Geometric Morphometric Analysis Research Articles

Mandibular shape as a proxy for the identification of functional feeding traits of midge larvae (Diptera: Chironomidae)

The identification of functional feeding traits in aquatic macroinvertebrates often requires a morphology-based identification of species, which is important for trait-based methods of biological assessment. The extent of functional homogenization is compared along scales of impairment, where trait-based information is used as an input in models that examine degradation pathways. However, trait-based information is not always readily available for all groups of aquatic insects, especially for species diverse families, such as chironomids (Diptera: Chironomidae). Taxonomic challenges and ambiguous traits complicate the use of chironomid larvae in trait-based bioassessment. Here, we examine the use of geometric morphometric analysis (GMA), deep learning (Convolutional Neural Networks), and computer vision (deep CNN) applied to the mouthparts (mandibles) of chironomid larvae as a proxy for identifying the relationship between the functional morphology and food acquisition behaviour. We determined the variability in morphology of mandibles for 23 taxa of chironomid larvae from different genera, subfamilies, and their Functional Feeding Group (FFG). Analysis using GMA showed that the five different FFGs examined had different mandibular traits that significantly varied in shape and size. A deep CNN model was then built that was able to classify the 23 taxa into their respective FFG automatically with 92.31 % accuracy. A gradient-weighted Class Activation Mapping (Grad-CAM) algorithm found that the most important part of mandibles for classification were the gula and mandibular joint. We introduced three additional species to the deep CNN models to test whether automatic classification would directly and automatically identify traits of the specimens independently from taxonomic identification. The deep CNN process avoids issues surrounding both taxonomic identification and previous knowledge of a specific taxon’s feeding trait, and in all cases the model classified taxa correctly based on their mandibular traits. The use of deep learning approaches could substantially enhance the use of trait-based approaches and increase the reliability and use of chironomids in bioassessment.

Integrative taxonomy of two morphologically similar species of the subgenus Cryobius Chaudoir, 1838 (Coleoptera: Carabidae: Pterostichus Bonelli, 1810) from northern Eurasia and North America

In this study, we synonymized Pterostichus (Cryobius) kolymensis Erjiomin, 1998 with P. (C.) mandibularoides Ball, 1966 by an integrative approach. Geometric morphometric analysis revealed no obvious differences in the shape of the pronotum and median lobe of the aedeagus between P. (C.) mandibularoides and P. (C.) kolymensis. According to DNA analysis, all examined specimens belong to P. (C.) mandibularoides with 11 unique haplotypes of COI from northern Canada, USA (Alaska) and Russia (Yakutia, Chukotka and Wrangel Island) and 1 haplotype of 28S rDNA from northern Eurasia (Russia). The median-joining haplotype network and the uncorrected COI p-distance values between different geographic populations of P. (C.) mandibularoides suggest the trans-Beringian origin of the species and its subsequent dispersal across North America and northern Eurasia is the most likely scenario of the biogeographic history of the species.

A Comparison of Semilandmarking Approaches in the Visualisation of Shape Differences.

In landmark-based analyses of size and shape variation and covariation among biological structures, regions lacking clearly identifiable homologous landmarks are commonly described by semilandmarks. Different algorithms may be used to apply semilandmarks, but little is known about the consequences of analytical results. Here, we assess how different approaches and semilandmarking densities affect the estimates and visualisations of mean and allometrically scaled surfaces. The performance of three landmark-driven semilandmarking approaches is assessed using two different surface mesh datasets with different degrees of variation and complexity: adult human head and ape cranial surfaces. Surfaces fitted to estimates of the mean and allometrically scaled landmark and semilandmark configurations arising from geometric morphometric analyses of these datasets are compared between semilandmarking approaches and different densities, as well as with those from warping to landmarks alone. We find that estimates of surface mesh shape (i.e., after re-semilandmarking and then re-warping) made with varying numbers of semilandmarks are generally consistent, while the warping of surfaces using landmarks alone yields surfaces that can be quite different to those based on semilandmarks, depending on landmark coverage and choice of template surface for warping. The extent to which these differences are important depends on the particular study context and aims.

Energetic Implications of Morphological Changes between Fish Larval and Juvenile Stages Using Geometric Morphometrics of Body Shape.

The fish body shape is a key factor that influences multiple traits such as swimming, foraging, mating, migrations, and predator avoidance. The present study describes the body morphological changes and the growth trajectories during the transformation from 24 to 54 days post-hatching in the golden grey mullet, Chelon auratus, using geometric morphometric analysis (GMA). The results revealed a decrease in morphological variability (i.e., morphological disparity) with the somatic growth. The main changes affected head size, elongation, and widening of the body. Given that this variability could affect the metabolism, some individuals with different morphologies and in different ontogenetic developmental stages were selected to estimate their potential respiration rate using the Electron Transport System (ETS) analysis. Differences were detected depending on the developmental stage, and being significantly smaller after 54 days post-hatching. Finally, a multivariate linear regression indicated that the specific ETS activity was partially related to the fish length and body shape. Thus, our findings emphasized the relevance of larval morphological variability for understanding the physiological processes that occur during the development.

A landmarking protocol for geometric morphometric analysis of squamate endocasts.

Landmark-based geometric morphometrics is widely used to study the morphology of the endocast, or internal mold of the braincase, and the diversity associated with this structure across vertebrates. Landmarks, as the basic unit of such methods, are intended to be points of correspondence, selected depending on the question at hand, whose proper definition is essential to guarantee robustness and reproducibility of results. In this study, 20 landmarks are defined to provide a framework to analyze the morphological variability in squamate endocasts. Ten species representing a cross-section of the diversity of Squamata from both phylogenetic and ecological (i.e., habitat) perspectives were considered, to select landmarks replicable throughout the entire clade, regardless of the degree of neuroanatomical resolution of the endocast. To assess the precision, accuracy, and repeatability of these newly defined landmarks, both intraobserver and interobserver error were investigated. Estimates of measurement error show that most of the landmarks established here are highly replicable, and preliminary results suggest that they capture aspects of endocast shape related to both phylogenetic and ecologic signals. This study provides a basis for further examinations of squamate endocast disparity using landmark-based geometric morphometrics.

Species morphospace boundary revisited through wing phenotypic variations of Antodynerus species (Hymenoptera: Vespidae: Eumeninae) from the Indian subcontinent

The main objective of this study was to investigate the taxonomic significance of wing phenotypic variations (size and shape) for classifying potter wasps. This is the first study investigating the wing size and shape variations, as well as wing asymmetry, sexual dimorphism, wing integration, and phylogenetic signal analysis of all known Antodynerus species from the Indian subcontinent: A. flavescens, A. limbatus, and A. punctatipennis. We used forewings and hindwings for geometric morphometric analysis, and we proved that each species’ wing had unique size and shape variations, as well as significant right–left wing asymmetry and sexual dimorphism across the Antodynerus species, as verified by discriminant function analysis. Wings of Vespidae are longitudinally folded; based on that, we tested two alternative wing modular hypotheses for evaluating the wing integration, using two subsets organization, such as anterior–posterior (AP) and proximal-distal (PD) wing modular organization. We proved that Antodynerus species wings are highly integrated units (RV > 0.5), and we rejected our hypothesis at p < 0.05. The morphospace distribution analysis revealed that each species has its unique morphospace boundary, although they share some level of homoplasy, which suggests to us that we can use wing morphometric traits for Antodynerus species delimitation. In addition, we revealed the phylogenetic signal of Antodynerus species. Surprisingly, we found a shape-related phylogenetic signal in the forewing, and there is no significant (p > 0.05) phylogenetic signal in forewing size, hindwing shape, and size. We observed that the Antodynerus species’ forewing shape is evolutionarily more highly constrained than the hindwing. We found that A. limbatus and A. flavescens with distinct geographical distribution share a similar evolutionary history, while A. punctatipennis evolved independently.

An Open-Source Photogrammetry Workflow for Reconstructing 3D Models.

Acquiring accurate 3D biological models efficiently and economically is important for morphological data collection and analysis in organismal biology. In recent years, structure-from-motion (SFM) photogrammetry has become increasingly popular in biological research due to its flexibility and being relatively low cost. SFM photogrammetry registers 2D images for reconstructing camera positions as the basis for 3D modeling and texturing. However, most studies of organismal biology still relied on commercial software to reconstruct the 3D model from photographs, which impeded the adoption of this workflow in our field due the blocking issues such as cost and affordability. Also, prior investigations in photogrammetry did not sufficiently assess the geometric accuracy of the models reconstructed. Consequently, this study has two goals. First, we presented an affordable and highly flexible SFM photogrammetry pipeline based on the open-source package OpenDroneMap (ODM) and its user interface WebODM. Second, we assessed the geometric accuracy of the photogrammetric models acquired from the ODM pipeline by comparing them to the models acquired via microCT scanning, the de facto method to image skeleton. Our sample comprised 15 Aplodontia rufa (mountain beaver) skulls. Using models derived from microCT scans of the samples as reference, our results showed that the geometry of the models derived from ODM was sufficiently accurate for gross metric and morphometric analysis as the measurement errors are usually around or below 2%, and morphometric analysis captured consistent patterns of shape variations in both modalities. However, subtle but distinct differences between the photogrammetric and microCT-derived 3D models could affect the landmark placement, which in return affected the downstream shape analysis, especially when the variance within a sample is relatively small. At the minimum, we strongly advise not combining 3D models derived from these two modalities for geometric morphometric analysis. Our findings can be indictive of similar issues in other SFM photogrammetry tools since the underlying pipelines are similar. We recommend that users run a pilot test of geometric accuracy before using photogrammetric models for morphometric analysis. For the research community, we provide detailed guidance on using our pipeline for building 3D models from photographs.

Maxillary dimensions and arch shape with palatally displaced canines.

The aim of this study was to explore the effect of palatally displaced canines on maxillary dimensions and arch shape. Occlusal and skeletal landmarks were plotted on cone beam computed tomography (CBCT) images of 156 orthodontic patients: 78 with palatally displaced canines (PDC) (27 left, 28 right, and 23 bilateral) and 78 controls using Mimics™ (Materialise, Belgium). Arch forms were created, and arch width, depth, and skeletal dimensions were measured. T-test (P < 0.05) was used to compare the groups. Geometric Morphometrics (GM) analysis was used to compare the groups and to explore the pattern of covariation between two sets of landmarks. The unilateral PDC group showed an increased first premolar, second premolar, molar widths, and an increased molar depth. No significant difference was found in arch form. The skeletal measurements were generally larger in the PDC group, but the transverse measurements were the most significant. Discriminant Function Analysis (DFA) with cross-validation allowed an accurate classification of 85.9% of the control group and 66.7% of the PDC group. The Mahalanobis distance displayed significant differences among three combinations of groups. Strong covariance was found between the second premolar and all other landmarks. The small sample sizes of the stratified groups precluded recognition of statistical significance. Patients with unilateral PDC displayed significantly wider first, second premolar, and first molar widths, and increased first molar depths. There were no significant differences in arch form; however, GM showed significant differences between the groups and a prominent covariance function for the 2nd premolars.

Integrative analysis reveals the divergence and speciation between sister Sooty Copper butterflies Lycaena bleusei and L. tityrus

The comparison of closely related taxa is cornerstone in biology, as understanding mechanisms leading up to differentiation in relation to extant shared characters are powerful tools in interpreting the evolutionary process. Hotspots of biodiversity such as the west-Mediterranean, where many lineages meet are ideal grounds to study these processes. We set to explore the interesting example of Sooty Copper butterflies: widespread Eurasian Lycaena tityrus (Poda, 1761) comes into contact in Iberia with closely related and local endemic, L. bleusei (Oberthür, 1884), which hasn’t always been considered a distinct species. An integrative analysis was designed, combining the use of extensive molecular data (five genes), geometric morphometrics analyses, verified and up-to-date distribution data, and environmental niche modelling, aimed at deciphering their true relationship, their placement within European Lycaena and trace their evolutionary history. We revealed several levels of differentiation: L. bleusei and L. tityrus appear to be reciprocally monophyletic independent gene-pools, distinct in all genes analysed, having mutually diverged 4.8 Ma ago. L. tityrus but not L. bleusei, further displays a genetic structure compatible with several glacial refugia, where populations assignable to infraspecific taxa surface. Conversely, L. bleusei shows a loss in mtDNA diversity in relation to nuDNA. Morphological analyses differentiate both species according to size and shape but also discriminate strong seasonal and sexual traits and a geographical phenotype segregation in L. tityrus. Finally, updated distribution and its modelling for current and glacial timeframes reveal both species respond differently to environmental variables, defining a mostly parapatric distribution and an overlapping belt where sympatry was recovered. During the last glacial maximum, a wider expansion in L. bleusei distribution explains current isolated populations. Our study highlights the importance of gathering several lines of evidence when deciphering the relationships between closely related populations in the fringe of cryptic species realm.

Late Acheulean Handaxes from Northeastern Caucasus: Morphology and Technology

We describe the variability of morphological and technological features of handaxes from two culturally and chronologically consecutive Acheulean assemblages of Dagestan, Northeastern Caucasus. The early one, dating to MIS 11–10, is represented by three sites: Darvagchay-Zaliv-1 (complex IV, layer 3), Darvagchay-Zaliv-4 (layer 5), and Darvagchay-Zaliv-2. The late complex, dating to MIS 7, includes the sites of Darvagchay-Zaliv-1 (complex IV, layer 2), Darvagchay-Zaliv-4 (layer 3), and Darvagchay-Karier. We examine analogies from other Acheulean sites in the Caucasus. Two-dimensional geometric-morphometric analysis was used to study the shape of tools from Dagestan. The findings suggest that the shape of unifacial tools is the same as that of Ьifaces. The comparison of tools from two cultural and chronological horizons, including those from contemporaneous sites in the Caucasus, indicates a higher variability in earlier tools. Based on the scar pattern analysis, three chaînes opératoires in manufacturing handaxes were reconstructed. Tools of the later complex had been subjected to a more thorough reduction than those of the early complex. Technological continuity was traced over a considerable timespan (MIS 11–7). It was manifested in the standardization of bifacial shape and the gradual sophistication of chaînes opératoires. Given the high morphological homogeneity of tools from Dargvachay complexes and other contemporaneous industries of the Caucasus, it can be suggested that these technological tendencies are characteristic of the entire Caucasus.

Morphological characterization of some poorly known populations of the genus Spalerosophis Jan, 1865 (Reptilia: Colubridae): is the geometric morphometrics useful to identify them as taxonomic units?

Despite the use of traditional morphology as a standard method for species identification, additional methods like image-based analysis can be desirable to differentiate species and populations. In this study, we used traditional morphology and geometric morphometrics (GM) to describe three distinct populations of the genus Spalerosophis and test the hypothesis that all populations are morphologically distinct. A total of 132 specimens were analysed and based on morphological traits (morphometric, meristic, and colour pattern) subcaudal scales was the only distinguishable trait between Spalerosophis diadema cliffordii and Spalerosophis diadema schirasianus. In addition, Spalerosophis atriceps showed significant differences in most studied characters compared to the other two populations. In the geometric morphometric analysis, we placed 2D Landmarks on the dorsal view images of the head of 93 specimens. Canonical variate analysis (CVA) showed significant differences among the head shape of all three populations. There was an increase in the head width, snout length, and curvature in the posterior part of parietals from west Africa in S. d. cliffordii to the north of India in S. atriceps. This may be the result of variations in their environmental factors, diet and the amount of time that has passed since their separation.

Geometric morphometric analysis of morphological variation in Bogor and Solok populations of bony lip barb (Osteochilus vittatus)

Bony lip barb (Osteochilus vittatus) represents a freshwater species belonging to the Cyprinidae family, which is naturally widely distributed in Southeast Asia. In Indonesia, it is reported to occur widely in the inland waters of the main islands of Java, Sumatra, and Kalimantan. Geographic isolation may contribute to divergent evolution, resulting in phenotypic diversity. The present study used the geometric morphometric method to identify and describe morphological feature differences between geographically distant populations, namely Bogor (West Java) and Solok (West Sumatera). Seventy individual samples were collected from Bogor and Solok, respectively. Images of each sample were taken using a digital camera, then digitized on 17 landmark points using tpsdig software, followed by shape analysis using MorphoJ software. Results showed that Geometric Morphometric analysis could identify and distinguish the body shape of both populations. Morphologically, the Bogor population had a slender body shape, while the Solok population had a shorter and broader (stubby) body shape. A combination of landmark points forming the dorsal arch (LMs 2, 3, and 15), those forming the ventral curve (LMs 9-14), and those located in the peduncle area (LM15) contributed most to the body shape differences. Possible factors causing the observed phenomena are discussed.

Anatomic variations in the frontal and occipital bones: a comparative study of neurocranial morphology

Developmental variations in the cranial vault arise during early ontogenesis due to premature or delayed suture closure, non-union between the normal ossification centers, and emergence of additional ossification centers. These variations cause abnormal calvarial partition and are often associated with modifications of the overall cranial configuration. This study aims to evaluate the impact of metopic suture persistence and the development of supernumerary bones in the occipital region on neurocranial morphology. A series of 245 crania of Bulgarian males was investigated. According to the presence or absence of developmental variations in the frontal and occipital bone they were divided into four series: control (n = 115); crania with a retained metopic suture (n = 32); crania with supernumerary bones in the occipital region (n = 67); and metopic crania with supernumerary bones in the occipital region (n = 31). Polygonal 3D models were generated, on which the 3D coordinates of 35 landmarks describing the neurocranium were collected. Geometric morphometric analyses were applied to compare the size and shape of the landmark configurations. Significant size differences were observed only in the frontal and occipital bone configurations between the metopic crania with occipital supernumerary bones and the non-metopic crania. Significant shape differences were found in all comparisons between the metopic and non-metopic groups for all configurations, except the occipital one. Metopism has a significant impact on overall neurocranial morphology, which is intensified by the presence of supernumerary bones in the occipital region.

Возможности неразрушающего анализа каменных артефактов на примере материалов позднепалеолитических комплексов Южного Приангарья и Верхней Лены

The results of non-destructive analysis of stone artifacts from siliceous rocks from the Late Upper Paleolithic (LUP) sites of the Belaya and Upper Lena Rivers are presented. X-ray fluorescence analysis carried out using a portable device (pXRF) and geometric-morphometric analysis of 3D models were selected as the main methods. The purpose of pXRF was to highlight criteria for differentiating rocks from different sites, issues of searching for sources of raw materials, including the problem of identifying local and non-local components in archaeological complexes, as well as the possibilities of this method in expanding the source base and geography of research. To do this, we selectively analyzed materials from two archaeological sites: 1) Maltinka 1 on the Belaya River (36 samples), and 2) Makarovo 2 on the Upper Lena (12 samples), as well as rock pieces collected near the archaeological site Sosnovyi Bor on the Belaya River. The method of studying 3D models of artifacts we used on a limited collection of the Maltinka 1 site (11 samples) to test how promising it is to use geometric-morphometric analysis in relation to specific LUP materials of Baikal-Yenisei Siberia. Based on the pXRF results, it was established that the siliceous rocks of the Belaya River and Upper Lena collection have significant differences and various origins. Most of the artifacts and rock pieces from Belaya River demonstrate certain similarities in chemical composition. It is concluded that these are local siliceous rocks originating from the deposits of the Lower Cambrian Angara Formation, the outcrops of which are found in many areas of the Belaya River valley. Samples from the Makarovo 2 site show greater variability in chemical composition. It has been suggested that the source for them could be the pebble horizons of the ancient Manzurka Alluvium. One sample from the Upper Lena corresponds in chemical composition to the Belaya collection, which allows us to put forward a version about its imported nature. However, this hypothesis requires testing by expanding collections of artifacts and raw material sources. As a result of the 3D analysis of cores and core preforms, it was established that the samples are quite similar in morphological characteristics, which indicates a high degree of standardization in the production of bifacial blanks. This method has been demonstrated to be effective but is most useful only when the sample and methodologies are expanded.

Digital Morphology: The Final Frontier

Morphology is central to biological anthropology and its allied fields of anatomical sciences, forensics, and other related disciplines. Many biological anthropology students have their first real foray into the discipline after completing a course in osteology, craniometry, or vertebrate morphology. Unfortunately, the natural history collections that support this type of research and training have not grown. Many countries have strict rules about natural history specimen collections, and these collections seem to be concentrated in a few developed countries, regardless of where the specimens had been collected. Thus, access to comparative material can be problematic where such collections are not readily available. Even if collections are available, accessing them can be severely restricted due to external circumstances, as the prolonged pandemic has shown. Luckily, digital morphology has emerged over the last decade as a new field that stands to change the landscape of specimenbased research and training. Concerted 2D and 3D digitization efforts, the emergence of online aggregate specimen repositories, and availability of comprehensive open-source software tools (such as 3D Slicer) for utilizing these resources has conveniently transformed the field of quantitative and comparative morphology. In this brief review, I will focus explicitly on the 3D Slicer ecosystem and how it can be leveraged as part of a curriculum or research program on digital morphology. In a nutshell, the primary differentiator of the 3D Slicer is not that it is just free but that it is open-source and extensible, making access to digital data more equitable for everyone. I will particularly focus on the 3D Slicer’s SlicerMorph extension, which facilitates 3D geometric morphometric data collection and analysis within the Slicer ecosystem, so all the steps in the digital morphology workflow from import, visualization, and data collection to visualizing the morpho-space can be achieved in a single, well-documented environment.

Asymmetric Plastral Allometry between Sexes in Captive YellowBellied Slider Turtles (Trachemys scripta scripta Schoepff 1792)

This study aimed to contribute to a better understanding of the role of asymmetric shape changes related to variation in size in the yellow-bellied slider turtles (Trachemys scripta scripta), imported in Spain as pets. Values were obtained from geometric morphometric analysis of 17 anatomical landmarks on plastron (ventral aspect of the body) from 33 males and 63 females. The allometry was described by a multivariate regression where the independent variable was size, expressed as centroid size, and dependent variables was the set of shape coordinates. The results demonstrated the existence of sex-related differences in plastron asymmetries, but, interestingly, the allometric slopes were not sexually dimorphic. The expression of these allometric trajectories may be the reflection of some functional features, such as feeding or movement.

Do brachycephaly and nose size predict the severity of obstructive sleep apnea (OSA)? A sample-based geometric morphometric analysis of craniofacial variation in relation to OSA syndrome and the role of confounding factors.

Obstructive sleep apnea is a common disorder that leads to sleep fragmentation and is potentially bidirectionally related to a variety of comorbidities, including an increased risk of heart failure and stroke. It is often considered a consequence of anatomical abnormalities, especially in the head and neck, but its pathophysiology is likely to be multifactorial in origin. With geometric morphometrics, and a large sample of adults from the Study for Health in Pomerania, we explore the association of craniofacial morphology to the apnea-hypopnea index used as an estimate of obstructive sleep apnea severity. We show that craniofacial size and asymmetry, an aspect of morphological variation seldom analysed in obstructive sleep apnea research, are both uncorrelated to apnea-hypopnea index. In contrast, as in previous analyses, we find evidence that brachycephaly and larger nasal proportions might be associated to obstructive sleep apnea severity. However, this correlational signal is weak and completely disappears when age-related shape variation is statistically controlled for. Our findings suggest that previous work might need to be re-evaluated, and urge researchers to take into account the role of confounders to avoid potentially spurious findings in association studies.

Reexamining Ceramic Standardization During Agricultural Transition: A Geometric Morphometric Investigation of Initial – Early Yayoi Earthenware, Japan

Abstract The quantifiable and reproducible representation of variability in material culture has continued to play a key role in the elucidation of shifting patterns of production organization in prehistoric archaeology. The study of standardization of ceramics has traditionally illuminated on how agents shift means of production to a common goal. However, while geometric morphometric (GMM) approaches to standardization quantification overcome issues of reproducibility faced in traditional literature, the lack of widespread radiocarbon dating in Japan requires adherence to traditional methods of temporal control. This study seeks to extrapolate ceramic standardization in a quantifiable means, while also maintaining temporal control utilizing traditional methods. In a pilot case study of the agricultural transition period of the Yayoi period of the Japanese peninsula (∼900/800 BC–300 BC), results of mortuary vessels show that while a previous model based on visually determined traditional methods assumed that ceramic manufacture was centralized in the Hakata Bay subregion of the northern Kyushu island region; utilizing GMM analysis to extrapolate variable standardization is able to identify a decline in morphological variation, despite increases in population density and potential variability between migrant and indigenous production patterns. These results further illuminate the strong correlation between production intensity and its effect on standardization practices in material culture production, as seen in modern ethnoarchaeological literature.

Ecomorphological differences among forest and rock dwelling species of Darevskia Arribas, 1999 (Squamata, Lacertide) in the Elburz Mountains, Iran

Ecological pressure is the major driver of morphological adaptation. Different habitat preferences even among closely related species, often result in the evolution of different body shapes. In the present study, we employed geometric morphometric and principal component analyses (PCA) to compare body shape and head plate morphology among seven species in the genus Darevskia Arribas, 1999 from the Elburz Mountains, Iran that occur in either rocky or forested habitats. The geometric morphometric analysis and the PCA of meristic characters recovered a wide degree of overlap between the rock and forest dwelling species. The PCA of the morphometric characters showed wide separation among the rock and forest dwelling species as well as among some of the rock dwelling species. These results strongly suggest that body shape is correlated with the habitat type whereas head plate morphology and scale meristics are not. Furthermore, the results suggest that the rock dwelling species may be occupying and navigating their microhabitat in different ways. Ecological observations are needed to test this hypothesis.

FACIAL REDUCTION ACROSS THREE REPRESENTATIVE TAXA: A GEOMETRIC MORPHOMETRIC APPROACH

Facial reduction is a phenomenon described extensively in the evolutionary, clinical, and veterinary literature. Despite the fact that this phenomenon applies to a variety of species and can even be found in the clinical medical and veterinary literature (midfacial hypoplasia, craniosynostosis conditions, etc.), it has not been analyzed comprehensively using a geometric morphometric approach. The goal of this study was to improve our understanding of facial reduction as both an evolutionary process and as the result of selective breeding. Three representative taxa (bats, primates, and dogs) were selected for this project for their presence of both a normocephalic and brachycephalic morphotype. Bats and primates evolved their facial reduction as the result of natural selection and other evolutionary processes over a long period of time with a large amount of genetic diversity. Dogs, on the other hand, developed their squished-face morphotype over the space of a few thousand years. Despite this fact, dogs have been proposed as a model for evolutionary facial reduction. Although dogs were able to achieve similar—if not more pronounced—facial reduction, they did so in a completely different way than bats and dogs. &#x0D; This project included the analysis of specific patterns of localized shape change across these representative three taxa. The impact of this facial reduction on the soft tissue structures of the skull—namely, the brain—was assessed through the study of canine endocasts. We analyzed all three taxa through the analysis of six previously-established modules. These modules include the six main areas proposed by Goswami (2006): face, orbit, oral, zygomatic, cranial vault and cranial base. Modularity and integration were evaluated for these modules in order to better understand the constraints present during facial reduction. Finally, both global and modular facial reduction were analyzed in the three representative taxa using geometric morphometric analysis. Despite being proposed as a model of evolutionary facial reduction, dogs demonstrate major differences in cranial morphology as the result of selective breeding processes. Furthermore, facial reduction that is the result of evolutionary processes is not consistent between bats and primates, and instead, bats share much of their cranial morphology in common with dogs. Overall, it is clear that facial reduction is a multi-faceted morphological phenomenon of evolutionary significance.