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Abstract

Ankylosaur braincase and endocranial morphologies are poorly known. Furthermore, cranial endocasts have been described for fewer than ten taxa so far. The complete inner ear morphology is known for only three species – Euoplocephalus tutus, Kunbarrasaurus ieversi, and Pawpawsaurus campbelli. Here, the first cranial endocast morphologies are presented for the Mongolian Cretaceous ankylosaurids Talarurus plicatospineus and Tarchia teresae. The study of paleoneurological features of these Mongolian taxa adds novel anatomical information to both species allowing the first comparison with ankylosaurids from North America. The development of a cerebellar flocculus that leaves an impression on the vestibular eminence – floccular recess – is observed in Euoplocephalus, Talarurus and T. teresae. Because this structure hasn't been identified in any nodosaurid so far, its presence in ankylosaurid cranial endocasts may represent a possible synapomorphy with unknown paleobiological implications.

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... The reasons behind the striking enlargement of this structure have been debated for a long time (e.g. Edinger 1942;Balanoff et al. 2010;Miyashita et al. 2011;Paulina-Carabajal 2012;Paulina-Carabajal et al. 2018b). As mentioned above, possible explanations involve a simple positive allometric relationship of the pituitary gland with a large body size (e.g. ...
... Thus, the presence of flocculus in theropods -and its apparent absence in most sauropods-was first related to bipedalism, the reason why bipedal ornithischians were expected to have an enlarged flocculus. However, this structure it is absent in most ornithischian clades and has been found only in a few taxa including the basal dryosaurid Dysalotosaurus (Galton 1989;Lautenschlager and Hübner 2013), and the quadrupedal ankylosaurs of the ankylosaurids family (Miyashita et al. 2011;Paulina-Carabajal et al. 2016b, 2018b, and stegosaurs (Galton 1988(Galton , 2001, making the paleobiological inferences of this structure, controversial at least. Recent works focused on bird brain evolution and the origins of flight assumed a positive relationship between floccular size and aerial maneuverability. ...
... The olfactory tracts are relatively anteroposteriorly elongated in basal and derived ceratopsians (Forster 1996;Zhou et al. 2007), but are shorter and the olfactory bulbs are just in front the cerebral hemispheres in hadrosaurids (Evans et al. 2009;Becerra et al. 2018), and ankylosaurs (e.g. Miyashita et al. 2011;Ősi et al. 2014;Paulina-Carabajal et al. 2016b, 2018b, with an intermediate situation observed in stegosaurs and pachycephalosaurs (Giffin 1989;Galton 2001;Bourke et al. 2014). The olfactory system in hadrosaurids constitutes between 3% and 7% of the endocranial volume, something similar to the sauropod Nigersaurus (Evans et al. 2009). ...
Chapter
This chapter aims to provide an overview of the state of knowledge on non-avian dinosaur paleoneurology, throughout the history and synthesis of recent advances in the field. Today, the endocranial morphology of approximately 150 dinosaur taxa has been described using natural or artificial cranial endocasts. They represent all major clades, although there is a bias towards Cretaceous -and more derived- forms. From this sample more than a half of the publications were made in the last 20 years, hand in hand with the use of non-invasive technologies. This larger amount of anatomical data opened the door to more comprehensive analyses (quantitative methods), allowing us to better understand the evolution of the dinosaur brain pattern and sense biology through deep time.
... Although the size of the floccular fossa has been found to fail as a proxy for ecology or behavior in certain extant mammals and birds 47 , it has repeatedly been used to tentatively establish such a meaning for fossil taxa (e.g. 15,33,48 ). Additionally, ontogeny possibly plays a role in the expression of the flocculus on the endocast 28 . ...
... Additionally, ontogeny possibly plays a role in the expression of the flocculus on the endocast 28 . A lack of a floccular recess is common for ankylosaurs, except for a group within Ankylosaurinae 13,15 , and no floccular recess has been found in any nodosaurid endocast so far 32,40 . However, a floccular recess is present in the ankylosaurine ankylosaurids E. tutus 14,39 and T. teresae 40 . ...
... Animals are likely to perceive sounds they are able to produce themselves (Walsh et al. 34 and references therein). Because ankylosaurids seem to possess longer cochlear ducts than nodosaurids, it has been hypothesized that ankylosaurids had more sophisticated sound producing and perception capabilities in comparison to nodosaurids 15,40 . The presence of relatively shorter and less convoluted nasal passages, which are possibly involved in sound production, in the nodosaurid P. mirus, compared to the ankylosaurid E. tutus, potentially supports this interpretation 6,30,40,42 . ...
Article
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Nodosauridae is a group of thyreophoran dinosaurs characterized by a collar of prominent osteoderms. In comparison to its sister group, the often club-tailed ankylosaurids, a different lifestyle of nodosaurids could be assumed based on their neuroanatomy and weaponry, e.g., regarding applied defensive strategies. The holotype of the nodosaurid Struthiosaurus austriacus consists of a single partial braincase from the Late Cretaceous of Austria. Since neuroanatomy is considered to be associated with ecological tendencies, we created digital models of the braincase based on micro-CT data. The cranial endocast of S. austriacus generally resembles those of its relatives. A network of vascular canals surrounding the brain cavity further supports special thermoregulatory adaptations within Ankylosauria. The horizontal orientation of the lateral semicircular canal independently confirms previous appraisals of head posture for S. austriacus and, hence, strengthens the usage of the LSC as proxy for habitual head posture in fossil tetrapods. The short anterior and angular lateral semicircular canals, combined with the relatively shortest dinosaurian cochlear duct known so far and the lack of a floccular recess suggest a rather inert lifestyle without the necessity of sophisticated senses for equilibrium and hearing in S. austriacus. These observations agree with an animal that adapted to a comparatively inactive lifestyle with limited social interactions.
... Aspects of ankylosaurian anatomy, phylogeny, and paleobiogeography have been thoroughly studied in the last few decades (e.g., Maryańska, 1977;Tumanova, 1987Tumanova, , 2012Coombs and Maryańska, 1990;Carpenter, 2001;Vickaryous et al., 2004;Thompson et al., 2012;Arbour and Currie, 2016). Despite this progress, our knowledge of the neurocranial osteology and endocranial morphology within the clade is comparatively poor (see the recent review by Paulina-Carabajal et al. [2018]). ...
... The hypophyseal fossa of Bissektipelta was well vascularized. Large cerebral carotid arteries entered the hypophyseal cavity transversely as in most other ankylosaurs (e.g., Paulina-Carabajal et al., 2018); the sphenopalatine arteries branched off of them and left the hypophyseal cavity slightly anteriorly (a+vCC and a+vSP in Fig. 4B, C). The cerebral carotid and sphenopalatine veins that drained the cavernous sinus and the orbit/palate apparently shared canals with similarly named arteries. ...
... The cerebellar region is more defined than in ZIN PH 1/16 as a slight roundish bulge on the lateral surface of the endocast (cbl, Fig. 14A). It has relatively small projections that protrude into the anterior semicircular canal and are comparable to the larger flocculi in other dinosaurs (e.g., Sampson and Witmer, 2007;Miyashita et al., 2011;Paulina-Carabajal et al., 2018). The brainstem is as broad transversely as deep dorsoventrally and has a flat ventral surface with an incision posterior to the pituitary (Fig. 14D). ...
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We describe in detail three braincases of the ankylosaur Bissektipelta archibaldi from the Late Cretaceous (Turonian) of Uzbekistan with the aid of computed tomography, segmentation, and 3D modeling. Bissektipelta archibaldi is confirmed as a valid taxon and attributed to Ankylosaurinae based on the results of a phylogenetic analysis. The topographic relationships between the elements forming the braincase are determined using a newly referred specimen with preserved sutures, which is an exceedingly rare condition for ankylosaurs. The mesethmoid appears to be a separate ossification in the newly referred specimen ZIN PH 281/16. We revise and discuss features of the neurocranial osteology in Ankylosauria and propose new diagnostic characters for a number of its subclades. We present a 3D model of the braincase vasculature of Bissektipelta and comment on vascular patterns of armored dinosaurs. A complex vascular network piercing the skull roof and the wall of the braincase is reported for ankylosaurs for the first time. We imply the presence of a lepidosaur-like dorsal head vein and the venous parietal sinus in the adductor cavity of Bissektipelta. We suggest that the presence of the dorsal head vein in dinosaurs is a plesiomorphic diapsid trait, and extant archosaur groups independently lost the vessel. A study of two complete endocranial casts of Bissektipelta allowed us to compare endocranial anatomy within Ankylosauria and infer an extremely developed sense of smell, a keen sense of hearing at lower frequencies (100–3000 Hz), and the presence of physiological mechanisms for precise temperature control of neurosensory tissues at least in derived ankylosaurids.
... All caputegulae are pitted externally. The neuroanatomy of MPC-D 100/1353 was fully described before by Paulina-Carabajal et al. 9 . The premaxillae are fused dorsally, but the palatal surfaces are separate (Figs. 2, 3). ...
... The narrow, sharp, and medially curved anterior portion of the caputegulae lies in a broad, deep postorbital fossa posterior to the supraorbital. The anterior tip of the right horn was slightly broken sometime after CT scanning of the braincase by Paulina-Carabajal et al. 9 . A narrow, deep sulcus separates the irregular ventral margin of the base of the external layer of the squamosal horn and the underlying squamosal horn proper. ...
Article
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A new ankylosaurid dinosaur, Tarchia tumanovae sp. nov., has been recovered from the Upper Cretaceous Nemegt Formation of Mongolia. It includes a well-preserved skull, dorsal, sacral, caudal vertebrae, sixteen dorsal ribs, ilia, a partial ischium, free osteoderms, and a tail club. The squamosal horns of T. tumanovae are divided into two layers, the external dermal layer and the underlying squamosal horn proper. The irregular ventral margin of the base of the upper dermal layer may represent a resorption surface, suggesting that the squamosal horns of some ankylosaurids underwent extreme ontogenetic remodeling. Localized pathologies on the dorsosacral ribs and the tail provide evidence of agonistic behaviour. The tail club knob asymmetry of T. tumanovae resulted from restricted bone growth due to tail club strikes. Furthermore, T. tumanovae had an anteriorly protruded shovel-shaped beak, which is a morphological character of selective feeders. Ankylosaurid diets shifted from low-level bulk feeding to selective feeding during the Baruungoyot and the Nemegt “age” (middle Campanian-lower Maastrichtian). This ankylosaurid niche shifting might have been a response to habitat change and competition with other bulk-feeding herbivores.
... In proterochampsid archosauriforms (e.g., Tropidosuchus romeri, Pseudochampsa ischigualastensis) (Trotteyn & Paulina-Carabajal, 2016) the floccular lobes are absent as well, but in the non-archosaurian archosauriforms T. primus, Euparkeria capensis, and E. africanus the floccular lobes can be clearly recognized (Gower & Sennikov, 1996;Sobral et al., 2016;Stocker et al., 2016). Among avemetatarsalians, a large floccular lobe can be recognized in the basal sauropodomorph Saturnalia tupiniquim, in theropod dinosaurs, and in ornithischian stegosaurs and ankylosaurids (Trotteyn et al., 2015;Bronzati et al., 2017;Paulina-Carabajal et al., 2017). ...
... mississippiensis: OUVC 9761;G. gangeticus: Bona, Paulina-Carabajal & Gasparini, 2017), ornithischians A. ardevoli: Cruzado-Caballero et al., 2015; Anchiceratops ornatus: (Hopson, 1979); T. plicatospineus: Paulina-Carabajal et al., 2017), and sauropodomorphs (Diplodocus longus: S. tupiniquim: Bronzati et al., 2017) in which the hypoglossal nerve exits through multiple foramina. ...
Article
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The paleoneuroanatomy of pseudosuchian archosaurs is poorly known, based on direct examination of the internal morphology of braincases and a few artificial endocasts. Among aetosaurs, only one endocast has been described almost a century ago by Case (1921) corresponding to Desmatosuchus spurensis from the Chinle Formation (Norian) of Texas, US, based on a resin cast. Here, we describe the first natural endocast of an aetosaur, Neoaetosauroides engaeus from the Los Colorados Formation (Norian) of NW Argentina, and also developed the first digital endocast of this taxon including the encephalon, cranial nerves, inner ear, and middle ear sinuses. The neuroanatomy of Neoaetosauroides engaeus exhibits several differences from that of Desmatosuchus spurensis despite their phylogenetic proximity, which may be a reflection of their different habits. The information provided by the endocasts of Neoaetosauroides engaeus about its olfactory region and the orientation of its head, based on the inclination of the inner ear, could support the proposal for an animalivorous diet, instead of an herbivorous one as in most aetosaurs. The new information here obtained contributes to the knowledge of the neuroanatomical diversity of archosauriforms and more specifically among pseudosuchians and their paleobiological roles in the Triassic continental communities.
... The branches of the hypoglossal nerve (CN XII) pierce the exoccipital through a single foramen (Figure 2a- -Carabajal et al., 2018) and birds, in which this nerve has multiple exits. It appears that there is remarkable variation concerning the ramification of the hypoglossal nerve within archosaurs, and it is difficult to recognize a pattern among them so far. ...
Article
Non‐crocodylomorph loricatans, traditionally known as “rauisuchians,” are considered as the top predators of the Triassic continental faunas that reigned before the emergence of the well‐known theropod dinosaurs. In particular, Saurosuchus galilei is a large quadrupedal prestosuchid loricatan found in the Ischigualasto Formation from northwestern Argentina. Here, we reevaluated the braincase of S . galilei and present the first paleoneurological study based on the partial natural casts of the holotype and the digital cranial endocast of the referred specimen PVSJ 32. The braincase of S . galilei was here reinterpreted, identifying the sutures of the supraoccipital, otoccipital, basioccipital, parabasisphenoid, prootic, and laterosphenoid. A unique feature identified in the braincase of S . galilei is the presence of deep paracondylar recesses associated with pharyngotympanic pneumaticity, which has not been identified in any other “rauisuchians” so far. Most of the structures of the encephalon were recognized in the cranial endocast and natural casts including cranial nerves V–XII, olfactory bulbs, main blood vessels and sinuses, and inner ear. These structures allowed us to quantify some of its sensorial capacities and recognize that S . galilei had an enhanced olfactory acuity, with coefficients higher than those expected for its body size, a condition previously observed in living crocodilians and tyrannosaurid dinosaurs. An improved sense of smell might have allowed Saurosuchus to track its prey from long distances and compensate for the poorer development of its other senses like vision and balance.
... The m. pseudotemporalis profundus (mPSTp) is also not included in our reconstructions as EPB indicates that this muscle likely originates from the surface of the epipterygoid 41 . Despite the presence of the epipterygoid in Ankylosauria 1,8,47 , this bone is not preserved in either specimen under study here and is thought to have been lost in other derived ornithischian clades (Hadrosauridae and Ceratopsidae), resulting in the loss of mPSTp or its replacement with a ligament 41,77 . Therefore, the mPSTp in the two study species, if present, likely did not play a major role in force production or cranial stress distribution during jaw closure. ...
Article
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Ankylosaurs were important megaherbivores of Jurassic and Cretaceous ecosystems. Their distinctive craniodental anatomy and mechanics differentiated them from coexisting hadrosaurs and ceratopsians, and morphological evidence suggests dietary niche partitioning between sympatric ankylosaurids and nodosaurids. Here, we investigate the skull biomechanics of ankylosaurs relative to feeding function. First, we compare feeding functional performance between nodosaurids and ankylosaurids applying finite element analysis and lever mechanics to the skulls of Panoplosaurus mirus (Nodosauridae) and Euoplocephalus tutus (Ankylosauridae). We also compare jaw performance across a wider sample of ankylosaurs through lever mechanics and phylogenetic comparative methods. Mandibular stress levels are higher in Euoplocephalus , supporting the view that Panoplosaurus consumed tougher foodstuffs. Bite force and mechanical advantage (MA) estimates indicate that Panoplosaurus had a relatively more forceful and efficient bite than Euoplocephalus . There is little support for a role of the secondary palate in resisting feeding loads in the two ankylosaur clades. Several ankylosaurs converged on similar jaw mechanics, while some nodosaurids specialised towards high MA and some ankylosaurids evolved low MA jaws. Our study supports the hypothesis that ankylosaurs partitioned dietary niches in Late Cretaceous ecosystems and reveals that the two main ankylosaur clades evolved divergent evolutionary pathways in skull biomechanics and feeding habits.
... To incorporate additional palatal variations noted in SAMA P40536, K. ieversi, and other ankylosaurians, we added a new character (178 in Arbour and Currie, 2016;and 190 in Soto-Acuña et al., 2021) that describes the position of the choanae within the palate relative to the maxillary tooth row: choanae with their anterior margins inline or within the anterior third of the maxillary tooth row (178/190:0); choanae posteriorly situated with their anterior margins at least mid-way along the tooth row (178/190:1). Ankylosaurians were scored from the literature (Eaton Jr, 1960;Sereno and Zhimin, 1992;Lee, 1996;Godefroit et al., 1999;Carpenter et al., 2001aCarpenter et al., , 2008Carpenter et al., , 2011Vickaryous et al., 2001;Hill et al., 2003;Carpenter, 2004;Kilbourne and Carpenter, 2005;Parsons and Parsons, 2009;Arbour and Currie, 2013;Arbour et al., 2014a;Leahey et al., 2015;Kinneer et al., 2016;Arbour and Evans, 2017;Yang et al., 2017;Bourke et al., 2018;Paulina-Carabajal et al., 2018;Wiersma and Irmis, 2018;Norman, 2020;Park et al., 2020); however, we could not adequately code the outgroup taxon Huayangosaurus taibaii because the condition of its choanae is unknown. Character polarity was therefore determined from Hesperosaurus mjosi (Maidment et al., 2018) and a 3D cranial model of Stegosaurus armatus (specimen number; UMNH VPC 44, sketchfab. ...
Article
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Australian dinosaur research has undergone a renaissance in the last 10 years, with growing knowledge of mid-Cretaceous assemblages revealing an endemic high-paleolatitude Gondwanan fauna. One of its most conspicuous members is ankylosaurs, which are rare but nonetheless occur in most Australian dinosaur-bearing formations spanning the uppermost Barremian to lower Cenomanian. Here we describe a partial ankylosaur skull from the marine Toolebuc Formation exposed near Boulia in western Queensland, Australia. This skull represents the oldest ankylosaurian material from Queensland, predating the holotype of Kunbarrasaurus ieversi, which was found in the overlying Allaru Mudstone. The ankylosaur skull is encased in a limestone concretion with the maxillary tooth rows preserved only as impressions. Synchrotron radiation X-ray tomography was used to non-destructively image and reconstruct the specimen in 3D and facilitate virtual preparation of the separate cranial bones. The reconstruction of the skull revealed the vomer, palatines, sections of the ectopterygoids and maxillae, and multiple teeth. The palate has posteriorly positioned choanae that differs from the more anterior placement seen in most other ankylosaurians, but which is shared with K. ieversi, Akainacephalus johnsoni, Cedarpelta bilbeyhallorum, Gobisaurus domoculus, and Panoplosaurus mirus. Phylogenetic analyses place the new cranial material within the recently named basal ankylosaurian clade Parankylosauria together with K. ieversi. This result, together with the anatomical similarities to the holotype of K. ieversi, permits its referral to cf. Kunbarrasaurus sp. This specimen elucidates the palatal anatomy of Australian ankylosaurs and highlights one of the most ubiquitous components of Australian mid-Cretaceous dinosaur faunas.
... Application of up-to-date imaging techniques, such as computed tomography (CT), has greatly increased the knowledge of braincase and endocranial morphology in different dinosaur lineages (e.g. Sampson & Witmer, 2007;Witmer & Ridgely, 2009;Miyashita et al., 2011;Lautenschlager et al., 2012;Knoll et al., 2012;Paulina-Carabajal et al., 2018;King et al., 2020), although this information is limited for early dinosaurs because of the scarcity of well-preserved braincases (Martínez et al., 2012;Bronzati et al., 2017Bronzati et al., , 2018bBronzati & Rauhut, 2017). Consequently, the endocranial anatomy and evolution of early sauropodomorphs is notably understudied, with only a few available models (Bronzati et al., 2017;Neenan et al., 2018). ...
Article
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Sauropodomorph 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.
... A subsellar recess seems to be absent in one specimen of Lesothosaurus diagnosticus (NHMUK PV RU B17) but is clearly present in another (NHMUK PV R8501). The absence of a subsellar recess was reported for ankylosaurid ornithischians (Paulina-Carabajal et al., 2018) and for the megaraptoran theropod Murusraptor barrosaensis (Paulina-Carabajal and Currie, 2017). Nevertheless, the presence or absence of the subsellar recess does not inform the relationships of early dinosauromorphs. ...
Article
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The braincase anatomy of the sauropodomorph dinosaur Saturnalia tupiniquim from the Late Triassic (Carnian) Santa Maria Formation of Brazil is described for the first time using 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 they might be plesiomorphic for Dinosauria. Likewise, the subsellar and basisphenoid pneumatic recesses were observed in all examined dinosauromorph taxa, with variation observed in the relative development of these sructures but not in their absence/presence. 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.
... Baruungoyot beds exposed at Khulsan have provided remarkable taxa which include Bagaceratops rostdestvenskii, Saichania chulsanensis, Tarchia gigantea, Parvicursor remotus, ?Mononykus sp., Avimimus cf. portentosus, Tylocephale gilmorei, Gobipteryx minuta, lizards, eggshells, and mammals (Elzanowski, 1974(Elzanowski, , 1977Kielan-Jaworowska, 1974;Mikhailov et al., 2004;Longrich et al., 2010;Arbour et al., 2014;Varricchio and Barta, 2015;Bell and Fanti, 2017, this volume;Paulina-Carabajal et al., 2017, this volume) (Table 1). ...
Article
Since the discovery of fossil-rich exposures at the Khulsan and Nemegt localities (Nemegt Basin, southern Mongolia), tens of paleontological expeditions returned to these exposures, which are considered some of the richest Cretaceous units in the world. However, limited data on the local geology and cartography have been limiting our comprehension on correlations between different sites and the stratigraphic occurrence of vertebrate remains. Although informative, hand-drawn maps from the 1940s still represent the sole tool for researchers to provide a framework for locating access path, quarries and major geological sections. In 2016, we started a project for the realization of high-resolution topographic maps of key localities within the Nemegt Basin based on drone-acquired images. Several tests were performed at pivotal localities such as Altan Uul 2 and 3, Tsagaan Khushuu, and Ulaan Khushuu providing partial maps of such localities, whereas the Nemegt and Khulsan localities were fully covered. Photogrammetric elaboration of high-resolution images resulted in digital surface models used to obtain high-resolution topographic maps and orthophotos. Rock cairns used in the 1940s for triangulation were relocated and painted with vivid colors in order to represent reliable ground control points. In this study, we introduce new topographic maps for both Khulsan and Nemegt localities as well as comprehensive geological maps. In so doing, we provide additional stratigraphic and geographic data on the approximately 25. m thick interfingering interval that characterize the transition from the Baruungoyot and overlying Nemegt formations. Data presented in this study provide a solid framework in which detailed geological and paleontological investigations can be referred in order to significantly improve our comprehension on the Late Cretaceous Nemegt ecosystems.
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Peripheral nerves in vertebrate systems have been studied for centuries. Nerve anatomy, including the connective tissues that cushion nerves, are well described in the literature. The outer connective tissues, known as the epineurium and perineurium, include a double layer of collagen fibers that form a double helical wrapping that is visible with polarized light microscopy and by other contrast methods. This wrapping is a diagnostic characteristic of nerve tissues. Decades of research into dinosaur bones have produced interesting endocasts of probable brain morphology, but no soft and flexible nerve tissues have been reported from dinosaur remains. In this study we provide evidence of nerve fragments, characterized by a double helical wrapping of collagen fibers, from a Triceratops condyle collected at the Hell Creek Formation, MT. Based on comparison with nerves from an avian model we conclude that these are fragments of nerves that once resided in vivo in Triceratops.
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The cerebellar floccular and parafloccular lobes are housed in fossae of the periotic region of the skull of different vertebrates. Experimental evidence indicates that the lobes integrate visual and vestibular information and control the vestibulo-ocular reflex, vestibulo-collic reflex, smooth pursuit and gaze holding. Multiple paleoneuroanatomy studies have deduced the behaviour of fossil vertebrates by measuring the floccular fossae (FF). These studies assumed that there are correlations between FF volume and behaviour. However, these assumptions have not been fully tested. Here, we used micro-CT scans of extant mammals (47 species) and birds (59 species) to test six possible morphological-functional associations between FF volume and ecological/behavioural traits of extant animals. Behaviour and ecology do not explain FF volume variability in four out of six variables tested. Two variables with significant results require further empirical testing. Cerebellum plasticity may explain the lack of statistical evidence for the hypotheses tested. Therefore, variation in FF volume seems to be better explained by a combination of factors such as anatomical and phylogenetic evolutionary constraints, and further empirical testing is required.
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Extant crocodilians are a highly apomorphic archosaur clade that is endothermic, yet often achieve large body sizes that can be subject to higher heat loads. Therefore, the anatomical and physiological roles that blood vessels play in crocodilian thermoregulation need further investigation to better understand how crocodilians establish and maintain cephalic temperatures and regulate neurosensory tissue temperatures during basking and normal activities. The cephalic vascular anatomy of extant crocodilians, particularly American alligator (Alligator mississippiensis) was investigated using a differential-contrast, dual-vascular injection technique and high resolution X-ray micro-computed tomography (μCT). Blood vessels were digitally isolated to create representations of vascular pathways. The specimens were then dissected to confirm CT results. Sites of thermal exchange, consisting of the oral, nasal, and orbital regions, were given special attention due to their role in evaporative cooling and cephalic thermoregulation in other diapsids. Blood vessels to and from sites of thermal exchange were studied to detect conserved vascular patterns and to assess their ability to deliver cooled blood to neurosensory tissues. Within the orbital region, both the arteries and veins demonstrated consistent branching patterns, with the supraorbital, infraorbital, and ophthalmotemporal vessels supplying and draining the orbit. The venous drainage of the orbital region showed connections to the dural sinuses via the orbital veins and cavernous sinus. The palatal region demonstrated a vast plexus that comprised both arteries and veins. The most direct route of venous drainage of the palatal plexus was through the palatomaxillary veins, essentially bypassing neurosensory tissues. Anastomotic connections with the nasal region, however, may provide an alternative route for palatal venous blood to reach neurosensory tissues. The nasal region in crocodilians is probably the most prominent site of thermal exchange, as it offers a substantial surface area and is completely surrounded by blood vessels. The venous drainage routes from the nasal region offer routes directly to the dural venous sinuses and the orbit, offering evidence of the potential to directly affect neurosensory tissue temperatures. The evolutionary history of crocodilians is complex, with large-bodied, terrestrial, and possibly endothermic taxa that may have had to deal with thermal loads that likely provided the anatomical building-blocks for such an extensive vascularization of sites of thermal exchange. A clear understanding of the physiological abilities and the role of blood vessels in the thermoregulation of crocodilians neurosensory tissues is not available but vascular anatomical patterns of crocodilian sites of thermal exchange indicate possible physiological abilities that may be more sophisticated than in other extant diapsids.
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Here we report new rebbachisaurid material (MMCh-PV 71) recovered from the Candeleros Formation (Cenomanian) of northwest Patagonia, Argentina. The cranial remains consist of a partial braincase and a right quadrate. Fractures in the braincase exposed the endocranial cavity, allowing the first study of the brain and inner ear morphologies of a South American rebbachisaurid. The braincase and cranial endocast both exhibit traits similar to those observed in the Cretaceous rebbachisaurs Nigersaurus from Africa and Limaysaurus from Argentina, although in terms of osteology, the South American taxa are highly similar. The endocast of MMCh-PV 71 is more similar to that of Nigersaurus than to those of Diplodocus and Camarasaurus, suggesting some probable rebbachisaurid features such as the noteworthy presence of the flocculus. The overall morphology of the quadrate shows similarities with Limaysaurus and Nigersaurus. However, differences such as the broader posterior fossa and the shape and orientation of the head and the pterygoid process indicate that the new specimen could represent a distinct taxon.
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Minmi is the only known genus of ankylosaurian dinosaur from Australia. Seven specimens are known, all from the Lower Cretaceous of Queensland. Only two of these have been described in any detail: the holotype specimen Minmi paravertebra from the Bungil Formation near Roma, and a near complete skeleton from the Allaru Mudstone on Marathon Station near Richmond, preliminarily referred to a possible new species of Minmi . The Marathon specimen represents one of the world’s most complete ankylosaurian skeletons and the best-preserved dinosaurian fossil from eastern Gondwana. Moreover, among ankylosaurians, its skull is one of only a few in which the majority of sutures have not been obliterated by dermal ossifications or surface remodelling. Recent preparation of the Marathon specimen has revealed new details of the palate and narial regions, permitting a comprehensive description and thus providing new insights cranial osteology of a basal ankylosaurian. The skull has also undergone computed tomography, digital segmentation and 3D computer visualisation enabling the reconstruction of its nasal cavity and endocranium. The airways of the Marathon specimen are more complicated than non-ankylosaurian dinosaurs but less so than derived ankylosaurians. The cranial (brain) endocast is superficially similar to those of other ankylosaurians but is strongly divergent in many important respects. The inner ear is extremely large and unlike that of any dinosaur yet known. Based on a high number of diagnostic differences between the skull of the Marathon specimen and other ankylosaurians, we consider it prudent to assign this specimen to a new genus and species of ankylosaurian. Kunbarrasaurus ieversi gen. et sp. nov. represents the second genus of ankylosaurian from Australia and is characterised by an unusual melange of both primitive and derived characters, shedding new light on the evolution of the ankylosaurian skull.
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A partial skull of ankylosaur from the Upper Cretaceous (Santonian) Csehbánya Formation in Iharkút and the endocranial cast taken from it are described. The morphology of the exoccipital, the elongated 'neck' region of the basioccipital, the shape of the occipital condyle, and the different flexure of the medulla relative to the forebrain unambiguously differentiate this specimen from the basicranium of Struthiosaurus, so it is assigned to Hungarosaurus sp. Whereas the endocranial cast reflects a brain generally similar to those of other ankylosaurs, the dorsally hypertrophied cerebellum (also present is Struthiosaurus transylvanicus) is quite unusual within the group suggesting a more sophisticated cerebral coordination of posture and movement, and perhaps a more cursorial locomotary habit than predicted for other ankylosaurs.
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The Ankylosauria is a group of herbivorous, quadrupedal, armoured dinosaurs subdivided into at least two major clades, the Ankylosauridae and the Nodosauridae. The most derived members of Ankylosauridae had a unique tail club formed from modified, tightly interlocking distal caudal vertebrae and enlarged osteoderms that envelop the terminus of the tail. We review all known ankylosaurid species, as well as ankylosaurs of uncertain affinities, in order to conduct a revised phylogenetic analysis of the clade. The revised phylogenetic analysis resulted in a monophyletic Ankylosauridae consisting of Ahshislepelta, Aletopelta, Gastonia, Gobisaurus, Liaoningosaurus, Shamosaurus and a suite of derived ankylosaurids (Ankylosaurinae). There is convincing evidence for the presence of nodosaurids in Asia during the Early Cretaceous. In the mid Cretaceous, Asian nodosaurids were replaced by ankylosaurine ankylosaurids. Ankylosaurines migrated into North America from Asia between the Albian and Campanian, where they diversified into a clade of ankylosaurines, here named Ankylosaurini, characterized by arched snouts and numerous flat cranial caputegulae. There is no evidence for any ankylosaurids in Gondwana; Ankylosauridae appears to be completely restricted to Asia and North America. The genus Crichtonpelta gen. nov. is created, type species Crichtonsaurus benxiensis Lü et al.
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Sinraptor dongi is a large theropod from the upper Shishugou Formation (Jurassic) of Xinjiang in northwestern China. The holotype includes a well-preserved braincase that recently benefited from additional preparation. The ossified ethmoidal elements are U-shaped in cross-section. When placed in anatomical position in the braincase, an unossified space remains between the sphenethmoid and the orbitosphenoid, suggesting there was a cartilaginous septosphenoid when the animal was alive. The morphology of the endocranial cavity and pneumatic recesses was studied using a latex endocast and CT scans. This led to the recognition of some traits that have not been previously described. The presence of a well developed caudal tympanic recess (generally considered as characteristic of coelurosaurs) is particularly interesting, as is the internal morphology of the basisphenoidal recess and its associated pneumatic cavities. There is a longitudinal passage connecting the lateral tympanic recess with the basisphenoidal recess that probably had both pneumatic and vascular functions. Endocranially, there is no medullar eminence, and the opening for the floccular recess is hourglass-shaped. The volume of the endocranial cavity, excluding the olfactory tract and bulbs, is 95 ml, and the encephalization quotient falls within the range calculated for other basal tetanurans. The angles formed between forebrain, midbrain and hindbrain are similar to those in carcharodontosaurids (Carcharodontosaurus and Giganotosaurus), although the relative positions of cranial nerves II-IV varies amongst these taxa. Cranial nerves IX, X and XI pass through a single half-moon-shaped opening. Within Allosauroidea, the cranial endocast of Sinraptor is morphologically more similar to those of Allosaurus, Carcharodontosaurus and Giganotosaurus than to that of Acrocanthosaurus.
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The discovery of a new ankylosaurid skull with some unusual features from the Baruungoyot Formation of Mongolia prompted a systematic review of ankylosaurid specimens from the Baruungoyot and Nemegt formations. Dyoplosaurus giganteus was found to possess no diagnostic features and is regarded as a nomen dubium. The holotype of Tarchia kielanae (previously synonymized with Tarchia gigantea) has one autapomorphy, an accessory postorbital ossification with surrounding furrow, and Tar. kielanae is here considered a valid species, making the combination Tar. gigantea unnecessary. An accessory postorbital ossification is also found in the holotype of Minotaurasaurus ramachandrani, and this species is here considered a junior synonym of Tar. kielanae. The newly described skull from the Baruungoyot Formation forms the holotype of a new genus and species, Zaraapelta nomadis gen. et sp. nov., diagnosed by unusual bilayered ornamentation on the squamosal horn and extensive postocular ornamentation. Two distinct tail club handle morphotypes are present in the Nemegt Formation and probably represent two different species. However, it is impossible to assign either tail club morphotype to the single valid species from the formation, Saichania chulsanensis, because of a lack of overlapping material. A revised phylogenetic analysis including newly identified characters found Zaraapelta nomadis to be most closely related to Tar. kielanae.
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Sinraptor dongi is a large theropod from the Upper Jurassic Shishugou Formation of Xinjiang in northwestern China. The holotype includes a well-preserved braincase that recently benefited from additional preparation. The ossified ethmoidal elements are U-shaped in cross-section. When placed in anatomical position in the braincase, an unossified space remains between the sphenethmoid and the orbitosphenoid, suggesting there was a cartilaginous septosphenoid when the animal was alive. The morphology of the endocranial cavity and pneumatic recesses was studied using a latex endocast and CT scans. This led to the recognition of some traits that have not been previously described. The presence of a well developed caudal tympanic recess (generally considered as characteristic of coelurosaurs) is particularly interesting, as is the internal morphology of the basisphenoidal recess and its associated pneumatic cavities. There is a longitudinal passage connecting the lateral tympanic recess with the basisphenoid recess that probably had both pneumatic and vascular functions. Endocranially, there is no medullar eminence, and the opening for the floccular recess has hour-glass shaped. The volume of the endocranial cavity, excluding the olfactory tract and bulbs, is 95 ml, and the encephalization quotient falls within the range calculated for other basal tetanurans. The angles formed between forebrain, midbrain and hindbrain are similar to those in carcharodontosaurids (Carcharodontosaurus and Giganotosaurus), although the relative positions of Cranial Nerves II-IV varies amongst these taxa. Cranial Nerves IX, X and XI pass through a single half-moon shaped opening. Within Allosauroidea, the cranial endocast of Sinraptor is morphologically more similar with that of Allosaurus, Carcharodontosaurus and Giganotosaurus than with Acrocanthosaurus. Key words: Braincase; Paleoneurology; Jurassic; China; Allosauroids
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Hitherto the earliest positive record of ankylosaurs(armored dinosaurs) has been from beds well up in the Lower Cretaceous; in fact, however, specimens referable to the ankylosaurian family Nodosauridae are present in the Middle and Upper Jurassic of England: from the Middle Callovian [partial mandible Sarcolestes leedsi Lydekker]], the Upper Oxfordian [femur Cryptodraco eumerus (Seeley)), maxilla Priodontognathus phillipsii (Seeley))], and the Upper Tithonian [caudal vertebra, tooth]. The Tithonian tooth and those of Priodontognathus are large and similar to those of the nodosaurids Priconodon and Sauropelta (Lower Cretaceous, U.S.A.). The incomplete mandible of Sarcolestes is similar to that of Sauropelta with a dermal scute fused to the lateral surface, and a tooth row extending to the anterior end of the jaw; an unusual feature is the caniniform first tooth. The quadrupedal ankylosaurs and stegosaurs probably represent separate evolutionary lines that extend back at least into the Lower Jurassic, and both lines probably evolved from ornithopod dinosaurs that were bipedal. Nodosaurid ankylosaurs occur in Europe from the Middle Jurassic to Late Cretaceous and probably reached North America via a filter route in the early Cretaceous.
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Extinct animal behavior has often been inferred from qualitative assessments of relative brain region size in fossil endocranial casts. For instance, flight capability in pterosaurs and early birds has been inferred from the relative size of the cerebellar flocculus, which in life protrudes from the lateral surface of the cerebellum. A primary role of the flocculus is to integrate sensory information about head rotation and translation to stabilize visual gaze via the vestibulo-occular reflex (VOR). Because gaze stabilization is a critical aspect of flight, some authors have suggested that the flocculus is enlarged in flying species. Whether this can be further extended to a floccular expansion in highly maneuverable flying species or floccular reduction in flightless species is unknown. Here, we used micro computed-tomography to reconstruct "virtual" endocranial casts of 60 extant bird species, to extract the same level of anatomical information offered by fossils. Volumes of the floccular fossa and entire brain cavity were measured and these values correlated with four indices of flying behavior. Although a weak positive relationship was found between floccular fossa size and brachial index, no significant relationship was found between floccular fossa size and any other flight mode classification. These findings could be the result of the bony endocranium inaccurately reflecting the size of the neural flocculus, but might also reflect the importance of the flocculus for all modes of locomotion in birds. We therefore conclude that the relative size of the flocculus of endocranial casts is an unreliable predictor of locomotor behavior in extinct birds, and probably also pterosaurs and non-avian dinosaurs.
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Until relatively recently, information on the internal skull structures of fossil taxa relied on fortuitous breaks, aggressive removal of rock matrix (Galton 1989, 2001), sectioning with a saw (Osborn 1912), or serial ground thin-sectioning (Stensiö 1963), all of which potentially risk damage to the fossil specimen (or even consume it entirely in the case of ground thin-sections). In some cases, casts of internal structures, such as the brain cavity and labyrinth of the inner ear, were preserved as ‘natural endocasts’ by infilling with more resistant matrix (e.g., Newton 1888). In most cases, however, physical endocasts are made after matrix removal by coating internal cavities with latex and then removing the cured replica, referred to as a latex endocast (Radinsky 1968; Jerison 1973; Hopson 1979). The process of making latex endocasts poses further risks to the fossil, and for many fragile specimens, such an approach has been unfeasible.
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An ankylosaurid braincase from the Upper Cretaccous Bissekty Fm. (Upper Turonian-Coniacian) at Dzharakuduk, central Kyzylkum Desert (Uzbekistan), is most similar to the braincase of Amtosaurus magnus from the upper part of the Upper Cretaceous Bainshire Fm. of Amtgai (Mongolia) in the structure of the ventral surface of the basioccipital, presence of a triangular anterior projection on the dorsum sellae, and dorsal position of the fenestra ovalis relative to the jugular foramen. It is referred to a new species. Amtosaurus archibaldi n. sp., which differs from A. magnus in having three instead of two foramina for the passage of branches of N. hypoglossus (XII), a smaller angle between the ventral surfaces of the basioccipital and basisphenoid (90° rather than 120°), and the more posterior position of the basipterygoid processes. Amtosaurus is an additional element shared by the Bissekty and upper Bainshire vertebrate assemblages. The alleged Campanian age for the Iren Dabasu Fm. is based on inadequate evidence, and this unit is more likely Late Turonian to ?Coniacian in age. The upper part of the Bainshire Fm. is Turonian-Santonian in age.
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Ankylosauria is a diverse clade of quadrupedal ornithischian dinosaurs whose remains are known from Middle Jurassic to latest Cretaceous sediments worldwide. Despite a long history of research, ankylosaur interrelationships remain poorly resolved and existing cladistic analyses suffer from limited character and taxon sampling. Here, we present the most comprehensive phylogenetic analysis of the group attempted to date. The traditional ankylosaurid–nodosaurid dichotomy is maintained. Ankylosauridae forms a well-resolved clade, which includes Zhongyuansaurus, the first ankylosaurid known to lack a tail club. Nodosauridae includes a number of taxa that were resolved either as ‘polacanthids’ or basal ankylosaurids in previous analyses. The use of a broader character sample allows analysis of the interrelationships of all valid ankylosaur species; this has revealed several previously unrecognized relationships. Stegosauria is recovered as the sister taxon to Ankylosauria, while Scelidosaurus is found to be a basal thyreophoran. Dedicated methods for coding continuous characters could be used in future to improve the resolution of ankylosaur phylogeny, particularly in order to explore the relationships within the poorly resolved nodosaurid clade.
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Internal cranial anatomy is a challenging area to study in fossilized skulls because of small sample sizes and varied post-mortem preservational alterations. This difficulty has led to the lack of correspondence between results obtained from direct osteological observation and from more indirect reconstruction methods. This paper presents corroborating evidence from direct osteological observation and from reconstruction based on computed X-ray tomography (CT) on the internal cranial anatomy of the ankylosaurid dinosaur Euoplocephalus tutus. A remarkable specimen of Euoplocephalus preserves rarely observed internal cranial structures such as vascular impressions in the nasal cavity, olfactory turbinates and possible impressions of conchae. Comparison with fossils and CT models of other taxa and other Euoplocephalus specimens adds osteological evidence for the previously reconstructed nasal cavity in this dinosaur and revises the previously described braincase morphology. A new interpretation of the ethmoidal homology identifies a mesethmoid, sphenethmoid and ectethmoid. These ethmoidal ossifications are continuous with the mineralized walls of the nasal cavity. The location of the olfactory fenestra provides further evidence that the olfactory regions of the nasal cavity are pushed to the sides of the main airway. This implies that the function of the vascular impressions in the nasal cavity and the looping of the cavity are not related to olfaction. A byproduct of the elongate, looping airway is a dramatic increase in surface area of the nasal respiratory mucosa, which in extant species has been linked to heat and water balance. A role in vocalization as a resonating chamber is another possible function of the looping and elongation of the nasal cavity. Olfaction remains as a possible function for the enlarged olfactory region, suggesting that multiple functions account for different parts of the ankylosaurid nasal cavity that underwent substantial modification. Cranial endocasts show negligible variation within Euoplocephalus, which lends some confidence to interspecific comparisons of endocranial morphology.
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Comparison of birds and pterosaurs, the two archosaurian flyers, sheds light on adaptation to an aerial lifestyle. The neurological basis of control holds particular interest in that flight demands on sensory integration, equilibrium, and muscular coordination are acute. Here we compare the brain and vestibular apparatus in two pterosaurs based on high-resolution computed tomographic (CT) scans from which we constructed digital endocasts. Although general neural organization resembles birds, pterosaurs had smaller brains relative to body mass than do birds. This difference probably has more to do with phylogeny than flight, in that birds evolved from nonavian theropods that had already established trends for greater encephalization. Orientation of the osseous labyrinth relative to the long axis of the skull was different in these two pterosaur species, suggesting very different head postures and reflecting differing behaviours. Their enlarged semicircular canals reflect a highly refined organ of equilibrium, which is concordant with pterosaurs being visually based, aerial predators. Their enormous cerebellar floccular lobes may suggest neural integration of extensive sensory information from the wing, further enhancing eye- and neck-based reflex mechanisms for stabilizing gaze.
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Fossils of the Early Cretaceous dinosaur, Nigersaurus taqueti, document for the first time the cranial anatomy of a rebbachisaurid sauropod. Its extreme adaptations for herbivory at ground-level challenge current hypotheses regarding feeding function and feeding strategy among diplodocoids, the larger clade of sauropods that includes Nigersaurus. We used high resolution computed tomography, stereolithography, and standard molding and casting techniques to reassemble the extremely fragile skull. Computed tomography also allowed us to render the first endocast for a sauropod preserving portions of the olfactory bulbs, cerebrum and inner ear, the latter permitting us to establish habitual head posture. To elucidate evidence of tooth wear and tooth replacement rate, we used photographic-casting techniques and crown thin sections, respectively. To reconstruct its 9-meter postcranial skeleton, we combined and size-adjusted multiple partial skeletons. Finally, we used maximum parsimony algorithms on character data to obtain the best estimate of phylogenetic relationships among diplodocoid sauropods. Nigersaurus taqueti shows extreme adaptations for a dinosaurian herbivore including a skull of extremely light construction, tooth batteries located at the distal end of the jaws, tooth replacement as fast as one per month, an expanded muzzle that faces directly toward the ground, and hollow presacral vertebral centra with more air sac space than bone by volume. A cranial endocast provides the first reasonably complete view of a sauropod brain including its small olfactory bulbs and cerebrum. Skeletal and dental evidence suggests that Nigersaurus was a ground-level herbivore that gathered and sliced relatively soft vegetation, the culmination of a low-browsing feeding strategy first established among diplodocoids during the Jurassic.
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Portions of the dinosaur-rich Upper Cretaceous Baruungoyot-Nemegt succession are exposed in four geographic areas of the Nemegt Basin, Mongolia: Nemegt, Altan Uul, Bügiin Tsav, and Hermiin Tsav. Lithostratigraphic correlations of these areas employ marker beds and non-random stratigraphic patterns of lithology, grain-size variation, and inferred paleoenvironments. Correlations suggest a minimum thickness of 350. m for the succession. Exposures at Nemegt, Altan Uul, and Bügiin Tsav form a 100. km east-west transect along the northern margin of the basin, exposing 265. m of section. From east to west the transect exposes higher portions of the succession, extending from the uppermost Baruungoyot Formation and encompassing an almost complete section of the Nemegt Formation, which has a minimum thickness of 235. m and can be consistently divided into three informal members: lower, middle, and upper. The lower Nemegt is well exposed at Nemegt and Altan Uul and is dominated by fluvial deposits. The middle and upper Nemegt are well exposed at Altan Uul 2 and Bügiin Tsav and consist of alluvial plain, paludal, lacustrine, and fluvial deposits. As confirmed by earlier studies, the Baruungoyot and Nemegt formations exhibit an interfingering transition at Nemegt. The Hermiin Tsav section is a geographic outlier, tens of kilometers west-southwest of the northern transect. It exposes about 150. m of section that overlaps with, but is mostly lower, stratigraphically, than the northern transect. The uppermost Hermiin Tsav section correlates with the lowermost Nemegt section, and also exhibits an interfingering contact between the Baruungoyot and Nemegt formations. The remaining section at Hermiin Tsav comprises sediments of the Baruungoyot Formation (135. m) that were deposited in alluvial fan, fluvial, paludal, lacustrine, and eolian environments, and can be divided into two informal members designated as lower and upper. The distribution of facies through the composite section records changes in paleoenvironments during the Late Cretaceous that may provide insights into the origins of the dinosaurian biostratigraphy.
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The “ethmoid complex” is an enigmatic element of the anterior portion of the braincase first described in Tyrannosaurus rex in 1912, which has since been recognized in many non-avian theropods. Because the “ethmoid complex” is a landmark for the reconstruction of the olfactory apparatus of non-avian theropods, we clarify the homology of this structure among archosaurs. The “ethmoid complex” consists of a trough-shaped element that is attached to an anteriorly-located median septum capped by a dorsal plate. Based on anatomical comparisons with the olfactory region of extant birds and crocodylians, the components of the “ethmoid complex” are shown to have cartilaginous or osteological homologues among extant archosaurs: the trough is homologous to the anterior portion of the planum supraseptale of crocodylians and embryonic birds, whereas the median septum and overlying dorsal plate are homologous to the avian mesethmoid and to the nasal septum and tectum nasi of crocodylians. Based on the location and ossification of olfactory region structures in non-avian theropods, the most appropriate terms for elements of the “ethmoid complex” are the sphenethmoid for the trough and the mesethmoid for the median septum and dorsal plate. The olfactory bulbs of nonavian theropods were housed within the sphenethmoid, which restricted the maximum size of the olfactory bulbs to a size smaller than the cerebral hemispheres.
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The taxonomic status of specimens referred to Tarchia kielanae, T. gigantea, and Minotaurasaurus ramachandrani has been contested. The holotype of T. kielanae, Zaklad Paleobiologii (Institute of Paleobiology)-Polish Academy of Sciences (ZPAL) MgD I/111, is redescribed. It has features common to both Palaeontological Institute-Russian Academy of Sciences (PIN) 3142/250, long considered Tarchia, and to M. ramachandrani but which are lacking in Saichania chulsanensis. The specimen PIN 3142/250 is not referable to Saichania but instead represents a new species, Tarchia teresae sp. nov. Similarly, the holotype skull of M. ramachandrani is not referable to T. kielanae, so Minotaurasaurus is a valid taxon. Tarchia is more derived than either Saichania or Minotaurasaurus while sharing features of both.
Chapter
This chapter focuses on Ankylosauria, a monophyletic clade of quadrupedal herbivorous dinosaurs characterized by the development of parasagittal osteoderms and osseous cranial ornamentation. All twenty-one taxa are clustered into one of two main lineages, Ankylosauridae or Nodosauridae. Fossil remains of ankylosaurs are found both in marine sediments and in nonmarine strata. The distribution of ankylosaur trackways and footprints is nearly global, including Asia, Europe, North America, and South America. Most of the tracks are concentrated in coastal and floodplain deposits, representing wet, well-vegetated habitats.
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Well preserved skulls of Triceratops are extremely abundant in Maastrictian rocks from western North America. Although ossification obscures sutural and structural details in many skulls, others reveal much previously undescribed morphology. The circumnarial area includes enlarged nares and a complex narial fossa. A nasal horn of varying size, augmented by an epinasal ossification, caps the snout. The anterodorsal orbital margin is formed by the lacrimal and the supraorbital, which has fused to the lateral side of the prefrontal. This thick and laterally extensive orbital rim restricted forward vision in Triceratops. The ossified braincase completely surrounds the brain cavity, and is overlain by a deep frontal and cornual sinus complex. These sinuses probably acted as shock absorbers to counteract stresses placed on the postorbital horns during intraspecific interactions. The frill is heavily vascularized, lacks fenestrae, and is well buttressed by expansive paroccipital processes. Endocasts reflect all twelve cranial nerves, major structures of the brain, and some arterial and venous drainage systems.
Article
Pawpawsaurus campbelli gen. et sp. nov. from the Paw Paw Formation (late Albian), Tarrant County, Texas, appears more primitive than other pre-Campanian nodosaurids, Silvisaurus condrayi and Sauropelta edwardsi. New cranial synapomorphies for the Nodosauridae are prominent W-shaped basioccipital tubera, anteriorly concave and anteroposteriorly flattened quadrate, and transversely continuous and straight posterior margin of the pterygoid aligned with the quadrate shaft. These synapomorphies are closely related to the downward orientation of the nodosaurid head in life. A pair of bony eyelids recovered with the skull are the first discovered for the Nodosauridae. Other Paw Paw Formation nodosaurid remains, including new postcranial elements and a baby nodosaurid, are taxonomically indeterminate.
Article
Euoplocephalus tutus Lambe (1902) from the Late Cretaceous of North America, was the first ankylosaurian dinosaur known from significant cranial material. Previous descriptions of this and other members of the Ankylosauria have been constrained by a paucity of material and an extremely apomorphic skull architecture, including the pervasive development of an embossing osseous ornamentation, and the absence of traditional morphological landmarks. A relative abundance of more recently collected and prepared cranial material attributable to Euoplocephalus enables a reappraisal of this taxon (including the type specimen), and permits it to be employed as a morphological representative of the clade. In recognition of previous difficulties encountered due to peculiarities of ankylosaurian anatomy, a fresh descriptive approach is necessitated. Herein, the skull is subdivided into five mutually exclusive topographic regions, within which individual elements are assigned with the assistance of outgroup comparison. Euoplocephalus is characterized by a distinctive pattern of cranial sculpturing across the preorbital area, relatively small, variably fluted teeth lacking a cingulum, a modified palpebral and a shallow nasal vestibule. Among ankylosaurine ankylosaurs, Euoplocephalus is unique in having medially inflected maxillary tooth rows. Osteological evaluation of the type skull of Anodontosaurus lambei Sternberg, 1929 supports its placement into synonymy with Euoplocephalus . © 2003 The Linnean Society of London, Zoological Journal of the Linnean Society, 2003, 137, 157−186.
Article
The “ethmoid complex” is an enigmatic element of the anterior portion of the braincase first described in Tyrannosaurus rex in 1912, which has since been recognized in many non-avian theropods. Because the “ethmoid complex” is a landmark for the reconstruction of the olfactory apparatus of non-avian theropods, we clarify the homology of this structure among archosaurs. The “ethmoid complex” consists of a trough-shaped element that is attached to an anteriorly-located median septum capped by a dorsal plate. Based on anatomical comparisons with the olfactory region of extant birds and crocodylians, the components of the “ethmoid complex” are shown to have cartilaginous or osteological homologues among extant archosaurs: the trough is homologous to the anterior portion of the planum supraseptale of crocodylians and embryonic birds, whereas the median septum and overlying dorsal plate are homologous to the avian mesethmoid and to the nasal septum and tectum nasi of crocodylians. Based on the location and ossification of olfactory region structures in non-avian theropods, the most appropriate terms for elements of the “ethmoid complex” are the sphenethmoid for the trough and the mesethmoid for the median septum and dorsal plate. The olfactory bulbs of nonavian theropods were housed within the sphenethmoid, which restricted the maximum size of the olfactory bulbs to a size smaller than the cerebral hemispheres.
Article
An overview of the palaeoneuroanatomy (brain and spinal cord) of the sauropod dinosaur Brachiosaurus is given. Although having a flexed brain configuration, Brachiosaurus presents on the whole a rather moderately derived neuroanatomical pattern. As other sauropods, Brachiosaurus shows an enlargement of the spinal cord in the sacral area. New Encephalization Quotients are calculated and found to be about 0.62 or 0.79 (depending on the body volume taken into consideration) when Hurlburt's formula is used. This suggests that Brachiosaurus, although it may not have been as a low encephalized taxon (by reptilian standards) as previously believed, did have an undersized relative brain volume.
Article
A fragmentary braincase from the Baynshirenskaya Svita (Cenomanian–Turonian) of Amtgay, Omnogov, People's Republic of Mongolia was described as the holotype specimen of the ankylosaurid dinosaur, Amtosaurus magnus Kurzanov and Tumanova 1978. However, the validity of this genus has been questioned by several authors. Recently, a second species, based on a fragmentary specimen consisting of a braincase and partial skull roof, was assigned to Amtosaurus as A. archibaldi Averianov 2002. Here we re-assess the status of Amtosaurus and of the referred species, A. archibaldi. We conclude that "Amtosaurus magnus" is a nomen dubium that should be regarded as Ornithischia indeterminate. However, "A." archibaldi is a valid taxon, characterized by an autapomorphic feature of the skull roof, and we refer this species to the new genus Bissektipelta.
Article
The specimen is identified as the partial cranium of a nodosaurid ankylosaur (Ornithischia: Thyreophora) on the basis of the presence of bone which is fused to the dorsal surface of the skull and has secondarily closed the upper temporal fenestrae. The only unequivocally nodosaurid material recovered from the Isle of Wight to date comes from Wealden facies, and has been referred to the genus Polacanthus ; it is considered highly probable that this new skull is referable to the same genus. Despite having undergone abrasion, through post-emergence water-rolling, the skull and cranial walls have proved to be relatively informative of the general anatomy of the braincase and the neural and vascular anatomy of this part of the head. The anatomy of the braincase of most ankylosaurs (with the notable exception of the juvenile specimens of the ankylosaurid Pinacosaurus ) is surprisingly poorly known, despite the relative abundance of cranial material in North American and Asian collections. The cranial neural and vascular anatomy is well shown in this specimen and enables the first detailed description of nodosaurid endocranial structures. The general form of the brain can be outlined from the structure of the endocast and the principal lobes can be identified; the majority of the cranial nerves have been identified, and a significant component of the associated vascular system is also visible. In most respects the endocast shows a neural anatomy which is common to that known in most dinosaurs. When compared to their nearest relatives, the ankylosaurid ankylosaurs ( Euoplocephalus ), the nodosaurid endocranial cast shows a more pronounced cerebral flexure, a forebrain which is broader and more expanded dorsally, and a more prominent cerebellum (although there is no evidence for a floccular lobe); there are minor differences in the arrangement of the cranial nerves, and the dorsal portions of the vascular system are better shown. Because of erosion, the olfactory lobes of this specimen of cf. Polacanthus are not preserved, and cannot be compared to those of ankylosaurid ankylosaurs; the latter are unusual in the strong separation of the lobes (reflected in the divergent olfactory stalks); this feature may be associated with the very complex passages within the nasal region of the skull, which are lacking in the nodosaurids described to date.
Article
Discussions of brain morphology and relative brain size in nonavian dinosaurs have been complicated by uncertainty in the extent to which the brain filled the endocranial cavity. Recently reported vascular imprints (valleculae) on the endocranial surfaces of the braincase suggest that nonavian maniraptoriform theropods had brains that tightly fit the endocranium. Similar impressions of the intracranial vascular system are reported here in two ornithischian clades, Hadrosauridae and Pachycephalosauridae. These structures are more widespread in dinosaurs than previously thought, and suggest that the brain closely fit the endocranium in some regions of the forebrain through hindbrain in several distantly related dinosaur groups.
Article
Brain and nasal cavity endocasts of four corythosaurian lambeosaurines (Dinosauria: Ornithischia) were investigated to test hypotheses of cranial crest function related to sensorineural systems. Endocasts were generated through computed tomography and three-dimensional rendering and visualization software. The sample comprises a range of ontogenetic stages from the taxa Lambeosaurus, Corythosaurus, and Hypacrosaurus. Results show that the morphology of brain endocasts differs little from that of hadrosaurines. The strikingly convoluted nasal vestibule of Hypacrosaurus altispinus, when interpreted in the context of lambeosaurine phylogeny, suggests selective pressure for nasal cavity function independent from changes in the external shape of the crest and associated visual display function. The plesiomorphically small olfactory bulbs and apparently small olfactory region of the nasal cavity argues against the hypothesis that increased olfactory acuity played a causal role in crest evolution. The elongate cochlea of the inner ear reveals that hearing in lambeosaurines emphasized low frequencies consistent with the hypothesized low-frequency calls made by the crests under the resonation model of crest function. The brain is relatively large in lambeosaurines compared with many other large dinosaurs, and the cerebrum is relatively larger than that of all non-hadrosaurian ornithischians and large theropods, but compares favorably with hadrosaurine hadrosaurids as well as some maniraptoran theropods. It is concluded that the large brains of lambeosaurines are consistent with the range of social behaviors inferred when the crest is interpreted as an intraspecific signaling structure.
Article
The paranasal air sinuses and nasal cavities were studied along with other cephalic spaces (brain cavity, paratympanic sinuses) in certain dinosaurs via CT scanning and 3D visualization to document the anatomy and examine the contribution of the sinuses to the morphological organization of the head as a whole. Two representatives each of two dinosaur clades are compared: the theropod saurischians Majungasaurus and Tyrannosaurus and the ankylosaurian ornithischians Panoplosaurus and Euoplocephalus. Their extant archosaurian outgroups, birds and crocodilians (exemplified by ostrich and alligator), display a diversity of paranasal sinuses, yet they share only a single homologous antorbital sinus, which in birds has an important subsidiary diverticulum, the suborbital sinus. Both of the theropods had a large antorbital sinus that pneumatized many of the facial and palatal bones as well as a birdlike suborbital sinus. Given that the suborbital sinus interleaves with jaw muscles, the paranasal sinuses of at least some theropods (including birds) were actively ventilated rather than being dead-air spaces. Although many ankylosaurians have been thought to have had extensive paranasal sinuses, most of the snout is instead (and surprisingly) often occupied by a highly convoluted airway. Digital segmentation, coupled with 3D visualization and analysis, allows the positions of the sinuses to be viewed in place within both the skull and the head and then measured volumetrically. These quantitative data allow the first reliable estimates of dinosaur head mass and an assessment of the potential savings in mass afforded by the sinuses.
  • F Knoll
  • D Schwarz-Wings
Knoll, F., Schwarz-Wings, D., 2009. Paleoneuroanatomy of Brachiosaurus. Ann. Paleontol. 95, 165-175.
Endo-cranium structure of some Mongolian ankylosaurs
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Kurzanov, S.M., Tumanova, T.A., 1978. Endo-cranium structure of some Mongolian ankylosaurs. Paleontol. Zh. 3, 90-96.
The braincases of Argentinean theropod dinosaurs: osteology and phylogenetic implications
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Paulina-Carabajal, A., 2009. The braincases of Argentinean theropod dinosaurs: osteology and phylogenetic implications. J. Vertebr. Paleontol. 30 (Abstracts: 162A).
Neuroanatomy of the primitive nodosaurid dinosaur Pawpawsaurus campbelli and paleobiological implications of some endocranial features
  • Paulina-Carabajal
Paulina-Carabajal, A., Lee, Y.-N., Jacobs, L.L., 2016a. Neuroanatomy of the primitive nodosaurid dinosaur Pawpawsaurus campbelli and paleobiological implications of some endocranial features. PLos One 11 (3), e0150845. http://dx.doi.org/10.1371/ journal.pone.0150845.
The armored dinosaurs of Mongolia. Transactions of the joint Soviet-Mongolian Paleontological
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