Morphological variation and covariation in mandibular molars of platyrrhine primates

Molars are highly integrated biological structures that have been used for inferring evolutionary relationships among taxa. However, parallel and convergent morphological traits can be affected by developmental and functional constraints. Here, we analyze molar shapes of platyrrhines in order to explore if platyrrhine molar diversity reflects homogeneous patterns of molar variation and covariation. We digitized 30 landmarks on mandibular first and second molars of 418 extant and 11 fossil platyrrhine specimens to determine the degree of integration of both molars when treated as a single module. We combined morphological and phylogenetic data to investigate the phylogenetic signal and to visualize the history of molar shape changes. All platyrrhine taxa show a common shape pattern suggesting that a relatively low degree of phenotypic variation is caused by convergent evolution, although molar shape carries significant phylogenetic signal. Atelidae and Pitheciidae show high levels of integration with low variation between the two molars, whereas the Cebinae/Saimiriinae, and especially Callitrichinae, show greater variation between molars and trend toward a modular organization. We hypothesize that biomechanical constraints of the masticatory apparatus, and the dietary profile of each taxon are the main factors that determine high covariation in molars. In contrast, low molar shape covariation may result from the fact that each molar exhibits a distinct ecological signal, as molars can be exposed to distinct occlusal loadings during food processing, suggesting that different selective pressures on molars can reduce overall molar integration.     

Analysis of quantitative trait locus effects on the size and shape of mandibular molars in mice

While >50 genes have been found to influence the development of teeth in mice, we still know very little about the genetic basis for the adaptive characteristics of teeth, such as size and shape. We applied interval mapping procedures to Procrustes size and shape data obtained from 10 morphological landmarks on the mandibular molar row of the F(2) progeny from a cross between the LG/J and SM/J strains of mice. This revealed many more QTL for molar shape (18) than for molar centroid size (3), although levels of dominance effects were comparable among QTL for size and shape. Comparisons of patterns of Procrustes additive and dominance shape effects and ordination of QTL effects by principal components analysis suggested that the effects of the shape QTL were dispersed among the three molars and thus that none of these molars represents a genetically distinct developmental structure. The results of an analysis of co-occurrence of QTL for molar shape, mandible shape, and cranial dimensions in these mice suggested that many of the QTL for molar shape may be the same as those affecting these other sets of characters, although in some cases this could be due to effects of closely linked genes.     

Common solutions to resolve different dietary challenges in the ruminant dentition: The functionality of bovid postcanine teeth as a masticatory unit

Plasticity of tooth shape in mammals is of great adaptive value for the efficient exploitation of specific feeding niches and is a crucial mechanism for ecological diversification. In this study, we aimed to infer chewing effectiveness from the functional shape of different postcanine teeth within bovids, the most diverse extant group of large herbivorous mammals. We consider the postcanine dentition as a masticatory unit and test for differences related to food biomechanical properties, dietary abrasiveness, and chewing dynamics. We compare functional properties of the postcanine tooth row among species with well‐known dietary strategies by integrating digitalization of high‐resolution occlusal surface 3D‐models of upper postcanine dentitions and quantification of the indentation index (D), a structural parameter representing enamel complexity. We test for differences in the occlusal shape among tooth positions in the postcanine dentition using robust, heteroscedastic tests in a one‐way analysis of variance. Our results show three distinct patterns of enamel complexity along the tooth row: (1) D is more homogeneously distributed among tooth positions; (2) D increases gradually in the mesiodistal axis along the tooth row; and (3) D increases abruptly only at the transition between premolars and molars. We interpreted these patterns as different adaptive configurations of the postcanine tooth row relating to diet. Grass‐ and fruit‐eating bovids show the same abrupt increase in enamel complexity at the transition from premolars to molars. Intermediate feeding and leaf‐browsing species show the same gradual, mesiodistal increase in complexity along the tooth row. The absolute physical dietary resistance (biomechanical properties plus abrasiveness) and its relation to mechanical constraints of the chewing stroke are the likely selective factors leading to convergence of enamel complexity patterns along the tooth row among taxa with different diets. J. Morphol. 275:328–341, 2014. © 2013 Wiley Periodicals, Inc.     

Enamel-dentine junction (EDJ) morphology distinguishes the lower molars of Australopithecus africanus and Paranthropus robustus

Tooth crown morphology plays a central role in hominin systematics, but the removal of the original outer enamel surface by dental attrition often eliminates from consideration the type of detailed crown morphology that has been shown to discriminate among hominin taxa. This reduces the size of samples available for study. The enamel-dentine junction (EDJ) is the developmental precursor and primary contributor to the morphology of the unworn outer enamel surface, and its morphology is only affected after considerable attrition. In this paper, we explore whether the form of the EDJ can be used to distinguish between the mandibular molars of two southern African fossil hominins: Paranthropus (or Australopithecus) robustus and Australopithecus africanus. After micro-computed tomographic scanning the molar sample, we made high-resolution images of the EDJ and used geometric morphometrics to compare EDJ shape differences between species, in addition to documenting metameric variation along the molar row within each species. Landmarks were collected along the marginal ridge that runs between adjacent dentine horns and around the circumference of the cervix. Our results suggest that the morphology of the EDJ can distinguish lower molars of these southern African hominins, and it can discriminate first, second, and third molars within each taxon. These results confirm previous findings that the EDJ preserves taxonomically valuable shape information in worn teeth. Mean differences in EDJ shape, in particular dentine horn height, crown height, and cervix shape, are more marked between adjacent molars within each taxon than for the same molar between the two taxa.     

Developmental plasticity associated with early structural integration and evolutionary patterns: Examples of developmental bias and developmental facilitation in the skeletal system

The relation of developmental plasticity to evolutionary diversification is a key component of evolutionary theory involving developmental bias, but the basis of the relationship varies among traits and among taxa. Here I review some scenarios of how structural integration during early organogenesis could influence this relationship. When condensations are highly integrated and dependent on each other during early organogenesis, both plasticity and evolution are restricted, for example size proportions in molar tooth rows and phalanges within a digit. When similar condensations develop and remain separate (in tracheal cartilages and feather buds), they show high levels of variation and diversity in number but not in shape and size, at least at early stages. When non‐similar structures form separately and then integrate while still undergoing patterning, high levels of plasticity (in number, size, shape; in rib uncinate processes) or new dimensions of ecologically‐significant variation (cusp offset, in mammal teeth) are seen. Although each of these structural integration scenarios is unique, the modulation of evolvability is detectable and informative. Parsing the influence of structural integration at these developmental levels, rather than later‐stage structural correlations or only through genetic covariation, may be necessary to advance understanding of evolvability of the phenotype.     

Interproximal wear facets and tooth associations in the Paşalar hominoid sample

Interproximal wear facets were examined on hominoid teeth from the middle Miocene site at Pa?alar, Turkey. The aim was to find matches between adjacent premolar and molar teeth from single individuals that were collected in the field as isolated teeth and use them to reconstruct tooth rows. These were then used to investigate: (1) the wear gradient on the molar teeth; (2) the dispersal of teeth from single mandibles and maxillae; (3) the size ratios among the molars; and (4) the number of individuals represented by the hominoid sample. Facets were scored for size and shape and were assessed visually using photographs and superimposed outline drawings on acetate transparencies. Out of a sample of approximately 1,500 teeth collected between 1983 and 1996, 532 molars and 258 premolars produced apparent matches making up 160 tooth rows. These were then examined rigorously for morphological consistency and state of wear, and, employing the criterion that only the most unequivocal associations should be used, the final number was reduced to 48 tooth rows-31 mandibular and 17 maxillary. The tooth associations represent a minimum of 21 individuals and probably as many as 34. Molar wear was rapid, with M1s having almost twice as much wear as M3s, as measured by a wear-gradient index. The M2s are intermediate but generally closer to M1s in degree of wear, as are P4s. This wear pattern suggests either delayed eruption of M3s or extremely abrasive diets causing rapid, heavy wear. There is some indication that the wear patterns in Griphopithecus alpani and Kenyapithecus kizili are different, with the latter perhaps having a lower wear gradient, but the K. kizili sample is very small. In both species, the M2 is the largest molar and the M1 is the smallest. Separation of individual teeth in the 48 tooth associations varied from widely separated-up to 8.5m apart-to within a few centimeters of each other. One tooth row (D922) was found with the teeth in contact but the maxillary bone had dissolved away. Two dispersal mechanisms have been identified from earlier taphonomic work: transport of disarticulated elements to the fossil site and reworking of sediments by spring action.     

Discrimination of extant Pan species and subspecies using the enamel–dentine junction morphology of lower molars

Previous research has demonstrated that species and subspecies of extant chimpanzees and bonobos can be distinguished on the basis of the shape of their molar crowns. Thus, there is potential for fossil taxa, particularly fossil hominins, to be distinguished at similar taxonomic levels using molar crown morphology. Unfortunately, due to occlusal attrition, the original crown morphology is often absent in fossil teeth, and this has limited the amount of shape information used to discriminate hominin molars. The enamel–dentine junction (EDJ) of molar teeth preserves considerable shape information, particularly in regard to the original shape of the crown, and remains present through the early stages of attrition. In this study, we investigate whether the shape of the EDJ of lower first and second molars can distinguish species and subspecies of extant Pan. Micro‐computed tomography was employed to non‐destructively image the EDJ, and geometric morphometric analytical methods were used to compare EDJ shape among samples of Pan paniscus (N = 17), Pan troglodytes troglodytes (N = 13), and Pan troglodytes verus (N = 18). Discriminant analysis indicates that EDJ morphology distinguishes among extant Pan species and subspecies with a high degree of reliability. The morphological differences in EDJ shape among the taxa are subtle and relate to the relative height and position of the dentine horns, the height of the dentine crown, and the shape of the crown base, but their existence supports the inclusion of EDJ shape (particularly those aspects of shape in the vertical dimension) in the systematic analysis of fossil hominin lower molars. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

Evolution of molar shape in didelphid marsupials (Marsupialia: Didelphidae): analysis of the influence of ecological factors and phylogenetic legacy

The diversity of items consumed by modern didelphids, varying from mostly fruits in Caluromys Allen to mostly small vertebrates in Lutreolina O. Thomas, may cause changes in molar size and shape. We evaluated the morphometric variation of the first and third upper and lower molars of 16 genera of didelphid marsupials, with the aim of assessing the relationship between molar shape change, diet and phylogeny. We used a geometric morphometric approach to analyse how shape changes with diet. We mapped shape onto the phylogeny of the group to reconstruct ancestral states and analyse the evolution of molar shape. Finally, we statistically estimated the effect of size, diet and phylogeny on molar shape. All the analyses indicated little correlation between diet and molar shape and a strong correlation between the position of each genus on the phylogeny and molar shape. We believe that the wide ecological niche used by most of the groups (at least regarding diet) makes the evolutionary changes not strong enough to override pre‐existing differences that occur among clades, and the absence of highly diet‐specialized species (e.g. hypercarnivory or obligate folivory) causes the need for retaining a molar shape that can be useful to process different kinds of food items. © 2014 The Linnean Society of London     

Modularity of a Cambrian ptychoparioid trilobite cranidium

SUMMARY Modularity of the cranidium of Crassifimbra? metalaspis, a Cambrian ptychoparioid trilobite, is investigated using landmark‐based geometric morphometric methods to gain insight into the integration among morphogenetic processes responsible for shaping the head of an ancient arthropod. Of particular interest is the extent to which the structure of phenotypic integration was governed by direct interactions among developmental pathways, because these interactions may generate long‐term constraints on evolutionary innovation. A modified two‐way ANOVA decomposes cranidial shape variation into components representing symmetric variation among individuals and fluctuating asymmetry (FA). The structure of integration of each of these components is inferred from correlated deviations in shape among nine partitions of the cranidium. Significant correlation among partitions in FA indicates direct interactions among their respective developmental pathways. An a priori hypothesis that modularity was determined by functional association among partitions is not well supported by the among‐partition correlation structure for either component of variation. Instead, exploratory analyses reveal that phenotypic integration was strongly influenced by spatially localized morphogenetic controls. Comparison of the structures of the Individuals and FA components of variation reveals that the two share relatively few commonalities: the structure of phenotypic integration was only weakly influenced by direct interactions. The large contribution of parallel variation to phenotypic integration suggests that modularity was unlikely to have imposed a long‐term constraint on evolutionary innovation in these early trilobites.     

Genetic integration of molar cusp size variation in baboons

Many studies of primate diversity and evolution rely on dental morphology for insight into diet, behavior, and phylogenetic relationships. Consequently, variation in molar cusp size has increasingly become a phenotype of interest. In 2007 we published a quantitative genetic analysis of mandibular molar cusp size variation in baboons. Those results provided more questions than answers, as the pattern of genetic integration did not fit predictions from odontogenesis. To follow up, we expanded our study to include data from the maxillary molar cusps. Here we report on these later analyses, as well as inter‐arch comparisons with the mandibular data. We analyzed variation in two‐dimensional maxillary molar cusp size using data collected from a captive pedigreed breeding colony of baboons, Papio hamadryas, housed at the Southwest National Primate Research Center. These analyses show that variation in maxillary molar cusp size is heritable and sexually dimorphic. We also estimated additive genetic correlations between cusps on the same crown, homologous cusps along the tooth row, and maxillary and mandibular cusps. The pattern for maxillary molars yields genetic correlations of one between the paracone–metacone and protocone–hypocone. Bivariate analyses of cuspal homologues on adjacent teeth yield correlations that are high or not significantly different from one. Between dental arcades, the nonoccluding cusps consistently yield high genetic correlations, especially the metaconid–paracone and metaconid–metacone. This pattern of genetic correlation does not immediately accord with the pattern of development and/or calcification, however these results do follow predictions that can be made from the evolutionary history of the tribosphenic molar. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

Geometric morphometric analysis as a proxy to evaluate age‐related change in molar shape variation of low‐crowned Notoungulata (Mammalia)

Shape and age variation in dentition of Paleogene extinct native South American ungulates (Notoungulata) has been traditionally described using qualitative and quantitative approaches, and has played a controversial role in the systematics of several groups. Such is the case of the Notopithecidae, a group of notoungulates with low‐crowned teeth, known from the middle Eocene of Patagonia (Argentina). In this group, as well as in other contemporary families, extreme morphological changes associated to increasing dental wear were originally assumed to represent taxonomic differences; thus, dozens of species were erected, clearly reflecting the difficulty of defining discrete characters. In this contribution, a total of 89 upper molars and 91 lower molars were analyzed distributed in two factors, wear and species; three species of notopithecids were considered as study case, Notopithecus adapinus, Antepithecus brachystephanus, and Transpithecus obtentus, based on the large and well‐identified sample of upper and lower molars for each species. We have coupled geometric morphometric analyses with traditional comparative methods to get a better understanding and interpretation of both the changes in tooth shape contour and the link between shape and ontogeny. In addition, we evaluate the utility of this approach to identify which changes are strictly wear‐related and also test the qualitative characteristics used for diagnosing and differentiating notopithecid species. Our study yielded consistent results when applying independent geometric morphometric analyses on complex structures such as brachydont molar teeth. The landmark data is highly congruent with alternative sources of evidence, such as morphological studies using discrete characters. In notopithecid species, wear is the main factor affecting molar shape, followed by species (in lower molars) and allometry; in addition, lower teeth morphology is more definitive in separating species than upper molars, a fact that entails a key point for systematic studies of Paleogene brachydont notoungulates.     

Loss of molar occlusion and mandibular morphology in adults in an ancient human population consuming a coarse diet

The purpose of the study is to investigate the link between number of molar teeth retained in occlusion and mandibular morphology in adults in an ancient, high dental wear human population. The study material comprises skeletons from Mediaeval Wharram Percy, England (N = 50 female, 69 male adults). It was hypothesized that adults retaining fewer occluding molars would show reduction in mandibular dimensions, particularly in the ascending ramus and gonial regions where the main muscles of mastication have their insertions. Molar occlusal status is assessed using the concept of functional units. Mandibular morphology is assessed using a suite of ten linear measurements plus the mandibular angle. Results show no evidence for any association between number of molars retained in occlusion and mandibular angle. There was an association between mandibular size and number of molars retained in occlusion, with smaller mandibular dimensions in those retaining fewer occluding molars. Some measurements were affected more than others so that there was also some shape alteration. Alteration of mandibular dimensions was more clearly demonstrable in females than in males. Only in females could significant reduction in the ascending ramus and gonial regions be demonstrated. Reasons for the apparent difference in response to loss of molar occlusion between male and female mandibles are unclear, but sex differences in bony metabolism mediated by hormonal factors may be implicated. Results suggest that care should be exercised when including mandibles from individuals showing loss of molar occlusion in morphological studies. Am J Phys Anthropol 152:383–392, 2013. © 2013 Wiley Periodicals, Inc.     

Morphological integration in the hominin dentition: evolutionary, developmental, and functional factors

As the most common and best preserved remains in the fossil record, teeth are central to our understanding of evolution. However, many evolutionary analyses based on dental traits overlook the constraints that limit dental evolution. These constraints are diverse, ranging from developmental interactions between the individual elements of a homologous series (the whole dentition) to functional constraints related to occlusion. This study evaluates morphological integration in the hominin dentition and its effect on dental evolution in an extensive sample of Plio- and Pleistocene hominin teeth using geometric morphometrics and phylogenetic comparative methods. Results reveal that premolars and molars display significant levels of covariation; that integration is stronger in the mandibular dentition than in the maxillary dentition; and that antagonist teeth, especially first molars, are strongly integrated. Results also show an association of morphological integration and evolution. Stasis is observed in elements with strong functional and/or developmental interactions, namely in first molars. Alternatively, directional evolution (and weaker integration) occurs in the elements with marginal roles in occlusion and mastication, probably in response to other direct or indirect selective pressures. This study points to the need to reevaluate hypotheses about hominin evolution based on dental characters, given the complex scenario in which teeth evolve.     

Does space in the jaw influence the timing of molar crown initiation? A model using baboons (Papio anubis) and great apes (Pan troglodytes, Pan paniscus)

Radiographic and histological studies of baboon (Papio hamadryas, P. anubis) and chimpanzee (Pan troglodytes) permanent tooth development have found that periods of molar crown mineralization overlap markedly in chimpanzees but are staggered in baboons. Here we test the hypothesis that these intertaxon differences in molar initiation are primarily due to the space available in the mandibles of each species for these teeth. This study includes radiographic, linear measurement, and three-dimensional (3D) coordinate landmark data taken from baboon (Papio anubis n=51) and great ape (Pan paniscus n=43, P. troglodytes n=60) mandibles and permanent molars across a broad developmental range for each taxon. Unexpectedly, 3D multivariate statistical shape analysis of the molar crypt, crown, and root data shows that all three species trajectories of molar row shape change are indistinguishable from each other. Qualitative analysis of these 3D data reveals subtle and inconclusive intergeneric differences in the space maintained between adjacent molars during growth. The space distal to each newly initiated molar is slightly greater in the baboon. Bivariate analyses comparing molar row and mandibular corpus proportions in Papio and Pan fail to show clear or consistent taxonomic differences in the ratio of space afforded developing molars in the alveolar bone. Thus, there is a poor correlation between mandibular proportion and both intermolar spacing and 3D molar development pattern. Contrary to earlier studies, these results suggest that pattern of molar crown initiation and temporal overlap of adjacent mineralizing crowns is not significantly different between Papio and Pan. This may be due in part to the inclusion here of not only 3D molar crown data but also 3D molar crypt data. This study strongly refutes the hypothesis that space available in the mandible directly underlies different times of permanent molar crown initiation between Papio and Pan.     

Geometric morphometric 3D shape analysis and covariation of human mandibular and maxillary first molars

Dental casts of 160 Greek subjects (80 males, 80 females) were scanned by a structured‐light scanner. The upper and lower right first molar occlusal surface 3D meshes were processed using geometric morphometric methods. A total of 265 and 274 curve and surface sliding semilandmarks were placed on the upper and lower molar surfaces, respectively. Principal component analysis and partial least square analysis were performed to assess shape parameters. Molars tended to vary between an elongated and a more square form. The first two principal components (PCs), comprising almost 1/3 of molar shape variation, were related to mesiodistal–buccolingual ratios and relative cusp position. Distal cusps displayed the greatest shape variability. Molars of males were larger than those of females (2.8 and 3.2% for upper and lower molars respectively), but no shape dimorphism was observed. Upper and lower molar sizes were significantly correlated (r² = 0.689). Allometry was observed for both teeth. Larger lower molars were associated with shorter cusps, expansion of the distal cusp, and constriction of the mesial cusps (predicted variance 3.25%). Upper molars displayed weaker allometry (predicted variance 1.59%). Upper and lower molar shape covariation proved significant (RV = 17.26%, P < 0.0001). The main parameter of molar covariation in partial least square axis 1, contributing to 30% of total covariation, was cusp height, in contrast to the primary variability traits exhibited by PC1 and PC2. The aim of this study was to evaluate shape variation and covariation, including allometry and sexual dimorphism, of maxillary and mandibular first permanent molar occlusal surfaces. Am J Phys Anthropol 152:186–196, 2013. © 2013 Wiley Periodicals, Inc.     

Dental homologies in lamniform sharks (Chondrichthyes: Elasmobranchii).

The dentitions of lamniform sharks are said to exhibit a unique heterodonty called the "lamnoid tooth pattern." The presence of an inflated hollow "dental bulla" on each jaw cartilage allows the recognition of homologous teeth across most modern macrophagous lamniforms based on topographic correspondence through the "similarity test." In most macrophagous lamniforms, three tooth rows are supported by the upper dental bulla: two rows of large anterior teeth followed by a row of small intermediate teeth. The lower tooth row occluding between the two rows of upper anterior teeth is the first lower anterior tooth row. Like the first and second lower anterior tooth rows, the third lower tooth row is supported by the dental bulla and may be called the first lower intermediate tooth row. The lower intermediate tooth row occludes between the first and second upper lateral tooth rows situated distal to the upper dental bulla, and the rest of the upper and lower tooth rows, all called lateral tooth rows, occlude alternately. Tooth symmetry cannot be used to identify their dental homology. The presence of dental bullae can be regarded as a synapomorphy of Lamniformes and this character is more definable than the "lamnoid tooth pattern." The formation of the tooth pattern appears to be related to the evolution of dental bullae. This study constitutes the first demonstration of supraspecific tooth-to-tooth dental homologies in nonmammalian vertebrates.     

Incremental enamel development in modern human deciduous anterior teeth

This study reconstructs incremental enamel development for a sample of modern human deciduous mandibular (n = 42) and maxillary (n = 42) anterior (incisors and canines) teeth. Results are compared between anterior teeth, and with previous research for deciduous molars (Mahoney: Am J Phys Anthropol 144 (2011) 204-214) to identify developmental differences along the tooth row. Two hypotheses are tested: Retzius line periodicity will remain constant in teeth from the same jaw and range from 6 to 12 days among individuals, as in human permanent teeth; daily enamel secretion rates (DSRs) will not vary between deciduous teeth, as in some human permanent tooth types. A further aim is to search for links between deciduous incremental enamel development and the previously reported eruptionsequence. Retzius line periodicity in anterior teeth ranged between 5 and 6 days, but did not differ between an incisor and molar of one individual. Intradian line periodicity was 12 h. Mean cuspal DSRs varied slightly between equivalent regions along the tooth row. Mandibular incisors initiated enamel formation first, had the fastest mean DSRs, the greatest prenatal formation time, and based upon prior studies are the first deciduous tooth to erupt. Relatively rapid development in mandibular incisors in advance of early eruption may explain some of the variation in DSRs along the tooth row that cannot be explained by birth. Links between DSRs, enamel initiation times, and the deciduous eruption sequence are proposed. Anterior crown formation times presented here can contribute toward human infant age-at-death estimates. Regression equations for reconstructing formation time in worn incisors are given.     

Morpho morphometrics: Shared ancestry and selection drive the evolution of wing size and shape in Morpho butterflies

Butterfly wings harbor highly diverse phenotypes and are involved in many functions. Wing size and shape result from interactions between adaptive processes, phylogenetic history, and developmental constraints, which are complex to disentangle. Here, we focus on the genus Morpho (Nymphalidae: Satyrinae, 30 species), which presents a high diversity of sizes, shapes, and color patterns. First, we generate a comprehensive molecular phylogeny of these 30 species. Next, using 911 collection specimens, we quantify the variation of wing size and shape across species, to assess the importance of shared ancestry, microhabitat use, and sexual selection in the evolution of the wings. While accounting for phylogenetic and allometric effects, we detect a significant difference in wing shape but not size among microhabitats. Fore and hindwings covary at the individual and species levels, and the covariation differs among microhabitats. However, the microhabitat structure in covariation disappears when phylogenetic relationships are taken into account. Our results demonstrate that microhabitat has driven wing shape evolution, although it has not strongly affected forewing and hindwing integration. We also found that sexual dimorphism of forewing shape and color pattern are coupled, suggesting a common selective force.     

Evidence of strong stabilizing effects on the evolution of boreoeutherian (Mammalia) dental proportions

The dentition is an extremely important organ in mammals with variation in timing and sequence of eruption, crown morphology, and tooth size enabling a range of behavioral, dietary, and functional adaptations across the class. Within this suite of variable mammalian dental phenotypes, relative sizes of teeth reflect variation in the underlying genetic and developmental mechanisms. Two ratios of postcanine tooth lengths capture the relative size of premolars to molars (premolar–molar module, PMM), and among the three molars (molar module component, MMC), and are known to be heritable, independent of body size, and to vary significantly across primates. Here, we explore how these dental traits vary across mammals more broadly, focusing on terrestrial taxa in the clade of Boreoeutheria (Euarchontoglires and Laurasiatheria). We measured the postcanine teeth of N = 1,523 boreoeutherian mammals spanning six orders, 14 families, 36 genera, and 49 species to test hypotheses about associations between dental proportions and phylogenetic relatedness, diet, and life history in mammals. Boreoeutherian postcanine dental proportions sampled in this study carry conserved phylogenetic signal and are not associated with variation in diet. The incorporation of paleontological data provides further evidence that dental proportions may be slower to change than is dietary specialization. These results have implications for our understanding of dental variation and dietary adaptation in mammals.