Anatomical Record最新文献

The pygmy sperm whale (Kogia breviceps) possesses an exocrine gland associated with its false gill slit pigmentation pattern. The cervical gill slit gland is a compound tubuloalveolar gland that produces a holocrine secretion and displays maturational changes in size and secretory histology. While the morphology of the cervical gill slit gland has been described in detail, to date, the chemical composition of its secretion remains uncharacterized. This study used histochemical staining techniques and quantitative lipid analysis to identify and characterize the constituents expressed in the secretory cells and secretion of the cervical gill slit gland. Results demonstrate that the secretion, like those of terrestrial artiodactyls that function in chemical communication, includes a complex mixture of carbohydrates, proteins, and lipids. Differences in staining intensity across germinal and secretory epithelial layers demonstrate differential expression, or maturation, of mucins and proteins. Additionally, a highly unusual and primary constituent of the secretion is uric acid. Uric acid was identified within the secretion using histochemical stains and polarized light imaging, and chemically verified using scanning electron microscopy with energy dispersive spectrometry. While uric acid is not a common constituent of mammalian exocrine glands, urate-based compounds are abundant in the secretions of marine organisms used in chemical communication. Thus, uric acid may contribute to the chemical message produced by K. breviceps in its marine environment. We hypothesize that the chemical signals produced by the gill slit gland may be shared at close-range by conspecifics, and that the mode of sensory reception is likely gustation.

Nothronychus graffami was a large therizinosaur represented by a single well-preserved individual from the Turonian Tropic Shale of southern Utah. It is characterized by an enlarged abdomen, small tail, and an extensively pneumatized axial skeleton, and is frequently regarded as herbivorous. Given the overall tail reduction and the development of a wide fused synsacrum with widely spaced acetabulae, it is reconstructed with an anteriorly rotated femur and a displaced resting ground reaction force anterior to the center of mass. The axis of the ground reaction force would shift laterally during locomotion to maintain stability as observed in extant broad abdomened neornitheans. A waddling gait is inferred for Nothronychus. This pattern is significantly different than in Falcarius, a basal therizinosaurian, where a plesiomorphic narrow abdomen, narrowly spaced acetabulae, and altiliac ilium are observed. Falcarius was capable of a more cursorial gait than derived therizinosaurs. In contrast to Nothronychus, Falcarius was probably at least omnivorous to carnivorous, so herbivory almost certainly evolved within the therizinosaur lineage. Following previous work on Tyrannosaurus and Coelophysis, moment arms were computed for Nothronychus for major muscles spanning the hip, knee, and ankle. A ball-and-socket joint is present at the hip, so three-dimensional movement was considered possible there. The knee and ankle were represented by two-dimensional hinge joints. Some muscles altered their function as the pubis shifted from a propubic orientation to an opisthopubic one. These included flexion to extension and the addition of increased abduction/adduction in the affected muscles. The results supported convergence with an avian locomotor model, such as reduction in M. caudofemoralis longus.

This research delves deeper into previous works on femoral cross-sectional properties during ontogeny by focusing for the first time on the human femoral midneck. The ontogenetic pattern of cross-sectional properties at femoral midneck is established and compared with those at three different femoral locations: the proximal femur, the midshaft, and the distal femur. The study sample includes 99 femora (70 non-adults and 29 adults) belonging to archaeological specimens. Cross-sectional properties were extracted from computed tomographic scans and analyzed with the MomentMacro plugin of ImageJ. Ontogenetic trends of these variables were assessed using locally estimated scatterplot smoothing and segmented regressions, along with Wilcoxon post hoc tests for all possible age group pairings. Our results show that the femoral midneck exhibits a unique growth pattern. Area variables showed rapid growth until adolescence, followed by a more gradual increase leading into adulthood. Nonetheless, the relative cortical area does not demonstrate any significant drops or rise during growth. The morphology of the midneck section of the femur remains stable during ontogeny, with early adolescence and the onset of adulthood marking two periods of significant change. In contrast to the femoral diaphysis, the acquisition of a mature bipedal gait does not appear to constitute a period of significant morphological change at the femoral midneck cross section.

In the context of an increasing interest for Pseudosuchia, we have compiled a Special Issue, comprising 14 collaborative studies that deepen our understanding of pseudosuchian evolution. These contributions range from the description of a new taxon to exhaustive reviews of thermometabolism, morphological adaptation, systematics, and detailed investigations into ontogeny, paleoneurology, paleohistology, and paleobiology. Through these papers, we explore the evolutionary history of pseudosuchian archosaurs, spotlighting their rise and diversification following the end-Permian mass extinction.

Crocodylians evolved a unique gular valve that is capable of creating a water-tight seal between the oral and pharyngeal cavities, allowing the animal to safely submerge with an open mouth. The gular valve has traditionally been described as consisting of two separate parts: an active mobile ventral portion (consisting of the tongue and portions of the hyolingual apparatus) and a dorsal portion, which is a static fold on the hard palate (often termed the palatal velum). The results of the present study argue that the two portions of the gular valve are functionally integrated, not separate, and that the dorsal portion (herein the dorsal gular fold) is a dynamic element the shape and tension of which are influenced by active and passive forces. Using gross dissection, histology, and DiceCT, the present study documents a previously underscribed component of the gular valve, the velar chord, which links the hyolingual apparatus to the dorsal gular fold, functionally integrating the two halves of the gular valve. Through endoscopic videography and a variety of manipulations on living crocodylians, this study demonstrates that changes in the tension on the velar chord directly alter the shape and tension of the dorsal gular fold. The shape changes observed in the dorsal gular fold could be accommodated by a shallow depression in the ventral surface of the palatine bones, herein termed the velar fossa. The velar fossa is a prominent feature of Alligator mississippiensis and was observed in other crocodilians; however, a survey of living and fossil crocodylians demonstrated that the velar fossa is not a universal feature in this clade. Understanding the functional linkage between the dorsal and ventral portions of the gular valve has implications beyond the dive reflex of crocodylians, since active manipulation of the dorsal gular fold likely plays a role in a variety of behavioral and physiological processes such as deglutition and vocalization.

Understanding patterns of cortico-cortical connections in both frequently and infrequently studied species advances our knowledge of cortical organization and evolution. The agouti (Dasyprocta aguti, a medium-size South American rodent) offers a unique opportunity, because of its large lissencephalic brain and its natural behaviors, such as gnawing and hiding seeds, that require bimanual interaction while sitting on its hindlimbs and aligning its head to receive images of the horizon on the retinal visual streak. There have been no previous studies of the intrinsic and extrinsic ipsilateral projections of the agouti's primary somatosensory cortical area (S1). In the present study, we utilized biotinylated dextran (BDA) anatomical tract-tracer injections combined with microelectrode electrophysiological mapping, correlated with analysis of cytochrome oxidase (CO) histochemical staining, to investigate the ipsilateral corticocortical connectivity of the agouti's S1. By injecting BDA into electrophysiologically identified regions within the S1, we revealed ipsilateral intrinsic connections, as well as connections with cortical areas rostral and caudal to S1, and homotopic labeling in the second somatosensory cortical area (S2). In addition, we identified a focal cluster of labeled axons and axonal terminals adjacent to the rhinal fissure, tentatively named the parietal rhinal area (PR). The analysis of CO reactivity allowed delineation of the boundaries and subdivisions of S1, as well as the locations and limits of primary auditory and visual areas. These findings provide support for the notion of a similar pattern of somatosensory cortical organization and connectivity across mammalian species.

Masticatory muscles are composed of the temporalis, masseter, and pterygoid muscles in mammals. Each muscle has a different origin on the skull and insertion on the mandible; thus, all masticatory muscles contract in different directions. Collecting in vivo data and directly measuring the masticatory muscles anatomically in various Carnivora species is practically problematic. This is because some carnivorans can be ferocious, rare, or even extinct. Consequently, the most practical method to collect data on the force generated by the masticatory muscle is to estimate the force based on skulls. The physiological cross-sectional area (PCSA) of each masticatory muscle, which correlates to the maximum force that can be produced by a muscle, was quantified. Using computed tomography, we defined the three-dimensional measurement area for 32 carnivoran species based on the origin and insertion of masticatory muscles specified by observable crests, ridges, and scars. Subsequent allometric analysis relating the measurement area on skull surface to the PCSA for each masticatory muscle measured in fresh specimens revealed a strong correlation between the two variables. This finding indicates that within Carnivora, an estimation of absolute masticatory muscle PCSA can be derived from measurements area on skull surface. This method allows for the use of cranial specimens, housed in museums and research institutions, that lack preserved masticatory muscles in quantitative studies involving masticatory muscle PCSA. This approach facilitates comprehensive discussions on the masticatory muscle morphology of Carnivora, including rare and extinct species.

Crocodylomorphs have colonized various environments from fully terrestrial to fully aquatic, making it an important clade among archosaurs. A remarkable example of the rich past diversity of Crocodylomorpha Hay, 1930 is the marine colonization undergone by several crocodylomorph lineages, particularly Thalattosuchia Fraas, 1901 during the Early Jurassic-Early Cretaceous, and Dyrosauridae de Stefano, 1903 during the Late Cretaceous-Early Eocene. Thalattosuchia represents the most impressive and singular marine radiation among Crocodylomorpha, occupying various ecological niches, before enigmatically disappearing in the Cretaceous. Dyrosauridae, on the other hand, is known for surviving the end-Cretaceous mass extinction in abundance but subsequently vanished. The evolutionary path undertaken by crocodylomorphs into the aquatic environments and the reasons for their disappearance outside marine extinction events during the Mesozoic remains a mystery. Despite a well-preserved fossil record, attention has primarily centered on craniodental adaptations, overlooking the swimming-related adaptations recorded in the postcranial skeleton. This research primarily involves a comprehensive examination of the pectoral girdle of the most representative members of Thalattosuchia and Dyrosauridae, highlighting their evolutionary trajectories over time. Additionally, this work aims to test the phylogenetic signal residing in the postcranial anatomy of Crocodylomorpha. As such, the most recent and complete Crocodylomorpha phylogenetic dataset has been repurposed: 42 new postcranial characters have been added and several others have been revised to address our phylogenetic question. We stress that postcranial anatomy constitutes an important tool supply to better understand the relations of extinct crocodyliforms, but also offers insights on their development, ecology, and biomechanics.

Crocodylomorphs constitute a clade of archosaurs that have thrived since the Mesozoic until today and have survived numerous major biological crises. Contrary to historic belief, their semiaquatic extant representatives (crocodylians) are not living fossils, and, during their evolutionary history, crocodylomorphs have evolved to live in a variety of environments. This review aims to summarize the non-semiaquatic adaptations (i.e., either terrestrial or fully aquatic) of different groups from different periods, highlighting how exactly those different lifestyles are inferred for those animals, with regard to their geographic and temporal distribution and phylogenetic relationships. The ancestral condition for Crocodylomorpha seems to have been a terrestrial lifestyle, linked with several morphological adaptations such as an altirostral skull, long limbs allowing a fully erect posture and a specialized dentition for diets based on land. However, some members of this clade, such as thalattosuchians and dyrosaurids display adaptations for an opposite, aquatic lifestyle, interestingly inferred from the same type of morphological observations. Finally, new techniques for inferring the paleobiology of those extinct animals have been put forward in the last decade, appearing as a complementary approach to traditional morphological descriptions and comparisons. Such is the case of paleoneuroanatomical (CT scan data), histological, and geochemical studies.