Anatomical Record-Advances in Integrative Anatomy and Evolutionary Biology最新文献

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.

Saber-teeth are a striking example of convergent evolution in vertebrate predators, having evolved multiple times in mammals and their early ancestors. While there is broad consensus that saber-toothed taxa employed a distinct biting strategy compared to conical-toothed carnivores, like the lion, the precise mechanics and variability of this bite remain debated. In this review, we integrate current knowledge of pointed tooth mechanics and puncture mechanics to explore predatory function, focusing on the canine shear-bite hypothesis. We quantify the key morphological characteristics of saber-teeth–elongation, slenderness, curvature, sharpness, and cross-sectional shape in a sample of saber-and conical-toothed taxa. Using the morphological diversity observed and insights from experimental studies, we examine the capacity of saber-teeth to perform the canine shear-bite, contrasting them with the clamp-and-hold bite of extant carnivores with conical canines. Our findings indicate that the morphological characteristics associated with extreme saber-tooth forms, as seen in Smilodon, suggest the prioritization of deeper puncture and slicing actions and limiting of lateral loads, favorable for a canine shear-bite. However, we also demonstrate that these morphological characteristics exist on a continuum accross saber-toothed taxa suggesting greater functional diversity beyond the shear-bite versus clamp-and-hold bite dichotomy. While this study refines our understanding of saber-tooth function, key gaps remain, particularly regarding the role of cross-sectional shape, curvature, and serrations in puncture mechanics.

Most carnivorans and all modern felids have ossified bacula; however, no machairodont baculum has ever been identified. This is true despite the many fairly complete skeletons found around the world of several sabertooth taxa. Although the bacula of modern felids are much smaller than those of canoids (even the least weasel's baculum is longer than the tiger's barely 1 cm baculum!), among the 166,000 bones found at the Rancho La Brea Tar Pits (RLB) of perhaps 3000 Smilodon fatalis individuals there are other small and delicate bones—including clavicles, hyoids, and tiny ossicles—from that taxon. Furthermore, the matrix from that site found around the large fossils is painstakingly sorted under microscopes, resulting in the identification of thousands of microfossils. Despite these concerted efforts, including the posting of images of modern felid bacula near the RLB fossil lab to help form potential search parameters for those sorting the matrix, the search continues for this elusive bone. It is possible that RLB's unique “pit wear”—abrasion related to the notable seismic activity in Southern California—has pulverized this bone that may have been less dense than the other small bones that are found at the site. Parsimoniously, machairodonts should have bacula, but our failure to identify a sabertooth baculum in the richest fossil carnivoran locality in the world naggingly forces us to consider whether, at some point, we have to accept this stubborn absence of evidence as legitimate evidence of absence.

Facial morphology is a defining aspect of Homo sapiens that distinguishes our species from fossil ancestors and plays a central role in estimating age, sex, and ancestry in both past and present populations. Understanding how the face develops during postnatal ontogeny is essential for interpreting adult facial variation. Periosteal bone modeling (i.e., patterns of resorption and formation) provides direct evidence of bone growth activity underlying morphological variation. This study quantifies periosteal bone modeling in a cross-sectional ontogenetic sample of individuals ranging from birth to adulthood from three geographical populations: Western Europe, Greenland, and South Africa. Epoxy replicas were analyzed using digital microscopy to quantify bone resorption, and digital maps of the bone modeling patterns were created for each facial region—brow ridge, zygomatic, maxilla, and mandible—and projected onto three-dimensional surface models. In parallel, geometric morphometric and multivariate statistical analyses were used to evaluate ontogenetic patterns. Results highlight a consistent sequence of resorption and deposition during human ontogeny and a strong pattern of covariation between bone modeling and shape for most facial regions. The face is largely resorptive from early ontogeny, with deposition increasing with age; the maxilla is significantly more resorptive than other facial regions. Greater resorption in the midface corresponds to significant facial growth and development in early ontogeny, and a developmental shift around adolescence marks the transition from primarily downward to more forward-oriented growth. Overall, the combined approach underscores the developmental coordination of the face and suggests that the human facial growth pattern reflects the need to maintain a non-projecting face from birth on.

Hibernation induces significant molecular and cellular adaptations in the retina to maintain function under reduced metabolic conditions. This study aimed to investigate the expression of neuronal, synaptic, and glial markers in the retina of Spermophilus xanthoprymnus during pre-hibernation and hibernation periods using immunohistochemical staining. Synaptophysin expression, restricted to the inner plexiform layer (IPL) and outer plexiform layer (OPL) during pre-hibernation, significantly increased in both layers during hibernation, with additional expression observed in the outer nuclear layer. NeuN immunoreactivity remained unchanged in the ganglion cell layer (GCL) but increased notably in the INL during hibernation. Calbindin-D28k expression, prominent in the INL and plexiform layers during pre-hibernation, decreased markedly in hibernation. In contrast, parvalbumin expression increased across all retinal layers, except the photoreceptor layer, during hibernation. Glial fibrillary acidic protein (GFAP) expression, observed in the NFL and GCL, was significantly reduced during hibernation. Iba-1 immunoreactivity, sparse in the IPL and OPL during pre-hibernation, showed a pronounced increase in the IPL, OPL, and INL during hibernation periods. In conclusion, the expression of synaptophysin, NeuN, calbindin-D28k, parvalbumin, GFAP, and Iba-1 was investigated for the first time in the retina of the Anatolian ground squirrel during pre-hibernation and hibernation. This study reveals region-specific shifts in retinal marker expression during pre-hibernation and hibernation, providing a basis for future research into visual system adaptations and retinal plasticity under metabolic suppression.

Fasting is a practice in the aquaculture industry that aims to reduce feed costs. This practice can affect the gastrointestinal system of fish. The intestine plays a pivotal role in the nutrition and overall health of fishes. The present study sought to evaluate the effects of fasting and refeeding on body weight, intestine somatic index (ISI), intestinal histometry (area, height, and thickness of the villi), and goblet cell volume (acidic and neutral mucins) of pacu (Piaractus mesopotamicus). To this end, the effects of 10, 20, and 30 days of fasting and 15 and 50 days of refeeding were evaluated. The results demonstrated that fasting resulted in notable alterations in all assessed parameters. The body weight and ISI of fasted pacu were significantly reduced compared to those of the control group. The levels of acidic and neutral mucins were elevated after 10 days of fasting, whereas the area and height of the villi decreased after 20 days of fasting. Following the 15-day refeeding period, pacu exhibited an increase in body weight and ISI. However, a 50-day refeeding period was required to observe an increase in villus height, which differed from that in the control group. After 50 days of refeeding, the fish exhibited intestinal conditions that were restored to the levels observed in the control specimens. Feed deprivation alters intestinal biometry and histomorphology. However, the effects of fasting were attenuated and even improved with subsequent refeeding. These results suggest that a fasting/refeeding management strategy is appropriate for pacu farming.

The temporal bone petrosa is connected to the occipital bone at two sites: one junction with the basilar part (medial junction) and another with the lateral part (lateral junction). Using histological specimens from 45 human fetuses (approximately 7–39 weeks of gestational age or GA), we aimed to describe possible changes in histology and topographical anatomy during processes toward the ossified union. In the early term, the junctions were characterized by dense mesh-like fibers that likely corresponded to the thickened basal laminae of the composite cartilage cells. Notably, the mesh-like structure disappeared until 12 weeks of GA and, irrespective of whether a remnant fibrous tissue was present or absent, cartilage tissues became continuous between the occipital and petrosal sides. Until 25 weeks of GA, the inferolateral marginal part of the spheno-occipital junction cartilage extended to the medial junction and attached to the ossified petrosa. The medial junction sometimes contained an irregularly shaped cartilage mass or a woven bone with bone trabeculae, but it was usually attached directly to the bony petrosa without any interruption by calcified cells. In contrast, at the late-term lateral junction, a cartilage mass was sandwiched by bipolar ossification centers on the temporal and occipital bone sides. As the endochondral ossification advances, bones at and around the lateral junction seemed to grow and cover the expanding mastoid air cells. However, the fetal medial junction might grow, in accordance with midline growth at the spheno-occipital junction cartilage. Alternatively, the bony union of these two junctions might establish postnatally.

Autonomic nerves are crucial in cardiac function and pathology. However, data on the distribution of cholinergic and noradrenergic nerves in normal and pathologic human hearts is lacking. Nonfailing donor hearts were pressure-perfusion fixed, imaged, and dissected. Left ventricular cardiomyopathy samples were also obtained. Fixed frozen sections were immunostained for nerves, and adjacent tissue underwent clearing for 3D visualization. Cholinergic and noradrenergic nerves were evenly abundant in both atria, except the sinoatrial node, where vesicular acetylcholine transporter (VAChT) nerves were dominant. Noradrenergic consistently outnumbered cholinergic nerves in right (RV) and left ventricular (LV) regions. Noradrenergic innervation of LV regions varied between donors. Cholinergic innervation was higher in RV compared to LV samples, which generally had reduced VAChT nerves. Marked neural remodeling occurred in three cardiomyopathy cases. Tyrosine hydroxylase (TH) nerve density was increased in the right atrial appendage, and all nerves showed a trend to decrease in the left atrial appendage. Cholinergic innervation was reduced in the LV, and TH innervation was heterogeneous. Noradrenergic nerves were present in granulation tissue but absent in regions of dense scar. Some border zone regions had reduced TH innervation but no hyperinnervation. Dual innervation of most atrial regions supports balanced regulation of atrial function. Higher cholinergic input to the sinoatrial node favors vagal dominance in heart rate regulation. Innervation patterns support a significant role of noradrenergic input to the ventricle, especially on the left. Both atrial and ventricular nerves remodel in cardiomyopathy, providing a foundation for asymmetric neural input and dysregulation of cardiac electromechanical function.

Silesaurids (Archosauria: Dinosauriformes) are found in Middle to Upper Triassic deposits across Pangea, but few stratigraphic sections record the evolution of the group in one geographic area over millions of years. Here, we describe silesaurid remains from the oldest of the Upper Triassic stratigraphic sequence from the base of the Dockum Group, from the type locality of the Otischalkian faunachronozone. Isolated limb bones diagnostic of silesaurids include humeri, femora, and tibiae of a seemingly unique Silesaurus-like taxon from the same locality (Otis Chalk Quarry 3). The femora consist of four specimens of different lengths that sample the variation of character states associated with ontogeny, also sampled previously in both silesaurids (e.g., Asilisaurus kongwe and Silesaurus opolensis) and within neotheropods within Dinosauria (e.g., Coelophysis bauri). Our observations of the variation in the silesaurid sample further reinforce the interpretation of high variation of morphological features common in dinosauriforms. Furthermore, we show that overpreparation of bone surfaces has hidden some of this variation in previous interpretations. The tibia growth series shows that the fibular crest of the tibia develops during ontogeny, yet another phylogenetically informative character for dinosaurs and their kin that is at least ontogenetically variable in silesaurids. The presence of silesaurids at the base of the Dockum Group (late Carnian or early Norian) conclusively shows that the group was present near the onset of deposition of Upper Triassic rocks and survived for millions of years in the same geographic area at low latitudes throughout the Late Triassic.