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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.
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... Similar to the case in UMNH VP18055 (Franzosa, 2004), the endocast of the pituitary fossa is not entirely represented ventrally though is likely larger than reconstructed, as indicated by the ventrally extensive pituitary fossa in the endocast of UMNH VP 18050 (Witmer & Ridgely, 2009). As noted in Majungasaurus, Tyrannosaurus, Alioramus, Viavenator, Giganotosaurus, and other specimens of Allosaurus Franzosa, 2004;Hopson, 1979;Paulina-Carabajal & Canale, 2010;Paulina-Carabajal & Filippi, 2017;Sampson & Witmer, 2007;Sanders & Smith, 2005;Witmer & Ridgely, 2009), there is a dorsally expanded peak, likely representative of a dural venous sinus, present on the dorsal surface of the endocast of the cerebral hemispheres (Figs. 1, 2). ...
... Preservation and resolution make it difficult to distinguish the opening for the vestibulocochlear nerve (CN VIII), which is expected ventral to the endosseous labyrinth and rostral to the passageway for CN IX and CN X. The glossopharyngeal and vagus nerves (CN IX and CN X) extend laterally in the jugular/vagal canal (metotic fissure) (Franzosa, 2004;Paulina-Carabajal & Canale, 2010;Sampson & Witmer, 2007;Witmer & Ridgely, 2009;Figs. 1-3). ...
... They resemble other known Allosaurus endocrania (Franzosa, 2004: UMNH VP 18055;Hopson, 1979;Osborn, 1912: AMNH 5753;Rogers, 1999: UMNH VP 7435;Witmer & Ridgely, 2009: UMNH VP 18050) and compare favorably with other basally branching theropods such as Ceratosaurus, Majungasaurus, and Viavenator (Paulina-Carabajal & Filippi, 2017;Sampson & Witmer, 2007;Sanders & Smith, 2005) supporting previously proposed endocranial conservatism among non-coelurosaurian theropods (Sampson & Witmer, 2007). General anatomical differences from more derived theropods include: a dorsoventrally oriented endocast, elongate olfactory tract, no representation of optic tecta, present but minimally extensive dorsal venous sinuses, and a straight caudal semicircular canal (as opposed to rostrocaudally oriented endocasts with short olfactory tracts, laterally placed optic tecta, extensive dorsal venous sinuses, and bowed caudal semicircular canals in coelurosaurs: Bever et al., 2013;Paulina-Carabajal & Canale, 2010;Sampson & Witmer, 2007;Witmer & Ridgely, 2009). ...
... The olfactory tract is approximately 30 mm long and 15 mm transversely wide, resulting in a relatively robust structure, as is a common feature among abelisaurids (e.g., Sampson and Witmer, 2007;Paulina-Carabajal and Succar, 2015;Paulina-Carabajal and Filippi, 2018, and references therein) and carcharodontosaurids (Larsson, 2001;Paulina-Carabajal and Canale, 2010;Paulina-Carabajal and Nieto, 2020). The olfactory bulbs are relatively large, oval, and markedly divergent from the midline, as in other abelisaurids (Fig. 4F). ...
... The general shape of the natural endocast from the Cerro Overo site resembles most non-maniraptoran theropods, being longer than wide and lacking observable anatomical definition from the optic lobes and the cerebellum. The Larsson, 2001;Sanders and Smith, 2005;Sampson and Witmer, 2007;Paulina-Carabajal and Canale, 2010;Paulina-Carabajal and Filippi, 2018). ...
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We present here a natural cranial endocast assigned to an abelisaurid theropod found in Cretaceous rocks of the outcropping Bajo de la Carpa Formation (Santonian) in Neuquén Province, Northern Patagonia, Argentina. The specimen was found in association with fragmentary braincase remains, which include an otic capsule and part of the skull roof. These fragments bear abelisaurid features that support the taxonomic assignment. The general shape of the endocast is similar to that in other abelisaurids, being anteroposteriorly elongated with long and robust olfactory tract and olfactory bulbs, rounded cerebral hemispheres, and pronounced and triangular dural peak. It is the second natural endocast described for a dinosaur in Argentina and the first for a theropod. The comparison with other Patagonian abelisaurids indicates the endocast belonged to a small to mid-sized specimen that highly resembles that of Viavenator and Llukalkan. However, the skull roof ornamentation is markedly different, and comments are made on certain features of the ornamentation of the frontal in the new specimen and other close relatives.
... This is the volume of the entire endocast, often including the region of the olfactory tract and bulbs as well as portions of the cranial spinal cord, among other structures. For our analysis, we exclusively relied on the so-called "brain" endocast volume instead (BrEV; Figure 3), which was popularized by Jerison (1973) and has been commonly used since then (e.g., Hurlburt, 1996;Hurlburt et al., 2013;Larsson et al., 2000;Paulina-Carabajal & Canale, 2010). It excludes the spinal cord portion of the endocast caudal to cranial nerve XII, the volume of nerve trunks from infillings of respective foramina and blood vessel casts, the labyrinth of the inner ear, the infundibulum, the pituitary fossa, and especially the volume of the olfactory bulbs and tracts (Figure 4). ...
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Recent years have seen increasing scientific interest in whether neuron counts can act as correlates of diverse biological phenomena. Lately, Herculano‐Houzel (2023) argued that fossil endocasts and comparative neurological data from extant sauropsids allow to reconstruct telencephalic neuron counts in Mesozoic dinosaurs and pterosaurs, which might act as proxies for behaviors and life history traits in these animals. According to this analysis, large theropods such as Tyrannosaurus rex were long‐lived, exceptionally intelligent animals equipped with “macaque‐ or baboon‐like cognition”, whereas sauropods and most ornithischian dinosaurs would have displayed significantly smaller brains and an ectothermic physiology. Besides challenging established views on Mesozoic dinosaur biology, these claims raise questions on whether neuron count estimates could benefit research on fossil animals in general. Here, we address these findings by revisiting Herculano‐Houzel's (2023) work, identifying several crucial shortcomings regarding analysis and interpretation. We present revised estimates of encephalization and telencephalic neuron counts in dinosaurs, which we derive from phylogenetically informed modeling and an amended dataset of endocranial measurements. For large‐bodied theropods in particular, we recover significantly lower neuron counts than previously proposed. Furthermore, we review the suitability of neurological variables such as neuron numbers and relative brain size to predict cognitive complexity, metabolic rate and life history traits in dinosaurs, coming to the conclusion that they are flawed proxies for these biological phenomena. Instead of relying on such neurological estimates when reconstructing Mesozoic dinosaur biology, we argue that integrative studies are needed to approach this complex subject.
... The brain of extinct animals is rarely preserved, but aspects of its shape can sometimes be inferred using models of the brain cavity (Balanoff et al., 2016;Dozo et al., 2022). Such models (known as endocasts) can occur naturally (e.g., Bisconti et al., 2021;Triviño et al., 2018), be constructed artificially with wax, latex, or similar materials (e.g., Dempster, 1935;Holloway, 2018;Paulina-Carabajal & Canale, 2010), or be generated digitally following nondestructive computed tomography (CT) and postprocessing of aligned slice data (e.g., Allemand et al., 2017Allemand et al., , 2023Balanoff et al., 2016;Perez-Martinez & Leal, 2021). ...
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Understanding the origins of the vertebrate brain is fundamental for uncovering evolutionary patterns in neuroanatomy. Regarding extinct species, the anatomy of the brain and other soft tissues housed in endocranial spaces can be approximated by casts of these cavities (endocasts). The neuroanatomical knowledge of Rhynchocephalia, a reptilian clade exceptionally diverse in the early Mesozoic, is restricted to the brain of its only living relative, Sphenodon punctatus, and unknown for fossil species. Here, we describe the endocast and the reptilian encephalization quotient (REQ) of the Triassic rhynchocephalian Clevosaurus brasiliensis and compare it with an ontogenetic series of S. punctatus. To better understand the informative potential of endocasts in Rhynchocephalia, we also examine the brain-endocast relationship in S. punctatus. We found that the brain occupies 30% of its cavity, but the latter recovers the general shape and length of the brain. The REQ of C. brasiliensis (0.27) is much lower than S. punctatus (0.84-1.16), with the tuatara being close to the mean for non-avian reptiles. The endocast of S. punctatus is dorsoventrally flexed and becomes more elongated throughout ontogeny. The endocast of C. brasiliensis is mostly unflexed and tubular, possibly representing a more plesiomorphic anatomy in relation to S. punctatus. Given the small size of C. brasiliensis, the main differences may result from allometric and heterochronic phenomena, consistent with suggestions that S. punctatus shows peramorphic anatomy compared to Mesozoic rhynchocephalians. Our results highlight a previously undocumented anatomical diversity among rhynchocephalians and provide a framework for future neuroanatomical comparisons among lepidosaurs.
... Basal neotheropods and most non-coelurosaur theropods have in general terms anteroposteriorly long and narrow cranial endocasts (in dorsal view the lateral expansion of the cerebral hemisphere does not overpass the lateral semicircular (Franzosa and Rowe 2005), Giganotosaurus (Paulina-Carabajal and Canale 2010) and Sinraptor (Paulina-Carabajal and Currie 2012). Not to scale canal of the inner), which is a conservative trait shared with other basal saurischians. ...
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.
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Recent years have seen increasing scientific interest in whether neuron counts can act as correlates of diverse biological phenomena. Lately, Herculano-Houzel (2023) argued that fossil endocasts and comparative neurological data from extant sauropsids allow to reconstruct telencephalic neuron counts in Mesozoic dinosaurs and pterosaurs, which might act as proxies for behaviors and life history traits in these animals. According to this analysis, large theropods such as Tyrannosaurus rex were long-lived, exceptionally intelligent animals equipped with 'macaque- or baboon-like cognition' whereas sauropods as well as most ornithischian dinosaurs would have displayed significantly smaller brains and an ectothermic physiology. Besides challenging established views on Mesozoic dinosaur biology, these claims raise questions on whether neuron count estimates could benefit research on fossil animals in general. Here, we address these findings by revisiting Herculano-Houzel's (2023) work, identifying several crucial shortcomings regarding analysis and interpretation. We present revised estimates of encephalization and telencephalic neuron counts in dinosaurs, which we derive from phylogenetically informed modeling and an amended dataset of endocranial measurements. For large-bodied theropods in particular, we recover significantly lower neuron counts than previously proposed. Furthermore, we review the suitability of neurological variables such as neuron numbers and relative brain size to predict cognitive complexity, metabolic rate and life history traits in dinosaurs, coming to the conclusion that they are flawed proxies of these biological phenomena. Instead of relying on such neurological estimates when reconstructing Mesozoic dinosaur biology, we argue that integrative studies are needed to approach this complex subject.
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The digital reconstruction of neurocranial endocasts has elucidated the gross brain structure and potential ecological attributes of many fossil taxa, including Irritator, a spinosaurine spinosaurid from the "mid" Cretaceous (Aptian) of Brazil. With unexceptional hearing capabilities, this taxon was inferred to integrate rapid and controlled pitch-down movements of the head that perhaps aided in the predation of small and agile prey such as fish. However, the neuroanatomy of baryonychine spinosaurids remains to be described, and potentially informs on the condition of early spinosaurids. Using micro-computed tomographic scanning (μCT), we reconstruct the braincase endocasts of Baryonyx walkeri and Ceratosuchops inferodios from the Wealden Supergroup (Lower Cretaceous) of England. We show that the gross endocranial morphology is similar to other non-maniraptoriform theropods, and corroborates previous observations of overall endocranial conservatism amongst more basal theropods. Several differences of unknown taxonomic utility are noted between the pair. Baryonychine neurosensory capabilities include low-frequency hearing and unexceptional olfaction, whilst the differing morphology of the floccular lobe tentatively suggests less developed gaze stabilisation mechanisms relative to spinosaurines. Given the morphological similarities observed with other basal tetanurans, baryonychines likely possessed comparable behavioural sophistication, suggesting that the transition from terrestrial hypercarnivorous ancestors to semi-aquatic "generalists" during the evolution of Spinosauridae did not require substantial modification of the brain and sensory systems.
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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.