Fig 5 - available via license: CC BY
Content may be subject to copyright.
![Schematic Nothronychus mckinleyi braincase in A, lateral and B, posterior views. Red represents skull originating from neural crest, blue, cephalic mesoderm origin, and green cephalic mesoderm origin. Modified from Smith [10] with permission from Journal of Vertebrate Paleontology. Scale bar equals approximately 2 cm. https://doi.org/10.1371/journal.pone.0198155.g005](publication/326724960/figure/fig3/AS:654629767499779@1533087307898/Schematic-Nothronychus-mckinleyi-braincase-in-A-lateral-and-B-posterior-views-Red.png)
Schematic Nothronychus mckinleyi braincase in A, lateral and B, posterior views. Red represents skull originating from neural crest, blue, cephalic mesoderm origin, and green cephalic mesoderm origin. Modified from Smith [10] with permission from Journal of Vertebrate Paleontology. Scale bar equals approximately 2 cm. https://doi.org/10.1371/journal.pone.0198155.g005
Source publication
The soft-tissue reconstruction and associated osteology of the North American therizinosaurian Nothronychus mckinleyi is updated. The cranial nerve topology is revised, bringing it more in line with coelurosaurs. The trunk of the trigeminal nerve is very short, with an incompletely intracranial trigeminal ganglion, an ophthalmic branch diverging an...
Citations
... A deep pneumatic chamber ventral to maxillomandibular foramen extends posteriorly near the independent facial foramen in Ornithomimus (Tahara & Larsson, 2011). The pneumatic recess is located further ventrally, immediately ventral to the hyomandibular ramus in therizinosaurids (Smith et al., 2018). In birds, the prootic recess is so extensively elaborated and covered laterally that its accurate position is poorly described (e.g., Witmer, 1990). ...
Crocodylia has an extensive epithelial pneumatic space in the middle ear, paratympanic sinus system. Although fossil and extant crocodylian paratympanic sinus systems have been studied recently using the computed tomography (CT) and three‐dimensional (3D) reconstruction data, due to the soft tissue nature of the pneumatic system and presence of its surrounding soft tissue structures, some boundaries, and definitions of each extension remain ambiguous. We describe the comprehensive paratympanic sinus system in posthatched alligator using soft tissue enhanced CT data with 3D reconstructions. The data are compared to the available data to discuss the ontogenetic pattern in alligator. We introduce further divided entities of the pneumatic system based on their associated bony and soft tissue structures and epithelial membrane and clarify the pneumatic terminologies. We then re‐visit the potential homology of the paratympanic sinus in Archosauria. Epithelial boundaries of the ventral portion of the pneumatic system from the histological data suggest that the dual origin of the basioccipital diverticulum derived from the tympanic sinus and basicranial diverticulum medially. The presence of the epithelial boundary and pneumatic changes in ontogeny suggests that the middle ear may function differently in developmental stages. Lastly, a morphogenetic tree is constructed to help future work of comparative developmental studies of the paratympanic sinus system between crocodiles and birds.
... The presence of subotic recess is known in ornithomimosaurs (Osmólska et al., 1972:fig. 5A;Makovicky and Norell, 1998;Tahara and Larsson, 2011), therizinosaurs (Smith et al., 2011(Smith et al., , 2018 and some troodontids (Currie and Zhao, 1993b;Norell et al., 2000Norell et al., , 2009Yin et al., 2018) and also reported in an alvarezsaur Xiyunykus (Xu et al., 2018) and an oviraptorosaur Conchoraptor (Kundrát and J a n á č e k , 2 0 0 7 ) . 12B). ...
... 13C, E). Overall, the inner ear morphology is notably similar to that well-developed cerebellar floccular lobes are shared with Erlikosaurus (Lautenschlager et al., 2012), Nothronychus (Smith et al., 2018) and Falcarius (Smith, 2014), and can be considered a unique feature of Therizinosauria shared with Fukuivenator. ...
A bizarre coelurosaurian theropod Fukuivenator paradoxus is known only from the holotype specimen preserving majority of the skeleton from the Kitadani Dinosaur Quarry of the Lower Cretaceous Kitadani Formation, Tetori Group, Fukui, Japan. With aids of computed tomography techniques, a re-examination of the holotype specimen reveals additional features of Fukuivenator which was unobservable in the original description, such as the presence of parietals and a quadrate, and the fusion of the posteriormost caudal vertebrae. The thorough description in this study results in the emendation of diagnosis including the retraction of the large promaxillary fenestra subequal in size to maxillary fenestra, and the addition of the large maxillary fenestra expanded well dorsally above the suprantral strut. Expansion of morphological information elaborates the phylogenetic dataset, resulting in locating Fukuivenator as an unambiguous member of Maniraptora at the basalmost position of Therizinosauria. This phylogenetic position of Fukuivenator is supported by several therizinosaurian synapomorphies such as the subotic recess on the braincase, 11 cervical vertebrae some of which having two pneumatic foramina, and distal articular condyles on the anterior surface of the humerus. Among numerous diagnostic features, eight characters shared with some non-maniraptoran coelurosaurs and five shared with different clades within Maniraptora, highlighting the notably mosaic condition of Fukuivenator proposed in the original description. The combination of characters for herbivorous and carnivorous diets suggests the omnivory of Fukuivenator, projecting the dietary shift in the earliest evolutionary stage of Therizinosauria. Also, the large olfactory ratio revealed by the revised brain endocast highlights the unusually high olfactory acuity further developed than the plesiomorphic condition, implying that the acute sense of smell might be a characteristic of therizinosaurian theropods.
... Beyond tyrannosauroids, Ornithomimus is the phylogenetically closest plesiomorphic taxon published with extensive internal reconstruction (Tahara and Larsson 2011). The endocranial anatomy of multiple oviraptorosaurs and therizinosauroids have been recently reconstructed (Kundrát 2007;Kundrát and Janá cek 2007;Balanoff et al. 2009Balanoff et al. , 2014Balanoff et al. , 2018Smith et al. 2011Smith et al. , 2018Lautenschlager et al. 2012;Balanoff and Norell 2012;Smith 2014), but they represent highly modified coelurosaur conditions. Without this recent progress, tyrannosaurids would appear to have markedly greater variation in braincase morphology than other theropod lineages (Bever et al. 2011) by the virtue of simply having more taxa with reconstructed braincases within tyrannosaurids than in each of other comparative clades. ...
For sheer complexity, braincases are generally considered anatomically conservative. However, recent research on the braincases of tyrannosaurids have revealed extensive morphological variations. This line of inquiry has its root in Dale Russell’s review of tyrannosaurids in which he established Daspletosaurus torosus — a large tyrannosaurine from the Campanian of southern Alberta. In the wake of systematic revisions to tyrannosaurines previously assigned to Daspletosaurus, one potentially distinct species remains undescribed. This paper describes and compares a braincase referable to this species with that of the holotype for Daspletosaurus torosus using computerized-tomography-based reconstructions. The two braincases have numerous differences externally and internally. The specimen of Daspletosaurus sp. has a bottlenecked olfactory tract, short and vertical lagena, and a developed ascending column of the anterior tympanic recess. The holotype of Daspletosaurus torosus has many unusual traits, including an anteriorly positioned trochlear root, elongate common carotid canal, distinct chamber of the basisphenoid recess, asymmetry in the internal basipterygoid aperture, and laterally reduced but medially expanded subcondylar recess. This comparison also identified characters that potentially unite the two species of Daspletosaurus, including deep midbrain flexures in the endocasts. However, many character variations in the braincases are known in other tyrannosaurids to correlate with body size and maturity, or represent individual variations. Therefore, taxonomic and phylogenetic signals can be isolated from background variations in a more comprehensive approach by using additional specimens. New information on the two braincases of Daspletosaurus is consistent with the emerging view of tyrannosaurid braincases as highly variable, ontogenetically dynamic character complexes.
... In dorsal view, the lateral margin of the cerebral hemisphere does not overpass the lateral semicircular canal of the inner ear, resembling the condition in non-coelurosaurian neotheropods (e.g., Sinosaurus triassicus: Xing et al., 2014;Majungasaurus crenatissimus: Sampson and Witmer, 2007; Acrocanthosaurus atokensis : Franzosa and Rowe, 2005). By contrast, the cerebral hemispheres are more laterally expanded, surpassing the level of the lateral semicircular canal of the inner ear in several coelurosaurs (e.g., Alioramus altai: Bever et al., 2013;Citipati osmolskae: Franzosa, 2004; but see Nothronychus mckinleyi: Smith et al., 2018). In lateral view, the shape of the cranial endocast is sigmoidal, with the angles between the forebrain, midbrain, and hindbrain similar to those observed in other basal theropods (e.g., Witmer and Ridgely, 2009), in which the forebrain and hindbrain are approximately horizontal and parallel to each other, with the midbrain obliquely angled between them. ...
Zupaysaurus rougieri is an early neotheropod from the middle Norian Los Colorados Formation of northwestern Argentina represented by an almost complete skull and several postcranial bones. Most of its braincase morphology has remained obscured by other skull bones and sediment. Additional mechanical preparation and X-ray computed tomography on the single known specimen of Zupaysaurus has allowed a detailed description of the braincase, the cranial endocast, and the inner ear of this Triassic dinosaur. Basal theropod braincases are poorly sampled and there is little information on this region, and even poorer knowledge on the brain and inner ear anatomy of Triassic forms. The virtual reconstruction of the braincase of Zupaysaurus shows anteroventrally oriented, finger-like basipterygoid processes, an elongate and horizontally projected cultriform process, and well-developed preotic pendant, basisphenoid recess, and subsellar recess. The endocranial morphology is partially reconstructed, showing an anteroposteriorly short but dorsoventrally tall cranial endocast, with well-marked demarcations between the forebrain, midbrain, and hindbrain. The inner ear preserves the three semicircular canals, but not the lagena. The posterior semicircular canal is proportionally large when compared with that of other theropods. The new information presented here on Zupaysaurus rougieri contributes to the knowledge of the neuroanatomy of basal theropods and sheds light on the evolutionary patterns of the
braincase morphology in nonavian Theropoda.
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.
Nothronychus was a large, derived therizinosaur from the Upper Cretaceous of Utah and New Mexico. The genus is known from elements that have been referred to single individuals. Therizinosaurs were unusual maniraptoran theropods close to the origin of birds. The axial skeleton is extensively pneumatized, but CT scans reveal an apneumatic synsacrum. Inferred air sacs invade the basicranium, the presacral vertebrae, and the proximal caudal vertebrae, but bypassed the sacrum resulting in a caudosacral hiatus similar to some sauropods and reflecting the development of multiple diverticula from the abdominal air sac. The vertebral pneumatic chambers are described here and compared with those observed in the theropod Allosaurus and the recent avian Dinornis. The vertebrae of Nothronychus are intermediate between those two theropods. It is inferred to have possessed avian‐like abdominal air sacs. This theropod would have had unidirectional lungs, as in birds, but this character cannot be related to endothermy.
Dinosaurs are notable for their extensive skeletal pneumaticity, a feature that may have helped facilitate the development of various ‘extreme’ body plans in this group. Despite its relevance to understanding the evolution of the avian body plan, this feature has only been described in detail for a few non-avian dinosaurs, and cranial pneumaticity outside the braincase remains poorly documented. I describe facial pneumatic features in members of the Dromaeosauridae, a clade of hypercarnivorous dinosaurs closely allied to birds. Variation in the pneumaticity of the nasals and jugals, the position and shape of the pneumatic fenestrae of the maxilla and the border of the antorbital fossa shows that facial pneumaticity differed substantially among closely related dromaeosaurids and other bird-like dinosaurs. Ancestral state reconstructions of facial pneumaticity in coelurosaurs suggest a complex evolutionary history for these features. Surprisingly, the general trend along the path towards birds was the loss or reduction of superficial pneumatic features on the snout and cheek. Some facial pneumatic features seem to have evolved secondarily in some derived bird-like forms. The results show superficial facial pneumaticity did not increase in coelurosaurs and emphasize the complexity of the evolution of pneumatization in the lineage leading to birds.
