Journal of Anatomy最新文献

Marsupials are born at an early stage of development, and compared to eutherians, skin development is slow, and a functional change during skin ontogenesis occurs. The skin development in 36 gray short-tailed opossums (Monodelphis domestica) has been examined using histological, morphometric, and μCT methods during postnatal development from neonate to adult. The aim of the study is to follow the structural and functional transition of the skin in this immature marsupial species. Additionally, the postnatal development of the external appearance and the cardiac and respiratory systems is looked at to assess skin development in relation to the general development. The skin of the newborn gray short-tailed opossum is thin and undifferentiated (no hair follicles, no sebaceous and sweat glands). Numerous subepidermal capillaries allow for gaseous exchange via the skin. A dense cutaneous capillary net with a high capillary volume density (0.25 ± 0.04) is present at term, indicating significant cutaneous gas exchange in the neonate. The capillary volume density decreases markedly during the first postnatal week (0.08 ± 0.01). In the same time period, the skin diffusion barrier increases from 27 ± 4 to 87 ± 1 μm. From this age on, the skin development is characterized by thickening of the different cutaneous layers and beginning formation of hair follicles. First, hair covering the skin, sweat glands, and subcutaneous fat are observed by day 28, indicating the onset of thermoregulation. The total skin thickness in the gray short-tailed opossum increases from 58 μm at birth to 726 μm by day 35, when the pelage is fully developed. The cardiac and respiratory systems are immature at birth. A fenestrated interatrial septum is present for the first 4 days, allowing skin respiration. Between day 4 and day 7, the lung enters the saccular stage of lung development and is mature enough to meet the respiratory needs of the growing organism. During a long period of postnatal development, the structural differentiation of the skin results in a functional shift from transcutaneous gas exchange to thermoregulation in later life.

The hindlimb skeleton of the holotype (LB1) of Homo floresiensis is relatively complete and includes both fibulae, which despite being well preserved have yet to be subject to a quantitative comparative analysis with other hominids. A new distal fragment of a fibula has also been recovered from the H. floresiensis-bearing sediments at Liang Bua (Flores, Indonesia). In this study, we used 3D geometric morphometrics (3DGM) to quantify detailed aspects of the external shape and articular facet morphology of the proximal and distal ends of these H. floresiensis fibulae. The comparative sample included fibulae from 57 extant great apes (Pongo, Gorilla, and Pan), 41 recent and fossil Homo sapiens, five Australopithecus afarensis, and five Neandertals. Shape variation was analyzed using principal component analysis of Procrustes coordinates, and mean differences among taxa were tested using a Procrustes ANOVA with a randomization procedure. Size comparisons were made using centroid size and tested via correlations with principal component scores. Results demonstrate that H. floresiensis fibulae possess the absolute smallest mean linear dimensions and mean centroid sizes among our comparative sample. The proximal and distal fibular ends of H. floresiensis exhibit four key features adapted for obligate bipedalism while also displaying a suite of plesiomorphic traits shared with extant great apes and A. afarensis that, compared with that of H. sapiens and Neandertals, suggest a more versatile ankle joint with a greater range of motion and enhanced load-bearing capabilities of the fibula. Our results are consistent with other aspects of the H. floresiensis lower limb, such as long feet relative to the femur and a long forefoot relative to the hindfoot, that together suggest an australopith-like locomotor repertoire that included both obligate bipedalism and climbing.

Several sauropodomorph dinosaurs have been excavated from the Elliot Formation (EF) of Southern Africa which include important taxa such as Massospondylus, Melanorosaurus and Antetonitrus. The study of the bone microstructure of smaller, bipedal Sauropodomorpha and larger, quadrupedal Sauropoda allow us to infer how the growth dynamics changed during the evolution of gigantism. Historically, osteohistological studies of Sauropodomorpha tended to have focused on either early diverging taxa (e.g. Plateosaurus & Massospondylus) or on derived taxa (diplodocids & titanosaurs), whereas studies on the growth dynamics of the transitionary groups (i.e. Sauropodiformes & early Sauropoda) are poorly known. Here, we assess the palaeobiology of two sauropodiformes and an early sauropod by analysing their bone histology. Thin sections of the long bones of two indeterminate sauropodiformes NMQR 3314 and NMQR 1551, and an indeterminate sauropod SAM-PK-K382 were prepared. The general histology of the long bones of all three dinosaurs were similar. Rapid growth through the deposition of fibrolamellar bone tissue characterised their respective ontogenies. Lines of arrested growth (LAGs) were commonly located in the mid and outer cortex signalling the onset of uninterrupted growth. Differences in the histology of these dinosaurs were principally related to the pathological bone tissue evident in the femur of the sauropodiform NMQR 1551 and to the formation of annuli around LAGs in Sauropoda indet., as well as in the location of LAGs in the compacta. The number of LAGs in the cortex varied among the taxa but generally the outer regions of the cortex showed an accumulation of LAGs. The growth dynamics of our three sauropodomorph dinosaurs are similar to early sauropods such as Antetonitrus. It appears that the abundance of fibrolamellar bone tissue and uninterrupted growth at later ontogenetic stages are likely key traits in the early evolution of gigantism in Sauropoda, which supports the occurrence of a mosaic of growth dynamic patterns among transitionary Sauropodomorpha.

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Cover image: see R. Racicot et al., ‘Variation in whale (Cetacea) inner ear anatomy reveals the early evolution of ‘specialized’ high frequency hearing sensitivity’, this issue.

Among living crocodylians, alligatoroids exhibit a wide range of body sizes and a biogeographic distribution that spans tropical-to-subtropical climates. The fossil record of alligatoroids, however, reveals even greater diversity, including multiple examples of gigantism and a broader distribution that extends into polar latitudes. Osteohistological studies on extant alligatoroids show that living alligators and caimans both exhibit seasonal growth, with roughly comparable growth rates. However, alligators and caimans diverged from one another over 60 million years ago; the dearth of studies on extinct alligatoroids makes it unclear if the shared condition in extant taxa reflects convergent responses to rapid climatic changes in the recent past or represents the ancestral condition in alligatoroids. Additionally, sample sizes are often limited to one or two individuals, especially in extinct crocodylians, obscuring any intraspecific variation present. To address this uncertainty, we conducted the largest monospecific osteohistological study of an extinct crocodylian to date, based on a sample of nine femora, providing unique insight into the intraspecific variation in growth of the early-diverging alligatoroid Diplocynodon hantoniensis from the late Eocene of the UK. The bone microanatomy of D. hantoniensis shows moderate compactness, with a well-defined medullary cavity, and osteohistological features that are generally consistent with those of extant alligatoroids. Samples vary greatly along a continuum in the degree of remodelling and vascularity, highlighting both the importance of evaluating intraspecific variation and limitations of basing histological assessments on singleton samples. Ontogenetic assessment indicates that our sample captures a range of skeletally immature to mature individuals, approximately corresponding to femoral size, but with notable exceptions possibly driven by sexual dimorphism. Body size estimates for D. hantoniensis (1.2-3.4 m) fall within the typical range of living American alligators (Alligator mississippiensis). Reconstruction from cyclical growth marks indicates a similar overall growth rate between D. hantoniensis and A. mississippiensis. As in extant alligatoroids more generally, this is determinate, seasonally-controlled growth. Femoral circumference scales positively with femoral length in D. hantoniensis, demonstrating similar allometry to A. mississippiensis. This differs from some other extant crocodylians (e.g. Crocodylus niloticus and Crocodylus johnstoni) and suggests conservation of allometric relationships in alligatoroids. This in-depth look into an early diverging alligatoroid indicates that seasonality and growth rates present in extant members were established near the base of the clade. Furthermore, it highlights the importance of including larger samples of singular species in order to capture potential variation when making clade-wide interpretations.

This is a study of the relationship between the segmental bone lengths of foot height, tibia length, femur length, and upper body length to determine whether they follow a pattern that is consistent with the Lucas sequence.

Cortical bone and dentine are two mineralized tissues sharing a common embryological origin, developmental, and genetic background, distinct from those of enamel. Understanding their relationship is crucial to decipher the factors acting on their postnatal development, and shedding light on the evolutionary patterns of tissue proportions. Here, we investigate the coordinated variation between cortical bone and dentine volumes measured from arm and forearm bones (humeri, ulnae, radii) and upper anterior teeth (central incisors, lateral incisors, canines) of modern humans. Given the shared characteristics of cortical bone and dentine, we expect similarities in their postnatal development, which may lead to covariation between their volumes. The degree of bone-dentine covariation may be influenced by the physiological response of upper limb bones to mechanical loading. No such covariation is expected with enamel volumes, due to the greater developmental independence of bone and enamel. Our sample includes 55 adults of African and European ancestries from South African osteological collections. Principal component analysis of cortical thickness variation along the shafts of paired humeri, ulnae, and radii is used to assess asymmetry. Bone regions with bilateral asymmetry in cortical bone thickness are considered sensitive to functional loads, while regions with minimal bilateral variation likely reflect genetic influences during bone postnatal development. Statistical analyses reveal strong positive correlations between cortical bone and dentine volumes across all bones and teeth, and weaker correlations between cortical bone and enamel. We outline a complex pattern of bone-dentine covariation that varies by skeletal location and tooth type. Contrary to our expectations, the presumed functional sensitivity of bone regions does not influence the covariation signal. Additionally, the strength of the covariation appears to align with the developmental sequence of the anterior teeth, with the upper canines showing the strongest correlation with cortical bone volumes, followed by lateral and central incisors. These results provide insights into the functional and biological factors influencing the coordinated variation of cortical bone and dentine volumes during postnatal development. Further research on the cortical bone-dentine covariation across different skeletal parts, including lower limb elements, would enhance our understanding of the effects of both endogenous and exogenous factors on the development of the mineralized tissues.

Ceratosaurus is a large-bodied non-avian theropod dinosaur known from the Upper Jurassic Morrison Formation of North America and is remarkable both for its exceptionally fast annual growth rate and its status as the only theropod currently known with postcranial osteoderms. We describe the osteohistology of three hind limb bones, two dorsal ribs, and one osteoderm representing four individuals of Ceratosaurus. In addition to describing the tissues of these bones, we compared the annual growth rates from three individuals in our sample to those of five other ceratosaurians. We fit seven growth models to two of the specimens in our sample and compared the results of the best-fit model(s) to those of two other ceratosaurians (Masiakasaurus knopfleri and Majungasaurus crenatissimus) for which sufficient growth data were available. The bone tissue of hind limbs in Ceratosaurus is highly vascularized, with dense plexiform or reticular vascular complexes and alternating strips of parallel or woven-fibered matrix. Few lines of arrested growth were recorded in hind limbs prior to specimens achieving asymptotic body size. Both sampled dorsal ribs are highly remodeled, with only small portions of primary bone visible in each section, revealing parallel-fibered bone with sparse primary osteons. Both dorsal ribs contain numerous lines of arrested growth throughout the cortex that allowed for more accurate estimates of individual age when paired with the data from hind limbs. The osteoderm is composed of a core of large Haversian canals and a perimeter of lamellar bone with dense Sharpey's fibers along the internal surface of the bone. Multiple LAGs are also present within the lamellar bone along the exterior margins. Maximum annual growth rates in Ceratosaurus were on average nine-fold faster than those of other ceratosaurians. Our sample lacks data from juveniles so confidence in inferred growth models is limited. Thus, to begin to constrain Ceratosaurus growth patterns, we averaged the results of all models that possessed an Akaike Information Criterion score corrected for small sample size (AICc) within 10 of the lowest scoring model. We found that the monomolecular model exhibited the lowest AICc value, with the von Bertalanffy and Gompertz models possessing AICc values within 10 units of it. In contrast, the logistic and Gompertz models were confidently selected for Masiakasaurus and Majungasaurus, respectively. Irrespective of growth model, maximum relative annual growth rates for Ceratosaurus were several-fold greater than those of Masiakasaurus and Majungasaurus. Both histological and growth model estimates of life history support an evolutionary trend towards more prolonged development in Ceratosauria through evolutionary time.

For all vertebrates, the anterior eye structures work together to protect and nourish the eye while ensuring that light entering the eye is correctly focused on the retina. However, the anterior eye structure can vary significantly among different vertebrates, reflecting how the structures of the anterior eye have evolved to meet the specific visual needs of different vertebrate species. Although conserved pathways regulate fundamental aspects of anterior eye development in vertebrates, there may also be species-specific differences underlying structural variation. Our knowledge of the cellular and molecular mechanisms underlying the development of structures of the anterior eye comes mainly from work in mammals, chicks, some amphibians, and small teleosts such as zebrafish. Our understanding of anterior eye development would benefit from comparative molecular studies in diverse vertebrates. A promising lizard model is the brown anole, Anolis sagrei, which is easily raised in the laboratory and for which genome editing techniques exist. Here, we provide a detailed histological analysis of the development of the anterior structures of the eye in A. sagrei, which include the cornea, iris, ciliary body, lens, trabecular meshwork, and scleral ossicles. The development of the anterior segment in anoles follows a pattern similar to other vertebrates. The lens forms first, followed by the cornea, iris, ciliary body, and tissues involved in the outflow of the aqueous humor. The development of the iris and ciliary body begins temporally and then proceeds nasally. Scleral ossicle development is generally comparable to that reported for chicks and turtles. Anoles have a remarkably thin cornea and a flat ciliary body compared to the eyes of mammals and birds. This study highlights several features in anoles and represents a deeper understanding of reptile eye development.

The greater rhea (Rhea americana) is the largest bird in South America. It is flightless and cursorial, with a precocial postnatal development. This study aims to describe the postnatal morphological changes in the pelvic girdle of Rhea americana, focusing on ontogenetic scaling and gross anatomy to provide insight into the potential relationship between structure and function in cursorial birds. The pelves of 18 specimens representing four postnatal stages, were studied. Gross anatomical observations and staining methods were used to identify bone and cartilage, providing detailed information about qualitative morphological changes. Quantitative changes were assessed through linear regression analysis using pelvic linear dimensions and body mass to determine allometric growth patterns. The pelvic girdles of immature specimens are characterized by unfused bones, including the vertebrae synsacrales and the medial borders of the ilia, and small cartilaginous areas at the caudal end of the ilium, ischium, pubis, antitrochanter and tuberculum preacetabulare. These immature traits persisted until the most advanced juvenile stages were studied, indicating the slow postnatal growth typical of precocial birds. Similar to other precocial birds, the greater rhea exhibits large bone areas in its pelvic girdle, providing the mechanical strength necessary for locomotion from hatching. The pelvic dimensions showed a combined pattern of allometric and isometric growth related to hindlimb function and body support. The positive allometric growth of the ilium contributed to its increasing verticalization and narrowing, providing an increased dorsoventral surface area for the attachment of the powerful proximal hindlimb muscles. In contrast, the isometric growth of the intertrochanteric width helps in the uniform distribution of loading caused by body mass, providing adequate stability and support.