Anatomical Record最新文献

Bats use sensory systems such as echolocation and vision to track prey, avoid obstacles, and inform their trajectories. In addition, though less studied, bats also have extensive networks of sensory hairs across their wings. Preliminary evidence has shown that these hairs are involved in flow sensing and relay sensory information during flight. However, little is known about the functional role of sensory hairs in flight control or potential intraspecific variation in hair distribution. Through a morphological study of specimens of Seba's short-tailed bat (Carollia perspicillata), we find relatively low intraspecific variability in sensory hair distribution and consistent regional density patterns. We compare flight kinematics from the same species in wind tunnel experiments before and after removal of sensory hairs from the ventral wings. Depilation of sensory hairs resulted in changes to kinematic variables at the whole- and within-wingbeat levels, such as wingbeat frequency, chordwise wing folding, and wing extension. Taken together, these findings indicate that sensory hairs relay sensory information and function to alter fine-scale wing shape and positioning, thereby impacting flight kinematics and dynamics.

Arboreal environments require specialized adaptations in sensory and neuroendocrine systems for species survival. This study examines the neuroanatomical and histological adaptations of the Gambian Sun squirrel (Heliosciurus gambianus), focusing on structures critical for visual processing, sensorimotor integration, and neuroendocrine regulation in arboreal habitats. Paraffin-embedded eye and brain samples from three male Gambian Sun squirrels captured at the University of Ibadan, Nigeria, were analyzed using standard hematoxylin and eosin and Masson trichrome staining techniques. The cornea displayed a unique undulating cellular arrangement, which may likely enhance visual acuity and protection in densely forested environments. Neuroanatomical examination revealed distinctive features in the median eminence, pineal gland, subcommissural organ, dorsal lateral geniculate nucleus, rostral colliculus, and optic nerve, which support sensorimotor coordination and neuroendocrine functions. These specialized traits enable environmental navigation and survival, emphasizing their role in arboreal adaptation. The findings provide a foundation for comparative studies with other rodents and contribute to understanding evolutionary strategies in tree-dwelling mammals. Additionally, this research offers potential applications in conservation efforts and neurobiological studies, including insights into human neurological functions.

Dental microwear texture analysis (DMTA) has become a well-established method for dietary inference and reconstruction in both extant and extinct mammals and other tetrapods. As the volume of available data continues to grow, researchers could benefit from combining published data from various studies to perform meta-analyses. However, the different optical profilometers used to capture three-dimensional surface scans for DMTA are known to produce variation even when measuring the same surface. In this study, we compare DMTA data of 36 guinea pigs that received different diets in a controlled feeding experiment, measured using five different instruments: three confocal-scanning microscopes and two confocal laser-scanning microscopes. Each dataset is filtered according to in-house standards of the respective laboratories. Our findings reveal inter-microscope differences in the majority of the 40 DMTA parameters analyzed. Height and volume parameters were the most consistent across instruments, whereas density and complexity parameters exhibited pronounced differences. We thus propose DMTA parameters that were stable regardless of microscope. Despite these inter-microscope variations, the overall results from all instruments consistently show the same dietary differentiation among the guinea pig feeding groups, supporting the suitability of DMTA for reproducible and objective dietary inferences. To enhance data exchange, inter-lab comparability, and collaboration in the future, we propose a roadmap that includes the introduction of device-specific correction equations.

The Muñoa's Pampas cat (Leopardus munoai) is a small wild cat endemic to the Uruguayan Savana ecoregion, occurring in southernmost Brazil, Uruguay, and northeastern Argentina. However, knowledge regarding the basic characteristics of this threatened species, including its cranial anatomy, is limited. This study presents the first detailed osteological description of the L. munoai skull and compares it, based on literature, with other species, particularly within the genus Leopardus. Additionally, we examined some internal cranial structures via computed tomography. Fourteen L. munoai specimens from Brazilian collections were analyzed. Key features observed include a minimally developed sagittal crest, the presence of the second upper premolar (P2) in most specimens, rostral zygomatic arches with slight lateral expansions, reduced mastoid processes, and an inverted "V"-shaped medial notch on the caudal margin of the palatine suture. Internally, trapezoidal frontal sinuses located at the postorbital process level were noted without extension into this region. A cavity was also identified at the rostral skull end bordered by the nasal and tubular structures extending laterally through the parietals. This study provides novel data on L. munoai, offering a detailed description of the external and internal structures and adding morphometric measurements for pampas cats from Rio Grande do Sul. Furthermore, it supports future osteological, morphometric, and taxonomic studies within Felidae.

Dietary morphology diversified extensively in Carnivoraformes (living Carnivora and their stem relatives) during the Cenozoic (the last 66 million years) as they evolved to capture, handle, and process new animal and plant diets. We used 3D geometric morphometrics, mechanical advantage, and finite element analysis to test the evolutionary relationship between mandibular form and biomechanical function as subclades independently made the transition from mesocarnivorous diets (50%-70% animal matter) to hypercarnivorous (>70% animal matter) and osteophagous ones (substantial bone processing). We found that mandible shape is correlated with these dietary categories, with mechanical advantage estimates, and with stress and strain caused by the interaction between canine loading and the position of the temporalis relative to the carnassial. The separation of dietary categories is likely related to differences in mandible shape regarding condyle shape, muscle attachment shape, carnassial length, and the length and curvature of the horizontal ramus. This is in turn related to mechanical advantage estimates as the most strongly associated are related to the lengthening of the temporalis lever arm and the shortening of the mandible and the bite point lever arm. The stress and strain differences are likely related to the variation in the distal (or rostral) part of the mandible associated with prey of different sizes (mesocarnivores usually take prey smaller than their own body size, whereas hypercarnivores take prey equal to or larger than themselves). Mesocarnivorous taxa, on average, have higher stress and strain on the mandible than the other diet groups.

Dental microwear texture analysis (DMTA) has emerged as a valuable method for investigating the feeding ecology of vertebrates. Over the past decade, three-dimensional topographic data from microscopic regions of tooth surfaces have been collected, and surface texture parameters have been published for both extant and fossil species. However, different types of measurement instruments and surface processing used by respective laboratories conducting DMTA have limited the potential data comparison. In this study, we propose correction formulae for the DMTA data produced by different instruments to facilitate intercomparison. We used six confocal instruments from five laboratories to scan standard tooth samples with strictly defined scan areas. We found significant differences in DMTA parameter values among the different machines, despite scanning the exact same spots. The degree of discrepancy varied considerably, with instruments from the same manufacturer and similar models showing less variation. Some parameters exhibited high correlations between instruments, enabling the development of regression equations for correction formulae. Using these correction formulae, we adjusted published DMTA data and conducted a meta-analysis of extant herbivores to examine the effects of internal and external abrasives. Our findings indicate overall positive effects of internal and external abrasives on DMTA, with varying responses to the abrasives between ruminant and non-ruminant herbivores. The meta-analysis supports the hypothesis that ruminants effectively "wash ingesta" in their rumens, mitigating the impact of external abrasives and reducing overall dental wear.

Opossums (Didelphidae) are American marsupials traditionally known for their generalized morphology and generalist feeding habits. They include a diversity of similar items in their diets, but the proportion of types of items consumed varies between taxa. Thus, feeding ecology shows varying degrees of omnivory or food preference that cannot be distinguished into strict dietary categories. With few exceptions, the anatomical and functional relationship between the masticatory muscles and variation in food resources used in opossums is unknown. Here we provide comparative descriptions of the jaw adductor muscle anatomy and architecture of nine Didelphidae genera. The muscles were dissected, weighed, and chemically digested for separation and measurement of the muscle fascicles. We estimated the potential physiological cross-sectional area (pPCSA) of the muscles and used 2D lever arm mechanics to calculate the potential bite force on the canine and first molar. We tested the allometric relationships of muscle variables and bite forces and the correlation of bite forces with diet and diet mechanical challenge (relative frequency of hard items). The adductor muscles were represented by the m. temporalis and m. masseter, with two layers (superficial and deep) each, and m. pterygoideus medialis across the sample. The m. zygomaticomandibularis was also identified in most genera, except for Didelphis and Lutreolina. Muscle anatomy is conserved but varies in the extent of the attachment areas, in part due to differences in skull morphology. The anatomical diversification and relationships between muscles corresponded to a generalized pattern in most genera, which proved to be efficient for adding different items to the diet. The mass, average fascicle length, and pPCSA of the adductor muscles scaled isometrically with size. Bite forces on the canine and first molar also scaled isometrically and were not correlated with diet or diet mechanical challenge. Therefore, the variation in quantitative myological data and bite force was consistent with size, and the increase in bite force supports dietary diversification associated with increased size in opossums.

With the development of dental microwear texture analysis (DMTA), there has been an increasing application of DMTA for dietary estimation in extant and fossil reptiles, including dinosaurs. While numerous feeding experiments exist for herbivorous mammals, knowledge remains limited for carnivorous reptiles. This study aimed to qualitatively and quantitatively evaluate the formation of dental microwear through repeated puncture of different types of food using isolated teeth from the American alligator (Alligator mississippiensis) in an in-vitro experiment. Eleven isolated teeth were mounted on a force gauge, and each tooth sample was repeatedly punctured 200 times into sardines (tooth sample size, N = 6) and crayfish (N = 5). The tooth surfaces were scanned using a confocal laser microscope before, during, and after the experiment to track changes in the tooth surface. Additionally, the maximum force during puncture was measured with the force gauge. Examination of surface roughness parameters before and after the experiment revealed a significant increase at the tooth apexes for both types of food. Furthermore, the trials with crayfish increased microwear depth and density more than the sardine trials. There was a significant positive correlation between the total force experienced by each tooth and the changes in surface roughness parameters in the crayfish trials, indicating that greater force results in more dental wear. The findings of this study are significant as they complement existing feeding experiments and comparative studies of wild species with different diets, and they demonstrate the effectiveness of experimental approaches in understanding the formation mechanisms of dental microwear.

The transition from milk to solid food requires drastic changes in the morphology of the feeding apparatus and its performance. As durophagous mammals, southern sea otters exhibit significant ontogenetic changes in cranial and mandibular morphology to presumably enable them to feed on a variety of hard-shelled invertebrate prey. Juvenile sea otters begin feeding independently by 6-8 months of age, but how quickly they reach sufficient maturity in biting performance remains unknown. Here, I found that the theoretical bite force of southern sea otters does not reach full maturation until during the adult stage at 3.6 and 5.0 years of age in females and males, respectively. The slow maturation of biting performance can be directly attributed to the slow growth and development of the cranium and the primary jaw adductor muscle (i.e., the temporalis) and may ultimately impact the survival of newly weaned juveniles by limiting their ability to process certain hard-shelled prey. Alternative foraging behaviors such as tool use, however, may mitigate the disadvantages of delayed maturation of biting performance. In analyses of sexual dimorphism, I found that female otters reached bite force maturation earlier, whereas male otters exhibit initial rapid growth in bite force-to quickly reach sufficient biting performance needed to process prey early in life-followed by a slower growth phase toward bite force maturation that coincides with sexual maturity. This biphasic growth in bite force suggests that male-to-male competition for resources and mates exhibits strong selection in the growth and development of skull form and function in male otters. Overall, this study demonstrates how the analysis of anatomical data can provide insight on the foraging ecologies and life histories of sea otters across ontogeny.

Psittaciformes, the order encompassing parrots and their relatives, are highly diverse and generally known for having a strong beaks used for multiple behaviors. The muscles related to the masticatory apparatus should reflect this functional complexity; however, few studies have described the cranial myology across the order. Through original dissections, we describe and compare the masticatory musculoskeleton of 27 species-the most taxonomically diverse sample of psittaciformes to date. As in previous studies, we found osteological differences in the configuration of the suborbital arch, zygomatic process, and temporal fossa, and while most muscles are relatively similar across the order, there are notable exceptions found in the morphology of the m. pseudomasseter, m. adductor mandibulae externus, pars rostralis, and a venter externus portion of the m. pterygoideus ventralis, pars lateralis. Our findings reinforce the amazing anatomical diversity found within this group-data that can be incorporated into future studies of the biomechanics and diversification of this order. Further analysis should focus on (a) filling in more of the remarkable number of species across the order, especially uncommon and functionally interesting taxa unavailable in the present study, (b) examining dietary specialization to understand whether dietary adaptive signals are encoded within this anatomy, and (c) advancing to anatomical studies with other techniques such as DiceCT to visualize the relationship and biomechanics of these muscles in 3D space and be able to evaluate specimens relatively non-destructively, a priority for hard-to-dissect (e.g., small) taxa and (e.g., rare) specimens that collections wish to more fully preserve.