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In this contribution we introduce a new Late Triassic archosaur, Incertovenator longicollum gen. et sp. nov., with an unusual combination of character states that are present in certain early avemetatarsalian and pseudosuchian archosaur clades. The holotype consists of a partial postcranial skeleton, preserving most of the axial skeleton and displaying a marked anteroposterior elongation in the cervical vertebrae. We include I. longicollum gen. et sp. nov. into one of the most comprehensive early archosaur phylogenetic data sets available, and recover it as either an early diverging avemetatarsalian, closely associated with the clade Aphanosauria and Ornithodira, or as an early diverging loricatan closely related to Mandasuchus tanyauchen in the most parsimonious trees. We further evaluate which alternative phylogenetic positions can I. longicollum gen. et sp. nov. take in the suboptimal trees, and determined which character states support those alternative positions in comparison with those of the unconstrained analysis. The analyses recover the new taxon in three main general phylogenetic placements within Archosauria, as well as one position outside this clade, highlighting widespread morphological evolutionary convergence towards neck elongation in several clades of Triassic archosauriforms.

La Facultad de Ciencias Exactas y Naturales (FCEN) de la Universidad de Buenos Aires (UBA) se alojó inicialmente en la Manzana de las Luces de la Ciudad Autónoma de Buenos Aires, para luego reubicarse en los Pabellones I y II del complejo Ciudad Universitaria. Los estudios paleoherpetológicos en UBA se iniciaron con el Dr. Osvaldo Reig quien estuvo tres períodos en la institución: primero a fines de los 50, luego desde inicios a mediados de los 60 y finalmente a principios de los 80. Durante su primera época continuó con sus estudios de materiales fósiles de arcosaurios triásicos y anuros mesozoicos y cenozoicos. En su segundo período en la FCEN estuvo más enfocado en estudios microevolutivos basados en materiales actuales. La Dra. Ana María Báez se especializó en el estudio de los anfibios anuros, interactuando internacionalmente con destacados investigadores y formando profesionales en dicha temática y se desempeñó como profesora de la FCEN hasta el 2006. Tras su cese de actividades como profesora, este rol fue ocupado por su discípula la Dra. Claudia A. Marsicano, quien se dedicó al análisis de los anfibios temnospóndilos, aunque actualmente amplió sus estudios a las faunas de tetrápodos del Permo-Triásico de Gondwana. La Dra. C. A. Marsicano fundó el Laboratorio de Estudios Paleobiológicos en Ambientes Continentales y formó tesistas de grado y doctorado en paleoherpetología. En la actualidad los investigadores en paleoherpetología más jóvenes en la FCEN son Juan M. Leardi, que estudia crocodilomorfos, y Raúl O. Gómez, especializado en anuros y otros vertebrados.

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 of subtympanic 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 aperture, absence/presence of lateral pharyngeal foramen). The functional significances of these traits are still unclear. Extending the sampling to other Thalattosuchia will help to test the timing of acquisition and distribution of these morphological modifications among the whole lineage. Also comparison with extant marine tetrapods (including physiological information) will be crucial to understand if some (and/or which) of the morphological peculiarities of thalattosuchian braincases are products of directional natural selection resulting in a fully adaptation to a nektonic life style.

Notosuchia is a diverse clade of Crocodyliformes that achieved a remarkable diversity during the Cretaceous. This group is particu- larly abundant in continental deposits of Gondwana throughout the Cretaceous, especially in South America. Notosuchia was first recognized as a distinct group by the early work of Gasparini in the 1970’s and in the last decades numerous discoveries and studies have increased the geographical, temporal and taxonomical scope of this clade. Here we analyze the patterns of diversity of Notosuchia during the Creta- ceous, considering their taxic and phylogenetic diversity, as well as implementing sampling corrections aiming to account for the uneven fossil record of different stages of the Cretaceous. We identify two subsequent pulses of diversification in the late Early Cretaceous and the middle Late Cretaceous, followed by two separate extinction events that occurred during the latest Cretaceous (Campanian/Maastricht- ian). We discuss the contribution of the South American, African, and Malagasy fossil records to the diversity curves, which indicates the African fossil record dominates the first pulse of diversification and the South American fossil record exclusively compose the second pulse of diver- sification. Finally, we analyze the patterns of diversity shown by the different subclades of Notosuchia throughout the Cretaceous, which reveal markedly different evolutionary dynamics of four major groups of notosuchian crocodyliforms.

Background Macelognathus vagans Marsh, 1884 from the Late Jurassic Morrison Fm. of Wyoming was originally described as a dinosaur by Marsh and in 1971 Ostrom suggested crocodilian affinities. In 2005, Göhlich and collaborators identified new material of this species from Colorado as a basal crocodylomorph. However, a partial skull found in association with mandibular and postcranial remains was not described. Methods Due to the small size and delicate structures within the braincase, micro CT studies were performed on this specimen. The new anatomical information was incorporated in a phylogenetic dataset, expanding both character and taxon sampling. Results This new material reinforces the non-crocodyliform crocodylomorph affinities of Macelognathusas it bears a large otic aperture, unfused frontals and lacks ornamentation on the dorsal cranial bones. The internal structures also support these affinities as this specimen bears traits (i.e., heavily pneumatized and expanded basisphenoid; the presence of additional pneumatic features on the braincase; and the otoccipital-quadrate contact) not present in most basal crocodylomorphs. Furthermore, the presence of a wide supraoccipital and a cranioquadrate passage are traits shared with Almadasuchus from the early Late Jurassic of Argentina. Macelognathus was recovered as one of the closest relatives of crocodyliforms, forming a clade (Hallopodidae) with two other Late Jurassic taxa (Almadasuchus and Hallopus). Discussion The clade formed by Almadasuchus + Hallopus + Macelognathus, the Hallopodidae, is characterized by a higher degree of suturing of the braincase, posteriorly closed otic aperture (paralleled in mesoeucrocodylians) and cursorial adaptations. Also, the phylogenetic position of this lineage of derived crocodylomorphs as the sister group of Crocodyliformes implies a large amount of unsampled record (ghost lineage), at least 50 million years.