Skeletal morphology is determined by a combination of genetic background and phenotypic plasticity induced by mechanical loading across the lifespan (e.g., exercise), among other factors. Changes in limb morphology associated with locomotor activity experienced throughout individual ontogeny and in species over evolutionary time can provide insight into the adaptation of vertebrate locomotor systems. Here, a mouse line artificially selected for increased voluntary wheel-running distance is used to explore the effects of selective breeding on the genetic "baseline" morphology of the hind limb skeleton and to describe its plastic response to chronic exercise, including potential genotype by environment interactions. This experimental design additionally allowed for testing two hypotheses: (1) that bone plasticity itself is a trait that can evolve in direction and magnitude, and (2) that bone plasticity can influence the trajectory of selection for locomotor phenotypes. Using a combination of 3D shape analyses, we find that 82 generations of selective breeding result in substantial changes in the morphology of the hind limb skeleton, as well as subtle changes in the skeletal response to exercise that support the evolvability of bone plasticity (i.e., skeletal plasticity differs based on genetic background). We additionally find that the evolved bone shape of selected mice does not resemble the plastic exercise response of control-line animals. These results provide further evidence of genetic variations among populations in the plastic bone response to mechanical loading and inform our understanding of the plastic and evolutionary lability of the skeletal system in response to locomotor demands.
To demonstrate the prenatal morphology of the palatine aponeurosis (AP) and establish how the tendon of the tensor veli palatini (TVP) muscle meets the aponeurosis, we examined serial histological sections of 25 heads from human fetuses at approximately 9-16 weeks of gestational age (GA). At 9 weeks GA, the initial AP was identified as mesenchymal condensation that extended anteriorly to attach to the palatine bone. The TVP muscle extended inferiorly and curved along the greater palatine nerve; however, the TVP tendon does not reach the AP. At 10 weeks GA, the AP had developed as a tendinous origin of the levator veli palatini and palatopharyngeus muscles and connected the muscles to the palatine bone. The TVP provided a fan-like tendinous end and issued a few fibers to the AP. At 11-12 weeks GA, as the pterygoid grows inferiorly and the soft palate grows posteriorly, the hamulus becomes an attachment site for the TVP tendon, thus establishing a pulley. Simultaneously, the TVP tendon became continuous with the AP. The AP was initially composed of longitudinal collagenous fibers; however, transverse fibers rapidly increased after the TVP reached the AP. The AP and TVP seemed to develop independently in the initial phase immediately after secondary palatal fusion and met later. Guidance of the TVP tendon by the greater palatine nerve was analogous to that reported for the developing obturator internal tendon along the sciatic nerve.
In two-dimensional culture, endothelial cells grow as a monolayer on a flat surface, as a monolayer monoculture or as co-culture. This type of culture has the disadvantage that it lacks resemblance to the physiological conditions of an organism and the absence of a complex biological microenvironment. Moreover, studies on in vitro two-dimensional monolayer cell cultures are not capable of mimicking the nutrient and oxygen gradient. Two-dimensional assays are sufficient to induce endothelial cell cord formation, but they cannot reproduce the necessary cues for lumen formation. Three-dimensional assays have as their endpoint the formation of capillary-like cords or tubes by endothelial cells cultured either on the surface of (planar models) or within extracellular matrix. More recent applications include endothelial cell spheroids, embryoid bodies assay, and organoids.
Navicular syndrome (NS) is a chronic, degenerative condition of the equine thoracic limb that compromises the distal sesamoid bone (DSB) and associated structures responsible for stabilization and load absorption during locomotion. Although historically attributed to vascular alterations, its etiology is now recognized as biomechanical, characterized by chronic overload of the deep digital flexor tendon. Conventional diagnostic techniques-radiography, scintigraphy, and ultrasonography-lack the sensitivity and precision required to detect early microarchitectural alterations. This study aimed to evaluate changes in the trabecular microarchitecture of the DSB in horses with and without NS using micro-computed tomography (micro-CT) and to explore its diagnostic potential. Samples from eight horses (NS group, n = 4; Not affected group (control), n = 4) were analyzed. Micro-CT images were processed to obtain parameters such as bone volume, relative density, trabecular thickness and separation, porosity, and connectivity. Group comparisons were performed using nonparametric tests and Pearson correlation analyses to explore internal structural relationships. Correlations between groups were then compared using Fisher's Z test. Horses with NS exhibited lower bone volume, trabecular density, thickness, and connectivity, alongside increased trabecular separation, porosity, and anisotropy compared to controls. In healthy horses, strong positive correlations between volume and density, and inverse relationships with trabecular fragmentation, indicated an elevated, well-connected architecture. By contrast, affected horses displayed deteriorated microarchitecture with compensatory trabecular consolidation, reduced trabecular numbers, and a more cylindrical structure-signifying pathological adaptation. Two correlations differed significantly between groups, underscoring disease-induced microstructural reorganization. Micro-CT effectively identified navicular syndrome-specific microarchitectural changes not detectable with conventional methods, yielding quantifiable metrics (thickness, separation, and porosity) that may serve as early diagnostic and monitoring biomarkers. These findings justify broader studies with larger sample sizes and longitudinal designs to validate clinical applicability.
Phorusrhacidae were apex predators that primarily dominated South America ecosystems for at least 40 million years with their imposing size and predatory lifestyle-yet some aspects of their biology remain poorly understood. Osteohistology is a tool for understanding growth dynamics and biomechanical adaptations. Despite their ecological significance, histological analyses of these birds were non-existent until the recent publication of a sampled metatarsus. Here, we present the first osteohistological data of a phorusrhacid femur together with other hindlimb elements representing two taxa, Andrewsornis abbotti and Physornis fortis, from the late Oligocene of Argentina. Ground-section microscopy reveals highly vascularized fibrolamellar bone tissue, indicating rapid, sustained growth with lines of arrested growth appearing only in the outer circumferential layer. Extensive secondary remodeling, particularly at muscle attachment sites, highlights high mechanical stress, consistent with active cursorial locomotion. Body mass estimates (60-89 kg for Andrewsornis abbotti) and high relative cortical thickness in both specimens (bone compactness = 0.55-0.78) provide additional data for comparative studies. Our findings confirm the uninterrupted growth strategy of phorusrhacids, consistent with other large-bodied flightless neognaths but in contrast to most giant flightless palaeognath birds.
In this study, the anal glands of 10 adult Anatolian ground squirrels (Spermophilus xanthophrymnus) were examined through dissection, scanning electron microscopy (SEM), and light microscopy. The anal glands consist of three independent complexes positioned ventrolaterally to the anus. These glandular complexes were connected with the anal canal, the rectum, and with each other through muscular and connective tissue layers coursing in multiple directions. Each anal gland complex consisted of a glandular component and a sac-like structure. The sac structures of the anal gland complexes, which can evert, were visualized for the first time in this study using SEM. At the basal regions of the anal sacs, two distinct types of glandular clusters were identified. Type I apocrine glands, characterized by short excretory ducts, were located adjacent to the sac base, whereas Type II holocrine glands, with longer tubular ducts, were situated more distally. The study identified the presence of numerous interconnected sinusoidal vascular structures in both the glandular region of the anal complex and in the inner portions of the muscle bundles surrounding the anal complexes. These sinusoidal capillaries, previously unreported in the anal glands, likely represent erectile structures that engorge with blood and generate pressure to facilitate anal complex function.
The morphological structure of the tongue, which plays a fundamental role in the processes of receiving, selecting, recognizing and swallowing food, varies among species depending on the environment and diet of the creature. This study aimed to describe the morphology of the tongue of the Crimean barbel (Barbus tauricus) for the first time. Eight adult Barbus tauricus (all females, 1-2 years old, 8.5-9.3 cm total length, omni-insectivorous bottom feeder) tongues used for consumption were examined using macroanatomical, light, and scanning electron microscopy (SEM). In Barbus tauricus, the tongue was triangular in shape, widening from tip to root, and consisted of three parts: apex, corpus and radix linguae. No macroscopic papillae were observed on the tongue surface. In histological examinations, microscopic papillae were not observed in the tongue, which is composed of a mucosa, submucosa, and an osteocartilaginous supporting layer, whereas the presence of Type I, Type II, and Type III taste buds and epidermal club cells (ECCs) was detected. Scanning electron microscopy (SEM) analyses demonstrated the surface location of taste pores and taste buds. In conclusion, this study presents, for the first time, the morphological structure of the Barbus tauricus tongue in detail, demonstrating its food processing, taste, and morphological features.
Regional variations in the cortical bone microarchitecture of an adult human maxilla were previously linked to local differences in occlusal stress. However, maxillary microarchitectural patterns during permanent teeth eruption have not been investigated. Thus, our pilot study aimed to analyze patterns of buccal and palatal maxillary cortical microarchitectural changes in subadults using high-resolution 3D methodology (micro-CT). Dry subadult maxillary bone samples harvested from the region of the first permanent molar were divided into four groups: immature maxillary bones with a partially erupted first permanent molar without occlusal contact (group I, n = 5), maxillary bones with a fully erupted first permanent molar with occlusal contact with the opposing mandibular permanent molar and a partially erupted second permanent molar (group II, n = 5), maxillary bones having fully erupted first and second permanent molars with occlusal contacts (group III, n = 5), and maxillary bones with completed third permanent molar eruption and developed occlusal contacts (group IV, n = 5). Our data revealed a specific pattern of declining trend in total and open cortical porosity, coupled with an increasing trend in cortical thickness and pore separation in the maxillary bone during permanent teeth eruption. The intensity and complexity of functional loads (occlusal forces and direct contact with the tongue) may induce specific patterns of cortical maxillary bone microarchitectural changes in subadults. Considering its potential clinical relevance for orthodontic treatment and occlusal development, future studies (including more detailed micro-scale bone quality assessments) are necessary to fully understand maxillary bone alterations during permanent teeth eruption.
The supracranial crests of lambeosaurine hadrosaurids have long been a focus of study due primarily to their extreme morphology. The external anatomy of lambeosaurine crests is understood to be highly variable between species, but variation in their internal anatomy is less well understood. The poor understanding of taxonomic variation in internal anatomy is due in large part to data limitations, where comparisons were historically made using fragmentary specimens, or more recently using CT imaging of primarily immature specimens. Here, we provide a detailed comparison of the internal anatomy of mature individuals of the lambeosaurines Corythosaurus casuarius, Corythosaurus intermedius, and Lambeosaurus lambei, and contrast their morphology with previously described juvenile congeners and mature Hypacrosaurus altispinus. The lateral diverticula of Corythosaurus spp. and L. lambei are large and lobate, with short anterior projections and well-developed posterior projections, lacking the elongated anterior expansions to the diverticula that are unique to H. altispinus. The s-loop of the nasal vestibule is highly developed in L. lambei, forming exaggerated loops anterior to the orbit. The s-loops of Corythosaurus spp. and L. lambei curve from lateral to medial within the premaxilla, differing from the direction of curvature of the s-loops in H. altispinus that curve from medial to lateral. Very few differences occur between C. casuarius and C. intermedius, suggesting that there is minimal interspecific variation between these congeneric species. Our results demonstrate that lambeosaurine nasal passages are highly variable between genera, supporting strong internal differences in crest morphology, even in closely related genera within the same tribe.
The Upper Cretaceous São José do Rio Preto Formation (Bauru Group, southeastern Brazil) has yielded a fragmentary but taxonomically diverse record of titanosaur sauropods, although elements from cervical series remain scarce. Here, we describe a nearly complete sauropod axis from the Vila Ventura Paleontological Area, representing an uncommon occurrence within this unit and the Bauru Group as a whole. The Vila Ventura axis exhibits a broad axial intercentrum with paired ventral fossae, an elongated, goblet-shaped axial pleurocentrum that is longer than high, and a tall neural arch. Microcomputed tomography imaging reveals extensive camellate-type internal pneumaticity, including radial and circumferential camellae in the pleurocentrum with incipient development of internal bony plates—traits that are previously found in highly nested titanosaurs, such as saltasaurines. Comparative osteological analysis, however, indicates closer affinities with colossosaurians (e.g., Bonitasaura , Futalognkosaurus , Pitekunsaurus ), particularly in centrum proportions and laminar configuration, including an enlarged odontoid, a V-shaped ventral median keel with ventrolateral excavations in the pleurocentrum, a stout prespinal lamina terminating in an anterior spinal projection, and well-developed pneumatopores in the spinodiapophyseal fossae. Additionally, the specimen exhibits unique features, such as a stranded and laterally expanded spinoprezygapophyseal lamina and a transversely broad anterior spinal projection. An evaluation of axis morphology highlights the underrepresentation of phylogenetic characters from this element in current datasets, despite its potential diagnostic value for assessing lower-level relationships within Titanosauria. This discovery increases the diversity of Brazilian titanosaur records and emphasizes the importance of axial elements in understanding sauropod functional morphology and phylogeny.
Proteidae comprise two extant and several extinct genera of paedomorphic salamanders. The extinct proteids are diagnosed based on the vertebral morphology, with only a few isolated skull bones known to date. New cranial material of Mioproteus wezei from the Late Pliocene of Northern Caucasus (Russia), includes articulated skull fragments, numerous isolated bones, and elements of the hyobranchial apparatus. This cranial material, so far the most complete for any fossil proteid, allowed reconstruction of the entire skull of M. wezei. The skull is heavily ossified with a wide orbital region, characterizing a typically aquatic, paedomorphic animal with functional eyes. It shows greater similarity to that of the black olm, Proteus anguinus parkelj, than to the white olm, P. anguinus anguis, supporting the plesiomorphic status of the former. The results provide first insights into skull evolution within the Mioproteus-Proteus lineage, indicating a gradual decrease in orbit diameter, narrowing and elongation of the rostral region and increase in tooth count.
The Aliança Formation (Jatobá Basin) represents lacustrine deposits formed in oxygenated waters that hosted a diverse fauna, including Hybodontiform sharks. Within this group, the Family Lonchidiidae comprises 11 valid genera, with Parvodus previously reported in Brazilian deposits from the Brejo Santo Formation (Araripe Basin, Late Jurassic) and the Aliança Formation (Jatobá Basin, Late Jurassic). Here, we describe a new species of Parvodus based on isolated teeth from the Aliança Formation. A taxonomic reassessment of the genus is also presented, integrating its stratigraphic and geographic distribution. The new species provides novel insights into the evolutionary history of Lonchidiidae, with implications for the paleobiogeography of the group and the paleoenvironmental interpretation of the Aliança Formation. Importantly, this record expands the known distribution of Parvodus into the Upper Jurassic of South America.
The capability for sustained running has convergently evolved multiple times in mammals, and involves myriad anatomical, physiological, and behavioral adaptations. The ribcage plays a critical role in both respiration and locomotion but its adaptations to running are largely unexplored. Robustly testing adaptation in wild populations is challenging, so we use artificial selection for voluntary wheel-running behavior (i.e., High Runner or HR mice) to directly test form-function relationships associated with sustained running. We compared ribcage configuration and shape of HR (males: 52, females: 47) to control (males: 48, females: 48) mice using rib counts and 3D Geometric Morphometrics. Two of four HR lines had an additional rib and increased variation in the proportion of true to false ribs, suggesting that ribcage patterning has been impacted by selection. This variability among lines suggests that selection for wheel running has resulted in adaptations that are expressed variably among the selected lines, resulting in "multiple solutions" to selection. Total ribcage shape did not vary significantly between HR and Control mice. Instead, the effect of selection varied along the ribcage, with significant effects in the caudal ribs. Further, the caudal ribcage of HR mice showed increased disparity, within-rib, and among-rib integration compared to controls. The strong response of caudal ribs indicates a modular pattern of adaptation, with cranial ribs possibly constrained by their role in ventilation. This study demonstrates that adaptation in the mammalian ribcage is likely shaped by a complex interplay of selection and craniocaudal integration and may result in variation at multiple anatomical levels (count, shape, modularity).
The Early Pleistocene fossil site of Schernfeld, a karst fissure filled with an ossiferous breccia, is well known due to the abundant fossil remains, mainly of micromammals and carnivores. Since the discovery, the taxonomic status of the Schernfeld mustelids has caused controversy and, consequently, various authors have listed different species. Until recently, none of these species has been the subject of adequate studies. A detailed revision of the Schernfeld mustelids material was made through comparative morphology based on mustelids from other European Early and early Middle Pleistocene sites. It reveals the presence of five mustelids: Gulo gulo schlosseri , Martes vetus , Meles meles , Mustela palerminea , and Mustela praenivalis . Their remains are characterized by ancestral features, especially in M. vetus , M. palerminea , and M. praenivalis . Due to the morphology of mustelids and the taxonomical composition of the Schernfeld fauna, the biochronological age of the entire assemblage was re‐evaluated and assessed for ca. 1.9–1.7 mya.
Nasal turbinals are key osseous structures for air conditioning and olfaction in mammals, with their morphology reflecting both ecological adaptations and evolutionary history. This study evaluates how climatic gradients and locomotor strategy (subterranean or surface dwelling species) influence turbinal complexity in caviomorph rodents. Using microCT imaging, we quantified respiratory (RZ) and olfactory (OZ) turbinal morphology across eight caviomorph rodents and two outgroups from xeric, mesic, and generalist habitats, including subterranean and surface-dwelling species. Our results revealed that xeric-adapted subterranean species exhibited significantly expanded RZ surface areas and greater structural complexity, consistent with enhanced water retention demands in arid environments. While surface-dwelling species showed larger absolute OZ areas compared to subterranean taxa, this difference became non-significant after accounting for body size, suggesting olfactory structures are less influenced by locomotor strategy than by allometric or phylogenetic factors. Respiratory turbinals appeared more variable across habitats, whereas olfactory turbinals showed comparatively conserved morphology among ecological groups. This pattern could reflect differing evolutionary pressures acting on thermoregulatory versus sensory systems in rodents. The observed trade-off between respiratory efficiency and olfactory capacity suggests how multiple selective forces may shape anatomical specialization in response to environmental challenges. These findings provide new insights into functional constraints governing nasal evolution, proposing a framework for interpreting ecological adaptations in caviomorphs. Our study illustrates how integrating quantitative morphometrics with ecological data can elucidate complex structure-function relationships in mammalian anatomy.
Since Raymond Dart's first attempt to identify the lunate sulcus ("Affenspalte," simian sulcus) in a fossil hominin endocast-that of the Taung child (Australopithecus africanus)-paleoneurologists have debated this structure, which in the brains of monkeys and apes roughly coincides with the rostral boundary of the primary visual cortex. The classic view has been that the evolutionary expansion of the parietooccipital cortex "pushed" the lunate sulcus toward the back of the brain. However, there has been little consensus about how and when this might have happened during hominin evolution, as it has proven difficult to establish phylogenetic homology of potential lunate sulci in living humans with the lunate sulcus of great apes. Here we review the comparative neuroanatomical evidence and propose the hypothesis that the lunate sulcus underwent de-opercularization, that is, the structures buried within the sulcus expanded and became part of the external cortical surface. During this process, the lunate sulcus became shallow, fragmented, and eventually obliterated. Specifically, rather than migrating toward the occipital pole during brain evolution, the lunate sulcus was a hotspot for the evolutionary expansion of annectant gyri and their eventual emergence on the parietooccipital cortical surface. We test the de-opercularization hypothesis with an analysis of the parietooccipital endocranial region of early Homo from Dmanisi, Georgia, and conclude that in these fossils the lunate sulcus may have been in the evolutionary process of fragmentation as their brains became larger and their occipital lobes more caudally projected compared to earlier hominins.
The braincase and inner ear of the largest species of legless anguine lizards, Pseudopus apodus, are described in detail based on high-resolution x-ray microcomputed tomography. Here, the ontogeny of its braincase is briefly described. The detailed anatomy of the individual braincase bones of P. apodus is presented and compared with those of the modern anguine species Anguis fragilis and species of Ophisaurus, Dopasia, and Hyalosaurus. Because only the extant species of Anguinae are studied and discussed here, the generic names of modern taxa defined genetically-Ophisaurus (North America), Dopasia (Southeast Asia), and Hyalosaurus (North Africa)-are used here. The shape of the supraoccipital in juveniles was similar for all species found in all three geographic territories. During growth, the shape of the supraoccipital changes significantly in Pseudopus, Dopasia, and Ophisaurus, and its shape is very similar to that in adults of the anguine taxon Ophisauriscus quadrupes from the Middle Eocene of Germany. Instead, the shape of the supraoccipital in the adults of Hyalosaurus and Anguis is very similar to that in the juveniles of Pseudopus, Dopasia, and Ophisaurus. This suggests that paedomorphosis probably played a role in the shape formation of the supraoccipital in Hyalosaurus and Anguis. The morphological and proportional changes in several other braincase structures during ontogeny are also described.
Mysticetes, or baleen whales, have an air sac on the ventral surface of the larynx known as the "laryngeal sac." The primary hypothesis regarding this structure's function is that it is involved in sound production. However, several other functions have been proposed, including air recycling, air storage, and even buoyancy control. In this study, we analyzed ontogenetic development and sexual dimorphism of the laryngeal sac with an aim of elucidating the function of this organ. The larynx of 61 (male: n = 40, female: n = 21) common minke whales Balaenoptera acutorostrata, collected from off the Japanese coast were used for present study. We isolated the larynx, situated between the hyoid bone and the trachea, during the flensing process. Seven linear measurements were taken using calipers, and the weight was obtained using a digital weight scale. Allometric equation and proportions to total body length or weight were used to compare laryngeal morphological differences between sexes and maturity. Measurements of laryngeal sac size were significantly larger in sexually mature males. Furthermore, examination of two male individuals of approximately the same body length but different maturities showed the sexually mature male had a larger laryngeal sac, compared to sexually immature male. The thickness of the laryngeal sac's muscle wall and the volume of the sac's lumen may be related to testes development (sexually mature whales have heavier testes). Only the width of the hyoid bone (basihyal and paired thyrohyals) was proportionally constant within all measurement sites, regardless of sex or maturity. We propose that baleen whales utilize their well muscularly developed laryngeal sac in a manner analogous to the human tongue, actively modifying its shape and volume to influence vocal production. Specifically, this structure may function as a resonance filter that creates a formant structure and contributes to the modification of phonemes generated by the U-folds of the larynx. Furthermore, the ability to produce complex vocalizations through this mechanism may have led to the enlargement of the laryngeal sac in males via sexual selection, where it also serves as a signal of their reproductive status.
