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

The vertebral column consists of multiple homologous elements that have specialized within and between taxa and serve important functions in positional support and as protection for the central nervous system. The study of modularity and integration provides new insights into the evolution of complex structures such as the vertebral column. Patterns of modularity and integration may reflect underlying genetic-developmental patterns and facilitate evolution. Previous studies have identified mixed modularity patterns within and between elements across mammals generally, within primates and carnivorans. Here, we assess modularity within and between elements in the complete post-axial vertebral column in four catarrhine taxa: Macaca (n = 96), Hylobates (n = 77), Pan (n = 92), and Homo (n = 151). We use the Covariance Ratio (CR) to estimate r² and the standardized eigenvalues (SVE) variance for comparative purposes. Our results show that there is general, widespread integration within the catarrhine vertebral column, both within and between elements. Hominoids tend to display greater modularity than do macaques, but these estimates are rarely significant. Clusters of modularity in the mid-cervical and upper thoracic regions may relate to special nervous system structures in these areas, and locomotor behaviors in general may influence patterns of modularity in primates. In particular, we find that size is a pervasive factor affecting integration among vertebral elements, though its effects on specific structures are variable. Our results generally do not agree with those found across mammals or within carnivorans, and future studies should focus on genus-level assessments across a variety of taxa.

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.

Primates are often considered to have a poor sense of smell. While all studies identify small olfactory bulbs (OB; the region of the brain responsible for processing scent) among haplorhines, whether or not strepsirrhines also possess small OBs is less clear, as is the evolutionary backdrop from which these patterns emerged. Here, we examine the relative size of the olfactory bulbs in cranial endocasts of living and fossil primates and their kin (Euarchontoglires [Primates, Dermoptera, Scandentia, Rodentia, Lagomorpha]), testing previous hypotheses. Regression analyses of OB volume and mass relative to endocranial volume (ECV) and body mass (BM), and ANOVAS of residuals, were performed on a dataset of 181 extant and 41 extinct species. Analyses show clear differences in the relative size of the OBs, with haplorhines possessing distinctly smaller OBs relative to all other clades. Pairwise tests indicate haplorhine OBs are significantly smaller than those of all other clades, including strepsirrhines; when the haplorhines are removed from analyses, strepsirrhines are significantly smaller than all other clades. This suggests that a reduction in OB size occurred at the crown primate node, a pattern also seen in ancestral state reconstruction (ASR) analyses. The ASR analyses suggest multiple iterations of olfactory bulb size decrease occurred in Haplorhini, reflecting large amounts of parallelism. These results likely differ from previous studies due to the inclusion of additional fossils and more appropriate outgroups based on up-to-date phylogenetic hypotheses.

Early life behaviors have a profound role in shaping adult craniofacial morphology. During early life, all mammals undergo the dynamic transition from suckling to mastication, a period coinciding with rapid cranial biomineralization. Osteogenesis imperfecta (OI), a genetic disorder that impacts the production of type I collagen, disrupts biomineralization, leading to craniofacial growth differences affecting quality of life. This study investigates craniofacial development during infant oral motor developmental stages in OI mice compared to unaffected wild-type littermates (WT mice). We hypothesize OI mice will exhibit smaller overall size, and the adult OI phenotype will develop postnatally in response to masticatory loading. Point cloud and fixed landmarks were collected from micro-computed tomography scans, then geometric morphometric analyses and interlandmark distances (ILDs) compared craniofacial size and shape between OI and WT mice at birth (P0; n = 27 OI murine/20 WT) and postnatal Days 7 (P7; n = 21/21), 14 (P14; n = 16/20), 21 (P21; n = 20/26), and 28 (P28; n = 26/33). This study found no size and shape differences between genotypes at birth. Starting at P7, OI mice are significantly (p < 0.05) smaller and display pronounced shape changes (p < 0.001) characterized by a larger neurocranium and a shorter viscerocranium. At P21, significant differences emerge in cranial base orientation, neurocranial width, viscerocranial shortening, and zygomatic arch displacement. These findings underscore the importance of early life oral motor stages in developing the adult OI craniofacial phenotype and oral health, suggesting earlier craniofacial interventions may improve effective treatment of OI.

Seeleyosaurus guilelmiimperatoris is an early-diverging plesiosauroid from the lower Toarcian (Lower Jurassic) of the Posidonienschiefer Formation (Posidonia Shale) of Holzmaden, southwestern Germany. It is known from almost complete skeletons of two osteologically mature individuals, the holotype and a referred specimen that was largely destroyed during World War II. Although well-preserved and substantially complete, the anatomy of Seeleyosaurus and its taxonomic and phylogenetic significance remain insufficiently understood. Here, we provide a complete osteological description of the taxon. Seeleyosaurus guilelmiimperatoris can be diagnosed based on a unique combination of characters, including one autapomorphy: the tall and basally constricted neural spines of the posterior cervical, pectoral, and dorsal vertebrae which have a sinusoidal shape in lateral view. Our study supports the validity of the plesiosauroid taxon Plesiopterys wildi, which was considered a junior synonym of Seeleyosaurus in a previous joint assessment of the taxa. Our phylogenetic evaluation places S. guilelmiimperatoris among Microcleididae, in congruence with previous studies. However, in contrast to earlier phylogenetic reconstructions, our analyses, which take into account numerous changes to the character matrix, reconstruct S. guilelmiimperatoris as falling within the Microcleidus clade. While we admit that Seeleyosaurus might potentially be considered a species of Microcleidus, we refrain from promoting this nomenclatural change pending an osteological and taxonomic reassessment of Microcleidus spp. as well as other, potentially closely related forms, such as Lusonectes sauvagei.

Terrestrial vertebrates from at least 30 distinct lineages in both extinct and extant clades have returned to aquatic environments. With these transitions came numerous morphological adaptations to accommodate life in water. Relatively little attention has been paid to the cervical region when tracking this transition. In fully aquatic cetaceans, the cervical vertebrae are compressed, largely because a loss of neck mobility reduces drag. We ask whether this pattern of cervical evolution is present in the more recently evolved semiaquatic pinnipeds. Here, we compare neck morphology and function in three families of pinnipeds, the Otariidae, Phocidae, and Odobenidae as well as between pinnipeds and their terrestrial arctoid relatives (ursids and mustelids). Using cranial CT scans, we quantified the occipital surface area for neck muscle attachment as well as vertebral size and shape using linear measurements. Results show that pinnipeds have a relatively larger occipital surface area than ursids and terrestrial mustelids, suggesting that marine carnivorans have enlarged their neck muscles to assist with head stabilization during swimming. Within pinnipeds, we found quantitative differences in cervical morphology between otariids and phocids that coincide with their locomotor style. Phocids are hindlimb-dominated swimmers that propel themselves with pelvic oscillations. Their necks are relatively stiff and their cervical vertebrae are compressed anteroposteriorly with reduced muscular attachment areas. By contrast, otariids are forelimb-dominated swimmers that locomote in water and on land using their pectoral limbs, often recruiting their neck to initiate turns underwater as well as assisting in “walking” on land. Consequently, otariids have stronger, more flexible necks than phocids, which is reflected in more elongate cervical vertebral centra with larger muscle attachments. The walrus (Odobenidae) has a cervical vertebrae morphology intermediate to that of phocids and otariids, consistent with a phocid swimming mode combined with a more muscular neck that likely functions in intraspecific conflict and haul-out behavior.

The oval window (OW) is an opening connecting the inner and middle ear. Its area has been shown to consistently scale with body mass (BM) in primates, and has been used alongside semi-circular canal (SCC) size to differentiate Homo sapiens and fossil hominins, including Paranthropus robustus. However, while the morphology of other inner ear elements, such as cochlea and SCCs, has been extensively studied in primates, OW shape has received little attention. In this study, we assess OW morphological variability in extant primates, and compare P. robustus to extant hominids. The potential of OW size to predict BM is also assessed. For this, measurements were performed on 3D scans from extant primate species and of P. robustus from the sites of Kromdraai, Swartkrans, and Drimolen. Size was assessed using perimeter (OWP), area (OWA), and centroid size (OWCS). Shape was assessed using geometric morphometric methods. The OW has no sexual dimorphism; there is no size difference between juveniles and adults, but there is a slight shape difference between human juveniles and adults, with a seemingly opposite ontogenetic trajectory compared to other primates. P. robustus has an intermediary OW shape between apes and humans, with more ape-like specimens from Kromdraai and more human-like ones from Drimolen. Overall, OW morphology discriminates primate species well enough, especially H. sapiens. BM is well explained by OWA, but OWA is not reliable as a BM proxy due to high prediction errors. Nonetheless, the OWA of P. robustus suggests a BM close to that of a chimpanzee.

The feet of people in non-industrial societies often have higher, stiffer longitudinal arches (LAs) and larger intrinsic muscles than those of many people in post-industrial societies. The prevailing explanation for this phenomenon is that people in post-industrial societies commonly wear shoes that restrict foot mobility, while people in non-industrial societies are often habitually barefoot or minimally shod. However, people in post-industrial societies also tend to be less physically active than in non-industrial societies, and it is possible that this, too, is a major determinant of their foot form and function. Here, we test the hypothesis that among people in post-industrial societies, lower physical activity levels are associated with lower, less stiff LAs and smaller intrinsic muscles. In a cross-sectional analysis of 40 adults in the United States, none of whom were habitually barefoot or minimally shod, we measured daily physical activity using accelerometry, LA height and static stiffness using photography, LA dynamic stiffness using kinematic and kinetic data, and intrinsic muscle size using ultrasound. Using Bayesian models, we found very low probabilities of positive associations between physical activity (step count, time spent in moderate-to-vigorous activity) and LA height, LA static stiffness, and muscle size. For LA dynamic stiffness, we found small to moderate probabilities of positive associations with physical activity variables. These findings suggest that physical activity is unlikely a major determinant of variation in LA and intrinsic muscle form and function among post-industrial societies. It remains possible that physical activity affects LA and intrinsic muscle traits, but perhaps primarily among people who are habitually barefoot or minimally shod.

The impact of artificial selection on the masticatory apparatus of dogs has been poorly studied, and comparative data with dogs subjected to more natural constraints are lacking. This study explores the jaw musculature of Tunisian street dogs, which are largely free from the influence of breed-specific selection. The masticatory muscles (digastric, masseter, temporalis, and pterygoid) of 27 adult dogs were dissected and muscle mass and physiological cross-sectional area (PCSA) were quantified, providing a baseline for comparisons between dogs from more natural versus more controlled environments. Our findings reveal that the morphology of the jaw adductor muscles is remarkably conserved among dogs, despite significant variation in skull shape. Additionally, all masticatory muscles scale isometrically with body mass. Notably, females exhibit functional adaptations that optimize muscle strength, particularly in the temporalis muscle, despite showing smaller overall muscle volumes compared to males. This could be linked to differences in predation, competition for food, or factors related to sexual behavior. Preliminary evidence suggests that captivity may limit the development of muscle mass and PCSA in the temporalis muscle, likely due to changes in lifestyle and diet. Significant relationships were also observed between skull shape and muscle data, particularly in the mandible, indicating that skull variability reflects jaw adductor muscle anatomy to some degree. This study enhances our understanding of jaw muscle morphology and function in feral dog populations and offers insights into the adaptation of the masticatory apparatus in dogs.