Basipterygoid Processes Research Articles

Descriptive anatomy and three-dimensional reconstruction of the skull of the tetrapod Eoherpeton watsoni Panchen, 1975 from the Carboniferous of Scotland

ABSTRACT The early tetrapod Eoherpeton watsoni is known from the mid- to late Carboniferous (late Viséan to Namurian, approximately 346–313 Ma) of Scotland. The holotype is made up of a nearly complete but crushed skull with postcranial fragments. The skull anatomy of Eoherpeton was first described over 40 years ago; however, many details are obscured due to deformation of the specimen, including internal bone surfaces, the palatal bones and dentition, and suture morphology. Most phylogenetic analyses place Eoherpeton as an embolomere/reptilomorph on the lineage leading to amniotes, making it a key taxon for understanding anatomical changes during the fish-tetrapod transition. In this paper, we scanned the holotype using micro-computed tomography and digitally prepared the specimen. Based on these data, we present a revised description of the skull, including sutural morphology, that supplements and amends previous descriptions. New anatomical findings include the presence of a previously unknown tooth-bearing vomer, additional information on the shape of the basipterygoid processes and jaw joint, the ability to visualise the full extent of the pterygoid, and confirmation of the arrangement of the coronoid series. We also note the size of the pterygoid flange, which is larger than previously described for Eoherpeton. The pterygoid flange is widely considered to be characteristic of amniotes and serves as the origin of the medial pterygoideus muscle. The differentiation of the adductor muscles and appearance of medial pterygoideus are thought to have permitted a static pressure bite in amniotes, potentially resulting in greater bite forces and increased dietary range. Thus, the presence and extent of the pterygoid flange in Eoherpeton suggests this feature (and associated changes in feeding mechanism) may have evolved earlier than previously thought. Finally, the skull was digitally repaired and retrodeformed to create a new, hypothetical three-dimensional reconstruction of the skull of Eoherpeton.

A new amphibamiform (Temnospondyli: Branchiosauridae) from the lower Permian of the Czech Boskovice Basin

ABSTRACT The temnospondyl clade Amphibamiformes includes small newt-like forms that dwelled in freshwater lakes in the Pennsylvanian and Lower Permian of Europe and North America. Here we report a new genus and species, Piasimotriton kochovi, from the early Permian Boskovice Basin, Czech Republic. It has a unique combination of characters, among which the following ones rank as most important: (1) extremely elongated basipterygoid process forming a paired elongate facet for articulation with basal plate, (2) parasphenoid with broad and much abbreviated basal plate, about 2.5 times wider than long, (3) tooth crown with lateral crest, (4) premaxilla with 18 tiny teeth, and (5) a strong dermal ornament on the median skull elements. Piasimotriton kochovi has probably pedicellate teeth. Phylogenetic analysis finds Piasimotriton nests with the Melanerpeton clade with Melanerpeton, Leptorophus, and Schoenfelderpeton, with “Melanerpeton” gracile forming its sister taxon. The possession of various features that are also found in lissamphibians indicates a more widespread distribution of these within their putative stem-group. The stomach content of Piasimotriton kochovi consists of segmented thorax remains of small crustaceans. Piasimotriton probably competed with osteichthyans for arthropod prey and was only present in a short time interval of the lake’s existence.

New species from the early Eocene London Clay suggest an undetected early Eocene diversity of the Leptosomiformes, an avian clade that includes a living fossil from Madagascar

We report the first records of the leptosomiform taxon Plesiocathartes from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). Two species could be distinguished, one of which is described as Plesiocathartes insolitipes, sp. nov. (the other is classified as Plesiocathartes sp.). We furthermore describe two small leptosomiform-like birds from Walton-on-the-Naze, Waltonavis paraleptosomus, gen. et sp. nov. and W. danielsi, gen. et sp. nov., which are represented by partial skeletons of multiple individuals. In plesiomorphic characters of the coracoid and furcula, the new taxon Waltonavis is distinguished from Plesiocathartes and the extant Leptosomus; the skull of Waltonavis furthermore exhibits basipterygoid processes, which are absent in Leptosomus. Another new species, Lutavis platypelvis, gen. et sp. nov., is based on a partial skeleton from Walton-on-the-Naze and closely resembles Plesiocathartes in the overall shape of the tarsometatarsus. However, L. platypelvis is clearly distinguished from leptosomiform birds in the morphology of the hypotarsus, the more massive coracoid, and other skeletal features. Although we consider close affinities to Plesiocathartes and, hence, the Leptosomiformes to be possible, we could not identify derived characters that enable an unambiguous phylogenetic placement of L. platypelvis. In any case, the new species document an unexpected diversity of Plesiocathartes-like fossil in the London Clay and may open a new perspective for a reconstruction of the ancestral morphology of the avian clade Afroaves, which includes the Leptosomiformes and other arboreal landbirds.

A new ornithopod dinosaur, Transylvanosaurus platycephalus gen. et sp. nov. (Dinosauria: Ornithischia), from the Upper Cretaceous of the Haţeg Basin, Romania

ABSTRACT Rhabdodontid dinosaurs were a group of medium-sized iguanodontian ornithopods from the Late Cretaceous of Europe. The uppermost Cretaceous continental deposits from the Haţeg Basin of western Romania yielded a very rich assemblage of vertebrates including abundant rhabdodontid remains, which have been exclusively referred to the genus Zalmoxes thus far. Here we describe a new rhabdodontid dinosaur, Transylvanosaurus platycephalus gen. et sp. nov., from the uppermost Cretaceous of the Haţeg Basin. The holotype of the new taxon was discovered in early–late Maastrichtian strata near Pui in the eastern part of the basin and comprises the articulated basicranium and both frontals. Transylvanosaurus differs from all previously reported rhabdodontids in having particularly wide and crested frontals, elongated and straight paroccipital processes that make only a gentle lateral curve and project mostly posterolaterally, prominent and massive prootic processes that extend mainly anterolaterally and ventrally, wide and crest-like basal tubera that meet the long axis of the braincase at a very flat angle, widely splayed basipterygoid processes that extend mainly ventrolaterally and slightly anteriorly, as well as a well-developed notch on the lateral side of the basicranium that is continuous, straight, and inclined anteroventrally. Phylogenetic analyses employing two different datasets consistently recovered the new taxon within the Rhabdodontidae, at the base of the iguanodontian radiation. Based on the morphological comparisons presented herein, we propose a particularly close relationship between Transylvanosaurus and Rhabdodon from southern France, which in turn provides evidence for a more complex biogeographic history of the Rhabdodontidae than previously thought.

New digital braincase endocasts of two species of Desmatosuchus and neurocranial diversity within Aetosauria (Archosauria: Pseudosuchia).

In the present contribution we revise, figure, and redescribe several isolated braincases of the iconic aetosaur Desmatosuchus from the Placerias Quarry locality, Chinle Formation, Arizona, United States. The detailed study of the isolated braincases from the UCMP collection allowed us to assign them at the species-level and recognize two species of Desmatosuchus for the Placerias Quarry: D. spurensis and D. smalli. The former can be distinguished from the latter by the presence of a transverse sulcus on the parietals, deep median pharyngeal recess on the basisphenoid, almost no gap between the basal tubera and the basipterygoid processes, and the exoccipitals meeting at the midline. The presence of D. smalli at the Placerias Quarry has not been previously reported. Based on the braincases UCMP 27408, 27410, 27407, three new brain endocasts were developed through CT scan images, reconstructing the most complete endocranial casts known for an aetosaur, including the encephalon, cranial nerves, inner ear, and endocranial vasculature. The cranial endocasts also exhibited some differences between both species of Desmatosuchus, with D. spurensis having a distinguishable dural expansion and markedly asymmetric anterior and posterior semicircular canals of the labyrinth. Additionally, the combination of osteological features and the endocranial casts allowed us to identify and discuss the presence of an ossified orbitosphenoid on the anteriormost region of the braincase among aetosaurs. Furthermore, we were able to reinterpret some of the observations made by previous authors on the endocast of the holotype of Desmatosuchus spurensis (UMMP VP 7476) and provide some insight into their neurosensory capabilities.

The first braincase of the basal aetosaur Aetosauroides scagliai (Archosauria: Pseudosuchia) from the Upper Triassic of Brazil

ABSTRACT The phylogenetic relationships of Pseudosuchia, the crocodile-line of Archosauria, are still poorly resolved, in part, due to the lack of crucial braincase information for several key taxa. Recently, erpetosuchids and ornithosuchids have been recovered as close relatives to Aetosauria, sharing several braincase features. Here we provide the description of the first braincase of the basal aetosaur Aetosauroides based on specimens from the Upper Triassic Candelária Sequence of Brazil. Our study revealed the presence of an exoccipital lateral ridge and a medial ridge on the supraoccipital (both shared with all aetosaurs and erpetosuchids, but absent in ornithosuchids) and an anterolateral exit for the internal carotids (shared with all aetosaurs and ornithosuchids, but not with erpetosuchids). Aetosauroides lacks a medial contact between the exoccipitals (shared with the aetosaurs Desmatosuchus smalli and Tecovasuchus) and possesses a single hypoglossal foramen (contrasting with Stagonolepis robertsoni and Desmatosuchus spurensis). It also differs from the putative Argentinian Aetosauroides (PVSJ 326) by the presence of a ridge connecting the basal tubera medially (contrasting also with all stagonolepidoideans) and by a bulbous and ventrolaterally recurved basipterygoid process (contrasting with Paratypothorax). These features show that the braincase of aetosaurs is suitable for providing further phylogenetic information and may contribute to resolving controversies within Pseudosuchia relationships.

CT-scan description of Alexandronectes zealandiensis (Elasmosauridae, Aristonectinae), with comments on the elasmosaurid internal cranial features

ABSTRACT The holotype specimen of Alexandronectes zealandiensis is analyzed using digital reconstruction based on CT scans. Additional information regarding internal anatomy or obscured details are added. Additional features include: ectopterygoid rhombic in shape with posterior end pointed, a feature shared only with Aristonectes quiriquinensis; pterygoid shows a high dorsal crest located anteriorly and laterally to the level of the basipterygoid process; posterior margin of parabasisphenoid medially notched in ventral view and surrounding anteriorly and laterally a midline pit. Two canals for XII nerve are present in the right exoccipital-opisthothic and only one in the left one. Supraoccipital with two medially curved ridges on its posterior surface. Additionally, the presence of a stapes is described for the first time in an aristonectine elasmosaurid. The inner ear labyrinth is described and compared with that of other plesiosaurs, and the floccular recess (osseous correlate of the floccular lobe of the cerebellum) is described for first time among elasmosaurids. This feature is probably related to the presence of a long neck and with predatory behavior as the floccular lobe (housed in the floccular recess) stabilized the head via the cervical musculature, and stabilized the retinal image during rotational head movements.

The braincase, brain and palaeobiology of the basal sauropodomorph dinosaurThecodontosaurus antiquus

AbstractSauropodomorph dinosaurs underwent drastic changes in their anatomy and ecology throughout their evolution. The Late Triassic Thecodontosaurus antiquus occupies a basal position within Sauropodomorpha, being a key taxon for documenting how those morphofunctional transitions occurred. Here, we redescribe the braincase osteology and reconstruct the neuroanatomy of Thecodontosaurus, based on computed tomography data. The braincase of Thecodontosaurus shares the presence of medial basioccipital components of the basal tubera and a U-shaped basioccipital–parabasisphenoid suture with other basal sauropodomorphs and shows a distinct combination of characters: a straight outline of the braincase floor, an undivided metotic foramen, an unossified gap, large floccular fossae, basipterygoid processes perpendicular to the cultriform process in lateral view and a rhomboid foramen magnum. We reinterpret these braincase features in the light of new discoveries in dinosaur anatomy. Our endocranial reconstruction reveals important aspects of the palaeobiology of Thecodontosaurus, supporting a bipedal stance and cursorial habits, with adaptations to retain a steady head and gaze while moving. We also estimate its hearing frequency and range based on endosseous labyrinth morphology. Our study provides new information on the pattern of braincase and endocranial evolution in Sauropodomorpha.

Re-examination of the cranial osteology of the Arctic Alaskan hadrosaurine with implications for its taxonomic status.

Hadrosaurid fossils from the Liscomb Bonebed (Prince Creek Formation, North Slope, Alaska) were the first dinosaur bones discovered from the Arctic. While the Prince Creek Formation hadrosaurids were long identified as Edmontosaurus, a member of the sub-clade Hadrosaurinae, they were recently assigned to a newly-erected taxon, Ugrunaaluk kuukpikensis. However, taxonomic status of the new taxon is ambiguous largely due to the immature nature of the specimens upon which it was based. Here we reexamine cranial elements of the Prince Creek Formation hadrosaurine in order to solve its taxonomic uncertainties. The Prince Creek Formation hadrosaurine possesses a short dorsolateral process of the laterosphenoid, one of the diagnostic characters of Edmontosaurus. The Prince Creek Formation hadrosaurine also shows affinity to Edmontosaurus regalis in the presence of a horizontal shelf of the jugal. Our morphological comparisons with other North American Edmontosaurus specimens and our phylogenetic analyses demonstrate that the Prince Creek Formation hadrosaurine should be re-assigned to Edmontosaurus. Because the Prince Creek Formation Edmontosaurus shows differences with lower latitude Edmontosaurus in a dorsoventrally short maxilla, presence of a secondary ridge on the dentary teeth, and the absence of the transverse ridge between basipterygoid processes of the basisphenoid, we consider that the Prince Creek Formation Edmontosaurus should be regarded as Edmontosaurus sp. until further discoveries of mature hadrosaurines from the Prince Creek Formation Bonebed and/or equivalently juvenile Edmontosaurus specimens from the lower latitudes allow direct comparisons. The retention of the Prince Creek Formation hadrosaurine as Edmontosaurus re-establishes a significant latitudinal distribution for this taxon. Despite the large latitudinal distribution of the taxon, the morphological disparity of Edmontosaurus is small within Hadrosaurinae. The small morphological disparity may be related to the relatively low latitudinal temperature gradient during the latest Cretaceous compared to present day, a gradient which might not have imposed significant pressure for much morphological adaptations across a broad latitudinal range.

Cranium and Vertebral Column of Xingxiulong chengi (Dinosauria: Sauropodomorpha) from the Early Jurassic of China.

The Lower Jurassic Lufeng Formation in Yunnan Province of southwestern China provides one of the most abundant records of sauropodomorphs in the world. However, most of them have not been fully described. Xingxiulong chengi is among the most complete non-sauropodan sauropodomorphs ever discovered from Lufeng Formation and is represented by three partial skeletons. Here, we provide a detailed osteological description of its axial skeleton, including both the cranial and postcranial elements, and compare its anatomy with that of other known non-sauropodan sauropodomorphs. In general, the cranium of Xingxiulong is more similar to those of more basal sauropodomorphs than to sauropodiforms, as evidenced by features such as an only slightly concave dorsal margin of the postorbital, a caudally placed rostral margin of the infratemporal fenestra not extending below the orbit, and long and slender basipterygoid processes divergent from each other at an angle of approximately 80 degrees. However, its postcranial axial skeleton possesses some unique or relatively derived features among basal sauropodomorphs, such as four sacral vertebrae and caudal dorsal vertebrae with laterally expanded neural spine tables. This provides future workers with a reassessment of non-sauropodan sauropodomorphs through the lens of Xingxiulong chengi, which will serve to increase our knowledge on the anatomy, phylogeny, and furthermore, evolution of sauropodomorph dinosaurs. Anat Rec, 303:772-789, 2020. © 2019 American Association for Anatomy.

New information on the braincase and endocranial morphology of the Late Triassic neotheropod Zupaysaurus rougieri using computed tomography data

ABSTRACTZupaysaurus rougieri is an early neotheropod from the middle Norian Los Colorados Formation of northwestern Argentina represented by an almost complete skull and several postcranial bones. Most of its braincase morphology has remained obscured by other skull bones and sediment. Additional mechanical preparation and X-ray computed tomography on the single known specimen of Zupaysaurus has allowed a detailed description of the braincase, the cranial endocast, and the inner ear of this Triassic dinosaur. Basal theropod braincases are poorly sampled and there is little information on this region, and even poorer knowledge on the brain and inner ear anatomy of Triassic forms. The virtual reconstruction of the braincase of Zupaysaurus shows anteroventrally oriented, finger-like basipterygoid processes, an elongate and horizontally projected cultriform process, and well-developed preotic pendant, basisphenoid recess, and subsellar recess. The endocranial morphology is partially reconstructed, showing an anteroposteriorly short but dorsoventrally tall cranial endocast, with well-marked demarcations between the forebrain, midbrain, and hindbrain. The inner ear preserves the three semicircular canals, but not the lagena. The posterior semicircular canal is proportionally large when compared with that of other theropods. The new information presented here on Zupaysaurus rougieri contributes to the knowledge of the neuroanatomy of basal theropods and sheds light on the evolutionary patterns of the braincase morphology in nonavian Theropoda.

A dvinosaurian temnospondyl from the Carboniferous-Permian boundary of Germany sheds light on dvinosaurian phylogeny and distribution

ABSTRACTA complete skull and well-preserved postcranium of a dvinosaurian temnospondyl from the Carboniferous-Permian boundary of Germany is referred to a new genus and species, Trypanognathus remigiusbergensis. The skull closely resembles that of the early Permian dvinosaurian genus Trimerorhachis in outline and suture topology, but the occiput and the palate differ substantially. Derived states are the penetration of vomerine tusks through the splenial and symphyseal tusks through the premaxilla. Trypanognathus shares with dvinosauroids the lack of a squamosal embayment, an elongated basipterygoid process, a foreshortened palatine ramus exclusively reaching the ectopterygoid, the absence of pterygoid denticles, and enlarged palatal tusks. The body is elongate with well-ossified, but small limbs, the presacral count is ca. 28, and the pleurocentra are large and reached ventrally almost as far as the intercentrum. The new taxon nests within Dvinosauria above the trimerorhachid clade and Erpetosaurus, at the base of the broad-skulled dvinosauroids. Trypanognathus occurs in a tetrapod fauna that closely resembles early Permian assemblages of western North America, with which it shares sphenacodontid and edaphosaurid synapsids, as well as eryopid temnospondyls.

Mesenchymal Cells Invasion During Initial Stages of Chondrogenesis

Mesenchymal cell invasion contributes to cartilage growth. The current study investigates mesenchymal cells during the initial stages of cartilage development. Mesenchymal cell invasion was detected during stages of mesenchymal condensation, the cartilage primordia upon differentiation of the pre-chondrocytes as well as fully differentiated chondrocytes. Mesenchymal cells located at multiple sites in cartilage primordia of wide surface area with the progression of age. The mesenchymal invasion was identified in cartilage primordia of the prospective body of the basioccipital bone, basipterygoid processes of the basioccipital bone, the optic process of the quadrate bone and cartilage primordia of the dentary, frontal bone, and the sternum. In conclusion, the invasive phenomenon of mesenchymal cells is not only limited to cartilage growth but also associated with early cartilage development.

Braincase anatomy of the early sauropodomorph Saturnalia tupiniquim (Late Triassic, Brazil)

ABSTRACTThe braincase anatomy of the sauropodomorph dinosaur Saturnalia tupiniquim from the Upper Triassic (Carnian) Santa Maria Formation of Brazil is described for the first time using computed tomography (CT). The braincase is characterized by a semilunar depression on the lateral surface of the basisphenoid, an occipital condyle whose ventral margin lies dorsal to the ventral margin of the cultriform process of the parabasisphenoid, a poorly developed preotic pendant, and anteriorly oriented basipterygoid processes. The comparative description improves our understanding of the early dinosaur braincase, which is poorly known relative to that of later representatives of the group. In addition, we discuss braincase features recently employed to investigate the phylogenetic relationships of dinosauromorphs, especially the pneumatic recesses of the braincase. Our study indicates that the semilunar depression and basioccipital recess are more widespread among dinosaurs and their closest archosauriform relatives than previously suggested. These structures are present in the three main dinosaurian lineages and also in non-dinosaurian dinosauromorphs, indicating that they might be plesiomorphic for Dinosauria. Likewise, the subsellar and basisphenoid recesses were observed in all examined dinosauromorph taxa, with variation observed in the relative development of these structures but not in their presence/absence. Our character reassessments and discussion of morphological variation as parts of transformation series strengthen the basis for integrating braincase features in future studies of dinosauromorph phylogeny.

Braincase anatomy of Pterodaustro guinazui, pterodactyloid pterosaur from the Lower Cretaceous of Argentina

ABSTRACTThe braincase anatomy of pterosaurs is poorly known because this region of the skull is rarely preserved, particularly in basal pterodactyloid pterosaurs (Archaeopterodactyloidea). We present new information on the braincase morphology of the Early Cretaceous Argentinean ctenochasmatid Pterodaustro guinazui. Morphological information collected from several specimens permits the description of many features of this area of the skull for the first time. The braincase of Pterodaustro is characterized by a skull roof with subtriangular, elongated frontals and rounded, posteroventrally oriented parietals; low nuchal crest; ossified ethmoidal elements; ossified interorbital septum; short and fan-shaped paroccipital processes with undulating lateral and medial surfaces; occipital condyle formed mainly by the exoccipitals; fork-shaped basioccipital; long, anteroventrally directed basisphenoid body with keeled ventral surface and short basipterygoid processes; well-developed rostral tympanic recess; rod-like columella; and separate foramina for cranial nerves XII and IX–XI within a common subdivided recess. We were able to identify foramina for cranial nerves II, V, VI, and VII; vascular foramina, such as the caudal middle cerebral vein, the dorsal head vein, and the internal carotid artery; and the columellar recess. This research reveals many features of the braincase of Pterodaustro—some of which are considered potential autapomorphies—for the first time. It also provides new insights into the neurocranial anatomy of pterosaurs, and in turn, contributes to the understanding of the evolution of the braincase in Pterosauria.Citation for this article: Codorniú, L., A. Paulina-Carabajal, and F. A. Gianechini. 2015. Braincase anatomy of Pterodaustro guinazui, pterodactyloid pterosaur from the Lower Cretaceous of Argentina. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1031340.

Different embryonic origin of the basipterygoid process in two species of Lacerta (Squamata: Lacertidae)

AbstractThe basipterygoid (or basitrabecular) process in lizards arises in ontogeny as an outgrowth from the posterior portion of the trabecle. The separate origin of the basipterygoid process has been currently recorded only in one lizard, the chamaeleonid Bradypodion pumilum. Herein, we describe the ontogeny of the basipterygoid process in two species of Lacerta. Although the basipterygoid process in L. viridis develops as in most other lizards, the L. agilis basipterygoid process arises as an independent nodule of cartilage and it fuses with the trabecle only later in ontogeny.

A new sauropod dinosaur from the Late Jurassic of China and the diversity, distribution, and relationships of mamenchisaurids

ABSTRACT—Qijianglong guokr, gen. et sp. nov., represents a mamenchisaurid eusauropod from the Late Jurassic of southern China. The holotype consists of an incomplete skull, partly articulated axial skeleton, and fragmentary appendicular skeleton. A well-preserved braincase and skull roof provide rare insights into the poorly known neurocranial anatomy of mamenchisaurids and reveal a unique combination of characters such as an accessory tuber at the base of planar basipterygoid process and parietal excluding frontal from the anterior margin of the supratemporal fenestra. The cervical vertebrae have a distinct finger-like process extending from the postzygapophyseal process beside a zygapophyseal contact. Qijianglong is the first mamenchisaurid from the Late Jurassic of China that is definitively distinct from Mamenchisaurus, indicating greater morphological and taxonomic diversity of the poorly represented Late Jurassic mamenchisaurids. The occurrence of Qijianglong is consistent with a scenario in which mamenchisaurids formed an endemic sauropod fauna in the Late Jurassic of Asia. Phylogenetically, Qijianglong represents a relatively plesiomorphic mamenchisaurid lineage. The mamenchisaurids form an ancient clade of basal eusauropod dinosaurs that likely appeared in the Early Jurassic. A cladistic analysis highlights the interrelationships of mamenchisaurids and suggests guidelines for mamenchisaurid taxonomic revision. It may be desirable to restrict generic names to the type species in order to avoid confusion.http://zoobank.org/urn:lsid:zoobank.org:pub:F93276CF-71FE-472E-9114-68294547C2A9SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Braincase Anatomy of the Basal TheropodSinosaurusfrom the Early Jurassic of China

The neuroanatomy of the mid-sized theropod Sinosaurus triassicus from the Lower Jurassic Lufeng Formation, Lufeng Basin in Yunnan Province, China was studied using X-ray computed tomography. The braincase is characterized by a large supraoccipital knob that is capped by a posterior projection of the parietal and two external foramina for the caudal middle cerebral vein, which is completely enclosed by the supraoccipital. The basicranium has well defined, short basipterygoid processes that project ventral to the basal tubera. The basisphenoid is expanded, projects posteroventrally, and is pierced by four pneumatic recesses. The endocranial morphology resembles that observed in other basal theropods—in particular some allosauroids—and has a strongly marked pontine flexure and a large dorsal expansion. The inner ear morphology is also similar to that observed in other basal theropods, with slender semicircular canals. The anterior semicircular canal is 20% larger than the posterior semicircular canal, and the angle formed between them is less than 90° when seen in dorsal view.

Anatomy and phylogenetic position of Venaticosuchus rusconii Bonaparte, 1970 (Archosauria, Pseudosuchia), from the Ischigualasto Formation (Late Triassic), La Rioja, Argentina

ABSTRACT—Ornithosuchidae is a group of Late Triassic pseudosuchian archosaurs of controversial phylogenetic affinities. This clade currently comprises three taxa: Venaticosuchus rusconii and Riojasuchus tenuisceps, both from Argentina, and Ornithosuchus longidens, from Scotland. V. rusconii was erected on the basis of an incomplete skull with articulated lower jaws and some elements of the postcranium that are currently lost. Venaticosuchus rusconii is redescribed here and included for the first time in a phylogenetic analysis to test its affinities with ornithosuchids. The bizarre morphology of V. rusconii has a unique combination of traits that distinguishes it from the other ornithosuchids, such as basipterygoid processes directed ventrally, dentary with the dorsal margin of the anterior end dorsally expanded, articular without a foramen on its medial side, and the absence of a surangular foramen, corroborating the validity of this taxon. V. rusconii is recovered as an ornithosuchid more closely related to R. tenuisceps than to O. longidens, based on the presence of a nearly pointed anterior margin of the antorbital fenestra, and a vertical bony strut of the jugal that separates the antorbital fenestra from the infratemporal fenestra.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Redescription of the Skull of Coloradisaurus brevis (Dinosauria, Sauropodomorpha) from the Late Triassic Los Colorados Formation of the Ischigualasto-Villa Union Basin, northwestern Argentina

ABSTRACTThe cranial anatomy of the basal sauropodomorph Coloradisaurus brevis from the upper levels of the Norian Los Colorados Formation is here redescribed and comparisons made based on the holotype skull and mandible. Coloradisaurus brevis is diagnosed by most of the features proposed in the original description and an additional set of autapomorphies, such as presence of circular upper temporal fenestrae, laminae on the ventrolateral margins of a ventral fossa of the basisphenoid and on the ventral region of the parasphenoid, and tab-like medial process at the posteromedial end of the mandible. Coloradisaurus is placed within Massospondylidae, as in recent analyses. This position is supported primarily by postcranial characters, but some cranial features identified in this study provide additional evidence supporting this position (e.g., jugal contribution to the antorbital fenestra, frontal proportionately longer than nasals). However, the cranial anatomy of Coloradisaurus also bears several characters that are shared with plateosaurids (e.g., low mandibular articulation, broad maxillary wall on the anterior margin of antorbital fossa, broad prefrontals, projection of infratemporal fenestra behind the orbit, stepped braincase, robust septum between basipterygoid processes). Thus, Coloradisaurus is interpreted as a massospondylid that has convergently acquired characters that are otherwise only known in plateosaurids, highlighting the conflicting pattern of character distribution among basal sauropodomorphs.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP