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Non‐crocodyliform crocodylomorphs, formerly referred to the informal group 'Sphenosuchia', are the earliest known crocodylomorph precursors of extant crocodylians. They are therefore crucial for our understanding of early crocodylian evolution and the origin of typical crocodylian characteristics, such as the formation of a secondary palate, complex cranial pneumaticity, and a reinforced braincase. Terrestrisuchus gracilis, known from the Upper Triassic fissure fill deposits of Pant‐y‐Ffynnon in southern Wales, is represented by almost 200 specimens, comprising articulated, partially associated, and isolated remains. In this contribution we provide a taxonomic revision of Terrestrisuchus gracilis and redescribe its cranial anatomy in detail, based in part on novel micro‐computed tomography data. The posterior skull region is extensively pneumatized as indicated, among other features, by large pre‐ and postcarotid recesses on the parabasisphenoid, and a large pneumatic cavity in the articular of the mandible. In contrast, the quadrate forms only a small, unfused contact with the prootic, suggesting that complex pneumatization of the postorbital region pre‐dated the co‐ossification of the quadrate and braincase in Crocodylomorpha. Terrestrisuchus gracilis preserves an ossified basihyal, which represents the first occurrence of this bone in non‐avemetatarsalian archosaurs. Finally, we show that Terrestrisuchus gracilis was probably cathemeral (i.e. active in a range of light levels), based on a phylogenetic flexible discriminant analysis of the relative dimensions of the sclerotic ring and orbit. [ABSTRACT FROM AUTHOR]

Crocodylomorphs constitute a clade of archosaurs that have thrived since the Mesozoic until today and have survived numerous major biological crises. Contrary to historic belief, their semiaquatic extant representatives (crocodylians) are not living fossils, and, during their evolutionary history, crocodylomorphs have evolved to live in a variety of environments. This review aims to summarize the non-semiaquatic adaptations (i.e., either terrestrial or fully aquatic) of different groups from different periods, highlighting how exactly those different lifestyles are inferred for those animals, with regard to their geographic and temporal distribution and phylogenetic relationships. The ancestral condition for Crocodylomorpha seems to have been a terrestrial lifestyle, linked with several morphological adaptations such as an altirostral skull, long limbs allowing a fully erect posture and a specialized dentition for diets based on land. However, some members of this clade, such as thalattosuchians and dyrosaurids display adaptations for an opposite, aquatic lifestyle, interestingly inferred from the same type of morphological observations. Finally, new techniques for inferring the paleobiology of those extinct animals have been put forward in the last decade, appearing as a complementary approach to traditional morphological descriptions and comparisons. Such is the case of paleoneuroanatomical (CT scan data), histological, and geochemical studies., (© 2024 American Association for Anatomy.)

The endosseous labyrinths are associated with several functions, including hearing and spatial orientation. Throughout their evolutionary history, crocodylomorphs have thrived in diverse environments, and the morphology of their endosseous labyrinths has been suggested as a proxy for inferring their lifestyle. However, the relationships between the shape of their endosseous labyrinths and ontogenetic and phylogenetic factors are difficult to interpret and have rarely been investigated in depth previously, particularly in terms of dataset size. Here, we present the most complete dataset to date on the endosseous labyrinths of extant crocodylians, including 111 specimens covering 22 species of different ontogenetic status (from hatchlings to adults). Using 3D geometric morphometrics, we show that allometry constitutes a major contributor of the shape variation of the crocodylian endosseous labyrinths and that the development of this structure is likely linked to the braincase conformation, in all extant genera. We also find a moderate phylogenetic signal, but only without considering the size effect, so it could not be translated into relevant discrete morphological characters. Based on these results, we discuss several remaining problems that prevent the inclusion of fossil forms with highly divergent lifestyles to study how ecological differences shaped the endosseous labyrinths of crocodylomorphs., (© 2024 Anatomical Society.)

Dinosaur fossils from the Lower Jurassic are very scarce in the Iberian Peninsula, which lacks a dinosaur track record. This study reports a new ichnosite from this age, at the Alvaiázere Municipality (Lusitanian Basin, Portugal) with several well-defined dinosaur and other archosaurs tracks. Seventeen tracks were identified at the top sedimentary surface of a fine-grained dolostone bed belonging to the Coimbra Formation (Sinemurian, Lower Jurassic). Therefore, the tracksite could have an age of ~196 to 194 Ma, based in the stratigraphic position of the tracksite in the Coimbra Formation succession. The ichnological comparison allows us to ascribe these tracks to Moyenisauropus and Batrachopus ichnogenera. The dinosaur tracks are assigned to the new ichnospecies Moyenisauropus lusitanicus isp. nov. The trackmaker could be a basal thyreophoran dinosaur related to Emausaurus or Scelidosaurus, and the presence of a manus-pes pair track set verifies that these tracks were made by a quadrupedal gait. The crocodylomorph trackmaker could be a teleosaurid. The analysed bioturbated fine-grained dolostone bed was deposited in very shallow subtidal to intertidal, carbonate lagoonal (?) environment. The evidence provided here indicates the presence of crocodylomorphs and thyreophoran dinosaurs in a tropical coastal wetland carbonate system developed during the Early Jurassic in the Lusitanian Basin (Atlantic western margin of Iberia). [ABSTRACT FROM AUTHOR]

The skull of living crocodylians is highly solidified and the jaw closing muscles are enlarged, allowing for prey capture by prolonged crushing between the jaws. Living species are all semi-aquatic, with sprawling limbs and a broad body that moves mainly from side-to-side; however, fossils indicate that they evolved from terrestrial forms. The most cursorial of these fossils are small, gracile forms often grouped together as the Sphenosuchia, with fully erect, slender limbs; their relationships, however, are poorly understood. A new crocodylomorph from deposits in northwestern China of the poorly known Middle Jurassic epoch possesses a skull with several adaptations typical of living crocodylians. Postcranially it is similar to sphenosuchians but with even greater adaptations for cursoriality in the forelimb. Here we show, through phylogenetic analysis, that it is the closest relative of the large group Crocodyliformes, including living crocodylians. Thus, important features of the modern crocodylian skull evolved during a phase when the postcranial skeleton was evolving towards greater cursoriality, rather than towards their current semi-aquatic habitus. [ABSTRACT FROM AUTHOR]

A new crocodylomorph taxon, Pattisaura gracilis, is described based on an associated partial skeleton from the Upper Triassic Dockum Group of northwest Texas. Pattisaura gracilis represents a non-crocodyliform crocodylomorph and can be characterized mainly by a set of character states from the skull, vertebral column, pelvis, and osteoderms. The discovery of P. gracilis expands the distribution range of non-crocodyliform crocodylomorphs in North America. P. gracilis may be closely related to Redondavenator quayensis from northeast New Mexico. With addition of P. gracilis, our phylogenetic analysis does not support the monophyly of Sphenosuchia and the presence of an Argentinian clade, a purely North American clade, or a Middle to Late Jurassic Hallopodidae among non-crocodyliform crocodylomorphs but confirms the closest relationship of Almadasuchus to Crocodyliformes and partly supports the existence of Solidocrania with Hallopus victor as its most basally branching member.http://zoobank.org/urn:lsid:zoobank.org:pub:572159ED-1546-4434-8AAA-052F56287539 [ABSTRACT FROM AUTHOR]

Hsisosuchus, with three known species, was the most common genus of crocodyliforms in the Sichuan Basin during the Jurassic. However, the overall shape of the ventral trunk shield of osteoderms has not been clarified due to the lack of complete specimens. A new specimen of Hsisosuchus recently recovered from the Upper Jurassic of Yunnan has the nearly complete ventral trunk shield preserved. This specimen provides an example for the first time for us to understand the shape and the way of the arrangement of the osteoderms in the ventral trunk shield in the genus. Compared with the articulated part of the ventral trunk shield preserved in two of the three species of the genus, the osteoderms of the ventral trunk shield of the new specimen are different in both shape and way of arrangement, indicating that the pattern of the ventral trunk shield is not constant within Hsisosuchus. With no skull and much of the postcranial skeleton poorly preserved as well as no corresponding element that can be used to compare with all the three species, the new specimen was considered as an indeterminate species of Hsisosuchus, awaiting more materials to clarify the problem. [ABSTRACT FROM AUTHOR]

The use of more than one nomenclatural code is becoming increasingly common in some biological sub-disciplines. To minimize nomenclatural instability, we have decided to establish a higher level systematization for Thalattosuchia under both the International Code of Phylogenetic Nomenclature ('PhyloCode') and the International Code of Zoological Nomenclature ('Zoological Code'). We undertook a series of phylogenetic analyses with an expanded dataset to examine the origins of Thalattosuchia within Crocodylomorpha, and determined the clade's diagnostic characters. Based on these analyses, we provide updated diagnoses for Thalattosuchia and its subclades under both the PhyloCode and Zoological Code. We also introduce two new nomina that are regulated under the PhyloCode (Neothalattosuchia and Euthalattosuchia), and the nomen Dakosaurina, which is registered under both nomenclatural codes. Moreover, we introduce PhyloCode-compliant phylogenetic definitions for Thalattosuchia and its subclades. As we cannot reliably discriminate between the positional hypotheses for Thalattosuchia within Crocodylomorpha, the clades' origins are as much of a mystery today as they were over a century ago. However, we hope that using the same diagnostic characters to define the same clades, with the same nomina, under both nomenclatural codes will be an example to others to follow. [ABSTRACT FROM AUTHOR]

Orthosuchus stormbergi was a small-bodied crocodyliform, representative of a diverse assemblage of Early Jurassic, early branching crocodylomorph taxa from the upper Elliot Formation of South Africa. The life history of these early branching taxa remains poorly understood, with only sparse investigations into their osteohistology, yet species like Orthosuchus have potential to inform about the macroevolution of growth strategies on the stem leading to crown crocodilians. In order to elucidate the growth patterns of Orthosuchus, we used propagation phase contrast X-ray synchrotron micro-computed tomography to virtually image the osteohistology of the postcrania of two specimens, including multiple elements from the type (SAM-PK-K409), and the femur of a referred specimen (BP/1/4242). In total, we scanned nine mid-diaphyseal sections of the humerus, radius, ulna, radiale, femur, tibia, fibula, and a rib. We then compared our results to osteohistological sections of crocodylomorph taxa from the published literature. Our results show that the most predominant bone tissue type in Orthosuchus is lamellar, with a few patches of woven and parallel-fibred bone. The type specimen contains four to five lines of arrested growth and the hindlimb elements present outer circumferential lamellae, whereas the referred specimen contains six to seven. Both specimens grew at similar rates, reaching adult skeletal body size at year four or five. The sectioned bones, most notably the radius and ulna, are comparatively thick walled and compact. Our virtual osteohistological sections are one of the first for an early branching crocodyliform, and the broad sample of skeletal elements makes Orthosuchus a key anchor point for understanding the plesiomorphic life history traits of the clade., (© 2024 The Author(s). Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.)

Land-to-sea evolutionary transitions are great transformations where terrestrial amniote clades returned to aquatic environments. These secondarily aquatic amniote clades include charismatic marine mammal and marine reptile groups, as well as countless semi-aquatic forms that modified their terrestrial locomotor anatomy to varying degrees to be suited for swimming via axial and/or appendicular propulsion. The terrestrial ancestors of secondarily aquatic groups would have started off swimming strikingly differently from one another given their evolutionary histories, as inferred by the way modern terrestrial amniotes swim. With such stark locomotor functional differences between reptiles and mammals, we ask if this impacted these transitions. Axial propulsion appears favored by aquatic descendants of terrestrially sprawling quadrupedal reptiles, with exceptions. Appendicular propulsion is more prevalent across the aquatic descendants of ancestrally parasagittal-postured mammals, particularly early transitioning forms. Ancestral terrestrial anatomical differences that precede secondarily aquatic invasions between mammals and reptiles, as well as the distribution of axial and appendicular swimming in secondarily aquatic clades, may indicate that ancestral terrestrial locomotor anatomy played a role, potentially in both constraint and facilitation, in certain aquatic locomotion styles. This perspective of the land-to-sea transition can lead to new avenues of functional, biomechanical, and developmental study of secondarily aquatic transitions. [ABSTRACT FROM AUTHOR]

Crocodylomorpha is the stem-lineage of modern crocodylians and the only pseudosuchian (i.e. crocodylian-line archosaurs) clade that survived the Triassic–Jurassic mass extinction event. Its earliest members, the non-crocodyliform crocodylomorphs, also known as 'sphenosuchians', were terrestrial and mostly small-bodied (<2 m long), although some large-bodied forms are known. Saltoposuchus connectens is one of the first described crocodylomorph species but it remains poorly studied, in part due to its contentious taxonomy. Here, all referred Saltoposuchus specimens are described in detail for the first time and its taxonomy is revised, with additional taxonomic implications for the British crocodylomorph Terrestrisuchus gracilis and the coelophysoid theropod Procompsognathus triassicus. Saltoposuchus connectens is clearly distinguished from Terrestrisuchus gracilis based on both cranial and postcranial features. The phylogenetic analysis finds that Saltoposuchus connectens , Terrestrisuchus gracilis , and Litargosuchus leptorhynchus form a clade of gracile, long-legged crocodylomorphs, identified as Saltoposuchidae Crush 1984. A histological section of a femur reveals highly vascularized fibrolamellar tissue in the second-largest specimen of Saltoposuchus connectens (SMNS 12596), indicating sustained high growth rates. A similar pattern was previously observed in Terrestrisuchus sp. contrasting with slower growth rates in the crocodylomorph Hesperosuchus agilis. These findings suggest that saltoposuchids had a high resting metabolic rate and active lifestyle. [ABSTRACT FROM AUTHOR]

Characterized by an elongated snout, proterochampsids are carnivorous non-archosaur archosauriforms. The clade is endemic to South America and its fossil record extends from the early Carnian to the late Carnian/early Norian. Nesting close to Archosauria, it is a key clade for understanding the origin and evolution of archosaurian traits. Unfortunately, hind limb elements are usually poorly preserved for the group. Therefore, the hind limb anatomy of proterochampsids still lacks detailed descriptions. In the present study, we partially fill this gap with the description of a new proterochampsid represented by a complete and well-preserved hind limb. Stenoscelida aurantiacus gen. et sp. nov. was excavated from the late Carnian/early Norian (Late Triassic) beds of southern Brazil. A phylogenetic investigation recovers the new taxon as a non-rhadinosuchine proterochampsid. The species bears an unusual set of traits for the group, which provides clues on the evolutionary origins of some muscle attachment structures. For instance, the femur of Stenoscelida aurantiacus gen. et sp. nov. possesses an anterior trochanter and an anterolateral scar. So far, these features have not been reported in other non-archosaurian archosauriforms. Therefore, the new specimen indicates that some typical archosaurian features evolved earlier than previously thought. The taxon also carries additional uncommon features for proterochampsids, such as an iliofibularis tubercle on the anterior margin of the fibula and a vestigial phalanx in digit V. In sum, Stenoscelida aurantiacus has one of the best-preserved hind limbs within Proterochampsidae and sheds light on the polarization of important traits regarding the evolutionary context of Archosauria. [ABSTRACT FROM AUTHOR]

Significant evolutionary shifts in locomotor behaviour often involve comparatively subtle anatomical transitions. For dinosaurian and avian evolution, medial overhang of the proximal femur has been central to discussions. However, there is an apparent conflict with regard to the evolutionary origin of the dinosaurian femoral head, with neontological and palaeontological data suggesting seemingly incongruent hypotheses. To reconcile this, we reconstructed the evolutionary history of morphogenesis of the proximal end of the femur from early archosaurs to crown birds. Embryological comparison of living archosaurs (crocodylians and birds) suggests the acquisition of the greater overhang of the femoral head in dinosaurs results from additional growth of the proximal end in the medial-ward direction. On the other hand, the fossil record suggests that this overhang was acquired by torsion of the proximal end, which projected in a more rostral direction ancestrally. We reconcile this apparent conflict by inferring that the medial overhang of the dinosaur femoral head was initially acquired by torsion, which was then superseded by mediad growth. Details of anatomical shifts in fossil forms support this hypothesis, and their biomechanical implications are congruent with the general consensus regarding broader morpho-functional evolution on the avian stem. [ABSTRACT FROM AUTHOR]

Although our knowledge on crocodylomorph palaeoneurology has experienced considerable growth in recent years, the neuroanatomy of many crocodylomorph taxa has yet to be studied. This is true for Australian taxa, where thus far only two crocodylian crocodylomorphs have had aspects of their neuroanatomy explored. Here, the neuroanatomy of the Australian mekosuchine crocodylian Trilophosuchus rackhami is described for the first time, which significantly increases our understanding on the palaeoneurology of Australian crocodylians. The palaeoneurological description is based on the taxon's holotype specimen (QMF16856), which was subjected to a μCT scan. Because of the exceptional preservation of QMF16856, most neuroanatomical elements could be digitally reconstructed and described in detail. Therefore, the palaeoneurological assessment presented here is hitherto the most in‐depth study of this kind for an extinct Australian crocodylomorph. Trilophosuchus rackhami has a brain endocast with a distinctive morphology that is characterized by an acute dural peak over the hindbrain region. While the overall morphology of the brain endocast is unique to T. rackhami, it does share certain similarities with the notosuchian crocodyliforms Araripesuchus wegeneri and Sebecus icaeorhinus. The endosseous labyrinth displays a morphology that is typical for crocodylians, although a stand‐out feature is the unusually tall common crus. Indeed, the common crus of T. rackhami has one of the greatest height ratios among crocodylomorphs with currently known endosseous labyrinths. The paratympanic pneumatic system of T. rackhami is greatly developed and most similar to those of the extant crocodylians Osteolaemus tetraspis and Paleosuchus palpebrosus. The observations on the neuroanatomy of T. rackhami are also discussed in the context of Crocodylomorpha. The comparative palaeoneurology reinforces previous evaluations that the neuroanatomy of crocodylomorphs is complex and diverse among species, and T. rackhami has a peculiar neuromorphology, particularly among eusuchian crocodyliforms. [ABSTRACT FROM AUTHOR]

Among archosaurs, thalattosuchian crocodylomorphs experienced the most extensive adaptations to the marine realm. Despite significant attention, the phylogenetic position of the group remains uncertain. Thalattosuchians are either the sister-group to Crocodyliformes, basal mesoeucrocodylians, or nest among longirostrine neosuchians. The earliest definite thalattosuchians are Toarcian, and already possess many synapomorphies of the group. All phylogenetic hypotheses imply a ghost lineage extending at least to the Sinemurian, and a lack of older or more plesiomorphic forms may contribute to the uncertain phylogenetic placement of the group. Here we describe a new species, Turnersuchus hingleyae, gen. et sp. nov., from the early Pliensbachian Belemnite Marl Member of the Charmouth Mudstone Formation (Dorset, U.K.). The specimen includes partially articulated cranial, mandibular, axial, and appendicular elements. It can be attributed to Thalattosuchia based on the following features: distinct fossa on the posterolateral corner of the squamosal; broad ventrolateral process of the otoccipital covering the dorsal surface of the quadrate; large supratemporal fenestrae lacking a flattened skull table; broadly exposed prootic; orbital process of quadrate lacking bony attachment with the braincase. This specimen represents the earliest thalattosuchian currently known from diagnostic material. Phylogenetic analyses of two published datasets recover Turnersuchus as the earliest diverging thalattosuchian, and sister to Teleosauroidea + Metriorhynchoidea. Bayesian tip-dating analyses suggest a Rhaetian or Sinemurian divergence of Thalattosuchia from other crocodylomorphs, depending on topology, with confidence intervals spanning from the Norian to the Pliensbachian. The new specimen extends the fossil record of Thalattosuchia, but the time-scaling analyses demonstrate that a significant ghost lineage remains. [ABSTRACT FROM AUTHOR]

Lufeng County in Southwest China is one of the most famous lagerstätten in which Early Jurassic dinosaurs can be found. The reason for the burial of large body size dinosaur fossils at this site is still an enigma, although it could be attributed to either suitable habitats or good preservation conditions. Both of these factors are indirectly regulated by climatic conditions. Therefore, a quantitative reconstruction of the terrestrial palaeoclimate of the Lufeng area during the Early Jurassic could help shed new light on this issue. In this study, we analysed the stable isotope compositions of oxygen and carbon (δ13C and δ18O) in apatite phosphate and carbonate from the tooth enamel and compact bones of basal sauropodiform and Sinosaurus fossils. The oxygen isotopes provided a mean annual temperature (MAT) of ≥21 ± 3°C, and the carbon isotopes allowed us to estimate a mean annual precipitation (MAP) of 965 ± 460 mm/yr during the Early Jurassic in Lufeng County. These conditions correspond to a relatively arid tropical savanna climate hospitable to vertebrate life. We also compared the spatial relationship between the global distribution of dinosaur fossils and climatically sensitive deposits during the Jurassic. The dinosaur fossil distribution reveals a strong preference for arid regions. We therefore suggest that 'savanna‐like' tropical conditions helped accommodate a large number of dinosaurs and preserve their carcasses in the Lufeng area during the Early Jurassic. [ABSTRACT FROM AUTHOR]

Present‐day crocodylians exhibit a remarkably akinetic skull with a highly modified braincase. We present a comprehensive description of the neurocranial osteology of extant crocodylians, with notes on the development of individual skeletal elements and a discussion of the terminology used for this project. The quadrate is rigidly fixed by multiple contacts with most braincase elements. The parabasisphenoid is sutured to the pterygoids (palate) and the quadrate (suspensorium); as a result, the basipterygoid joint is completely immobilized. The prootic is reduced and externally concealed by the quadrate. It has a verticalized buttress that participates in the canal for the temporal vasculature. The ventrolateral processes of the otoccipitals completely cover the posteroventral region of the braincase, enclose the occipital nerves and blood vessels in narrow bony canals and also provide additional sutural contacts between the braincase elements and further consolidate the posterior portion of the crocodylian skull. The otic capsule of crocodylians has a characteristic cochlear prominence that corresponds to the lateral route of the perilymphatic sac. Complex internal structures of the otoccipital (extracapsular buttress) additionally arrange the neurovascular structures of the periotic space of the cranium. Most of the braincase elements of crocodylians are excavated by the paratympanic pneumatic sinuses. The braincase in various extant crocodylians has an overall similar structure with some consistent variation between taxa. Several newly observed features of the braincase are present in Gavialis gangeticus and extant members of Crocodylidae to the exclusion of alligatorids: the reduced exposure of the prootic buttress on the floor of the temporal canal, the sagittal nuchal crest of the supraoccipital projecting posteriorly beyond the postoccipital processes and the reduced paratympanic pneumaticity. The most distinctive features of the crocodylian braincase (fixed quadrate and basipterygoid joint, consolidated occiput) evolved relatively rapidly at the base of Crocodylomorpha and accompanied the initial diversification of this clade during the Late Triassic and Early Jurassic. We hypothesize that profound rearrangements in the individual development of the braincases of basal crocodylomorphs underlie these rapid evolutionary modifications. These rearrangements are likely reflected in the embryonic development of extant crocodylians and include the involvement of neomorphic dermal anlagen in different portions of the developing chondrocranium, the extensive ossification of the palatoquadrate cartilage as a single expanded quadrate and the anteromedial inclination of the quadrate. [ABSTRACT FROM AUTHOR]

Crocodylomorpha, the pseudosuchian lineage including all taxa more closely related to crown Crocodylia than to phytosaurs, ornithosuchids, aetosaurs, poposauroids, and rauisuchids (Nesbitt, [22]; Irmis et al., [12]), diversified during the Late Triassic, along with other archosaurs (e.g., Ezcurra, [8]), to occupy ecological (e.g., fully terrestrial) and morphological (e.g., body sizes) spaces not represented by their living clades (Sereno and Larsson, [27]; Turner and Sertich, [31]; Melstrom and Irmis, [21]). A, biogeographic map of the earliest and early-diverging crocodylomorph specimens from the Late Triassic (late Carnian-early Norian) (Late Triassic continental reconstruction and taxon distribution from PBDB); B, right ilium of Otis Chalk crocodylomorph (TMM 31100-1494) in lateral view; C, right ilium of Batrachotomus kupferzellensis (SMNS 80269) in lateral view; D, partial right ilium of Hesperosuchus agilis (AMNH FARB 6758) in lateral view; E, right ilium of an undescribed crocodylomorph (NCSM 21722) in lateral view; F, right ilium referred to Trialestes romeri (PVL 3889) in lateral view; G, right ilium of Dibothrosuchus elaphros (IVPP V 7907) in lateral view; H, left ilium of Dromicosuchus grallator (NCSM 13733) in lateral view (reversed); I, left ilium of CM 73372 in lateral view (reversed); J, left ilium of Orthosuchus stormbergi (SAM-K-409) in lateral view (reversed). DISCUSSION We identify this ilium as belonging to an early-diverging crocodylomorph by the presence of a supra-acetabular buttress dividing the anterior and posterior processes of the ilium, in combination with the presence of an open acetabulum and a longer pre-acetabular process (broken but inferred). [Extracted from the article]

First appearing in the latest Cretaceous, Crocodylia is a clade of semi-aquatic, predatory reptiles, defined by the last common ancestor of extant alligators, caimans, crocodiles, and gharials. Despite large strides in resolving crocodylian interrelationships over the last three decades, several outstanding problems persist in crocodylian systematics. Most notably, there has been persistent discordance between morphological and molecular datasets surrounding the affinities of the extant gharials, Gavialis gangeticus and Tomistoma schlegelii. Whereas molecular data consistently support a sister taxon relationship, in which they are more closely related to crocodylids than to alligatorids, morphological data indicate that Gavialis is the sister taxon to all other extant crocodylians. Here we present a new morphological dataset for Crocodylia based on a critical reappraisal of published crocodylian character data matrices and extensive firsthand observations of a global sample of crocodylians. This comprises the most taxonomically comprehensive crocodylian dataset to date (144 OTUs scored for 330 characters) and includes a new, illustrated character list with modifications to the construction and scoring of characters, and 46 novel characters. Under a maximum parsimony framework, our analyses robustly recover Gavialis as more closely related to Tomistoma than to other extant crocodylians for the first time based on morphology alone. This result is recovered regardless of the weighting strategy and treatment of quantitative characters. However, analyses using continuous characters and extended implied weighting (with high k-values) produced the most resolved, well-supported, and stratigraphically congruent topologies overall. Resolution of the gharial problem reveals that: (1) several gavialoids lack plesiomorphic features that formerly drew them towards the stem of Crocodylia; and (2) more widespread similarities occur between species traditionally divided into tomistomines and gavialoids, with these interpreted here as homology rather than homoplasy. There remains significant temporal incongruence regarding the inferred divergence timing of the extant gharials, indicating that several putative gavialids (‘thoracosaurs’) are incorrectly placed and require future re-appraisal. New alligatoroid interrelationships include: (1) support for a North American origin of Caimaninae in the latest Cretaceous; (2) the recovery of the early Paleogene South American taxon Eocaiman as a ‘basal’ alligatoroid; and (3) the paraphyly of the Cenozoic European taxon Diplocynodon. Among crocodyloids, notable results include modifications to the taxonomic content of Mekosuchinae, including biogeographic affinities of this clade with latest Cretaceous–early Paleogene Asian crocodyloids. In light of our new results, we provide a comprehensive review of the evolutionary and biogeographic history of Crocodylia, which included multiple instances of transoceanic and continental dispersal. [ABSTRACT FROM AUTHOR]

A review of the type material of the crocodylomorph ichnotaxon Crocodylopodus meijidei Fuentes Vidarte and Meijide Calvo, 2001 from the Berriasian of Spain is carried out. The review allows a better characterization of this type ichnotaxon and provides interesting new data on the candidate trackmakers and especially on their locomotion. Three different size classes possibly related to different ontogenetic states or sexual dimorphism of the same small- to medium-sized crocodylomorph trackmaker are distinguished. Morphological differences within the sample such as digital impression lengths might be a consequence of differences in allometric growth, assuming similarities with extant crocodylians. Other differences are a consequence of variation in the morphological quality and mode of preservation across the sample. Some trackway features (intermediate-gauge trackways with high pace angulation, absence of tail, belly or drag marks) indicate the trackmakers, presumed neosuchian crocodylomorphs, were walking in a 'high-walk' mode with a semi-erect posture at a moderate speed. The trackmaker may have walked with more erect limb posture and with the center of mass located more anteriorly than occurs in extant species, albeit not as erect as quadrupedal animals such as mammals or other extinct archosaurs including trackmakers of other crocodylomorph ichnotaxa (e.g., Batrachopus). [ABSTRACT FROM AUTHOR]

The Placerias/Downs' Quarry complex in eastern Arizona, USA, is the most diverse Upper Triassic vertebrate locality known. We report a new short-faced archosauriform, Syntomiprosopus sucherorum gen. et sp. nov., represented by four incomplete mandibles, that expands that diversity with a morphology unique among Late Triassic archosauriforms. The most distinctive feature of Syntomiprosopus gen. nov. is its anteroposteriorly short, robust mandible with 3–4 anterior, a larger caniniform, and 1–3 "postcanine" alveoli. The size and shape of the alveoli and the preserved tips of replacement teeth preclude assignment to any taxon known only from teeth. Additional autapomorphies of S. sucherorum gen. et sp. nov. include a large fossa associated with the mandibular fenestra, an interdigitating suture of the surangular with the dentary, fine texture ornamenting the medial surface of the splenial, and a surangular ridge that completes a 90° arc. The external surfaces of the mandibles bear shallow, densely packed, irregular, fine pits and narrow, arcuate grooves. This combination of character states allows an archosauriform assignment; however, an associated and similarly sized braincase indicates that Syntomiprosopus n. gen. may represent previously unsampled disparity in early-diverging crocodylomorphs. The Placerias Quarry is Adamanian (Norian, maximum depositional age ~219 Ma), and this specimen appears to be an early example of shortening of the skull, which occurs later in diverse archosaur lineages, including the Late Cretaceous crocodyliform Simosuchus. This is another case where Triassic archosauriforms occupied morphospace converged upon by other archosaurs later in the Mesozoic and further demonstrates that even well-sampled localities can yield new taxa. [ABSTRACT FROM AUTHOR]

We describe the basal mesoeucrocodylian Burkesuchus mallingrandensis nov. gen. et sp., from the Upper Jurassic (Tithonian) Toqui Formation of southern Chile. The new taxon constitutes one of the few records of non-pelagic Jurassic crocodyliforms for the entire South American continent. Burkesuchus was found on the same levels that yielded titanosauriform and diplodocoid sauropods and the herbivore theropod Chilesaurus diegosuarezi, thus expanding the taxonomic composition of currently poorly known Jurassic reptilian faunas from Patagonia. Burkesuchus was a small-sized crocodyliform (estimated length 70 cm), with a cranium that is dorsoventrally depressed and transversely wide posteriorly and distinguished by a posteroventrally flexed wing-like squamosal. A well-defined longitudinal groove runs along the lateral edge of the postorbital and squamosal, indicative of a anteroposteriorly extensive upper earlid. Phylogenetic analysis supports Burkesuchus as a basal member of Mesoeucrocodylia. This new discovery expands the meagre record of non-pelagic representatives of this clade for the Jurassic Period, and together with Batrachomimus, from Upper Jurassic beds of Brazil, supports the idea that South America represented a cradle for the evolution of derived crocodyliforms during the Late Jurassic. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The early-branching crocodylomorph species Notochampsa istedana is known from a single South African specimen collected more than 100 years ago. This species is potentially important for understanding early crocodylomorph evolution, but it is of uncertain taxonomic status and its stratigraphic position is poorly constrained. Here we reinvestigate the anatomy, taxonomy, systematics and biostratigraphy of the holotype specimen, SAM-PK-4013. SAM-PK-4013 has a unique suite of features that distinguish it from the closely related taxa Orthosuchus and Protosuchus. These features include the length and shape of the dentary symphysis, the number and shape of dentary teeth, and the number of dorsal ribs with expanded intercostal ridges. Notochampsa is therefore a valid taxon, and our phylogenetic analysis recovers it as sister to Orthosuchus, in a monophyletic Notochampsidae. Notochampsa and Orthosuchus share a ventrally expanded squamosal flange and expanded intercostal ridges on the dorsal ribs. Notochampsidae is in turn sister to Protosuchidae, forming the monophyletic group Notochampsoidea. Fieldwork and stratigraphic revisions show definitively that SAM-PK-4013 is from the Clarens Formation, approximately ∼65 m above the Elliot contact, ageing Notochampsa to the Pliensbachian stage, a period of vertebrate body fossil scarcity. Thus, Notochampsa istedana is the youngest known occurrence of a crocodylomorph (and vertebrate body fossil) from the Karoo Basin of South Africa. [ABSTRACT FROM AUTHOR]

Present knowledge of Late Triassic tetrapod evolution, including the rise of dinosaurs, relies heavily on the fossil-rich continental deposits of South America, their precise depositional histories and correlations. We report on an extended succession of the Ischigualasto Formation exposed in the Hoyada del Cerro Las Lajas (La Rioja, Argentina), where more than 100 tetrapod fossils were newly collected, augmented by historical finds such as the ornithosuchid Venaticosuchus rusconii and the putative ornithischian Pisanosaurus mertii. Detailed lithostratigraphy combined with high-precision U–Pb geochronology from three intercalated tuffs are used to construct a robust Bayesian age model for the formation, constraining its deposition between 230.2 ± 1.9 Ma and 221.4 ± 1.2 Ma, and its fossil-bearing interval to 229.20 + 0.11/− 0.15–226.85 + 1.45/− 2.01 Ma. The latter is divided into a lower Hyperodapedon and an upper Teyumbaita biozones, based on the ranges of the eponymous rhynchosaurs, allowing biostratigraphic correlations to elsewhere in the Ischigualasto-Villa Unión Basin, as well as to the Paraná Basin in Brazil. The temporally calibrated Ischigualasto biostratigraphy suggests the persistence of rhynchosaur-dominated faunas into the earliest Norian. Our ca. 229 Ma age assignment to Pi. mertii partially fills the ghost lineage between younger ornithischian records and the oldest known saurischians at ca. 233 Ma. [ABSTRACT FROM AUTHOR]

Almadasuchus figarii is a basal crocodylomorph recovered from the Upper Jurassic levels of the Cañadón Calcáreo Formation (Oxfordian–Tithonian) of Chubut, Argentina. This taxon is represented by cranial remains, which consist of partial snout and palatal remains; an excellently preserved posterior region of the skull; and isolated postcranial remains. The skull of the only specimen of the monotypic Almadasuchus was restudied using high‐resolution computed micro tomography. Almadasuchus has an apomorphic condition in its skull shared with the closest relatives of crocodyliforms (i.e. hallopodids) where the quadrates are sutured to the laterosphenoids and the otoccipital contacts the quadrate posterolaterally, reorganizing the exit of several cranial nerves (e.g. vagus foramen) and the entry of blood vessels (e.g. internal carotids) on the occipital surface of the skull. The endocast is tubular, as previously reported in thalattosuchians, but has a marked posterior step, and a strongly projected floccular recess as in other basal crocodylomorphs. Internally, the skull of Almadasuchus is heavily pneumatized, where different air cavities invade the bones of the suspensorium and braincase, both on its dorsal or ventral parts. Almadasuchus has a large basioccipital recess, which is formed by cavities that excavate the basioccipital and the posterior surface of the basisphenoid, and unlike other crocodylomorphs is connected with the basisphenoid pneumatizations. Ventral to the otic capsule, a pneumatic cavity surrounded by the otoccipital and basisphenoid is identified as the rhomboidal recess. The quadrate of Almadasuchus is highly pneumatized, being completely hollow, and the dorsal pneumatizations of the braincase are formed by the mastoid and facial antra, and a laterosphenoid cavity (trigeminal diverticulum). To better understand the origins of pneumatic features in living crocodylomorphs we studied cranial pneumaticity in the basal members of Crocodylomorpha and found that: (a) prootic pneumaticity may be a synapomorphy for the whole clade; (b) basisphenoid pneumaticity (pre‐, postcarotid and rostral recesses) is a derived feature among basal crocodylomorphs; (c) quadrate pneumatization is acquired later in the history of the group; and (d) the rhomboidal sinus is a shared derived trait of hallopodids and crocodyliforms. The marine thallatosuchians exhibit a reduction of the pneumaticity of the braincase and this reduction is evaluated considering the two phylogenetic positions proposed for the clade. [ABSTRACT FROM AUTHOR]