Metotic Foramen Research Articles

Neuroanatomy of a diplodocid sauropod dinosaur from the Lower Cretaceous of Patagonia, Argentina

Diplodocid neuroanatomy is known from four Late Jurassic forms from North America and Africa. Recently, a partial braincase of a diplodocid sauropod (MMCh-Pv- 232), tentatively assigned to Leinkupal laticauda Gallina et al., 2014, preserving a complete basicranium, right laterosphenoid, prootic, parietal, otooccipital and right half of the supraoccipital, was recovered from Bajada Colorada Formation (Berriasian–Valanginian). Reconstructions of the braincase, cranial endocast and inner ear were performed via X-ray Computed Tomography and segmentation. The endocast is represented by the pituitary body (inclined at 69° from the base of the medulla oblongata –similar to Diplodocus), the caudal-most region of the cerebral hemispheres and the internal carotid arteries, the midbrain, showing Cranial Nerve (CN) III and CN IV exiting the braincase through a single opening; and the hindbrain, with CN V exiting the braincase through a single opening as in other sauropods, the ventral CN VI entering the pituitary fossa caudally, CN IX-XI exiting the braincase through a single opening (metotic foramen), and CN XII exiting the braincase through two canals. The inner ear preserved a caudoventrally inclined conical lagena, a sub-rectangular fenestra ovalis, the ampulla of the Anterior Semicircular Canal, the crus commune, and a Lateral Semicircular Canal. The length of the lagena suggests a lower auditive capacity in comparison to other sauropods. The morphological similarities of the braincase and endocast to other diplodocids reinforce the tentative assignation of MMCh-Pv-232 to Leinkupal, and expands the knowledge in neuroanatomy of South American sauropods.

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-description of the cranio-mandibular anatomy of Notosuchus terrestris (Crocodyliformes, Mesoeucrocodylia) from the Upper Cretaceous of Patagonia

Notosuchus terrestris was the first notosuchian described worldwide and the most abundant crocodyliform species in Gondwana during the Late Cretaceous. Here, the lectotype and more than 60 complete and fragmentary specimens were studied allowing the most detailed description of the cranio-mandibular anatomy of this taxon, including poorly known regions as the braincase. Thirty-fourth characters were described and confirmed by the first time for Notosuchus. Possible autapomorphies include: frontal with olfactory tract groove convex posteriorly and with well marked furrows for laterosphenoid, small premaxillary knob fits a maxillary notch in the palate adjacent to the toothrow, small bilobate trigeminal fossa with grooves for the branches the CN Vso, CN V2 and CN V3, parietal and laterosphenoid highly pneumatic, post-temporal fenestra obliterated, presence of vestigial quadratojugal spine, ascending process of quadratojugal with posterior groove, vomer lateromedially broad, incisive foramen in heart-shaped delimited by premaxillae and maxillae, and choana with narrow pterygoid septum. We propose a crista pseudo-tuberalis separating the occiput from the braincase wall, as present in some notosuchians. Contrary to previous work, the carotid foramen and the metotic foramen open within a fossa lateral to the occipital condyle, a common feature in advanced notosuchians.

Braincase redescription of Efraasia minor Huene, 1908 (Dinosauria: Sauropodomorpha) from the Late Triassic of Germany, with comments on the evolution of the sauropodomorph braincase

The braincase anatomy of the sauropodomorph dinosaur Efraasia minor (Late Triassic, Norian, Lowenstein Formation of Germany) is redescribed in detail, adding new information based on CT scan data. We discuss the evolution of sauropodomorph braincases from a phylogenetic perspective, focusing on non-neosauropodan representatives. For this, we revised braincase characters used in data matrices focused on this assemblage of taxa. This led to the recognition of problems with some of the phylogenetic characters, especially regarding the basal tubera complex, which did not accurately reflect the morphological variation observed among taxa within the group. We also discuss previous misidentifications of the soft tissues associated with the presence of a divided metotic foramen among sauropodomorphs. This has implications for the recognition of the structures associated with braincase foramina in non-sauropodan sauropodomorphs, and we propose that the path for the jugular vein was either through the posterior foramen resulting from this division or through the foramen magnum. Finally, our study demonstrates a series of differences regarding braincase anatomy between non-sauropodan and sauropod taxa. However, it remains unclear if these differences might be due to a drastic morphological change or if they simply reflect the small number of braincase materials of non-neosauropodan sauropods, which might indicate a more stepwise evolution.

New information on the braincase and inner ear ofEuparkeria capensisBroom: implications for diapsid and archosaur evolution

Since its discovery, Euparkeria capensis has been a key taxon for understanding the early evolution of archosaurs. The braincase of Euparkeria was described based on a single specimen, but much uncertainty remained. For the first time, all available braincase material of Euparkeria is re-examined using micro-computed tomography scanning. Contrary to previous work, the parabasisphenoid does not form the posterior border of the fenestra ovalis in lateral view, but it does bear a dorsal projection that forms the anteroventral half of the fenestra. No bone pneumatization was found, but the lateral depression of the parabasisphenoid may have been pneumatic. We propose that the lateral depression likely corresponds to the anterior tympanic recess present in crown archosaurs. The presence of a laterosphenoid is confirmed for Euparkeria. It largely conforms to the crocodilian condition, but shows some features which make it more similar to the avemetatarsalian laterosphenoid. The cochlea of Euparkeria is elongated, forming a deep cochlear recess. In comparison with other basal archosauromorphs, the metotic foramen is much enlarged and regionalized into vagus and recessus scalae tympani areas, indicating an increase in its pressure-relief mechanism. The anterior semicircular canal is extended and corresponds to an enlarged floccular fossa. These aspects of the braincase morphology may be related to the development of a more upright posture and active lifestyle. They also indicate further adaptations of the hearing system of Euparkeria to terrestriality.

Braincase redescription of Dysalotosaurus lettowvorbecki (Dinosauria, Ornithopoda) based on computed tomography

ABSTRACT Computed tomography (CT) has become a major tool to elucidate the anatomy of fossil taxa, including the braincase and inner ear. However, sample size is still limited and studies have concentrated mainly on saurischian dinosaurs. Here we report on the braincase anatomy of the Upper Jurassic ornithopod Dysalotosaurus using high-resolution X-ray micro-CT (μCT). The main trunk of the vena capitis dorsalis was found between the parietal and supraoccipital, leading to a nomenclatural revision of cephalic veins and reidentification of their bony correlates. Contrary to the condition in hadrosaurid ornithischians, the posterior semicircular canal is the shortest canal in Dysalotosaurus, whereas the lateral is the longest, lying dorsal to the vestibule, as in basal archosaurs. The anteroventral inclination of the lateral semicircular canal suggests that Dysalotosaurus must have oriented its head dorsally while alert. Because the cochlea is relatively short, Dysalotosaurus had reduced ability to discriminate between high- and low-frequency sounds, as in sauropods, basal ceratopsians, and other basal archosaurs. The metotic foramen, however, was fully subdivided into a fenestra pseudorotunda and a vagus foramen, a derived character for archosaurs that is usually associated with a more refined sense of hearing. Lack of a refined capacity for discrimination of sound frequencies due to a short cochlea together with the equal-sized and thick semicircular canals represent plesiomorphic characters for Dinosauria. The middle and inner ears of Dysalotosaurus bear a mosaic of primitive and derived features, pointing to a more complex evolutionary history of these structures.

Cranial endocast of the carcharodontosaurid theropod Giganotosaurus carolinii Coria Salgado, 1995

A complete endocast of Giganotosaurus carolinii CORIA & SALGADO, 1995 was made in latex after removing mechanically the sediment filling of the cerebral cavity of the braincase, thereby allowing the description of the endocranial anatomy of the specimen. The endocast was compared with the other few known natural or artificial theropod endocasts, including the two species of the African allosauroid species Carcharodontosaurus saharicus and C. idiguensis. As in Carcharodontosaurus, the olfactory bulbs in Giganotosaurus are aligned with the forebrain, the midbrain is posteroventrally inclined and the hindbrain is parallel but ventral to the forebrain, showing similarly angled cephalic and pontine flexures. The cranial nerves and blood vessels have a similar disposition as in Carcharodontosaurus saharicus. However, in Giganotosaurus there is only one branch for cranial nerve XII, and cranial nerve XI has a separate internal opening from the vagus foramen (metotic foramen). In C. saharicus, there is a separate opening as well, but it is anterior in position and was probably utilized by cranial nerve IX. The length of the endocast of Giganotosaurus, including the olfactory bulbs, is approximately 19 % longer than the endocast in Carcharodontosaurus saharicus.

The braincase of a specimen of Proterochampsa Reig (Archosauriformes: Proterochampsidae) from the Late Triassic of Argentina

The proterochampsids are a Triassic group of superficially crocodile-like forms belonging to the Archosauriformes. In the present contribution, we present new information regarding the braincase of the proterochampsid Proterochampsa Reig 1959, from the Ischigualasto Formation (Carnian) of Argentina, and discuss its phylogenetic considerations. Some unique neurocranial features of Proterochampsa are described, including: the prominence and thickness of the V-shaped ridge that surrounds the basisphenoidal fossa; the medially concave lateral arms of the same ridge; and the semilunar depression on the parabasisphenoid ventrolaterally exposed. Other features are only shared with likely unrelated archosauriforms, including: the great lateral development of the basipterygoid processes and caudal development of its distal end; an eight-shaped metotic foramen; laterally directed basipterygoid processes; and rostral boundary of the basisphenoidal recess V-shaped. Proterochampsa differs in many other aspects from the archosauriform Chanaresuchus, including: a proportionally shorter basioccipital basal tubera; cultriform process ovoid in cross-section; longitudinal sulcus dorsal to the basipterygoid process; deep basisphenoidal recess; and the absence of a prominent intertuberal plate. In many braincase features, Proterochampsa is more similar to archosaurs than to Euparkeria, erythrosuchids and Proterosuchus. They include a reduced semilunar depression. A ventral border of the basioccipital forming a wide convexity and a dorsoventrally thin paroccipital process likely represents a feature shared with Chanaresuchus, but not with Doswellia and other basal archosauriforms.

An incomplete Upper Cretaceous titanosaur (Sauropoda) braincase: new insights on the dinosaurian inner ear and endocranium

An incomplete braincase from the Upper Cretaceous Portezuelo Formation of northwestern Patagonia (Neuquén Province, Argentina) is described. The specimen preserves the lateral walls formed by the laterosphenoid, probably part of the orbitosphenoid, prootic, the exoccipital-opisthotic complex and fragments of the frontal, parietal and basisphenoid. Both inner ears are preserved allowing the production of latex endocasts. The external and internal morphology of the laterosphenoid and the prootic, the absence of a floccular recess, and the morphology and position of the cranial nerves V–VII, the oval window and the metotic foramen indicate that the new braincase belongs to a sauropod dinosaur, probably a titanosaur. The morphology of the inner ear is also reminiscent of that of Sauropoda, which is characterized by the presence of a simple, short and conical lagena, a posterior semicircular canal that is larger than the lateral semicircular canal, an anterior semicircular canal that is larger than the other two, and an angle between the vertical semicircular canals (anterior and posterior) of approximately 90°.

Braincase evolution in suchian archosaurs (Reptilia: Diapsida): evidence from the rauisuchian Batrachotomus kupferzellensis

The osteology of an almost complete braincase of the rauisuchian archosaur Batrachotomus kupferzellensis Gower from the Middle Triassic of Germany is described. There is a possibly discrete epiotic ossification, the metotic fissure is undivided by bone (i.e. there is a metotic foramen), the medial wall of the otic capsule is mostly ossified, the cerebral branch of the internal carotid artery entered the lateral surface of the parabasisphenoid, the ventral ramus of the opisthotic is more prominent laterally than a strong subvertical ridge on the exoccipital and basioccipital that lies posterior to the external foramen for the hypoglossal nerve, and the perilymphatic foramen faces away from the otic capsule in a posterior direction. Braincase morphology in the rauisuchians Saurosuchus galilei, Postosuchus kirkpatricki, and Tikisuchus romeri is reviewed. A matrix of 27 braincase characters for 12 archosaurian taxa is analysed. The most parsimonious hypothesis is consistent with the currently orthodox view of archosaurian phylogeny, except in that aetosaurians are more closely related to crocodylomorphs than is any rauisuchian. This phylogeny is used in a brief interpretation of the evolution of derived braincase features present in extant crocodilians. © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 49–76.

The braincase structure of Leptopleuron lacertinum Owen (Parareptilia: Procolophonidae)

ABSTRACT The braincase of Leptopleuron lacertinum Owen, a leptopleuronine procolophonid from the Late Triassic (lower Norian) of Scotland, is described for the first time. Morphologically, the braincase of Leptopleuron is similar to that of the Early Triassic genus Procolophon, and to a number of other procolophonids currently included in the subfamily Procolophoninae Romer, 1956. Several features of the braincase of Leptopleuron are derived within the Procolophonidae, but others are unique to this genus. Apomorphies include a strongly tripartite occipital condyle, a metotic foramen that is not walled by bone anteriorly, an ‘ascending process’ of the basisphenoid that forms a robust flat-ended expansion, and bears ventrally a thin laterally directed lamella, a ‘processus infrastapedialis columellae’ of the stapes that is aligned with the long axis of the footplate, loss of the foramen for nerve IX on the ventral ramus of the opisthotic, and a greatly expanded, vertical basisphenoid rostrum. These features may be autapomorphic for Leptopleuron, or represent synapomorphies of the Leptopleuroninae Ivakhnenko, 1979.

The braincase of the early archosaurian reptile Erythrosuchus africanus

The fimt detailed description of the braincase of the Triassic early archosaurian reptile Elythrosuchus is presented. Features plesiomorphic for archosaurs that are described include an ossified laterosphenoid, a ‘semilunar depression’, posteroventrally positioned internal carotid foramina, a basisphenoid ‘intertuberal plate’, an un‐ or incompletely ossified medial wall of the otic capsule and channel for the perilymphatic duct, a metotic foramen undivided by bone, and a short lagenar recess. Among the earliest archosaurs, the braincase of Erythrosuchus is considered to share more derived similarities with the erythrosuchid Shansisuchus than with other taxa, although further study is required to ascertain whether these similarities are homologous. An understanding of non crown‐group archosaur morphology is important for resolving controversial questions of homology concerning braincase features in extant archosaurs, as well as for improving estimates of archosaur phylogeny. The most recent common ancestor of crocodiles and birds is hypothesized to have lacked a ‘semilunar depression’ and basisphenoid ‘intertuberal plate’, and to have had laterally positioned internal carotid foramina, a short lagena, an undivided metotic foramen, an unossified eustachian system, and elements of the tympanic cavity that were not pneumatized.

THE DEVELOPMENT OF THE CHONDROCRANIUM IN THE SEAHORSE, HIPPOCAMPUS [LOPHOBRANCHII

SUMMARY 1 Three stages in the development of the chondrocranium of Hippocampus are studied. In the last stage it is fully formed. 2 The ethmoid plate has an upward and backward bend in the 9mm. stage of Hippocampus. This flexure gradually straightens and the normal horizontal condition is assumed in the fully formed chrondrocranium. 3 The lamina orbitonasalis and the nasal septum exhibit their independent origin from the ethmoid plate by retaining their identity even after fusing with the ethmoid plate. 4 The orbital cartilages are reduced and are in the form of a pair of short processes projecting back from the laminae orbitonasales. 5 The trabecula communis becomes disconnected from the basal plate in the 12mm. stage. It is present in the fully formed chondrocranium as a small posterior process of the ethmoid plate. Hence the ethmoid region of the chondrocranium is independent of the occipito-auditory region. 6 A pila lateralis develops in the 18mm. stage enclosing the trigeminal nerve. In the earlier stages there is only a groove, the incisivum pro-oticum. 7 A lateral commissure is completely developed forming the ventrolateral wall to the trigemino-facialis chamber. 8 There is a minute basicapsular fenestra in stage 1. It becomes confluent with the metotic foramen in later stages. 9 The otic capsule does not show external prominences of the semicircular canals. There are no complete cartilaginous septa separating the semicircular canals. 10 There is no tectum synoticum. A slender tectum posterius connects the two occipital processes. 11 A vestigial taenia tecti medialis is the only roofing cartilage in the chondrocranium. 12 The pterygoid process of the quadrate is vertical in the 9mm. stage and it assumes a horizontal position in the 18mm. stage. The process is continuous with the body of the quadrate by means of a thin cartilaginous extension in early stages. The two parts become separated as the ethmoid plate is straightened. The pterygoid process which is at first fused with the ethmoid plate articulates later by means of a distinct rostropalatine process with the pre-ethmoid cornu conforming to the “ acrartete ” condition of Swinnerton's description. 13 The quadrate in the 9mm. stage is fused with Meckel's cartilage and separates from it later. 14 Meckel's cartilages are obliquely situated in the early stages and undergo a rotation of about 90 degrees to assume a horizontal condition along with the straightening of the ethmoid plate. 15 The hyosymplectic cartilage is elongated and extends to Meckel's cartilage and lies below the quadrate in early stages. In later stages the anterior end of the hyosymplectic lies behind the quadrate. The hyomandibula articulates with the otic capsule in front of the region of the lateral semicircular canal. A spheno-pterotic ridge overhangs the articular facet. 16 The copula communis in the fully formed stage does not extend beyond the first branchial arch. There are no basibranchial elements in the branchial arches. 17 The hypohyal and ceratohyal are distinct cartilages and undergo a change in position and size during development. 18 A well developed rostral cartilage is present on the dorsal surface of the distal end of the ethmoid plate from the early stages: It also moves with the ethmoid plate to assume an anterior position. 19 Infralabial cartilages are present in the form of reduced dense cellular masses. 20 Sclerotic cartilages are present in the optic capsules.

THE DEVELOPMENT OF THE CHONDROCRANIUM IN OPHICEPHALUS*.

Summary. 1 Eight stages in the development of skull elements, commencing from the first day to twenty-five days after hatching, have been studied. 2 The mesenchymatous plate in contact with the ectoderm on either side of hypophysis is seen in stage 1 (2.75 mm.). 3 The trabeculae and parachordals arise independently in stage 2 (4.0 mm.). 4 The trabeculae are joined to the parachordals, leaving a wide hypophysial fenestra in stage 3 (4.0 mm.). The visceral arches chondrify and the first two branchial arches appear in this stage. The basibranchials have fused to form a copula communis. 5 In stage 4 (4.5 mm.) the rudiments of the occipital arches are noticed, A basicapsular fenestra is seen. The pterygoid process is noticed as an independent chondrification as in Clupea, and the quadrate is fused with the hyomandibula, as also in Clupea. All the five branchial arches have developed in Ophicephalus. The fifth branchial arch extends to a few sections. 6 In stage 5 (5.0 mm.) the pharyngobranchials have developed in connection with the first three branchial arches. The metotic foramen is delimited by the fusion of the occipital arch with the auditory capsule posteriorly. Meckel's cartilages have fused anteriorly at the symphysis. 7 In stage 6 (5.0 mm.) the pterygoid process is connected with the ethmoid plate by connective tissue. 8 In stage 7 (6.0 mm.) the pterygoid process extends posteriorly and is fused with the quadrate. An interhyal fused with the hyomandibula is noticed to be in contact with the ceratohyal. 9 In the fully formed chondrocranium, stage 8 (24.0 mm.), the rostral cartilage is developed and is not fused with any part of the ethmoid plate. The lamina orbitonasalis develops on each side of the middle region of the ethmoid plate. There is a small process directed posteriorly at the point where the lamina orbitonasalis has fused with the nasal septum, representing the anterior portion of orbital cartilage. The ophthalmic branch of the trigeminal nerve passes in a groove dorsal to the lamina orbitonasalis. The trabeeulae disorganize and are represented as a small extension posterior to the trabecula communis. The hypophysial fenestra is obliterated. The two orbital cartilages are united in the middle region of the chondrocranium by an epiphysial bar. A small taenia tecti medialis extends posteriorly from the middle region of the epiphysial bar. The trigemino-facialis chamber has no complete lateral commissure. The basicapsular fenestra and the metotic foramen are separated by the basivestibular commissure. The two auditory capsules are joined by a tectum synoticum. There is no tectum posterius. There are three prominences externally on the auditory capsules for the accommodation of the three semicircular canals. The hyomandibular branch of facial nerve passes in a foramen in the hyomandibula. The quadrate is fused with the hyomandibula. The hyomandibula is connected with the ceratohyal by a stylohyal. The pterygoid process is discontinuous with the quadrate. Meckel's cartilage articulates with the quadrate and there is a retroarticular process of Meckel's cartilage. In the branchial arches the basihyal is continuous with the copula communis. The ceratohyal shows a stout hypohyal in close contact with the basihyal. There is a foramen in the hypohyal for the hyoidean artery, recorded only in Solea. The first four branchial arches show differentiation into the hypo-, the cerato-, the epi-and the pharyngobranchials. The fifth branchial arch is small and consists of a single element—the ceratobranchial. The pharyngobranchials of the third and fourth arches are fused. 10 There are two small rods in connection with the second branchial arch ventrally on either side of the copula communis. I have called these the sub-copular rods. The homology of these rods is not clear. 11 In the chondrocranium the ethmoid region is completely separated from the auditory region by the discontinuity of trabeculae, the orbital cartilages and the pterygoid processes. 12 The chondrocranium is platytrabic, as no interorbital septum is noticed.