Among modern aquatic amniote clades that evolved pelagic locomotion, whales are a prime example, but timing and mode of evolutionary changes in their swimming are poorly understood. Here, we use 3D vertebral microanatomy derived from CT scanning to investigate swimming patterns in extinct whales. All vertebral centra from a single specimen of the extant common dolphin Delphinus delphis were used to provide a baseline for the correlation of microanatomical parameters and spinal movements in our dataset of fossil whales. We find that bone anisotropy, and to some extent bone compactness, mirrors the amount of compression and movement in vertebral regions. We use these parameters to infer regional movements and thus swimming mode for several lineages of stem cetaceans (Natchitochia jonesi, Pachycetus wardi, Zygorhiza kochii) and crown cetaceans (Maiabalaena nesbittae, an undescribed Oligocene odontocete and a modern minke whale). Natchitochia jonesi could walk on land, whereas Pachycetus wardi and Zygorhiza kochii were obligately aquatic, but show more spinal flexibility than modern taxa. The early Oligocene mysticete and odontocete differ in microstructural properties and might have experienced a different trajectory towards their extant bauplans. Overall, microanatomical data confirm increasing pelagic specializations in cetacean evolution that include a stiffer torso, but our data also highlight modular patterns of compactness within vertebral regions. Our approach is promising for future use of three-dimensional vertebral microanatomical data to understand locomotory patterns.

Fragmentary skull remains are common in zooarchaeological assemblages, yet they pose significant challenges for taxonomic identification because complete skulls are rare. This study investigated whether three resilient cranial regions: the body of the maxilla, the exoccipital region, and the bony palate, retain sufficient shape information to discriminate among caprine taxa. The sample comprised domestic sheep (Ovis aries), wild Marco Polo sheep (Ovis ammonpolii), domestic goat (Capra hircus), and Tatra chamois (Rupicapra tatrica). Three-dimensional landmarks were digitized on surface-scanned skulls. All three regions exhibited significant inter-group shape differences (p: 0.0001). The body of the maxilla provided the strongest discrimination (R[2] = 0.520), clearly separating ovine from caprine taxa along an axis linked to the relative position of the caudodorsal facial-orbital region versus the infraorbital and alveolar sectors. The exoccipital region showed intermediate discriminatory power, whereas the bony palate exhibited the weakest group structure and the greatest overlap. Centroid size differed significantly among groups (wild sheep being the largest), but shape differences remained significant after accounting for size. Isolated skull fragments, particularly the maxillary body, retain reliable diagnostic shape information for distinguishing caprine taxa. When analyzed using geometric morphometrics, these fragments can serve as valuable analytical units in zooarchaeological studies, even in highly fragmented assemblages.

Very little is known about the early brain evolution of Metatheria, and no brain endocast of this group has been described from prior to the Cretaceous-Paleogene (K-Pg) boundary. This has led to great uncertainty regarding the ancestral condition of the therian brain. Here, we aim to fill some of this gap by describing the first brain endocast of a Cretaceous metatherian, Lotheridium mengi from the Late Cretaceous of Henan, China. Lotheridium has an encephalization quotient comparable to the Cretaceous multituberculate Chulsanbaatar and eutherian Asioryctes and reaches the lower range of crown mammals. Together with patterns observed in other Mesozoic mammals, this suggests that increased encephalization evolved independently in several major mammalian lineages. The endocast is characterized by relatively small olfactory bulbs, well-developed petrosal lobules, and a prominent hypophyseal cast, differentiating it from earlier mammals. With the addition of a dorsally exposed midbrain, Lotheridium closely resembles the condition observed in Cretaceous eutherians. We propose that reduced olfactory bulb proportions and increased endocranial volume in Cretaceous eutherians and metatherians reflect a major shift in mammalian brain evolution, from primarily olfactory bulb expansion in the Jurassic to predominantly neocortical, brainstem, and cerebellar expansion in the Late Cretaceous. The endocranial morphology of Lotheridium further indicates that several neuroanatomical features characteristic of Paleogene and extant marsupials, including relatively enlarged olfactory bulbs and a smaller brain size compared to eutherians, are unlikely to represent the plesiomorphic condition for Metatheria. Ultimately, Lotheridium provides crucial new information regarding the ancestral condition of marsupial brains.

Postcranial skeletal proportions in living apes have been linked to patterns of arboreal behaviors within and between populations, offering a comparative baseline for interpreting arboreal behavior in fossil hominoids. We quantified metatarsal and proximal phalangeal lengths across all five pedal rays in Gorilla, comparing western lowland gorillas (Gorilla gorilla gorilla), low- and high-elevation Grauer's gorillas (Gorilla beringei graueri), and two ecologically distinct mountain gorilla (Gorilla beringei beringei) populations: those of Bwindi Impenetrable National Park, Uganda, and the Virunga Massif (Volcanoes National Park, Rwanda). The Bwindi sample, assembled from individuals recovered by the Mountain Gorilla Skeletal Project between 2017 and 2025, represents the first substantial pedal dataset for this population. After separately scaling element lengths by estimated body mass and hindlimb length, Bwindi gorillas' third and fourth metatarsal lengths fell consistently between those of the more arboreal western lowland and highly terrestrial Virunga gorillas, while proximal phalangeal and hallux lengths varied little across populations. Additionally, Virunga gorillas showed longer second metatarsals compared to other populations, a feature we link to their strongly terrestrial locomotor habits. In comparing relative manual and pedal element lengths from the same individuals, metacarpals were relatively longer than metatarsals across all populations in rays 2-5, with this pattern reversed in the hallux; among these, only the second ray showed a significant interpopulation difference, with western lowland gorillas exhibiting relatively longer metacarpals than all other groups. Though interpopulation differences in the lengths of pedal elements were generally weaker than those found in the manual elements of the same individuals, these findings suggest that habitat-associated variation in foot morphology can be detected between populations of gorilla subspecies, underscoring the value of fine-grained, population-level skeletal comparisons for refining locomotor inference in the hominoid and hominin fossil record.

Hybridisation between Andrias japonicus and A. cf. davidianus lineages is a major conservation concern in Japan, but whether hybrid individuals retain the suction-feeding pattern described for non-hybrid Andrias remains unclear. We analysed suction feeding in six hybrid giant salamanders using 20 captive feeding events recorded with lateral and frontal high-speed videography. Skull, lower jaw, hyobranchial and prey movements were digitised to quantify trajectories, velocities and accelerations during the active expansion phase of prey capture. The hybrids displayed the characteristic suction-feeding sequence described for cryptobranchids, including mandibular opening, hyobranchial expansion, prey acceleration and capture once suction was initiated. Event-level variation occurred in relation to prey position, attack configuration and individual morphometrics, highlighting the flexibility of suction feeding performance among hybrid specimens. Overall, hybrid specimens retained suction-feeding kinematics within the functional pattern previously described for Andrias, suggesting that hybridisation does not disrupt the core biomechanical organisation of prey capture within the functional range examined here. When compared with published data for non-hybrid A. davidianus and A. japonicus, these results indicate a broadly conserved suction feeding mechanism rather than a distinct hybrid-specific feeding mode. Therefore, any potential ecological advantage of hybrids is unlikely to result from a fundamental change in the suction feeding sequence alone.

The ability to quantify 3D morphologies is critical for anatomical research; however, setting up high-density landmark sets and positioning them on all specimens can represent a substantial challenge. The coherent point drift (CPD) algorithm, a technique for registering two point clouds based on the Gaussian mixture model, was recently used to investigate human variation; however, its performance has yet to be compared to other 3D shape analysis methods. Here we compare the results of a CPD analysis to a sliding semilandmark and weighted spherical harmonic (SPHARM) analysis of the same 60 human and African ape calcanei and a CPD analysis and SPHARM-sliding analysis (a combination SPHARM and sliding semilandmark analysis) of 40 primate third manual proximal phalanges (mPP3s) to determine methodological comparability. Additionally, we run a CPD analysis on a small but wide-ranging sample of primate ulnae to demonstrate its utility for proximodistally long and mediolaterally narrow long bones. All specimens were surface or micro-CT scanned. All calcanei were subjected to a CPD analysis with 2000 semilandmarks, a sliding semilandmark analysis with 1007 semilandmarks, and a SPHARM analysis. All mPP3s underwent a CPD analysis with 2500 semilandmarks and a SPHARM-sliding analysis with 2562 semilandmarks. For the ulna, a CPD analysis with 1252 semilandmarks was run. Shape variation for all analyses was summarized using (separate) principal component analyses (PCAs). Results of the respective analyses for the calcaneus and mPP3 were compared by calculating the maximum and root mean square distances (RMSD) between average taxon shape configurations (scaled based on centroid size) generated from each analysis. All three calcaneus analyses separate taxa along the first two PCs, with humans separating from African apes along PC1 and chimpanzees and gorillas separating across PC2. For the two mPP3 analyses, the three great ape taxa consistently separate along PC1, and Papio separates from the other taxa along PC2. The average RMSD between CPD and sliding semilandmark analyses for the calcaneus was 0.24 mm, and 0.21 mm between CPD and SPHARM analyses. For the mPP3, the average RMSD between CPD and SPHARM-sliding was 0.14 mm. These results indicate that CPD is a comparable 3D shape analysis method to these other approaches. The CPD analysis was also able to place a semilandmark set on primate ulnae ranging from gorillas to tarsiers and capture morphological variations including shaft curvature, relative olecranon process length, and overall robusticity. CPD analyses are less time intensive than sliding semilandmark analyses; however, the sliding semilandmark analysis was better able to capture variation surrounding the borders of the articular facets (although differences were relatively minor), suggesting that these analyses may be better suited when the researcher is interested in a specific anatomical feature. CPD did capture edges better than SPHARM analyses; however, this is likely not an issue for small, relatively round bones such as carpals and most tarsals. In sum, CPD produces similar results to sliding semilandmark, SPHARM, and SPHARM-sliding approaches and has benefits for analyses of long bones with complex morphologies or among taxa that exhibit large amounts of morphological variation.

Pelvic floor dysfunction is a common condition in adult women. In addition to the levator ani, the obturator internus, a lateral pelvic wall muscle, has been suggested to be anatomically and mechanically associated with pelvic floor morphology. Here, we quantitatively characterized age-related morphological changes in the obturator internus and levator ani using geometric morphometric analysis. We hypothesized a significant association between principal components accounting for major shape variation and age. This cross-sectional study included 27 adult women aged 25-83 years with gynecological conditions but without pelvic floor disorders based on clinical assessment and imaging findings. Standardized pelvic magnetic resonance imaging scans were obtained between April 2024 and July 2024 at a single tertiary care center. Elliptic Fourier analysis was applied to the segmented obturator internus contours; a landmark-based method was used to evaluate the combined shape of the obturator internus and levator ani. Principal component analysis and linear regression were performed to assess associations with age. Procrustes analysis of variance was used to evaluate the overall shape-age relationships. Elliptic Fourier analysis revealed that increasing age was significantly associated with relative narrowing of the superior portion, an inferior morphological shift of the medial surface groove, and increased prominence of the medial eminence of the obturator internus. A landmark-based analysis revealed similar age-related shape changes, including inferiorly directed shape changes of the groove, verticalization of the levator ani, and widening of the levator hiatus. Procrustes analysis revealed a significant relationship between age and overall shape variation. Aging was associated with coordinated age-related morphological remodeling of the obturator internus and levator ani.

Quantitative data on the spatial development of intrarenal S100-positive nerve-associated profiles in human foetal kidneys remain limited, despite the established importance of renal nerves. Building on the previously published semiquantitative observations, this study aimed to generate a quantitative, compartment-resolved map of S100-positive nerve-associated profiles in human foetal kidneys. Formalin-fixed, paraffin-embedded human foetal kidney specimens ranging from 14 to 30 gestational weeks were analysed using S100 immunohistochemistry. Based on gestational age, specimens were divided into three groups: ≤18 gestational weeks (G1, n=6), 19-24 gestational weeks (G2, n=6), and ≥ 25 gestational weeks (G3, n=6). Cortical maturation was assessed by measuring nephrogenic zone and maturation zone thickness and calculating the cortical maturation index (CMI). Morphometric analysis of cortical S100-positive nerve-associated profiles was performed using digital image analysis. Distribution patterns of S100-positive profiles were assessed qualitatively. Group-wise analysis demonstrated significantly lower cortical S100-positive area in G1 compared with G2 and G3 (median: 985 μm[2] vs. 1733 μm[2] and 2400 μm[2], respectively; p < 0.001). Cortical S100-positive area increased significantly with gestational age and foetal weight and showed an inverse correlation with CMI (ρ = -0.410, p < 0.001), indicating parallel progression of S100-positive area and cortical maturation. In multivariate linear regression analyses, cortical S100-positive area remained independently associated with gestational age (β = 125.0, p = 0.006) and foetal weight (β = 1.50, p = 0.006), explaining 57.6% of the variance (adjusted R[2] = 0.485). Perivascular localisation was the most frequently observed distribution pattern, while juxtaglomerular and intraglomerular patterns were also identified, including in the earliest gestational-age group. This study provides the first quantitative, compartment-resolved analysis of intrarenal nerve-associated profiles in the human foetal kidney. Cortical S100-positive area increases with gestational age in parallel with cortical maturation and shows a predominantly perivascular distribution, consistent with a neurovascular co-development model and establishing a morphological framework for future functional studies of renal innervation.

Developmental anomalies provide a powerful window into the rules and constraints shaping morphological evolution. Here, we use anatomical network analysis to investigate how congenital perturbations affect the structural organization of anuran limbs. We analyzed a specimen of Leptodactylus bufonius exhibiting bilateral brachydactyly in both fore- and hindlimbs and unilateral polyphalangy, and compared its limb networks to those of a typical conspecific. Developmental perturbations resulted in structural reorganization, including reduced node and link number and increased graph density. At the node level, betweenness centrality markedly declined in stylopodial and zeugopodial elements, disrupting the characteristic proximodistal hub-periphery organization of the limb. This shift reflects a loss of proximodistal polarization associated with distal reduction. Modular organization was robust to these perturbations: module number remained unchanged in the forelimbs and in the left hindlimb, and decreased in the right hindlimb, which exhibited the most extensive morphological reduction. Although module membership showed subtle changes, the overall number and composition of modules remained broadly conserved across reference and anomalous limbs. Thus, despite substantial anatomical perturbation, modular organization was largely maintained, with marked reorganization occurring only in the most severely affected limb. The anomalous morphology studied here demonstrates that developmental systems can accommodate profound modifications while maintaining organismal viability. Our study engages with the broader community discussion on modularity and the methodological frameworks used to investigate it. More broadly, this study highlights how anatomical network approaches can contribute to evo-devo research by quantifying how developmental disruptions reshape the organization of complex morphological systems.

Here, we reassess the taxonomic affinities and functional morphology of TMM 44190-1, an isolated metacarpal II from the Eocene La Meseta Formation, Marambio (Seymour) Island, Antarctic Peninsula, previously referred to an indeterminate xenarthran. We evaluated its morphological similarities using three-dimensional geometric morphometrics. A principal component analysis, based on a sample of 50 metacarpals representing 38 taxa, including Paleogene terrestrial mammals from Antarctica and South America, as well as extant mammals exhibiting a wide range of terrestrial locomotor habits, was conducted. Additionally, TMM 44190-1 was compared with Eocene taxa from Antarctica and South America, including Gondwanatheria, Metatheria (Sparassodonta, Pucadelphyidae, and Didelphimorphia), South American native ungulates (Astrapotheria, Litopterna, Xenungulata, and Notoungulata), and Xenarthra (Cingulata and Pilosa). Both geometric morphometric and qualitative anatomical evidence consistently support the previous assignment of TMM 44190-1 to Xenarthra and further allow a more precise taxonomic placement, identifying the specimen as an indeterminate Folivora.

The cochlear dimensions relevant to hearing capability generally follow a pattern of allometric scaling with body mass in mammals. Nevertheless, humans exhibit cochlear dimensions larger than expected from the body mass, and it has been proposed that this is related to encephalization. In this study, we investigate whether the link between brain mass and cochlear morphology is unique to humans and whether cranial features other than brain mass impinge on the cochlear morphology in catarrhine primates that exhibit considerable variation in brain mass. Cochlear and cranial dimensions (cochlear length, oval window area, endocranial volume, cranial size, and interaural distance) were measured on three-dimensional surface models for 30 hominoid individuals (humans, chimpanzees, gorillas, orangutans, and gibbons) and 20 cercopithecine individuals (Japanese macaques, mandrills, and baboons). Relations between cochlear and cranial variables were evaluated using generalized linear mixed model (GLMM) and phylogenetic generalized least squares (PGLS) analyses. The endocranial volume better predicts cochlear morphology than the other cranial measurements in catarrhines. Specifically, the average cochlear length per turn exhibits a strong correlation, while the oval window area exhibits a weaker correlation with the endocranial volume in both GLMM and PGLS. Humans do not deviate from the common allometric pattern of cochlear length against endocranial volume in the catarrhine primates studied here. It appears that humans do not necessarily represent an exceptional cochlear morphology in catarrhine primates after accounting for the cranial dimensions and phylogeny. Our data thus indicate that the link between endocranial volume and cochlear morphology could be a more general pattern for catarrhine primates than previously recognized.

The sacroiliac joint (SIJ) serves as a central interface for force transmission from the hindlimbs to the axial skeleton in animals of all species. Its specialized morphology reflects this functional requirement, comprising a smooth auricular surface and a rugose tuberosity covered by interosseous ligaments. In both human and equine medicine, the SIJ is recognized as a primary source of varied back pain. Despite its biomechanical and clinical significance, very limited data exist in small animal medicine concerning the structure, innervation, and clinical relevance of the SIJ. The present study investigated the morphological variation and innervation of the SIJ in the domestic cat (Felis catus). Macroscopic assessment of the joint's innervation was performed on 40 specimens, and 20 dorsal sacroiliac ligaments were analyzed microscopically for the presence of nervous tissue. Additionally, the individual components of the joint were scanned three-dimensionally and measured. The auricular surfaces were subsequently categorized into distinct morphological types. Current investigations have revealed that the dorsal branches of the seventh lumbar and the first sacral spinal nerves course dorsally within the dorsal sacroiliac ligaments, which was confirmed microscopically. Analysis of the size and shape of the articular surfaces showed that the auricular surface can be classified into five different morphological types. No evidence of sexual dimorphism was detected. However, interindividual variation in the size of specific joint components was observed. These findings provide an initial anatomical basis for a better understanding of the SIJ of domestic cats. This enhanced understanding can help optimize diagnostic or therapeutic approaches in small animal medicine. The results therefore may contribute to a preliminary framework for future clinical studies.

Anatomical structures can capture evolutionary history as well as short-term ecological adjustments, but distinguishing these signals remains challenging at fine spatial and temporal scales. In murine rodents, representing one of the most diverse mammalian radiations, mandibular and dental morphology provide powerful markers of both phylogenetic divergence and feeding-related adaptation. This study investigates these signatures in two mouse species co-occurring on the island of Cyprus: the introduced house mouse Mus musculus domesticus and the endemic Mus cypriacus. Although morphologically similar and occasionally syntopic, the two species differ in habitat use and dietary strategies, ranging from anthropogenic resources in M. m. domesticus to a more natural and diversified trophic niche in M. cypriacus. Using 3D geometric morphometrics, shape variation of mandibles and molars was quantified, allowing to identify interspecific differences, allometric patterns, and age-related trajectories of dental wear. The morphometric descriptors were questioned regarding their respective ability to trace phylogenetic divergence, ecological specialization, and ontogenetic dynamics. The results highlight how subtle morphological descriptors can reveal fine-scale ecological processes and species-specific adaptive pathways.

Many species of gecko and all but one species of anole possess enlarged, serially arranged scales on the ventral surfaces of their digits that collectively are referred to as toe pads. These are commonly considered key innovations and have been the subject of many studies within and beyond the biological sciences. The definition of squamate toe pads, however, remains vague. This is particularly problematic for comparative morphological and biomechanical studies wherein toe pad area is commonly employed as a dependent or independent variable or covariate. Lack of a standardized means of delimitation of toe pads impedes accurate measurement of these ecologically and evolutionarily important features and compromises effective comparison between species and studies. Herein, we take a comprehensive approach to the delimitation of the toe pads of the Tokay gecko (Gekko gecko), the species of gecko most frequently studied in relation to the phenomenon of gecko adhesion. In addition to consideration of the broadly adopted, but somewhat arbitrarily delineated, circumscription of toe pads based on characteristics of scale dimensions alone, we also investigate their boundaries by examining the relationship between subdigital scales and subcutaneous anatomical features (employing osteological and tendon-based [TB] criteria). We find that the methods employing only external dimensions of subdigital scales to delimit toe pads overestimate their area, thereby resulting in functional studies that likely underestimate toe pad adhesive stress (force per unit area). Of the two approaches that anatomically delimit toe pads, that based upon tendinous connections (demarcating what we refer to as the LDT region of the digits) encompasses all epidermal filaments that are true setae (those bearing spatulate tips), the only structures empirically validated to facilitate whole-animal adhesion. As such, we encourage future studies to employ the TB approach to accurately delimit gekkotan (and anoline) toe pads in a functionally and anatomically meaningful (and standardized) fashion and provide guidelines about how this can be achieved.