This study aimed to provide a comprehensive anatomical description of the skull of the Persian squirrel (Sciurus anomalus) and to compare these findings with computed tomography (CT) and radiographic features. In this study, four live adult male Persian squirrels were utilised for CT and radiographic imaging, and four dead adult male Persian squirrels were used for anatomical evaluations. The live subjects were anaesthetised to obtain standard diagnostic images. For anatomical preparation, the skin and musculature were meticulously removed. The skulls were then processed using boiling and maceration techniques to eliminate the remaining soft tissues. Hydrogen peroxide was employed for bleaching the bones. Finally, the prepared skulls were subjected to detailed morphological examination. The hypoglossal canal was observed to be double. Instead of a nuchal crest, a nuchal line was present. The jugular process was markedly small. A fossa was identified between the pterygoid bone and the pterygoid process of the basisphenoid bone. The pterygoid canal was located between the presphenoid and the palatine and pterygoid bones. The alar canal was absent. There was a distinct spinous foramen. The styloid process was absent. The cerebellar fossa of the petrous temporal bone was significantly enlarged. The zygomatic process of the temporal bone was relatively small. The zygomatic arch was markedly ventrally positioned. A thin zygomatic process of the maxillary bone was present. The incisive bone was highly developed. The nasal process of the incisive bone articulated with the frontal bone. The maxilla possessed a distinct facial tuberosity. The endoturbinates III and IV were large. The incisor teeth were in a close relationship with the nasal cavity. The interfrontal and interparietal sutures were not visible. The CT and radiographic images obtained in this research can serve as a diagnostic reference for the cranial anatomy of the Persian squirrel, facilitating the interpretation of pathological alterations in this species.

Robinow syndrome has characteristic craniofacial and dental features and can be caused by gain- or loss-of-function variants in Wnt family member 5A (WNT5A) non-canonical signaling. The craniofacial and dental manifestation of Robinow syndrome is heterogenous, as is the effect of altered Wnt5a in animal models. The relationship between Wnt5a and craniofacial and dental phenotypes is not fully understood. To investigate the role of Wnt5a in bone during craniofacial and dental development, we utilized a Wnt5a conditional loss-of-function (LOF: Wnt5a[fl/fl];Ctsk[cre]) and a Wnt5a conditional gain-of-function (GOF: Rosa26-LSL-Wnt5a;Ctsk[cre]) model to determine the effect of both LOF and GOF of Wnt5a in bone cells during craniofacial and dental development. Postnatal day 10 conditional LOF Wnt5a, GOF Wnt5a, and control skulls were scanned by micro-CT and assessed using traditional and geometric morphometrics. Mandibular bone apoptosis was further assessed by TUNEL staining. Conditional Wnt5a LOF resulted in midface hypoplasia, increased maxillary intermolar width, increased rostral basisphenoid width, and delayed molar eruption. Wnt5a LOF mandibles did not have altered BMD or bone microarchitecture unlike our previous study examining Wnt5a LOF femurs. In contrast, conditional Wnt5a GOF results in macrocephaly, shortened hard palate, increased zygomatic length, micrognathia, and mandibular process dysmorphology. The micrognathia and mandibular process dysmorphology in the Wnt5a GOF mice were not due to increased apoptosis. A partially penetrant snout deviation was present in both the Wnt5a LOF and GOF mice. Craniofacial and dental phenotype differed between mice with conditional GOF and LOF of Wnt5a, consistent with the craniofacial phenotype heterogeneity in WNT5A-associated Robinow syndrome. We detected tooth eruption delay, mandibular condyle dysmorphology, and facial asymmetry in mice with altered Wnt5a that have not been previously reported in patients with WNT5A-associated Robinow syndrome. Our data suggest precise regulation of Wnt5a is essential for proper craniofacial and dental development.

In non-human primates, the presphenoid-ethmoid synchondrosis (PSept) functions as a major growth center of the midline skull base, yet whether humans possess a developmental analogue remains unresolved. To clarify whether a human counterpart exists, we re-examined the basisphenoid-ethmoid (SPH-ETH) junction using sagittal histological sections from 20 human fetuses (11-39 weeks) preserved in the Akita University collection. At 15-16 weeks, chondrocytes in the anterior portion of the SPH-immediately anterior to the pituitary fossa-became slender or irregularly shaped with increased extracellular matrix, forming a distinct low-density zone (<8 cells per 0.1 mm[2]) compared with adjacent SPH cartilage (>15 cells per 0.1 mm[2]). In late-term fetuses (≥29 weeks), this zone expanded vertically to reach both the superior and inferior perichondria and appeared less basophilic, often containing fibrous or mesh-like structures. Notably, two late-term fetuses (35 and 39 weeks) displayed an additional anterior ossification center immediately in front of this low-density zone, creating a bipolar ossification pattern analogous to that of the PSept in non-human primates. In these specimens, parallel collagen bundles oriented supero-inferiorly were also observed across the interface. Taken together, these findings identify a reproducible, sparsely populated, fiber-containing cartilage region at the human SPH-ETH junction, frequently associated with an anterior ossification center. We propose that this region represents the human analogue of the PSept and that the "transient presphenoid" becomes incorporated into the definitive ethmoid during late fetal development.

A 2-month-old male suckling lamb presented with spontaneous early weaning, hyporexia, weight loss, swelling of the nostrils and upper lip, fever, lethargy, recumbency and death. Necropsy revealed enlargement and deformity of the nasal region, ulceration of the upper lip, a rostral oronasal fistula and extensive ulceration of the hard palate. Mid-sagittal sectioning of the head showed a necrotic, yellow-black, irregularly shaped, friable mass extending through the mucocutaneous region of the nostrils, hard palate and nasal septum. Additionally, yellow purulent exudate was observed in the sella turcica at the basisphenoid bone, from which Klebsiella sp was isolated. Histological examination demonstrated marked multifocal pyogranulomatous rhinitis associated with negatively stained hyphal profiles. The hyphae stained with Grocott's methenamine silver stain and immunolabelled with anti-Pythium insidiosum antibody. The pituitary region contained extensive liquefactive necrosis, a myriad of bacteria and fibrinosuppurative inflammation. Based on epidemiological, clinical, anatomopathological, immunohistochemical and microbiological findings, a diagnosis of rhinofacial pythiosis with secondary basilar empyema was established. Nasal lesions caused by P. insidiosum in sheep may serve as a portal for opportunistic bacterial infections and precipitate basilar empyema.

The medial pterygoid plate plays a critical role in mammalian craniofacial function during suckling and swallowing. The plate supports the tensor veli palatini (TVP) muscle, which stiffens the soft palate to create a posterior seal. Despite its functional importance, the developmental origins and structural integration of the medial pterygoid plate and associated pterygoid hamulus remain incompletely understood. In this study, we investigated the ontogeny and lineage of the medial pterygoid plate using wildtype and conditional knockout mice with immunofluorescence and lineage tracing. Analysis from embryonic day (E)14.5 to E17.5 confirmed that the medial pterygoid plate formed as a bipartite structure, which later fused to the basisphenoid. The dorsal region of the medial pterygoid plate ossified via Runx2-dependent intramembranous bone formation, while the ventral region formed as a secondary cartilage, undergoing Sox9-dependent chondrogenesis, followed by endochondral ossification. The pterygoid hamulus was evident at E14.5 as a condensation of Sox9-positive mesenchyme at the end of the medial pterygoid plate. Confirming the different modes of development, the ventral and dorsal parts of the medial pterygoid plate showed distinct timing and pattern of collagen remodelling, as shown by B-CHP. Lineage tracing with Wnt1Cre;tdTom and Mesp1Cre;tdTom mice demonstrated that the entire pterygoid process formed from neural crest-derived mesenchyme. In keeping with this, conditional loss of Runx2 in the neural crest lineage disrupted ossification of the dorsal part of the medial pterygoid plate, whereas conditional loss of Sox9 abolished chondrogenesis of the ventral part of the medial pterygoid plate and the pterygoid hamulus. Notably, TVP muscle fibres were able to maintain their orientation around the residual cartilage in conditional Wnt1creRunx2flfl mutants, while the TVP in conditional Wnt1creSox9flfl mutants formed a ball of cells that failed to extend towards the palatal region. The ventral portion of the medial pterygoid plate and hamulus is therefore required to guide early muscle pathfinding. These findings establish the medial pterygoid plate as a compound craniofacial element with distinct ossification modes and an important role interacting and directing neighbouring tissues.

Basilar invagination (BI) is a congenital malformation of the skull base, in which underdevelopment of the cranial base displaces the odontoid process cranially and posteriorly. Few studies have examined the role of sphenoid bone in BI, despite its central position occupying large portion of the skull base. The objective of this study is to compare the craniometric measurements centered on the sphenoid bone between the two types of BI, and normal controls. This is a cross-sectional study based on MRI and CT databases from authors practice, from 1985 to June 2024. The craniometrics of the sphenoid bone were measured in BI subtypes and controls. A total of 106 images were selected for this study, comprising 34 BI1 patients, 38 BI2 patients, and 34 control individuals. In the horizontal plane, the sphenoid crest-clivus distance in BI2 was significantly greater than BI1 and control group, with no significant difference between BI1 and control group. For all vertical measurements, such as basisphenoid length, BI2 values were significantly shorter compared to BI1 and control group, again with no significant difference between BI1 and control group. There were no significant differences among the groups in the sphenoid angle. Craniometric analysis focused on the sphenoid bone supports a clear distinction in BI2 patients, suggesting more extensive and pronounced cranial changes. In contrast, the changes in BI1 patients were not significantly different from those in normal subjects, indicating that these malformations are primarily associated with the underlying cranio-cervical segmentation defect.

The human sphenoid bone (SB), centrally located at the cranial base, is structurally and developmentally complex. It arises from multiple cartilaginous precursors and undergoes both endochondral and intramembranous ossification, forming essential elements such as the sella, orbital walls, and numerous foramina. This review integrates embryological, anatomical, and radiological findings to present a comprehensive view of SB development and variation. Embryological studies reveal a layered ossification sequence, with accessory centers in the presphenoid and basisphenoid that influence adult morphology and variants, such as the caroticoclinoid foramen. In adulthood, the SB consists of a central body, paired greater and lesser wings, and the pterygoid processes, which articulate with key craniofacial bones and transmit vital neurovascular structures. Notable variants include duplication or absence of foramina, ossification of ligaments such as the pterygoid and pterygospinous ligaments, and the formation of bony bridges among the clinoid processes. These variants may affect cranial nerve trajectories and surgical access, posing potential risks during neurosurgical, endoscopic, and dental interventions. Emissary structures such as the sphenoidal emissary foramen and the newly described sphenopterygoid canal underscore the region's vascular complexity. Additionally, variations in the optic and Vidian canals, as well as the superior orbital fissure, can also impact surgical approaches to the orbit, sinuses, and skull base. Understanding the full spectrum of sphenoid bone embryogenesis and morphology is essential for safe clinical practice and practical radiological imaging.

Morphological modifications are a potential mechanism for functional species and phylogenetic diversification. The sella turcica in mammals is a structure associated with the basisphenoid bone and serves as the receptacle for the pituitary gland; however, little is known about the morphological variation that may affect functionality in chiropterans. In this study, we provide morphological and morphometric evidence of differences between populations of Pteronotus mesoamericanus [the Gulf of Mexico] and P. mexicanus [the Pacific Coast] by describing variations in the dimensions of the dorsum sellae and the processus clinoideus caudalis of the sella turcica. We obtained 20 a priori designed measurements of the dorsum of the sella turcica from 243 skulls of both species from various locations in Mexico. The dorsum sellae were found at an average distance of 3.4 mm from the lower edge of the foramen magnum. The dorsum of the sella turcica has a truncated pyramidal shape, with the processus clinoideus caudalis located at the tip of the pyramid. Ten of the measurements obtained were found to be significant for both regions (the Pacific Coast and the Gulf of Mexico). We propose that these measurements be tested in future studies of populations from the Mormoopidae family in the Antilles, Central America, and South America for comparative purposes, and to help distinguish different lineages and functions.

The Shishugou Formation of the Middle to Late Jurassic in Xinjiang, China, has produced abundant tetrapod fossils including dinosaurs and tritylodontids. Bienotheroides is a genus of highly specialized tritylodontids, characterized by a short and wide snout, ventrally expanded zygomatic process, strongly reduced maxilla, short and flat basisphenoid, and maxillary teeth cusp formula 2-3-3. Here, we report a new tritylodontid, Bienotheroides wucaiensis sp. nov. from the lower Upper Jurassic level of the formation at Wucaiwan, Xinjiang, Northwest China, represented by a well-preserved cranium and associated postcranial skeleton. Micro-computed tomography and 3D reconstruction reveal the medial view of the cranial structure and the replacement upper incisors, providing new anatomical information of Bienotheroides. The absence of a septomaxilla in B. wucaiensis reveals the homoplastic evolution of this feature within tritylodontids, as it remains in basal mammaliaforms but is lost in later descendants.

Ornithopod dinosaurs appeared during the Middle Jurassic, but it was in the Lower Cretaceous they started their successful evolutionary history. Different phylogenies describing the evolutionary relationships of Ornithopoda are mostly based on cranial features, however there is a lack of well-preserved and complete skulls for the basal member of the clade, hampering our knowledge on the mode and tempo of these herbivorous dinosaurs. Here we describe YLSNHM 01942, a well-preserved skull of a juvenile neornithischian from the Liaoning Province of China. The specimen was scanned with a μCT scan, and all the elements were segmented and extrapolated for description. The specimen shows a ventral deformation due to the compression of the sediment, and a few rostral elements were artificially added. The specimen is attributed to the basal ornithopod Jeholosaurus shangyuanensis because of the presence of a large foramen in the quadratojugal, however it lacks the nodular ornamentation on the postorbital and jugal, herein interpreted as an ontogenetic feature. This, together with the disarticulation degree of the cranial elements, suggest YLSNHM 01942 represents a juvenile Jeholosaurus. The endosseous labyrinth is tentatively reconstructed, although the disarticulation of the neurocranial bones hampers its complete reconstruction. Thanks to the analysis of previously undescribed inner neurocranial bones (such as the prootics, the exoccipital/ophistotic, basioccipital, and basisphenoid), we improve the previous phylogenetical scoring for J. shangyuanensis, and perform a phylogenetical analysis adding the basal ornithopod Changmiania liaoningensis and the recently re-evaluated Ajkaceratops kozmai. The phylogenetical analysis reports a well-supported base of Ornithopoda, with C. liaoningensis as the most basal ornithopod, and a resolved topology for Nanosaurus agilis, Changchunsaurus parvus, Haya griva, Yandusaurus hongheensis and J. shangyuanensis.

Shrews are among the most speciose of mammalian clades, but their evolutionary history is poorly understood. Their fossil record is fragmentary and even the anatomy of living groups is not well documented. Here, we incorporate the oldest, most complete fossil shrew yet known into the first phylogenetic analysis of the group to include molecular, morphological and temporal data. Our study reveals previously unknown diversity among total- and crown-group soricids. This includes a novel element of the mammalian skeleton: a robust, needle-like sesamoid extending cranially from the second thoracic neural arch in Myosoricini, comparable in length to these species' humeri. Additionally, 'red-toothed' shrews have an unusually elongate basicranium, and 'white-toothed' shrews probably evolved from a common ancestor with dental pigmentation. The fossil Domnina and crown soricids have a double-jaw articulation and incomplete zygomatic arch, but unlike nearly all crown species, Domnina has open vomeronasal canals and a tympanic process of the basisphenoid. Domnina and other heterosoricids are phylogenetically outside crown Soricidae. The oldest, well-supported total-group soricoids are North American, not Asian, and Soricidae probably originated during the Palaeocene or early Eocene. The diverse mammalian genus Crocidura originated and began to diversify during the Miocene.