The Australasian crocodylian fossil record is dominated by the extinct endemic clade Mekosuchinae, with known members spanning the Eocene-to-Holocene. This diverse clade exhibited high morphological disparity, from early members superficially similar to Crocodylus, to more terrestrial forms later in the clade's evolutionary history. However, it remains unclear why mekosuchines went extinct whilst Crocodylus continues to thrive in the region, and how the ancestors of this terrestrial clade reached Australasia without long-distance transoceanic dispersal. One possible explanation is that there was intraclade variation in the growth pattern and life habit of mekosuchine species, and that these, in turn, differ from those of Crocodylus. Here, we present the first osteohistological study of mekosuchines, evaluating the femora of the middle-late Eocene species Kambara taraina and late Oligocene-middle Miocene Baru (B. wickeni, B. darrowi). Bone compactness profiles are more characteristic of a terrestrial habit than those of extant crocodylians, with Baru darrowi demonstrating the most terrestrialized profile. Apposition rates are similar in absolute value to those of extant crocodylians, indicating a comparable metabolism; however, high appositional rates throughout mid-cortical cyclical growth marks suggest that mekosuchines were able (or needed) to maintain a moderate rate of growth for longer than extant crocodylians. Our results indicate that mekosuchines were more terrestrial than Crocodylus and that later-diverging mekosuchines showed increased terrestrialization; however, they do not indicate that early mekosuchines were well-adapted to transoceanic dispersal. Heightened terrestrialization and an extended moderate growth period might have made mekosuchines more vulnerable to late Cenozoic aridification in Australia than semi-aquatic Crocodylus.
Composed of various minerals, the eggshell provides ideal conditions for embryonic development, and understanding its composition and structure is essential for clarifying its relationship with bone formation. This study characterized the structure and mineral profile of the Rhinoclemmys punctularia punctularia eggshell in relation to embryonic osteogenesis. Fertilized eggs were collected and incubated under controlled humidity (80%) and temperature (28.5°C ± 0.5°C). From the 15th day of incubation onward, embryos (n = 39) were analyzed at different developmental stages using a clearing and double-staining technique. Eggshell ultrastructure and mineral composition (n = 23) were evaluated by scanning electron microscopy coupled with energy-dispersive spectroscopy. Three developmental periods were established: pre-ossification (PO), with no signs of mineralization; ossification in progress (EO), marked by the first ossification centers; and complete ossification (OC), in which all bones were mineralized. Osteogenesis began on the 30th day of incubation in the dermatocranium. Ultrastructural analysis revealed three shell layers: cuticle, mineral layer, and organic layer. Calcium weight percentage on the eggshell surface decreased significantly by 5% (p = 0.037) during embryonic development. Eggshell thickness also declined significantly (p = 0.00242), from 389.86 ± 40.14 μm in PO to 323.11 ± 37.00 μm in EO and 320.65 ± 40.23 μm in OC. These findings indicate that eggshell mineral dynamics play a fundamental role in embryonic osteogenesis, contributing to a better understanding of skeletal development and providing insights for evolutionary studies.
Extant turtles occupy freshwater, marine, and terrestrial habitats, and their nasal region provides important evidence for the evolution of respiration- and sensory-related cranial morphology. However, developmental data on the turtle nasal capsule remain limited, particularly in Pleurodira. Here, we describe nasal capsule development in the pleurodiran turtle Emydura subglobosa based on histological cross-sections of five distinct developmental stages and three-dimensional reconstructions. The nasal capsule underwent marked reorganization between Emyd. subglobosa developmental stages 4- and 5- (ES 4- and ES 5-), during which its basic architecture became established. Several features are notable. First, the nasal entrance shows distinctive pleurodiran specializations, including a processus supranarinus communis formed by medial fusion of the paired processus supranarini and a dorsally projecting processus rostralis medialis formed from the paired processus infranarini. In addition, Emyd. subglobosa possesses a fenestra rostralis at the nasal entrance, a feature not identified in other turtles examined to date. Second, the floor of the nasal capsule exhibits the expanded solum nasi complex characteristic of turtles, including the lamina transversalis anterior, pars paraseptalis, and pila supraglandularis, together with a canalis praepalatinus and a posteriorly facing fenestra basalis. Third, the pars ectochoanalis differs between the two major turtle clades: in pleurodires, it extends only slightly caudally, whereas in cryptodires it typically extends farther caudally and forms the ventral margin of the ductus nasopharyngeus. These findings provide a developmental framework for interpreting pleurodiran nasal morphology and a broader comparative framework for understanding turtle nasal evolution.
All infant mammals must suckle in order to effectively acquire milk from a nipple. Yet, not all infants are able to do so. Preterm infants in particular face significant feeding challenges, often failing to establish successful breastfeeding due to complex neurophysiologic challenges. Unlike the cisternic structure of conventional commercial bottle nipples, often modeled after ruminant anatomy, human and porcine maternal nipples are ducted structures that require intraoral suction for milk release. To investigate how this structural difference impacts feeding success across gestational age, we used a validated infant pig model and high-speed biplanar fluoroscopy (100 fps), synchronized with intraoral pressure recordings to compare suckling mechanics between term and preterm neonates feeding on either a cisternic or a suction-dependent ducted (biomimetic) nipple. We found a profound gestational-age-dependent divergence in performance. The ducted nipple was successful for term infants because it paralleled natural breastfeeding and replicated its biomechanics by reducing the ability to express milk, thereby enhancing suction generation. While both term and preterm infants positioned the ducted nipple further into the mouth, preterm infants failed to adjust their tongue kinematics to compensate for this change. This inability led to minimal suction generation and poor milk acquisition. The lack of kinematic compensation in preterm infants isolates a critical physiological adaptability deficit, stemming from both neurological (lack of flexible seal adjustment/disordered coordination of the suck-swallow-breathe sequence) and anatomical constraints related to an inadequate seal on the nipple. Future research must explore these deficits' interactions to understand suckling physiology and develop targeted interventions for this population.
Human childbirth has often been considered uniquely difficult among mammals, yet recent evidence suggests that obstructed labor and fetopelvic disproportion are widespread across placental mammals. Here, we propose the "costly son" hypothesis: because male offspring are typically larger at birth, they impose greater obstetric risk on mothers and themselves by increasing the likelihood of fetopelvic disproportion and dystocia. We compiled sex-specific birth weight data for 140 placental mammal species across 11 orders and reviewed published evidence on sex differences in dystocia risk. Male neonates were more commonly larger at birth than females, and male-biased birth size differences were strongly associated with male-biased adult sexual size dimorphism. Species with male-biased adult size dimorphism had sixfold greater odds of exhibiting male-biased birth weight differences than species with female-biased dimorphism. Male-biased birth weight differences existed irrespective of developmental mode (precocial or altricial), indicating that sex differences in fetal growth arise early in gestation. Evidence from humans, livestock, and at least one non-human primate suggests that male fetal sex is associated with elevated dystocia risk, that is, precocial taxa where birth size approaches the mechanical limits of the maternal birth canal. We further hypothesize and discuss how parity and sex ratio adjustment may modulate these risks and associated trade-offs in a Trivers-Willard context. Our findings identify fetal sex as an underappreciated dimension of mammalian obstetrical dilemmas and suggest that the evolutionary benefits of producing larger sons are balanced by increased risks of birth complications and mortality.
Previous studies in Lagidium peruanum and Lagidium viscacia reported strict right-sided dominance in ovulation and embryo implantation, although bilateral ovarian functionality may represent an intrinsic reproductive strategy to the genus. Here, we analyzed the morphology, histochemistry (periodic acid-Schiff [PAS] and Alcian blue [AB]) and lectin histochemistry of both ovaries in L. peruanum (Chinchillidae) during early, middle, and late gestation. Through gestation, the ovarian cortex contained follicles at different developmental and atretic stages, as well as interstitial glands. The medulla was composed mainly of vascularized connective tissue. Embryonic remnants, including cortical and medullary cords, were found in the cortex and the medulla during all gestational stages. A single persistent primary corpora lutea (CL) was observed in the left ovary at all gestational stages, while a secondary CL was detected only during early stages. These findings differ from previous reports describing the primary CL in the right ovary. The zona pellucida of some follicles was PAS and AB positive, and lectin histochemistry revealed dynamic glycosylation patterns in the follicles between both ovaries and throughout gestation. The ovarian morphology of L. peruanum supports the hystricomorph ovarian bauplan. However, variable ovarian laterality, persistence of embryonic structures, and differences in the number and distribution of CL among chinchillids (which includes Lagidium, Chinchilla, and Lagostomus) suggest previously unrecognized diversity in ovarian organization and reproductive strategies within the clade.
The Iberian wolf (Canis lupus signatus) is an endangered subspecies characterized by highly fragmented populations and increasing human-carnivore conflict across the Iberian Peninsula. Although body mass strongly influences predator-prey dynamics and ecological performance, quantitative assessments of sexual size dimorphism (SSD) and body mass (BM) variation in this subspecies remain scarce. Here, we conducted a morphometric analysis of the lower carnassial tooth (m1) in 78 historical and contemporary museum specimens (1900-2006) to evaluate its applicability for non-invasive body mass estimation and sex discrimination. We assessed the anteroposterior length (m1L) and blade length (m1BL) as potential proxies for BM and SSD. Multivariate analyses (MANOVA) based on m1L and m1BL revealed significant morphometric differences between sexes (Pillai's trace = 0.3488, p < 0.001), and Linear Discriminant Analysis produced a cross-validated classification accuracy of 79.07%. We further developed a predictive equation specifically calibrated for the Iberian wolf using m1L, achieving a mean absolute error of 2.44 kg and a mean absolute percentage error of 7.58% under leave-one-out cross-validation, demonstrating robust predictive performance for mature individuals. In immature specimens, the equation likely estimates expected adult body mass, consistent with earlier dental maturation relative to overall skeletal growth. Sexual size dimorphism was further supported by body mass estimates, with males being on average 21.4% (RBM) and 11.6% (EBM) heavier than females. Spatial analyses indicated morphological stability, with no significant differences in body mass between mature males from north and south of the Douro River, Portugal. Comparative analyses within Canis place the Iberian wolf within the range of variation of medium-sized wolves. Overall, carnassial morphometrics provide a robust and accurate approach for assessing ecomorphological traits, offering valuable data to support field monitoring, forensic applications, and conservation research in threatened canids.
The tapinocephalid dinocephalian Moschops is one of the most iconic taxa of the middle Permian, yet its paleobiology remains one of the least well-known. Here, we address some aspects of paleoneurology and paleobiology of Moschops using CT scanning of four well preserved skulls from the upper Abrahamskraal Formation of South Africa. Two of the specimens preserve articulated scleral ossicle rings, the dimensions of which are more consistent with a diel activity pattern, although intermediate between diurnal, nocturnal, and cathemeral. The bony labyrinth for the inner ear (preserved in one specimen) has comparatively short semicircular canals, and the agility score aligns with those of modern large herbivores that are able to swim. This is consistent with previous hypotheses inferring that some tapinocephalid dinocephalians may have been semi-aquatic. The four individuals form a partial ontogenetic series, and we show that the endocast grows markedly with body size in Moschops, as does the encephalization quotient. The latter is an unusual pattern for vertebrates. We also report the first possible evidence for the preservation of soft brain tissues in a non-mammalian synapsid, which sparks exciting perspectives for future studies of non-mammalian synapsid paleoneurology.
The resilience of mammalian tooth enamel to fatigue and fracture stems from its anisotropic structure, which is manifest at various hierarchical levels from the nanoscale to the macroscale. At the nanoscale level, the alignment trajectories of thin hydroxyapatite nanocrystals and the organic matrix serve to convey anisotropy and deformability. Various prism packing configurations provide additional structural heterogeneity at the microscale level, while at the mesoscale, the angles at which parazonal and diazonal prisms decussate furnish yet more structural incongruity. At the macroscale level, Hunter-Schreger band (HSB) packing patterns appear to conform to masticatory loading mechanics. This study undertakes a quantitative evaluation of the strength of enamel decussation at the mesoscale in human permanent molars by measuring the degree to which prism pitch angle deviates in adjacent diazones and parazones using scanning electron microscopy. While HSB packing tends to be denser in "functional" cusps, decussational strength tends to be greater in "guiding" cusps, and whereas HSB packing tends to be denser in maxillary molars, decussational strength tends to be greater in mandibular molars. The general lack of concordance between measures of decussation at the mesoscale and macroscale levels may suggest that decussational strength may serve to compensate for lower HSB packing densities in human permanent molars.
The orexinergic/hypocretinergic system appears to be a key promoter of arousal and food intake. Studies of this system in birds have revealed an organizational invariance of the two hypothalamic clusters forming this system, with a strong allometric relationship between orexinergic neuronal numbers and brain mass. Using orexin-A immunohistochemistry, we describe the distribution, morphology and nuclear parcellation of orexinergic neurons within the hypothalami of a further five bird species (helmeted guinea fowl, domestic duck, domestic goose, inca tern, and Caribbean flamingo) where this system had not been previously investigated and iterates the study of this system in the domestic chicken. These birds broaden the phylogenetic studies of this system in birds, with brains ranging in size from 2.8 to 12 g. As in previous studies, the orexinergic neurons were organized in two clusters, a densely packed paraventricular hypothalamic nucleus cluster located within the medial hypothalamus and a more loosely packed lateral hypothalamic cluster in the lateral hypothalamus. In the Caribbean flamingo, orexin-A immunopositive neurons were observed in the medial eminence. Stereological analysis revealed a strong correlation between brain mass and the total number of orexinergic neurons. Thus, unlike mammals, where variances in orexinergic cluster organization have been often noted, in the birds studied to date an organizational consistency is observed, to the exception of one variance noted in the Caribbean flamingo, despite the differences in brain and body mass, phylogenetic relationships, and life histories of the species studied.
Over 40 years ago, a peculiar fossil lagomorph was described from the Middle Miocene of Mallorca (Balearic Islands, Spain). Gymnesicolagus gelaberti possesses enormous teeth with striking morphological features, making its systematic placement enigmatic. Here we revise the holotype and the currently available type material, and we describe additional, previously unreported specimens. Alongside classical comparative approaches, we performed micro-CT-based 3D reconstructions of selected specimens to investigate internal dental features relevant for taxonomic purposes. Several of the peculiar dental traits of G. gelaberti can be interpreted as insularity-driven modifications consistent with the Island Rule (increased size, hypsodonty/hypselodonty). Other traits provide relevant phylogenetic signals linking G. gelaberti to the European MP30-MN1 stem lagomorphs of the "Amphilagus antiquus-Titanomys group". Most notably, a unique and exceptionally rare p3 morphotype discovered in this mainland stock may explain the puzzling p3 morphotype of G. gelaberti as the fixation of a rare character under the founder effect. The evolutionary history of G. gelaberti shows notable similarities to that of Paludotona spp., other endemic insular stem lagomorphs of the western Mediterranean. Both genera are interpreted as deriving from pre-MN2 continental ancestors, are characterized by extended ghost intervals during their early evolutionary histories, and persisted in isolation within fragmented insular domains for several million years.
The heart is the central organ of the cardiovascular system. The myocardium is composed of a three-dimensional network of fibers arranged in clockwise and counterclockwise helices, which are essential for proper cardiac contraction. This study aimed to describe the stratigraphic and morpho-functional pattern of the porcine myocardium to provide anatomical and physiological data applicable to both human and animal studies. The projection of myocardial bridges over the interventricular subsinuosal branch was also evaluated. Twenty hearts from domestic pigs were used. After fixation and anatomical preparation, the ventricular myocardial layers and myocardial bridges were dissected and analyzed macro and microscopically. The left ventricle was found to be composed of outer, middle, inner, and cylindrical septal layers, whereas the right ventricle consisted of outer, middle, and inner layers, with its septal wall organized as a transverse septal band. The origin of the myocardial fibers was associated with the four fibrous rings of the cardiac skeleton, and their insertion occurred predominantly within the walls of the interventricular septum. Myocardial bridges were classified as dorsal, middle, or ventral and were present in 65% of the hearts analyzed. Histological and ultrastructural analyses demonstrated collagen and elastic fibers between the myocardial bridges and the associated vessels. It is concluded that the layered and structural organization of the porcine myocardium are consistent with the distinct hemodynamic demands of each ventricle. These findings reinforce the functional significance of myocardial architecture in ventricular mechanisms and support the use of the pig as a relevant model for comparative and translational cardiovascular research. The topographic analysis of myocardial bridges revealed their depth-related relationship with the vascular wall and with the outer and middle myocardial layers, suggesting a potential influence on coronary blood flow and cardiac vascularization.
Snake vertebrae possess distinctive morphological features that differentiate them from those of other reptiles. While some of these structures are unique to particular snake groups, enabling direct taxonomic identifications, others are restricted to specific regions of the vertebral column. Among the latter are haemapophyses, paired structures emerging from the ventral surface of the centrum that characterize the caudal vertebrae of most, though not all, snakes. Practically confined to the caudal region, haemapophyses are absent from mid-trunk vertebrae, where other structures appear. Here, we report an extraordinary case of haemapophyses-like structures ("quasi-haemapophyses") occurring in mid-trunk vertebrae of the African elapoid snake Atractaspis corpulenta kivuensis. This bizarre taxon possesses, uniquely among all known snakes (extinct or extant), distinct "quasi-haemapophyses" throughout its mid-trunk and posterior trunk vertebrae, which diminish only in the posteriormost trunk region. Haemapophyses subsequently reappear, albeit in modified form, in the cloacal and caudal regions. In addition to a detailed analysis of vertebral morphology and intracolumnar variation, we compile and review all published figures of Atractaspis vertebrae, as well as providing documentation for additional species-rendering this the most comprehensive vertebral study conducted for the genus to date.
The aim of this study was to provide a detailed anatomical description of the aortic arch branches in Geoffroy's cat (Leopardus geoffroyi). Fifteen adult and subadult specimens were included in the study, comprising six adult males, three subadult males, two adult females, and four subadult females. Of these, five selected specimens underwent contrast-enhanced thoracic radiography, including three males (one adult and two subadults) and two females (one adult and one subadult). Latex injection followed by anatomical dissection was performed in five individuals, whereas the remaining 10 underwent direct anatomical dissection without prior injection. In all examined specimens, after the origin of the coronary arteries, the aorta first gave rise to the brachiocephalic trunk (truncus brachiocephalicus), followed by the left subclavian artery. In 13 of the 15 animals (86.7%), a bicarotid trunk originated from the brachiocephalic trunk. The length of the bicarotid trunk ranged from 0.4 to 2.5 cm (mean: 1.3 cm). The right subclavian artery originated as the continuation of the brachiocephalic trunk and gave rise to the internal thoracic, vertebral, costocervical, and superficial cervical arteries. In the remaining two individuals (13.3%), the bicarotid trunk was absent, and the left common carotid artery, right common carotid artery, and right subclavian artery arose directly from the brachiocephalic trunk in a trifurcation pattern. In these specimens, the right subclavian artery originated from the trifurcation and gave rise to the internal thoracic, vertebral, costocervical, and superficial cervical arteries. These branches were present in all individuals, though slight variations were observed in their order of origin and relative spacing. The left subclavian artery exhibited a comparable branching pattern. The combined use of radiographic and dissection techniques allowed precise characterization of the main thoracic arterial pathways. These findings expand the anatomical knowledge of L. geoffroyi and provide relevant information for diagnostic imaging, surgical approaches, and clinical management of Neotropical wild felids.
Musculoskeletal modeling offers a non-invasive approach to analyze human movement, enabling estimation of forces that are difficult to measure experimentally. In musculoskeletal modeling, the human body is represented as rigid segments connected by joints. Complex structures (i.e., the foot) are often modeled as a single rigid segment due to challenges in capturing the motion of individual bones with conventional gait analysis. Additionally, internal joint locations typically require invasive imaging to be accurately determined. Here, we propose a regression-based method to locate the in vivo positions of mid- and hindfoot joint centers using three-dimensional surface markers. Simulated weight-bearing computed tomography (SWCT) scans of 20 individuals were randomly assigned to training (n = 16) and validation (n = 4) datasets. Surface models of each foot were generated, and anatomical markers identified in Avizo Lite 9.0.1. Forty additional landmarks were placed within each foot to represent internal joint centers of 20 mid- and hindfoot joints. Best-fit models for each joint center were generated using stepwise regressions on the training set and evaluated on the validation set. Regression models showed strong predictive performance for all mid- and hindfoot joints based on external skin markers, with r2 values ranging from 0.79 to 0.98 and generally low standard errors of estimate (X: r2 = 0.91-0.99; SEE: 0.002-0.6 mm; Y: r2 = 0.93-0.99; SEE: 0.004-0.6 mm; Z: r2 = 0.70-0.96, SEE: 0.02-0.5 mm). These predictive equations thus provide a practical tool for researchers aiming to develop and validate detailed musculoskeletal models of the foot.
Mustela, one of the most species-rich and widespread genera of Carnivora, has a 4-million-year fossil record that mainly comprises permanent teeth, of which postcanines (premolars and molars) are most useful for taxonomic identification. To evaluate the utility of a simple method using linear measurements of permanent postcanines for body size estimation in extinct and extant Mustela, we correlated 25 linear measures of permanent postcanines with the condylobasal skull length (CBL; which in Mustela strongly correlates with both body mass and length) in three representative species of this genus (least weasel, M. nivalis; ermine, M. erminea; European polecat, M. putorius). Most postcanine measures were strongly correlated with CBL (Pearson's r > 0.70) in all species, which supports their utility for body size estimation in Mustela. Three of these measures (the mandibular first molar's mesiodistal length, the maxillary first molar's buccolingual width, and, to a lesser degree, the maxillary fourth premolar's mesiodistal length measured between the parastyle and protocone lobes) consistently showed a relatively high level of correlation with CBL in all species, and we therefore propose these measures as the best simple dental predictors of body size in Mustela. The differences in the strength of correlation of postcanine measures with CBL observed here between closely related species and between and within teeth emphasize the need for caution in using dental dimensions as a surrogate for body size.
Correct identification of Rhea americana and Rhea pennata in the fossil record has important paleoenvironmental implications; however, the strong similarity between their postcranial skeletons complicates taxonomic assignments. This study analyzes hindlimb morphology in both species to identify diagnostic characters useful for fossil and archaeological material and to reassess previously reported remains. Femora, tibiotarsi, and tarsometatarsi of adult and juvenile R. americana and R. pennata, comprising a total of 37 specimens, were comparatively analyzed using qualitative morphology and linear measurements. Several osteological differences were identified, particularly in distal tibiotarsal and tarsometatarsal morphology, including trochlear configuration and divergence patterns. Some differences are maintained in juvenile specimens, although ontogenetic variation may complicate identification in certain cases. Reevaluation of fossil and archaeological specimens supported revised taxonomic interpretations for several specimens, whereas poorly preserved or morphologically ambiguous materials were conservatively assigned to Rheidae indet. Although hindlimb bones of R. americana and R. pennata are broadly similar, distal tibiotarsal and especially tarsometatarsal morphology provide useful diagnostic characters. Trochlear configuration and divergence appear to be among the most consistent features, whereas other traits are affected by ontogenetic, intraspecific, and preservational variation. These results contribute to a more robust framework for identifying fossil rheids and highlight the importance of evaluating multiple characters when dealing with fragmentary material.
Traversodontids are non-mammaliaform cynodonts, herbivorous to omnivorous, that lived during the Triassic. In the Late Triassic, some members of this group increased in body size relative to other cynodont lineages and evolved postcranial adaptations associated with locomotion. The Late Triassic Siriusgnathus niemeyerorum is one such traversodontid. Originally described in 2018 based on cranial material, the species has since been the focus of considerable advances in our understanding of its skull anatomy; however, its postcranial skeleton remains undescribed. The present study examined the postcranial osteology of this traversodontid, focusing on the pectoral girdle and forelimb of the specimen CAPPA/UFSM 0109, paratype of the species. These remains show that Si. niemeyerorum presents a scapulocoracoid with concave anterior and posterior margins and a lateroventrally oriented glenoid fossa formed by the scapula and coracoid; a humerus with a short diaphysis and a broadly open deltopectoral crest; an ulna with a developed olecranon process; and a manus with a phalangeal formula of 2-3-3-3-3. One of the distal carpals (dc1) is greatly elongated and morphologically similar to a metacarpal, a feature observed in some gomphodonts. The combination of traits present in the scapulocoracoid (glenoid) and the robustness of the humerus suggests a lateralized ("sprawling") forelimb posture in Si. niemeyerorum, similar to that inferred for Exaeretodon argentinus and Exaeretodon riograndensis. In summary, this study expands current knowledge of traversodontid postcranial anatomy and provides new insights into the locomotor adaptations among non-mammaliaform cynodonts.
Diffusible iodine-based contrast-enhanced microCT (DiceCT) enables three-dimensional visualization of mineralized and soft tissues while preserving their spatial relationships in situ. We present a DiceCT-based digital atlas of a human hand from a consented female donor through the University of Missouri Gift of Body program, scanned at 48.8 μm resolution following Lugol's iodine staining. Bones, tendons, intrinsic muscles, neurovascular structures, the flexor retinaculum and carpal tunnel, and dorsal digital expansions were manually segmented to generate labeled multiplanar sections and three-dimensional reconstructions. The dataset resolves epidermal ridge detail on the palmar surface while capturing structures, including the carpal tunnel contents, extensor mechanism, neurovasculature, palmar fat pads, and metacarpophalangeal sesamoids. Reconstructions demonstrate relevant relationships among the median nerve, flexor tendons, and flexor retinaculum, the ulnar nerve within Guyon's canal and the radial artery within the anatomical snuffbox. Distal digital arterial anastomoses are visible near the terminal tufts, and radial artery branches supplying the dorsal and distal scaphoid poles provide context for scaphoid vascular vulnerability. Muscle volumes and physiological cross-sectional areas were calculated using all fascicles within each intrinsic muscle. Flexor pollicis brevis and adductor pollicis exhibited comparatively large relative physiological cross-sectional areas, whereas the lumbricals had the smallest values, consistent with previous architectural estimates. By documenting whole-hand anatomy and within-individual muscle architecture non-destructively, this atlas provides a high-fidelity resource for anatomical education, documentation of anatomical variation, clinical interpretation, and generation of anatomically consistent biomechanical models. These results support DiceCT as a platform bridging anatomical research, clinical translation, and pedagogical access to donor-specific human anatomy.
The question of dental reduction in primates has been a longtime debate, especially in Indriidae, where the tooth type of the dental comb has been extensively investigated. While the presence of two incisors without the canine is largely accepted today, some questions remain concerning the homology of teeth preserved in the lower postincisor dentition. Although the presence of the dc1, dp2, and dp3 is clearly distinguishable during development, two teeth disappear at the adult stage. Consequently, some authors identify the remaining postincisor replacement tooth as a P3, while some studies indicate the identity as the P2. Here, the observation of several specimens of Propithecus coquereli at different developmental stages (late fetal, newborn, infant, and adult) using 3D reconstructions and histological sections sheds light on the characterization of this tooth as P2, with a loss of the lower canine and P3. Among the deciduous teeth, dc1 and dp3 are smaller, at an advanced stage of eruption, and lack adjacent replacement teeth. In contrast, the first deciduous premolar (dp2) has a replacement tooth (P2) clearly adjacent to it at the late fetal stage. The development of the permanent dentition in P. coquereli reflects its precociality, with the replacement tooth buds already developed and the M3 showing an advanced stage of mineralization at birth. In addition, the morphological variability of P2 and P4 may have implications on diet adaptations, being involved in the two phases of oral food processing (ingestion and mastication). Thus, this work brings new insights concerning the issue of dental reduction in primates, clarifying the homology of teeth at the adult stage in this species. Addressing this question provides new perspectives on the history of dental reduction in the genus Propithecus and on the functional role of premolars in relation to dietary adaptations.
