Geometric Morphometric Approach Research Articles

Sexual Dimorphism of the Human Scapula: A Geometric Morphometrics Study in Two Portuguese Reference Skeletal Samples

The estimation of biological sex is of paramount relevance in the analysis of skeletal remains recovered in forensic contexts. This study aims to assess sexual dimorphism for identification purposes, from two reference samples of the Portuguese population, and a depiction of the size- and shape-related sexual dimorphism of the human scapula using geometric morphometrics approaches. The sample comprised 211 individuals (100 males and 111 females). A generalized Procrustes analysis (GPA) was performed for shape analyses, a principal component analysis (PCA) and a Procrustes ANOVA were implemented on the GPA transformed variables, and a discriminant analysis was used to assess the cross-validated accuracy of sex estimates. The data showed that male scapulae were larger, with medial and lateral curves more pronounced and an inferior angle more acute than females. The males and females were classified with low accuracy (66.82% and 65.88% for landmarks and semi-landmarks data) based on shape. Combining size and shape variables improved the accuracy of the prediction using landmarks data (80.09%). A combination of both variables might improve the chances of the geometric morphometrics methodology in correctly estimating the sex of unidentified individuals, especially if the skeletal elements show low sexual shape dimorphism.

Ecomorphology of the cervid intermediate phalanx and its implications for palaeoenvironmental reconstruction.

This paper reports on newly developed ecomorphological models for the cervid intermediate phalanx. Using a geometric morphometric approach, we quantitatively assess the overall gracility of the bone, the depth and concavity of the proximal articulation and the roundness and symmetry of the distal articulation in the intermediate phalanx, to establish relationships between morphology, locomotor behavior and environment. The morphology of the phalanx was found to vary along a gradient from gracile phalanges with shallow proximal articulations in forms adapted to yielding substrate, to robust phalanges with deeper proximal articulations in taxa adapted to firm substrate. Phylogeny and allometry are accounted for using regressions and phylogenetic comparative methods. Although the results indicate phylogeny explains part of the morphological variation, overall the shape of the intermediate phalanx appears mainly driven by differences in function. Consequently, this element promises to be a useful palaeoenvironmental proxy that can be applied on fossil assemblages with cervid remains.

Craniofacial form differences between obese and nonobese children

Current evidence suggests that obesity is correlated with differences in craniofacial form in children and adolescents. Here, we sought to test this hypothesis by evaluating the craniofacial form of obese and nonobese preorthodontic patients, using 2D cephalometric data combined with cephalometric and geometric morphometric approaches. Height, weight, age, and lateral cephalometric radiographs were gathered from patients aged 7-16 years before beginning orthodontic treatment at the University of British Columbia. Based on their body mass index, 24 obese patients were age, sex, and Angle classification of malocclusion matched with nonobese controls. Cephalometric radiographs were annotated, and coordinates of landmarks were used to obtain linear and angular cephalometric measurements. Geometric morphometric analyses were performed to determine overall craniofacial form differences between cohorts. Dental maturation index scores and cervical vertebral maturation scores were recorded as an indicator of skeletal maturation. Cephalometric analysis revealed that the maxillary length and gonial angle are the only marginally larger metrics in obese subjects than in control subjects. However, principal component and discriminant analyses (geometric morphometrics) confirmed that the overall craniofacial form of obese patients differs statistically from that of control patients. Obese patients tend to be slightly mandibular prognathic and brachycephalic. Dental maturation index scores were statistically higher in the obese group than in the control group, with no statistical difference in cervical vertebral maturation scores. Our data reveals a subtle but significant difference in cranial skeletal morphology between obese and nonobese children and adolescents, suggesting a correlation between craniofacial form and physiological/metabolic phenotypes of subjects. It is likely that with continued growth, these differences may increase. Recording body mass index as part of the orthodontic records for patients may help in supporting the assessment of craniofacial form.

Better sturdy or slender? Eurasian otter skull plasticity in response to feeding ecology.

Otters are semi-aquatic mammals specialized in feeding on aquatic prey. The Eurasian otter Lutra lutra is the most widely distributed otter species. Despite a low degree of genetic variation across its European range, the population from Great Britain exhibits distinct genetic structuring. We examined 43 skulls of adult Eurasian otters belonging to 18 sampling localities and three genetic clusters (Shetlands, Wales and Scotland). For each sample location, information regarding climate was described using bioclimatic variables from WorldClim, and information on otter diet was extracted from the literature. By using photogrammetry, 3D models were obtained for each skull. To explore any evidence of adaptive divergence within these areas we used a three dimensional geometric morphometric approach to test differences in skull size and shape between areas with genetically distinct populations, as well as the influence of diet, isolation by distance and climate. Males were significantly larger in skull size than females across all the three genetic clusters. Skull shape, but not size, appeared to differ significantly among genetic clusters, with otters from Shetland exhibiting wider zygomatic arches and longer snouts compared to otters from Wales, whereas otters from Scotland displayed intermediate traits. A significant relationship could also be found between skull shape variation, diet as well as climate. Specifically, otters feeding on freshwater fish had more slender and short-snouted skulls compared to otters feeding mostly on marine fish. Individuals living along the coast are characterised by a mixed feeding regime based on marine fish and crustaceans and their skull showed an intermediate shape. Coastal and island otters also had larger orbits and eyes more oriented toward the ground, a larger nasal cavity, and a larger distance between postorbital processes and zygomatic arch. These functional traits could also represent an adaptation to favour the duration and depth of diving, while the slender skull of freshwater feeding otters could improve the hydrodynamics.

Influence of nasal septum deviation on fluctuating asymmetries of the nasomaxillary complex: A cross‐sectional study

An important parameter in diagnostic analysis and treatment planning of different biological areas is facial symmetry, and several etiological factors have been attributed to skeletal facial asymmetry. Although causality cannot be determined, previous studies have reported a relationship between the anatomical deviation of the nasal septum and facial development. Diagnosis is critical for patients in growth stages due to the association between nasal septum deviation (NSD) and abnormal growth of the nasomaxillary complex. To understand this relationship, this study aimed to investigate the influence of nasal septum deviation on fluctuating asymmetries (FA) of the nasomaxillary complex at different stages of skeletal maturation. Another goal was to determine whether an association exists between the degrees of septal deviation severity and asymmetry of the nasomaxillary complex. This was a retrospective, cross-sectional observational study comprising 60 selected cone-beam computed tomography (CBCT) scans that were divided into four groups (n= 15) according to the degree of septal deviation and skeletal maturation: mild deviation (MD; <10°), moderate to severe deviation (MSD; ≥10°), early group (EG), and late group (LG). The angle and area of deviation were measured for the greatest NSD, and a geometric morphometric approach was used to evaluate the nasal septum (NS) shape. The morphology of the nasomaxillary complex and the presence of fluctuating asymmetries were evaluated using 23 two-dimensional landmarks on the nasomaxillary complex (nasal, lateral, and palatal regions) with Procrustes ANOVA and Mann-Whitney test. Additionally, Spearman's correlation and multivariate regression were used to correlate the NSD with asymmetries in these regions. No significant differences were observed in the Procrustes FA scores of the nasomaxillary complex between the MD-EG × MSD-EG and MD-LG × MSD-LG (p> 0.05). However, the results of the multivariate regression revealed more specific aspects of asymmetry (asymmetry component), there was a positive correlation between the NSD angle and the palatal regions (p= 0.035 and p= 0.047, middle and posterior, respectively), and the nasal septum shape and anterior palatal regions (p= 0.039). The nasal and lateral regions did not correlate with the NSD angle in the multivariate regression analysis (p> 0.05). The results of this study indicate that there were no significant differences in the fluctuating asymmetry of the nasomaxillary complex between the mild and moderate to severe nasal septum deviation groups, in both early and late skeletal maturation stages. However, a positive correlation was observed in the degree of nasal septum deviation angle and asymmetry components of the middle and posterior palatal regions, likewise between the nasal septum shape and asymmetry components of the anterior palatal region. The diagnosis of nasal septum deviation by both physicians and dentists is important, as a relationship was observed with fluctuating asymmetry component of the palatal region. This information can guide the decision of the treatment planning for these individuals, and should be considered, especially in cases of severe septum deviation, due to the great anatomical proximity of these structures.

Presence of morphological integration and modularity of the forcipular apparatus in Lithobius melanops (Chilopoda: Lithobiomorpha: Lithobiidae)

The presence of morphological integration and modularity of the forcipular apparatus, despite its evolutionary significance, has not been analyzed in centipedes. This morphological structure has a crucial role in feeding and defense, thanks to its poisonous part (forcipules), which is important for catching the prey. The aims of our study were: i) to test the hypothesis of modularity of the forcipular apparatus in centipede Lithobius melanops; and ii) to investigate the influence of allometry on overall morphological integration in the aforementioned species using a geometric morphometric approach. The presence of fluctuating asymmetry was obtained by Procrustes ANOVA. Allometry was significant only for the symmetric component of the forcipular apparatus. The modularity hypothesis was not accepted, because the covariance coefficients for symmetric and asymmetric components were lower than 89.5% and 72.1% (respectively) of other RV coefficients obtained by a random contiguous partition of the forcipular apparatus. Results of the present study indicate that allometry does increase the level of morphological integration in the forcipular apparatus. According to our results, the forcipular coxosternite and forcipules could not be considered as separate modules; namely, they probably share similar developmental pathways and function in different forms of behavior and survival in L. melanops.

Morphological disparity trends in Devonian trilobites from North Africa

AbstractThe Devonian was a time of drastic environmental change that shaped the morphology of trilobites. This study aims to investigate their morphological evolution and to show the influence of some abiotic and biotic factors (bathymetry, feeding habits and visual abilities) on their shape. A dataset was compiled to investigate the shape of three structures (cephalon as a whole, central part of the cephalon, and pygidium) of Devonian trilobites from North Africa, using a geometric morphometric approach. Based on empirical morphospaces, the morphological changes were quantified through the Devonian stages. The results reveal important variations in the morphological disparity of the glabella shape, the facial suture location, the pygidial length and the presence of spines. In the Lochkovian, morphological disparity was low, subsequently increased in the Pragian with numerous innovations, and reached a maximum in the Emsian. If the morphospace occupancy remained until the Eifelian, a severe loss of disparity occurred in the Givetian, a time known for important environmental changes. Disparity then remained low in the Late Devonian. The shapes inherited from the Silurian persisted throughout the Devonian whereas Pragian novelties were most affected by losses. These persistent shapes were more versatile for environmental adaptation, helping those trilobites to survive the environmental events. Similarly, the trilobite orders that survived Devonian events had a wide morphological spectrum and were better adapted to withstand environmental change.

Allometric Changes and Shape Comparisons of Two Southwestern Sucker Species and Their Hybrids Using a Geometric Morphometric Approach

AbstractHybridization between two sucker species, Razorback Sucker Xyrauchen texanus and Flannelmouth Sucker Catostomus latipinnis, historically has occurred but has been facilitated by anthropogenic habitat alteration. The ability to differentiate Razorback Suckers from Flannelmouth Suckers and hybrids is essential for the conservation and management of the endangered Razorback Sucker. The purpose of our study was to investigate allometry—that is, how shape changes with length—of Razorback Sucker, Flannelmouth Sucker, and their hybrids. Razorback Sucker and Flannelmouth Sucker were artificially spawned to produce four progenies: Razorback Sucker, Flannelmouth Sucker, female Razorback Sucker × male Flannelmouth Sucker and female Flannelmouth Sucker × male Razorback Sucker. We also used hatchery‐reared Razorback Sucker and wild‐captured Flannelmouth Sucker to fill the size‐class gaps in our data. We conducted geometric morphometric analyses and used conditional inference trees to determine the length at which body shapes begin to differentiate among these four fish types. We used piecewise linear models to understand the allometry of each fish type and to evaluate the size at which body shape begins to differ from the juvenile form. Although we found statistical shape differences between the two hybrids, they would be difficult to detect with the naked eye. The results of our study showed that fish that are smaller than 140 mm total length (TL) are difficult to differentiate using shape alone. With the information provided in this study, field biologists should be cautious when identifying suckers smaller than 140 mm TL in the Colorado River basin.

Maxillary lateral incisor agenesis is associated with maxillary form: a geometric morphometric analysis

Background and objectiveAgenesis of the maxillary lateral incisor occurs in up to 4% of all individuals and requires multidisciplinary treatment. Its developmental origins, however, are not fully understood. Earlier studies documented genetic factors contributing to agenesis but also an association with craniofacial morphology. In this study, we assessed the association between maxillary morphology and lateral incisor agenesis by a geometric morphometric approach to disentangle the roles of developmental plasticity and genetic factors.Materials and methodsWe quantified the maxillary alveolar ridge by 19 two-dimensional landmarks on cross-sectional images of 101 computed tomography scans. We compared the shape and size of the alveolar ridge across patients with unilateral or bilateral agenesis of maxillary lateral incisors and patients with extracted or in situ incisors.ResultsThe maxillary alveolar ridge was clearly narrower in patients with agenesis or an extracted incisor compared to the control group, whereas the contralateral side of the unilateral agenesis had an intermediate width. Despite massive individual variation, the ventral curvature of the alveolar ridge was, on average, more pronounced in the bilateral agenesis group compared to unilateral agenesis and tooth extraction.ConclusionsThis suggests that pleiotropic genetic and epigenetic factors influence both tooth development and cranial growth, but an inappropriately sized or shaped alveolar process may also inhibit normal formation or development of the tooth bud, thus leading to dental agenesis.Clinical relevanceOur results indicate that bilateral agenesis of the lateral incisor tends to be associated with a higher need of bone augmentation prior to implant placement than unilateral agenesis.

Functional and ecomorphological evolution of orbit shape in mesozoic archosaurs is driven by body size and diet

The orbit is one of several skull openings in the archosauromorph skull. Intuitively, it could be assumed that orbit shape would closely approximate the shape and size of the eyeball resulting in a predominantly circular morphology. However, a quantification of orbit shape across Archosauromorpha using a geometric morphometric approach demonstrates a large morphological diversity despite the fact that the majority of species retained a circular orbit. This morphological diversity is nearly exclusively driven by large (skull length > 1000 mm) and carnivorous species in all studied archosauromorph groups, but particularly prominently in theropod dinosaurs. While circular orbit shapes are retained in most herbivores and smaller species, as well as in juveniles and early ontogenetic stages, large carnivores adopted elliptical and keyhole-shaped orbits. Biomechanical modelling using finite element analysis reveals that these morphologies are beneficial in mitigating and dissipating feeding-induced stresses without additional reinforcement of the bony structure of the skull.

Phalanx morphology in salamanders: A reflection of microhabitat use, life cycle or evolutionary constraints?

Morphological patterns are modeled by the interaction of functional, phylogenetic, ecological, and/or developmental constraints. In addition, the evolution of life cycle complexity can favor phenotypic diversity; however, the correlation between stages of development may constrain the evolution of some organs. Salamanders present microhabitat and life cycle diversity, providing an excellent framework for testing how these factors constrain phenotypic evolution. We reconstructed the morphological evolution of the terminal phalanx using a sample of 60 extinct and living species of salamanders. Using a geometric morphometric approach combined with comparative analyses, we further investigated the impact of phylogenetic, ecological, and/or life cycle factors on the shape of the terminal phalanx. We find that the phylogeny has some influence in determining the dorsal shape of the phalanges; whereas a relationship between microhabitat or life cycle and the dorsal and lateral shapes of the phalanx was not observed in the analyzed species. The allometric pattern found in the phalanx shape implies that small phalanges are more curved and with more truncated end than bigger phalanges. The evolutionary rate of phalanx shape was higher in the semiaquatic species, and the morphological disparity was significantly higher on biphasic groups. These results contradict the hypothesis that a complex life cycle constrains body shape. Finally, the phalanx shape of the salamander remains quite conserved from the Mesozoic. This configuration would allow them to occur in the different microhabitats occupied by the salamander lineages.

Testing the Bordes method on handaxes: A geometric morphometric approach

Bordes’ typology has been in use for many years and is widely applied in studies of Early and Middle Palaeolithic stone tools, especially in vocabulary and typological classification in shaping artefacts (mainly flake tools and handaxes). However, over the years, this method has received different critiques, especially regarding the arbitrariness and subjectivism in the definition and classification of some artefacts. The application of geometric morphometric methods (2D or 3D) on the study of stone tools is starting to become widespread. These methodological approaches are highly suitable for measuring patterns in shape change between artefact groups, which would be impossible to establish with more “traditional” methods. This paper aims to analyse the accuracy and reliability of the main types of handaxes established by Bordes, by performing different methods of Geometric Morphometric Analysis. The evidence from this study suggests that a large percentage of the handaxe types noted by Bordes is reliable and correlates with statistically significant changes in shape and only a small percentage of forms have no geometric morphometric significance. Likewise, these findings support the suitability of Geometric Morphometric Analysis on lithic artefact assemblages focusing on the measurement and classification by shape changes.

Direct evidence that late Neanderthal occupation precedes a technological shift in southwestern Italy.

ObjectivesDuring the middle‐to‐upper Paleolithic transition (50,000 and 40,000 years ago), interaction between Neanderthals and Homo sapiens varied across Europe. In southern Italy, the association between Homo sapiens fossils and non‐Mousterian material culture, as well as the mode and tempo of Neanderthal demise, are still vividly debated. In this research, we focus on the study of two human teeth by using 3D geometric morphometric approaches for a reliable taxonomical attribution as well as obtaining new radiometric dates on the archeological sequence.Material and MethodsThis work presents two lower deciduous molars uncovered at Roccia San Sebastiano (Mondragone‐Caserta, Italy), stratigraphically associated with Mousterian (RSS1) and Uluzzian (RSS2) artifacts. To obtain a probabilistic attribution of the two RSS teeth to each reference taxa group composed of Neanderthals and Homo sapiens, we performed and compared the performance of three supervised learning algorithms (flexible discriminant analysis, multiadaptive regression splines, and random forest) on both crown and cervical outlines obtained by virtual morphometric methods.ResultsWe show that RSS1, whose Mousterian context appears more recent than 44,800–44,230 cal BP, can be attributed to a Neanderthal, while RSS2, found in an Uluzzian context that we dated to 42,640–42,380 cal BP, is attributed to Homo sapiens.DiscussionThis site yields the most recent direct evidence for a Neanderthal presence in southern Italy and confirms a later shift to upper Paleolithic technology in southwestern Italy compared to the earliest Uluzzian evidence at Grotta del Cavallo (Puglia, Italy).

Sexual Dimorphism in the Fibular Extremities of Italians and South Africans of Identified Modern Human Skeletal Collections: A Geometric Morphometric Approach.

Simple SummaryThe extremities of the fibula may reflect differences between males and females, although so far only few studies included this bone for post-cranial sex assessment. Our work explored shape and size variation between sexes in identified skeletal samples comprising different populations from Italy and South Africa and showed that fibular extremities are significantly smaller, with narrower articular surfaces in females than in males. Consistent sex-related differences are revealed in fibular form and size in Italians but not in South Africans. Potential application in forensic and bioarcheological contexts may benefit from the use of this approach.Fibular metric variations have revealed their potential in distinguishing between males and females; however the fibula remains scarcely analyzed in studies of sexual dimorphism. This work aims at investigating sexually dimorphic features in fibular proximal and distal epiphyses through geometric morphometrics methods. A total of 136 left fibulae, from two Italian and one South African identified skeletal collections were virtually acquired through CT and laser scanning and analyzed using geometric morphometric methods. Statistical analyses were performed on shape, form, and size variables. Results show that fibular epiphyses are smaller with narrower articular surfaces in females than in males in both extremities. Relevant sexual differences emerge in fibular form and size for the two Italian samples but not for the South African one, likely for its small sample size. Discriminant analysis on form principal components (PCs) offers accuracy above 80% when the samples are pooled, and reaches accuracy of 80–93% when the Italian samples are considered separately. However, our method on form PCs was not successful for the South African sample (50–53% accuracy), possibly due to the small sample size. These results show relevant morphological variation in relation to fibular form and size, with a degree of accuracy that indicates the utility of the present method for sexing human fibulae in both forensic and bioarchaeological contexts for Italian samples.

Review and redescription of species in the brasiliana group of Smicridea (Rhyacophylax) (Trichoptera, Hydropsychidae, Smicrideinae): exploration of the utility of geometric morphometrics as a method for delimitation and characterization of species in the genus.

The Smicrideabrasiliana species group includes five species distributed in northeastern Argentina and Brazil: Smicridea (Rhyacophylax) brasiliana (Ulmer), S. (R.) weidneri Flint, S. (R.) vermiculata Flint, S. (R.) arobasis Flint, and S. (R.) nanda Flint. The original descriptions of these species and their placement in the brasiliana species group were mainly based on the morphology of the male genitalia. However, the fine structure of the internal sclerites of the phallus, which proved to be useful for species delimitation, was not analyzed at the time. In this contribution, we provide a detailed description of the male genitalia and the morphology of the head, and analyze the shape of the wings using geometric morphometrics. The analyzed species can be easily differentiated by the shape of the phallus, especially by the structure of the internal sclerites, the shape of the head in dorsal view, and the shape of the cephalic setose warts. Furthermore, the geometric morphometric approach allowed their separation through the wing shape. The preliminary analysis of these features suggests that the brasiliana species group is not natural but its monophyly should be further tested within the framework of a phylogenetic analysis of all the species of the subgenus Rhyacophylax.

Genomic and gene expression associations to morphology of a sexual ornament in the chicken.

How sexual selection affects the genome ultimately relies on the strength and type of selection, and the genetic architecture of the involved traits. While associating genotype with phenotype often utilizes standard trait morphology, trait representations in morphospace using geometric morphometric approaches receive less focus in this regard. Here, we identify genetic associations to a sexual ornament, the comb, in the chicken system (Gallus gallus). Our approach combined genome-wide genotype and gene expression data (&gt;30k genes) with different aspects of comb morphology in an advanced intercross line (F8) generated by crossing a wild-type Red Junglefowl with a domestic breed of chicken (White Leghorn). In total, 10 quantitative trait loci were found associated to various aspects of comb shape and size, while 1,184 expression QTL were found associated to gene expression patterns, among which 98 had overlapping confidence intervals with those of quantitative trait loci. Our results highlight both known genomic regions confirming previous records of a large effect quantitative trait loci associated to comb size, and novel quantitative trait loci associated to comb shape. Genes were considered candidates affecting comb morphology if they were found within both confidence intervals of the underlying quantitative trait loci and eQTL. Overlaps between quantitative trait loci and genome-wide selective sweeps identified in a previous study revealed that only loci associated to comb size may be experiencing on-going selection under domestication.

Shape Differences in the Auricula of the Human Foetus: A Geometric Morphometric Approach

Shape Differences in the Auricula of the Human Foetus: A Geometric Morphometric Approach

Morphogenetic diversity of the selected hatchery populations of an Indian major carp (Labeo rohita, Hamilton, 1822) in the Mymensingh region of Bangladesh

Environmental changes due to the domestication of wild population in hatchery conditions often lead to morphogenetic alterations in fish. Therefore, this study aimed to determine the genetic purity, demographic history, and population structure of Labeo rohita collected from three hatcheries in Bangladesh using a geometric morphometric approach in conjunction with mtDNA cyt b gene sequences and microsatellite markers. The geometric morphometric analysis revealed significant variation in centroid size (body size) among the different populations of L. rohita. However, MANCOVA and subsequent ANCOVA models showed no significant variation in body shape (relative wraps, RWs) among those populations. Both DNA-based techniques amplified all genotypes and revealed a high degree of genetic diversity across all populations. Clustering analyses based on the Neighbour-Joining (NJ) phylogenetic approach found that the hatchery populations have indisputably diverged from the wild populations. The study of haplotype networks, neutrality testing, and mismatch distributions revealed a complex population expansion pattern involving genetic introgression resulting from human translocation. This tendency is exacerbated further by anthropogenic factors, resulting in the loss of various alleles from hatchery populations. The unevenness of pair-wise FST and the hierarchical analysis of molecular variance of population structure showed a distinct variation between wild and hatchery populations. This genetic loss occurs due to improper domestication processes of the hatchery populations. Ignorance of appropriate hatchery procedures may lead to adverse selection by using poor seed leading to stock deterioration in the hatchery population. This study could help to establish appropriate breeding strategies and provide essential information for the genetic improvement program of L. rohita.

The ontogenetic growth of Anhangueridae (Pterosauria, Pterodactyloidea) premaxillary crests as revealed by a crestless Anhanguera specimen

ABSTRACT The Anhangueridae are a clade of toothed pterodactyloid pterosaurs, known from their characteristic anteriorly expanded premaxillae and conspicuous rostral sagittal premaxillary and dentary crests. Most known anhanguerids come from the Lower Cretaceous Romualdo Formation within the Araripe Basin of northeast Brazil. With four currently valid genera and several specimens referred to the clade, anhanguerids are the most abundant and diverse tetrapod group in the Romualdo Formation. However, some studies suggest this diversity may be overestimated, as many taxa have been diagnosed based on subtle differences in their premaxillary crests, a structure argued to be either ontogenetically variable or sexually dimorphic. Here we describe an anterior fragment of a gracile pterosaur rostrum that possesses the single diagnostic feature of Anhanguera (fifth and sixth pairs of dental alveoli smaller than the fourth and seventh), but lacks a sagittal crest. The affinities of the new fossil among other toothed pterosaurs were tested through both cladistic and geometric morphometric approaches, which allow referral of the new specimen to Anhanguera. The absence of a crest in the new specimen of Anhanguera suggests that this structure varies in terms of ontogeny and/or sex, and that perhaps it was influenced by sexual selection.

Sexual dimorphism in shell size of the land snail Leptopoma perlucidum (Caenogastropoda: Cyclophoridae).

Sexual dimorphism in the shell size and shape of land snails has been less explored compared to that of other marine and freshwater snail taxa. This study examined the differences in shell size and shape across both sexes of Leptopoma perlucidum land snails. We collected 84 land snails of both sexes from two isolated populations on two islands off Borneo. A total of five shell size variables were measured: (1) shell height, (2) shell width, (3) shell spire height, (4) aperture height, and (5) aperture width. We performed frequentist and Bayesian t-tests to determine if there was a significant difference between the two sexes of L. perlucidum on each of the five shell measurements. Additionally, the shell shape was quantified based on nine landmark points using the geometric morphometric approach. We used generalised Procrustes and principal component analyses to test the effects of sex and location on shell shape. The results showed that female shells were larger than male shells across all five measurements (all with p-values < 0.05), but particularly in regards to shell height and shell width. Future taxonomic studies looking to resolve the Leptopoma species’ status should consider the variability of shell size caused by sexual dimorphism.