema de palanca de tercera clase y el momento en que se calcularon los brazos para la musculatura del aductor y el depresor. El estudio de las tres especies de ornitosuquidos ( Ornithosuchus , Venaticosuchus y Riojasuchus ) reveló mayores similitudes entre los ornitosuquidos y los aetosaurios, a pesar de sus diferentes hábitos alimenticios, que entre los ornitosuquidos y los crocodilianos. La fuerza de mordida relativa de Venaticosuchus resultó más alta que la de otros ornitosucidos, aetosaurios y caimanes. La elevada fuerza de mordida identificada para los ornitosucidos junto con su baja velocidad de mordida y la morfología de sus hocicos constreñidos, sugieren características más compatibles con los hábitos de alimentación de barrido. Los ornitosuquidos no fueron los depredadores del ápice de las comunidades continentales del Triásico Tardío, pero se consideró más probable que hubieran limpiado o cazado animales pequeños como procolofónidos, fenodoncios, aetosaurios juveniles, erpetosuchidos, cinodontes y dicinodontos que no los superaban en tamaño. Fil: Von Baczko, Belen. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina

Aetosaurs comprise a clade of quadrupedal, armored, omnivores to herbivores that lived across much of the supercontinent of Pangea during the Late Triassic. Their relative abundance in many units, and the rarity of other Triassic herbivores, points to them as key components of Late Triassic ecosystems. Debate persists about whether they were growing more or less slowly when compared to extant crocodylians, and bone histology is sparsely sampled within the group. We undertook a histological examination of Coahomasuchus chathamensis to address its ontogenetic trajectory and characterize its histology. We sampled a paramedian osteoderm from the holotype specimen, as well as five osteoderms (two paramedian, one lateral, and two of uncertain position) and two incomplete limb bones (radius and fibula), from referred specimens discovered at the type locality. Using these we estimated specimen ages with lines of arrested growth (LAGs) to determine that the study individuals reached from 2 to 7 years old. All of the sampled elements contained woven-fibered bone with extensive vasculature within the internal cortex. In some specimens, more poorly vascularized, parallel-fibered bone is evident externally. The holotype of C. chathamensis represents a juvenile individual, and raises the possibility that the holotype of C. kahleorum is a juvenile as well, complicating aetosaur systematics and diversity. When compared to aetosaurs of similar size, it is clear that C. chathamensis was growing comparatively rapidly, about 3 times the rate of similarly sized specimens of Aetosauroides scagliai from Argentina. This discovery reveals the presence of disparate growth strategies within Aetosauria. Anat Rec, 302:1504-1515, 2019. © 2018 American Association for Anatomy.

One of the most striking features of aetosaurs is the possession of an extensive bony armour composed of dorsal, ventral and appendicular osteoderms. With the purpose of establishing the main histological changes during ontogeny and the degree of histological variation within the armour, we analysed the bone histology of dorsal (paramedian and lateral), ventral and appendicular osteoderms from different taxa from the Late Triassic of South America, including Aetosauroides scagliai, Aetobarbakinoides brasiliensis and Neoaetosauroides engaeus. Histological data support an intramembranous origin for osteoderms. Nevertheless, evidence for metaplastic ossification (i.e. structural fibres) at advanced ontogenetic stages, in at least some elements, is also present. A variant type of parallel fibred bone, which we have named ‘crossed parallel fibred bone’, is characterized for aetosaurs. In this pseudosuchian group, osteoderms exhibit very important microstructural changes during ontogeny, which can be useful for determining ontogenetic stages from isolated elements. Histological data suggest a relatively early onset of sexual maturity among aetosaurs. Microanatomical analysis from different taxa reveal that having high values of compactness is the plesiomorphic condition for Aetosauria. The notably increased compactness of the osteoderms does not appear to be related to size, ontogeny, sex or reproductive status of the individuals. Although a high degree of compactness of osteoderms and other bones has been considered as evidence for an aquatic lifestyle in vertebrates, such an inference contradicts the current concept of a fully terrestrial lifestyle in aetosaurs. Fil: Cerda, Ignacio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina Fil: Desojo, Julia Brenda. 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. Departamento Científico de Paleontología de Vertebrados; Argentina Fil: Scheyer, Torsten. Universitat Zurich. Instituto Palaontologisches Institut And Museum; Suiza

Calyptosuchus wellesiis a medium-sized desmatosuchian aetosaur common in Adamanian (early to middle Norian) age rocks from the Chinle Formation and Dockum Group of the Western United States. Known chiefly from osteoderms, this taxon has never been fully described and non-osteoderm material assigned toCalyptosuchushas been done so based on questionable criteria. Mapping of aetosaurian elements from thePlaceriasQuarry allows for the recognition of associated material providing support for referrals of non-osteoderm material. Furthermore, another previously undescribed specimen from the Chinle Formation of Arizona provides more details about this taxon. PresentlyCalyptosuchuslacks discrete autapomorphies, but can be distinguished from other aetosaurs based on a unique combination of characters supported by a phylogenetic analysis.Calyptosuchusis one of the most common aetosaurians in the Western United States and an index taxon of the early Adamanian biozone. The nameCalyptosuchusis retained and encouraged as the applicable genus name for the specieswellesirather than the often usedStagonolepisbecause assignments of taxa to multi-species genus names are problematic and in this case provides a proposed taxonomic relationship that cannot be unambiguously supported, even by phylogenetic analyses. Because of the inherent limitations of the fossil record, referral of specimens and species to species and genera respectively is an epistemological problem in vertebrate paleontology.

The pseudosuchian archosaur Ornithosuchus, from the Lossiemouth Sandstone Formation (Late Triassic), Scotland, was the first ornithosuchid to be discovered, and the only one recorded, in the northern hemisphere. The fossil record of Ornithosuchus longidens is mainly based on natural moulds and, in a few cases, three-dimensional bony elements, complicating the interpretation of its anatomy. The taxonomy of this species has changed several times since the late 1800s and here we revisit its current status. The synonymy of Dasygnathoides longidens and Ornithosuchus woodwardi proposed by Walker (1964) is rejected, based on new interpretations of the holotype and referred specimens of Dasygnathoides longidens. The latter species is considered as a nomen dubium, because it lacks diagnostic features and cannot be identified beyond Pseudosuchia. As a result, Ornithosuchus woodwardi is resurrected as a valid species and its diagnosis is emended. The body size range of Ornithosuchus woodwardi is reduced to about a half, because ELGNM 1, previously considered the largest specimen of the genus, can no longer be referred to it. Dasygnathoides longidens cannot be assigned to any of the known archosauriforms from the Lossiemouth Sandstone Formation, but it still represents the largest predator currently known for its fauna. Fil: Von Baczko, Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Ezcurra, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina

Los aetosaurios son un grupo de arcosaurios pseudosuquios cuadrúpedos y acorazados del Triásico superior. Se Caracterizan por tener una coraza dorsal, una ventral, y osteodermos apendiculares, todos ornamentados. Los aetosaurios fueron propuestos como fósiles guía con base en características distintivas en algunos osteodermos. Por lo tanto, es importante comprender las variaciones intraespecíficas de estos elementos dentro del clado. En la presente contribución, se describen tres tipos de ornamentación en el área medial de los osteodermos paramediales de la coraza dorsal de Aetosauroides scagliai Casamiquela 1960: un “patrón radial”; un “patrón anastomosado”; y uno “intermedio” o “patrón transicional” entre el radial y el anastomosado. Las corazas articuladas de los especímenes PVL 2059 y PVL 2073 muestran los tres tipos de ornamentación, pero con una variación en la posición dentro de la coraza de los osteodermos con estas ornamentaciones. Recientes estudios paleohistológicos en osteodermos de A. scagliai muestran la ausencia de remodelación en los tejidos de los mismos permitiendo la estimación de edad mediante el conteo de LACs (líneas anuales de crecimiento). El PVL 2073 es ligeramente más corto (∼10% en los centros) pero también más joven ontogenéticamente (5 LACs) que el PVL 2059 (10 LACs; y osteodermos ligeramente más anchos). Combinando esta información y comparándola con los cocodrilos actuales (donde los machos son generalmente más grandes que las hembras para una misma edad), concluimos que la variación intraespecífica observada en A. scagliai es compatible con la hipótesis de un dimorfismo sexual. Estos resultados evidencian la necesidad de estudiar las variaciones intraespecíficas en aetosaurios. Aetosaurs are a group of quadrupedal, armoured pseudosuchian archosaurs from the Upper Triassic. They are characterized by dorsal and ventral carapaces, and appendicular osteoderms, all of them ornamented. Aetosaurs have been proposed as index fossils largely based on the distinctiveness of some osteoderms. Therefore, it is important to understand the intraspecific variation of these elements in the clade. In the present contribution, we describe three types of ornamentation on the medial area of paramedian osteoderms in the dorsal armour of Aetosauroides scagliai Casamiquela: the “radial pattern” the “anastomosing pattern”; and an “intermediate” or “transitional pattern”, that is an intermediate between “radial” and “anastomosing” patterns. The articulated dorsal armour preserved in specimens PVL 2059 and PVL 2073 possesses osteoderms carrying all three patterns of ornamentation, but they differ by the position of each type of osteoderm on the carapace. Recent studies on histological thin-sections of osteoderms of A. scagliai reveal the absence of osteoderm tissue remodeling, allowing the estimation of age by counting LAGs (lines of arrested growth). PVL 2073 is slightly shorter (∼10% longer centra) but also ontogenetically younger (5 LAGs) than PVL 2059 (10 LAGs; slightly wider osteoderms). Combining this information and comparing it with that of living crocodiles (where male specimens typically are relatively larger than females of the same age), we conclude that the intraspecific variation observed in A. scagliai is compatible with the hypothesis of sexual dimorphism. These results suggest the need to explore the sources of intraspecific variation in aetosaurs. Fil: Taborda, Jeremías Ramón Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Heckert, Andrew Bittinger. Appalachian State University; Estados Unidos Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina

Many of the major locomotor transitions during the evolution of Archosauria, the lineage including crocodiles and birds as well as extinct Dinosauria, were shifts from quadrupedalism to bipedalism (and vice versa). Those occurred within a continuum between more sprawling and erect modes of locomotion and involved drastic changes of limb anatomy and function in several lineages, including sauropodomorph dinosaurs. We present biomechanical computer models of two locomotor extremes within Archosauria in an analysis of joint ranges of motion and the moment arms of the major forelimb muscles in order to quantify biomechanical differences between more sprawling, pseudosuchian (represented the crocodile Crocodylus johnstoni) and more erect, dinosaurian (represented by the sauropodomorph Mussaurus patagonicus) modes of forelimb function. We compare these two locomotor extremes in terms of the reconstructed musculoskeletal anatomy, ranges of motion of the forelimb joints and the moment arm patterns of muscles across those ranges of joint motion. We reconstructed the threedimensional paths of 30 muscles acting around the shoulder, elbow and wrist joints. We explicitly evaluate how forelimb joint mobility and muscle actions may have changed with postural and anatomical alterations from basal archosaurs to early sauropodomorphs. We thus evaluate in which ways forelimb posture was correlated with muscle leverage, and how such differences fit into a broader evolutionary context (i.e. transition from sprawling quadrupedalism to erect bipedalism and then shifting to graviportal quadrupedalism). Our analysis reveals major differences of muscle actions between the more sprawling and erect models at the shoulder joint. These differences are related not only to the articular surfaces but also to the orientation of the scapula, in which extension/flexion movements in Crocodylus (e.g. protraction of the humerus) correspond to elevation/depression in Mussaurus. Muscle action is highly influenced by limb posture, more so than morphology. Habitual quadrupedalism in Mussaurus is not supported by our analysis of joint range of motion, which indicates that glenohumeral protraction was severely restricted. Additionally, some active pronation of the manus may have been possible in Mussaurus, allowing semi-pronation by a rearranging of the whole antebrachium (not the radius against the ulna, as previously thought) via long-axis rotation at the elbow joint. However, the muscles acting around this joint to actively pronate it may have been too weak to drive or maintain such orientations as opposed to a neutral position in between pronation and supination. Regardless, the origin of quadrupedalism in Sauropoda is not only linked to manus pronation but also to multiple shifts of forelimb morphology, allowing greater flexion movements of the glenohumeral joint and a more columnar forelimb posture., Facultad de Ciencias Naturales y Museo

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La presente tesis aborda un estudio anatómico, taxonómico y filogenético del clado Ornithosuchidae a fin de enriquecer el conocimiento del grupo y esclarecer las relaciones filogenéticas entre sus integrantes y con los demás grupos de arcosauriformes. En este estudio se realizó la descripción anatómica detallada del ornitosúquido argentino Riojasuchus tenuisceps y se desarrolló el primer estudio de su cavidad endocraneana realizado por medio de tomografías computadas identificando algunas de las estructuras que habrían conformado su encéfalo. Se realizó la descripción de nuevos materiales pertenecientes al ornitosúquido argentino Venaticosuchus rusconii. Por otra parte, se llevó a cabo una revisión taxonómica del ornitosúquido escocés Ornithosuchus “longidens” para poner a prueba su sinonimia con el taxón “Dasygnathoides (=Dasygnathus) longidens” tal y como fue propuesta por Walker (1964). Como resultado se reconoció al género y especie Dasygnathoides (=Dasygnathus) longidens como nomina dubia y se propuso regresar a la combinación nomenclatorial Ornithosuchus woodwardi designada por Newton (1894). A partir del estudio detallado de las tres especies de ornitosúquidos conocidas, se reexaminaron y corrigieron numerosas codificaciones de caracteres en la matriz de datos utilizada y se aportaron modificaciones de caracteres, nuevos caracteres y nuevos taxones para ampliar la misma. Como resultado del análisis filogenético se recuperó a Ornithosuchidae como un robusto grupo monofilético con altos valores de soporte nodal. Se identificó a Ornithosuchidae como el clado más basal dentro de Pseudosuchia. Sin embargo, no se obtuvo el elevado soporte presentado en trabajos previos, sino que la posición de Ornithosuchidae exhibió un comportamiento más inestable, pudiendo cambiar de su posición óptima en la base de Pseudosuchia a posicionarse en la base de Avemetatarsalia con tan solo un paso extra. Dentro de Ornithosuchidae, Ornithosuchus fue recuperado como taxón hermano de un clado formado por Riojasuchus y Venaticosuchus, como fuera propuesto por Baczko et al. (2014), viéndose a su vez reflejado en la distribución geográfica dispar de Ornithosuchidae. No obstante, se obtuvieron valores soporte aún mayores que los presentados por Baczko et al. (2014) para el nodo Riojasuchus + Venaticosuchus así como dos nuevas sinapormorfías para dicho nodo gracias al estudio detallado y a primera mano de todos los materiales de los ornitosúquidos conocidos. This thesis involves an anatomical, taxonomical and phylogenetic study of the clade Ornithosuchidae. Its aim is to enrich the knowledge of this group in an attempt to clarify its phylogenetic relationships with other arcosauriform groups and amongst the species it comprises. A detailed anatomical description of the Argentinean ornithosuchid Riojasuchus tenuisceps was carried out in this study as well as the first reconstruction of its endocranial cavity, which allowed identifying some of the structures of its encephalon. New cranial materials belonging to the Argentinean ornithosuchid Venaticosuchus rusconii were described. A taxonomic revision of the Scottish ornithosuchid Ornithosuchus “longidens” was carried out to test its synonymy with “Dasygnathoides (=Dasygnathus) longidens” as proposed by Walker (1964). As a result, the species and genre Dasygnathoides (=Dasygnathus) longidens were regarded as nomina dubia and the nomenclatural combination Ornithosuchus woodwardi was restored, as originally proposed by Newton (1894). Through the study of the three known species of ornithosuchids, several scorings and characters from chosen the data matrix were modified, and new characters and taxa were added to expand the matrix. From the resulting analysis, Ornithosuchidae was recovered as a robust monophyletic group with high nodal support. It was also identified as the most basal group within Pseudosuchia. However, the high nodal support recorded in previous publications was not recovered here, and Ornithosuchidae exhibited a more unstable behaviour, being able to change from its optimal position at the base of Pseudosuchia to the base of Avemetatarsalia with just one extra step. Within Ornithosuchidae, Ornithosuchus was recovered as a basal taxon, sister to a clade comprising Riojasuchus and Venaticosuchus, as proposed by Baczko et al. (2014), which is also reflected in the disjunct geographic distribution of Ornithosuchidae. Nontheless, the nodal values here obtained for the clade Riojasuchus + Veneticosuchus were even higher than those reported by Baczko et al. (2014), and two new synapomorphies were also recovered for that clade thanks to the detailed study of all knows ornithosuchid materials. Fil: von Baczko, María Belén. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Os arcossauros (Archosauria) são um grupo monofilético de diápsidos que apresentaram uma rica história evolutiva de diversificação de formas, com os únicos representantes viventes apenas as aves e os crocodilianos. A evolução do grupo durante o Período Triássico é uma das áreas dentro da paleontologia de vertebrados que tem apresentado um acréscimo de interesse nos últimos 20 anos. Isto se deve a uma gama de novas descobertas que, combinados com revisões de espécimes historicamente problemáticos e/ou pouco conhecidos na literatura, tem resultado em um melhor entendimento na variação morfológica do grupo e permitido análises filogenéticas mais robustas devido a um maior número amostral de táxons. A presente tese consiste em um detalhado Estado da Arte do conhecimento da origem e evolução dos arcossauros, com ênfase na linhagem Pseudosuchia A sua contribuição para esta área é na forma de três artigos: 1) A descrição da nova espécie de “rauissuquídeo” (“Rauisuchia”) Dagasuchus santacruzensis, da Zona de Associação (ZA) de Santacruzodon e sua importância para a distribuição paleofaunística do Triássico do Rio Grande do Sul; 2) A descrição de novos espécimes atribuídos ao “rauissuquídeo” (“Rauisuchia”) Prestosuchus chiniquensis, considerados como formas juvenis, que teriam importância na identificação das variações ontogenéticas desta espécie e as consequências disto na escolha de caracteres para matrizes de estudos filogenéticos; 3) A descrição de Pagosvenator candelariensis, da ZA de Dinodontosaurus, o primeiro erpetossuquídeo (Erpetosuchidae) para o Triássico do Rio Grande do Sul e suas implicações para o conhecimento sobre a distribuição paleobiogeográfica deste grupo e suas afinidades filogenéticas com outro grupo de arcossauros, os ornitossuquídeos (Ornithosuchidae). Archosaurs (Archosauria) are a monophyletic group of diapsids that display a rich and diverse evolutionary history, with the only extant forms being the birds and crocodilians. The evolution of this group during the Triassic Period is one the fields of study within vertebrate paleontology that has displayed an increase in interest in the past 20 years. This is due to a large number of new discoveries that combined with the revision and historically important but not well described specimens have resulted in a better understanding of the morphological and phylogenetic variation presented in early archosaurs. This, in turn, has allowed for better sampled data matrixes and better supported cladistic studies. This thesis presents a State of the Art of the current knowledge of the origins and evolution of Archosauria, with a focus on the Pseudosuchian lineage during the Triassic. Its contribution is in the form of three publications: 1) the description of a new species of “rauisuchian” (“Rauisuchia”) archosaur Dagasuchus santacruzensis, from the Santacruzodon Assembladge Zone (AZ) and discuss its importance in the paleofaunistic distribution of the Triassic of the Rio Grande do Sul State. 2) the description and study of new specimens attributed to the “rauisuchian” taxon Prestosuchus chiniquensis, which are identified as juvenile forms, which has important ramifications in the identification of ontogenetic variation in species and in establishing character states when constructing data matrixes for use in cladistic studies; 3) the description of Pagosvenator candelariensis, from the Dinodontosaurus AZ, which is the first erpetosuchid (Erpetosuchidae) for the Triassic of the Rio Grande do Sul State and has interesting implications in the paleobiogeographical distribution of this group and its phylogenetic affinities with another group of Triassic archosaurs, the ornithosuchians (Ornithosuchidae).

As the eponymous type species for rauisuchians, Rauisuchus tiradentes von Huene, 1938 represents an important but inadequately known specimen. The revision of the type material from the Upper Triassic (Carnian) Santa Maria Formation of Brazil reveals new anatomical data and previously unrecognised characters, including three new possible autapomorphies: a knob-like thickening on the base of the posterior process of the premaxilla; short and ventrally keeled cervicals lacking postzygodiapophyseal laminae; and mid-caudal vertebrae with an accessory neural spine and a postspinal lamina. Several elements are re-identified, including a postorbital (originally identified as postfrontal) and a pterygoid (originally identified as a prefrontal), and additional material from a secondary fossil site, originally assigned to R. tiradentes, including a left ilium, is excluded. Based on the recovered information and new morphological data, the systematic position of R. tiradentes is tested in a comparison of two phylogenetic reanalyses. Both analyses differ in respect to the phylogenetic position of R. tiradentes, and recover ‘rauisuchians’ as a paraphyletic assemblage of non-crocodylomoprh archosaurs. © 2014 The Linnean Society of London

The presence of early pseudosuchians and avemetatarsalians in Anisian beds of Africa demonstrates that the archosaur radiation was well underway by the beginning of the Middle Triassic. The rapid radiation produced a variety of forms, but many of the unique, well-diagnosed Late Triassic clades (e.g., Aetosauria, Ornithosuchidae) lack diagnosable members from the Middle Triassic. Here, we introduce a new Middle Triassic archosaur, Nundasuchus songeaensis, gen. et sp. nov., with an unusual mix of apomorphic character states found within Pseudosuchia and just outside Archosauria. The holotype consists of partial skeleton, including representative postcranial elements and parts of the skull. We added Nundasuchus songeaensis, gen. et sp. nov., into the two most comprehensive early archosaur phylogenetic data sets available, and in both analyses the new taxon falls within Pseudosuchia. However, a number of plesiomorphic archosaurian character states (e.g., posterolaterally directed tuber of the calcaneu...

Ornithosuchidae is a group of terrestrial quadrupedal pseudosuchian archosaurs from the Late Triassic of South America and Europe. Riojasuchus tenuisceps is arguably one of the best representative ...

The osteology of an almost complete braincase of the rauisuchian archosaur Prestosuchus chiniquensis from the Middle Triassic of Brazil is described for first time, based on two specimens (UFRGS-PV-0629-T and UFRGS-PV-0156-T). A comparative description with other taxa of rauisuchians is presented that forms the basis of a phylogenetic analysis. To perform the phylogenetic analysis, we describe and discuss each character codification for a modified version of the recent matrices of Gower (2002), Gower & Nesbitt (2006) and Brusatte et al. (2010). The analysis resulted in two most parsimonious trees that differ from the topologies recovered by Gower (2002) in a few aspects within Rauisuchia, and Prestosuchus chiniquensis was unequivocally depicted as deeply nested within Pseudosuchia, as the sister taxon of Batrachotomus kuperferzellensis in both topologies, supported by a single synapomorphy: the reduced to small fissure of the post-temporal fenestra between parietal, supraoccipital and exoccipital

Postosuchus kirkpatricki is a Late Triassic (Norian) ‘rauisuchid’ archosaur from North America. The initial description of the Postosuchus type material included elements from two poposaurids. This confusion has prevented adequate description of the material. Recent examination of the type material and other specimens of Postosuchus, and of related taxa, has helped clarify the osteology of Postosuchus. The type specimens represent c. 75% of the skeleton. Together with other referred material, Postosuchus remains one of the most completely known rauisuchids. The paratype skeleton, which is relatively complete, would have been c. 3.5–4 m in length, and the holotype would have been closer to 5–6 m. Analysis of the postcranial skeleton of Postosuchus suggests that it may have been an obligate biped (based in part on limb proportions, which are similar to some theropod dinosaurs, the size of the manus (30% of the size of the pes) and the highly reduced nature of the digits and vertebral measurements). Possible postcranial autapomorphies of Postosuchus include a large, rugose triangular supra-acetabular buttress confluent with the dorsal margin of the iliac blade, and a symmetrical pes with digits two and three being roughly equal in length. During the Triassic Period, archosaurian reptiles diversified into a large variety of carnivorous and herbivorous forms that dominated the global terrestrial landscape (Huene 1938; Bonaparte 1967; Chatterjee 1986; Long & Padian 1986; Parrish & Carpenter 1986; Benton & Clark 1988; Sereno 1991; Lucas 1998; Gower & Sennikov 2000; Langer 2005; Irmis et al. 2007; Sues & Fraser 2010). Of the two main lineages of archosaurs – Avemetatarsalia (bird-line) and Pseudosuchia (crocodile-line) – the pseudosuchians appear to have diversified more rapidly (Gower & Sennikov 2000; Nesbitt 2005a, b, 2011; Butler et al. 2009, 2011). ‘Rauisuchians’, a paraphyletic assemblage of pseudosuchians (alternatively see Brusatte et al. 2010, Butler et al. 2011) including Poposauroidea and Loricata (1⁄4 Paracrocodyliformes of Weinbaum & Hungerbuhler 2007), appear tentatively in Lower Triassic sediments in Asia and Europe and then in North America, with poposauroids having the oldest record (Butler et al. 2011; Nesbitt et al. 2011). Postosuchus kirkpatricki is a rauisuchid, a clade of pseudosuchians within the Paracrocodylomorpha (Fig. 1) and is one of the better-known genera of rauisuchid (Chatterjee 1985; Long & Murry 1995; Gower 2000; Weinbaum 2002; Weinbaum & Hungerbuhler 2007; Nesbitt 2011; Weinbaum 2011). Postosuchus was a relatively large animal estimated to have grown to between 5 and 7 m in length. Postosuchus has been considered by most workers to be closely related to crocodylomorphs (Benton & Clark 1988; Parrish 1993; Wu & Chatterjee 1993; Juul 1994; Long & Murry 1995; Gower 2000; Weinbaum & Hungerbuhler 2007; Nesbitt 2011; alternatively see Gower 2002 and Brusatte et al. 2010). However, the description of Postosuchus and its phylogenetic affiliations has been the subject of considerable debate since Chatterjee’s (1985) paper (Parrish 1993; Long & Murry 1995; Alcober & Parrish 1997; Gower 2000). Gower (2000) questioned the validity of some of Long & Murry’s (1995) identification of material (i.e. Long & Murry 1995, figs 125 & 136) from the Placerias Quarry to Postosuchus, but I agree with Long and Murry in attributing those elements to Postosuchus, as the morphology of those elements shows little variation from the type material. Material re-examined from the collection of the Museum of Texas Tech University, as well as a new, partially articulated skeleton from North Carolina (Peyer et al. 2008), an articulated, headless skeleton from Ghost Ranch, New Mexico, and specimens from other institutions have provided much data and context previously unknown from the Post Quarry ‘rauisuchians’. The specimen from Lithofacies II from the Deerfield Basin of North Carolina is intermediate in size between TTU-P 9000 and TTU-P 9002 (see Appendix I for institutional abbreviations). UNC-15575 was preserved with almost complete left and right pes and tarsus, and a mostly complete right manus and carpus (Peyer et al. 2008). Although the specimen is only From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.7 # The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics 10.1144/SP379.7 Geological Society, London, Special Publications published online February 13, 2013 as doi

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. Aetosaur- oides scagliai was recently recovered as the most basal aetosaur, placed outside of Stagonolepi- didae (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 vari- ation 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 ver- tebrates 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.

Unlike most rauisuchians, which are known based on partially preserved specimens, fossils attributed to Decuriasuchus quartacolonia include a monotaxonomic assemblage com- posed of nine associated individuals (MCN-PV10.105a-i), three with almost complete skulls (MCN-PV10.105a,c,d), and a partial disarticulated skull (MCN-PV10.004) collected in the Mid- dle Triassic (Ladinian, Dinodontosaurus Biozone) beds of the Santa Maria Formation, in south Brazil. Because of its completeness and possible phylogenetic position, as one of the most basal loricatans, D. quartacolonia is a key taxon for anatomic, evolutionary and biomechanical stud- ies of rauisuchians. The comparative description of its osteology reveals that the skull and mandi- ble of D. quartacolonia are very similar to those of cf. Prestosuchus chiniquensis and Saurosuchus galilei, sharing a drop-shaped subnarial fenestra, a subtriangular antorbital fenestra with an elon- gated and narrow anterior point, a 'roman nosed' nasal, and a posteroventrally oriented ridge on the lateral surface of the ventral ramus of the squamosal. Among the differences are the autapomor- phies of D. quartacolonia: numerous maxillary teeth (17), lateral expansion of the nasal/lacrimal covering the antorbital fenestra dorsally, and squamosal and quadratojugal forming a subtriangular projection that invades the lower temporal fenestra. The study of rauisuchians began in the middle of the 20th century, when the German palaeontolo- gist Friedrich von Huene discovered archosaur fossils in Brazil. Huene (1938b, 1942) described four new taxa currently considered as rauisuchians: Prestosuchus chiniquensis, Prestosuchus loricatus, Procerosuchus celer and Rauisuchus tiradentes. The generic name of the latter taxon, in honour of Guilherme Rau, a Brazilian-German dentist who collaborated with Huene, achieved family and class status in later works (e.g. Huene 1956; Krebs 1976; Bonaparte 1984; Parrish 1993; Brusatte et al. 2010; Nesbitt 2011). Since then, several fur- ther rauisuchian remains have been discovered in Brazil, including rather complete specimens such as that of cf. Prestosuchus chiniquensis (UFRGS-PV0156T; Barberena 1978). However, more recently, about 70 years after Huene's discov- eries, a new taxon was proposed (Franca et al. 2011a). Named Decuriasuchus quartacolonia, the taxon was based on a monotaxonomic assemblage

The rise and diversification of the dinosaurs in the Late Triassic, from 230 to 200 million years ago, is a classic example of an evolutionary radiation with supposed competitive replacement. A comparison of evolutionary rates and morphological disparity of basal dinosaurs and their chief “competitors,” the crurotarsan archosaurs, shows that dinosaurs exhibited lower disparity and an indistinguishable rate of character evolution. The radiation of Triassic archosaurs as a whole is characterized by declining evolutionary rates and increasing disparity, suggesting a decoupling of character evolution from body plan variety. The results strongly suggest that historical contingency, rather than prolonged competition or general “superiority,” was the primary factor in the rise of dinosaurs.

Phytosaurs are a clade of large, carnivorous pseudosuchian archosaurs from the Late Triassic with a near cosmopolitan distribution. Their superficial resemblance to longirostrine (long-snouted) crocodylians, such as gharials, has often been used in the past to infer ecological and behavioural convergence between the two groups. Although more than thirty species of phytosaur are currently recognised, little is known about the endocranial anatomy of this clade. Here, we describe the endocranial anatomy (including the brain, inner ear, neurovascular structures and sinus systems) of the two non-mystriosuchine phytosaursParasuchus angustifrons(=“Paleorhinus angustifrons”) andEbrachosuchus neukamifrom the Late Triassic of Germany based on digital reconstructions. Results show that the endocasts of both taxa are very similar to each other in their rostrocaudally elongate morphology, with long olfactory tracts, weakly demarcated cerebral regions and dorsoventrally short endosseous labyrinths. In addition, several sinuses, including large antorbital sinuses and prominent dural venous sinuses, were reconstructed. Comparisons with the endocranial anatomy of derived phytosaurs indicate that Phytosauria is united by the presence of elongate olfactory tracts and longitudinally arranged brain architecture—characters which are also shared with Crocodyliformes. However, a substantial morphological variability is observed in the cephalic and pontine flexure and the presence of a pineal organ across the different phytosaur species. These results suggest that the endocranial anatomy in Phytosauria generally follows a plesiomorphic pattern, with moderate variation within the clade likely resulting from divergent sensory and behavioural adaptations.

Aetosaurians are some of the most common fossils collected from the Upper Triassic Chinle Formation of Arizona, especially at the Petrified Forest National Park (PEFO). Aetosaurians collected from lower levels of the park includeDesmatosuchus spurensis,Paratypothorax,Adamanasuchus eisenhardtae,Calyptosuchus wellesi, andScutarx deltatylus. Four partial skeletons collected from the park between 2002 and 2009 represent the holotype and referred specimens ofScutarx deltatylus. These specimens include much of the carapace, as well as the vertebral column, and shoulder and pelvic girdles, and a new naming convention proposed for osteoderms descriptions better differentiates portions of the carapace and ventral armor. A partial skull from the holotype specimen represents the first aetosaur skull recovered and described from Arizona since the 1930s. The key morphological feature distinguishingScutarx deltatylusis the presence of a prominent, triangular boss located in the posteromedial corner of the dorsal surface of the dorsal paramedian osteoderms.Scutarx deltatyluscan be distinguished from closely related formsCalyptosuchus wellesiandAdamanasuchus eisenhardtaenot only morphologically, but also stratigraphically. Thus,Scutarx deltatylusis potentially an index taxon for the upper part of the Adamanian biozone.

The ‘rauisuchians’ are a group of Triassic pseudosuchian archosaurs that displayed a near global distribution. Their problematic taxonomic resolution comes from the fact that most taxa are represented only by a few and/or mostly incomplete specimens. In the last few decades, renewed interest in early archosaur evolution has helped to clarify some of these problems, but further studies on the taxonomic and paleobiological aspects are still needed. In the present work, we describe new material attributed to the ‘rauisuchian’ taxonPrestosuchus chiniquensis, of theDinodontosaurusAssemblage Zone, Middle Triassic (Ladinian) of the Santa Maria Supersequence of southern Brazil, based on a comparative osteologic analysis. Additionally, we present well supported evidence that these represent juvenile forms, due to differences in osteological features (i.e., a subnarial fenestra) that when compared to previously described specimens can be attributed to ontogeny and indicate variation within a single taxon of a problematic but important osteological structure in the study of ‘rauisuchians.’