Disparities in the analysis of morphological disparity

Widespread convergence towards functional optimization in the lower jaws of crocodile-line archosaurs

Extant crocodilian jaws are subject to functional demands induced by feeding and hydrodynamics. However, the morphological and ecological diversity of extinct crocodile-line archosaurs is far greater than that of living crocodilians, featuring repeated convergence towards disparate ecologies including armoured herbivores, terrestrial macropredators and fully marine forms. Crocodile-line archosaurs, therefore, present a fascinating case study for morphological and functional divergence and convergence within a clade across a wide range of ecological scenarios. Here, we build performance landscapes of two-dimensional theoretical jaw shapes to investigate the influence of strength, speed and hydrodynamics in the morphological evolution of crocodile-line archosaur jaws, and test whether ecologically convergent lineages evolved similarly optimal jaw function. Most of the 243 sampled jaw morphologies occupy optimized regions of theoretical morphospace for either rotational efficiency, resistance to Von Mises stress, hydrodynamic efficiency or a trade-off between multiple functions, though some seemingly viable shapes remain unrealized. Jaw speed is optimized only in a narrow region of morphospace whereas many shapes possess optimal jaw strength, which may act as a minimum boundary rather than a strong driver for most taxa. This study highlights the usefulness of theoretical morphology in assessing functional optimality, and for investigating form-function relationships in diverse clades.

A macroevolutionary analysis of European Late Upper Palaeolithic stone tool shape using a Bayesian phylodynamic framework

Phylogenetic models are commonly used in palaeobiology to study the patterns and processes of organismal evolution. In the human sciences, phylogenetic methods have been deployed for reconstructing ancestor-descendant relationships using linguistic and material culture data. Within evolutionary archaeology specifically, phylogenetic analyses based on maximum parsimony and discrete traits dominate, which sets limitations for the downstream role cultural phylogenies, once derived, can play in more elaborate analytical pipelines. Recent methodological advances in Bayesian phylogenetics, however, now allow us to infer evolutionary dynamics using continuous characters. Capitalizing on these developments, we here present an exploratory analysis of cultural macroevolution of projectile point shape evolution in the European Final Palaeolithic and earliest Mesolithic (approx. 15 000-11 000 BP) using a Bayesian phylodynamic approach and the fossilized birth-death process model. This model-based approach leaps far beyond the application of parsimony, in that it not only produces a tree, but also divergence times, and diversification rates while incorporating uncertainties. This allows us to compare rates to the pronounced climatic changes that occurred during our time frame. While common in cultural evolutionary analyses of language, the extension of Bayesian phylodynamic models to archaeology arguably represents a major methodological breakthrough.

Heterogeneous selectivity and morphological evolution of marine clades during the Permian-Triassic mass extinction

Morphological disparity and taxonomic diversity are distinct measures of biodiversity, typically expected to evolve synergistically. However, evidence from mass extinctions indicates that they can be decoupled, and while mass extinctions lead to a drastic loss of diversity, their impact on disparity remains unclear. Here we evaluate the dynamics of morphological disparity and extinction selectivity across the Permian-Triassic mass extinction. We developed an automated approach, termed DeepMorph, for the extraction of morphological features from fossil images using a deep learning model and applied it to a high-resolution temporal dataset encompassing 599 genera across six marine clades. Ammonoids, brachiopods and ostracods experienced a selective loss of complex and ornamented forms, while bivalves, gastropods and conodonts did not experience morphologically selective extinctions. The presence and intensity of morphological selectivity probably reflect the variations in environmental tolerance thresholds among different clades. In clades affected by selective extinctions, the intensity of diversity loss promoted the loss of morphological disparity. Conversely, under non-selective extinctions, the magnitude of diversity loss had a negligible impact on disparity. Our results highlight that the Permian-Triassic mass extinction had heterogeneous morphological selective impacts across clades, offering new insights into how mass extinctions can reshape biodiversity and ecosystem structure.

Male and female contributions to diversity among birdwing butterfly images

Machine learning (ML) newly enables tests for higher inter-species diversity in visible phenotype (disparity) among males versus females, predictions made from Darwinian sexual selection versus Wallacean natural selection, respectively. Here, we use ML to quantify variation across a sample of > 16,000 dorsal and ventral photographs of the sexually dimorphic birdwing butterflies (Lepidoptera: Papilionidae). Validation of image embedding distances, learnt by a triplet-trained, deep convolutional neural network, shows ML can be used for automated reconstruction of phenotypic evolution achieving measures of phylogenetic congruence to genetic species trees within a range sampled among genetic trees themselves. Quantification of sexual disparity difference (male versus female embedding distance), shows sexually and phylogenetically variable inter-species disparity. Ornithoptera exemplify high embedded male image disparity, diversification of selective optima in fitted multi-peak OU models and accelerated divergence, with cases of extreme divergence in allopatry and sympatry. However, genus Troides shows inverted patterns, including comparatively static male embedded phenotype, and higher female than male disparity - though within an inferred selective regime common to these females. Birdwing shapes and colour patterns that are most phenotypically distinctive in ML similarity are generally those of males. However, either sex can contribute majoritively to observed phenotypic diversity among species.

The influence of the land-to-sea macroevolutionary transition on vertebral column disparification in Pinnipedia

The repeated returns of vertebrates to the marine ecosystems since the Triassic serve as an evolutionary model to understand macroevolutionary change. Here we investigate the effects of the land-to-sea transition on disparity and constraint of the vertebral column in aquatic carnivorans (Carnivora; Pinnipedia) to assess how their functional diversity and evolutionary innovations influenced major radiations of crown pinnipeds. We use three-dimensional geometric morphometrics and multivariate analysis for high-dimensional data under a phylogenetic framework to quantify vertebral size and shape in living and extinct pinnipeds. Our analysis demonstrates an important shift in vertebral column evolution by 10-12 million years ago, from an unconstrained to a constrained evolutionary scenario, a point of time that coincides with the major radiation of crown pinnipeds. Moreover, we also demonstrate that the axial skeleton of phocids and otariids followed a different path of morphological evolution that was probably driven by their specialized locomotor strategies. Despite this, we found a significant effect of habitat preference (coastal versus pelagic) on vertebral morphology of crown taxa regardless of the family they belong. In summary, our analysis provides insights into how the land-to-sea transition influenced the complex evolutionary history of pinniped vertebral morphology.

Angiosperm flowers reached their highest morphological diversity early in their evolutionary history

Flowers are the complex and highly diverse reproductive structures of angiosperms. Because of their role in sexual reproduction, the evolution of flowers is tightly linked to angiosperm speciation and diversification. Accordingly, the quantification of floral morphological diversity (disparity) among angiosperm subgroups and through time may give important insights into the evolutionary history of angiosperms as a whole. Based on a comprehensive dataset focusing on 30 characters describing floral structure across angiosperms, we used 1201 extant and 121 fossil flowers to measure floral disparity and explore patterns of floral evolution through time and across lineages. We found that angiosperms reached their highest floral disparity in the Early Cretaceous. However, decreasing disparity toward the present likely has not precluded the innovation of other complex traits at other morphological levels, which likely played a key role in the outstanding angiosperm species richness. Angiosperms occupy specific regions of the theoretical morphospace, indicating that only a portion of the possible floral trait combinations is observed in nature. The ANA grade, the magnoliids, and the early-eudicot grade occupy large areas of the morphospace (higher disparity), whereas nested groups occupy narrower regions (lower disparity).

Mesozoic evolution of cicadas and their origins of vocalization and root feeding

Extant cicada (Hemiptera: Cicadoidea) includes widely distributed Cicadidae and relictual Tettigarctidae, with fossils ascribed to these two groups based on several distinct, minimally varying morphological differences that define their extant counterparts. However, directly assigning Mesozoic fossils to modern taxa may overlook the role of unique and transitional features provided by fossils in tracking their early evolutionary paths. Here, based on adult and nymphal fossils from mid-Cretaceous Kachin amber of Myanmar, we explore the phylogenetic relationships and morphological disparities of fossil and extant cicadoids. Our results suggest that Cicadidae and Tettigarctidae might have diverged at or by the Middle Jurassic, with morphological evolution possibly shaped by host plant changes. The discovery of tymbal structures and anatomical analysis of adult fossils indicate that mid-Cretaceous cicadas were silent as modern Tettigarctidae or could have produced faint tymbal-related sounds. The discovery of final-instar nymphal and exuviae cicadoid fossils with fossorial forelegs and piercing-sucking mouthparts indicates that they had most likely adopted a subterranean lifestyle by the mid-Cretaceous, occupying the ecological niche of underground feeding on root. Our study traces the morphological, behavioral, and ecological evolution of Cicadoidea from the Mesozoic, emphasizing their adaptive traits and interactions with their living environments.

The ontogeny of disparity in Cupressaceae seed cones

Ontogenetic shape change has long been recognized to be important in generating patterns of morphological diversity and may be especially important in plant reproductive structures. We explore how seed cone disparity in Cupressaceae changes over ontogeny by comparing pollination-stage and mature cones. We sampled cones at pollen and seed release and measured cone scales using basic morphometric shape variables. We used multivariate statistical methods, particularly hypervolume overlap calculations, to measure morphospace occupation and disparity. Cone scales at both pollination and maturity exhibit substantial variability, although the disparity is greater at maturity. Mature cone scales are also more clustered in trait space, showing less overlap with other taxa than at pollination. These patterns reflect two growth strategies that generate closed cones over maturation, either through thin laminar scales or relatively thick, peltate scales, resulting in two distinct regions of morphospace occupation. Disparity patterns in Cupressaceae seed cones change over ontogeny, reflecting shifting functional demands that require specific patterns of cone scale growth. The evolution of Cupressaceae reproductive disparity therefore represents selection for trajectories of ontogenetic shape change, a phenomenon that should be widespread across seed plants.

Measurement theory and paleobiology

Measurement theory, a branch of applied mathematics, offers guiding principles for extracting meaning from empirical observations and is applicable to any science involving measurements. Measurement theory is highly relevant in paleobiology because statistical approaches assuming ratio-scaled variables are commonly used on data belonging to nominal and ordinal scale types. We provide an informal introduction to representational measurement theory and argue for its importance in robust scientific inquiry. Although measurement theory is widely applicable in paleobiology research, we use the study of disparity to illustrate measurement theoretical challenges in the quantitative study of the fossil record. Respecting the inherent properties of different measurements enables meaningful inferences about evolutionary and ecological processes from paleontological data.

A dynamic and collaborative database for morphogeometric information of trilobites

Modern morphometric-based approaches provide valuable metrics to quantify and understand macroevolutionary and macroecological patterns and processes. Here we describe TriloMorph, an openly accessible database for morpho-geometric information of trilobites, together with a landmark acquisition protocol. In addition to morphological traits, the database contains contextual data on chronostratigraphic age, geographic location, taxonomic information and lithology of landmarked specimens. In this first version, the dataset has broad taxonomic and temporal coverage and comprises more than 55% of all trilobite genera and 85% of families recorded in the Paleobiology Database through the Devonian. We provide a release of geometric morphometric data of 277 specimens linked to published references. Additionally, we established a Github repository for constant input of morphometric data by multiple contributors and present R functions that help with data retrieval and analysis. This is the first attempt of an online, dynamic and collaborative morphometric repository. By bringing this information into a single open database we enhance the possibility of performing global palaeobiological research, providing a major complement to current occurrence-based databases.

Disparification and extinction trade-offs shaped the evolution of Permian to Jurassic Odonata

Owing to their prevalence in nowadays terrestrial ecosystems, insects are a relevant group to assess the impact of mass extinctions on emerged land. However, limitations of the insect fossil record make it difficult to assess the impact of such events based on taxonomic diversity alone. Therefore, we documented trends in morphological diversity, i.e., disparity, using wings of Permian to Jurassic Odonata as model. Our results show a decreasing trend in disparity while species richness increased. Both the Permian-Triassic and Triassic-Jurassic transitions are revealed as important events, associated with strong morphospace restructuring due to selective extinction. In each case, a recovery was assured by the diversification of new forms compensating the loss of others. Early representatives of Odonata continuously evolved new shapes, a pattern contrasting with the classical assertion of a morphospace fulfilled early and followed by selective extinctions and specialization within it.

Fossilization can mislead analyses of phenotypic disparity

Analyses of morphological disparity can incorporate living and fossil taxa to facilitate the exploration of how phenotypic variation changes through time. However, taphonomic processes introduce non-random patterns of data loss in fossil data and their impact on perceptions of disparity is unclear. To address this, we characterize how measures of disparity change when simulated and empirical data are degraded through random and structured data loss. We demonstrate that both types of data loss can distort the disparity of clades, and that the magnitude and direction of these changes varies between the most commonly employed distance metrics and disparity indices. The inclusion of extant taxa and exceptionally preserved fossils mitigates these distortions and clarifies the full extent of the data lost, most of which would otherwise go uncharacterized. This facilitates the use of ancestral state estimation and evolutionary simulations to further control for the effects of data loss. Where the addition of such reference taxa is not possible, we urge caution in the extrapolation of general patterns in disparity from datasets that characterize subsets of phenotype, which may represent no more than the traits that they sample.

Macroevolutionary patterns in the pelvis, stylopodium and zeugopodium of megalosauroid theropod dinosaurs and their importance for locomotor function

During the Mesozoic, non-avian theropods represented one of the most successful clades globally distributed, with a wide diversity of forms. An example is the clade Megalosauroidea, which included medium- to large-bodied forms. Here, we analyse the macroevolution of the locomotor system in early Theropoda, emphasizing the Megalosauroidea. We scored the Spinosaurus neotype in a published taxon-character matrix and described the associated modifications in character states, mapping them onto a phylogeny and using these to study disparity. In the evolution of Megalosauroidea, there was the mosaic emergence of a low swollen ridge; enlargement of the posterior brevis fossa and emergence of a posterodorsal process on the ilium in some megalosauroids; emergence of a femoral head oriented anteromedially and medially angled, and appearance of posterolaterally oriented medial femoral condyles in spinosaurids. The greatest morphological disparity is in the ilium of megalosaurids; the ischium seems to have a high degree of homoplasy; there is a clear distinction in the femoral morphospace regarding megalosauroids and other theropods; piatnitzkysaurids show considerable disparity of zeugopodial characters. These reconstructions of osteological evolution form a stronger basis on which other studies could build, such as mapping of pelvic/appendicular musculature and/or correlating skeletal traits with changes in locomotor function.

A multivariate approach to morphological study of shell form in cowries (Gastropoda, Cypraeidae): a case study with Umbiliaarmeniaca (Verco, 1912)

Multivariate approaches to morphological study of shell form have rarely been applied to cowries (Gastropoda: Cypraeidae) with preference, instead, for comparing formulaic notations of shell form that report averages (i.e., means) for key morphometrics such as shell dimensions, their ratios, and counts of apertural teeth. Although widely applied, the "shell formula" does not account for variation among individuals or support statistical comparison between taxa. This study applied a multivariate approach to analyse shell form within the four accepted subspecies of the cowrie, Umbiliaarmeniaca (Verco, 1912) and included a previously unstudied, and most northerly, population of U.armeniaca from Lancelin, Western Australia. Multivariate analyses readily separated the recognised subspecies of U.armeniaca (U.a.armeniaca, U.a.diprotodon, U.a.clarksoni and U.a.andreyi), but did not separate the Lancelin population from U.a.andreyi, indicating that the former represents a northward extension of U.a.andreyi that is not morphometrically distinguishable. These results provide improved understanding of infraspecific differences in shell form of U.armeniaca across its broad distribution, and demonstrate the utility of multivariate morphometric methods for statistical comparison of shell form between taxa. This approach is complimentary to existing research practices and has broad potential application in future morphometric studies of both extant and fossil taxa within the family Cypraeidae.

Towards a global perspective for Salvia L.: Phylogeny, diversification and floral evolution

Salvia is the most species-rich genus in Lamiaceae, encompassing approximately 1000 species distributed all over the world. We sought a new evolutionary perspective for Salvia by employing macroevolutionary analyses to address the tempo and mode of diversification. To study the association of floral traits with speciation and extinction, we modelled and explored the evolution of corolla length and the lever-mechanism pollination system across our Salvia phylogeny. We reconstructed a multigene phylogeny for 366 species of Salvia in the broad sense including all major recognized lineages and 50 species from Iran, a region previously overlooked in studies of the genus. Our comprehensive sampling of Iranian species of Salvia provides higher phylogenetic resolution for southwestern Asian species than obtained in previous studies. Our phylogenetic data in combination with divergence time estimates were used to examine the evolution of corolla length, woody versus herbaceous habit, and presence versus absence of a lever mechanism. We investigated the timing and dependence of Salvia diversification related to corolla length evolution through a disparity test and BAMM analysis. A HiSSE model was used to evaluate the dependency of diversification on the lever-mechanism pollination system in Salvia. A medium corolla length (15-18 mm) was reconstructed as the ancestral state for Salvia with multiple shifts to shorter and longer corollas. Macroevolutionary model analyses indicate that corolla length disparity is high throughout Salvia evolution, significantly different from expectations under a Brownian motion model during the last 28 million years of evolution. Our analyses show evidence of a higher diversification rate of corolla length for some Andean species of Salvia compared to other members of the genus. Based on our tests of diversification models, we reject the hypothesis of a direct effect of the lever mechanism on Salvia diversification. Therefore, we suggest caution in considering the lever-mechanism pollination system as one of the main drivers of speciation in Salvia.

Divergent vertebral formulae shape the evolution of axial complexity in mammals

Complexity, defined as the number of parts and their degree of differentiation, is a poorly explored aspect of macroevolutionary dynamics. The maximum anatomical complexity of organisms has undoubtedly increased through evolutionary time. However, it is unclear whether this increase is a purely diffusive process or whether it is at least partly driven, occurring in parallel in most or many lineages and with increases in the minima as well as the means. Highly differentiated and serially repeated structures, such as vertebrae, are useful systems with which to investigate these patterns. We focus on the serial differentiation of the vertebral column in 1,136 extant mammal species, using two indices that quantify complexity as the numerical richness and proportional distribution of vertebrae across presacral regions and a third expressing the ratio between thoracic and lumbar vertebrae. We address three questions. First, we ask whether the distribution of complexity values in major mammal groups is similar or whether clades have specific signatures associated with their ecology. Second, we ask whether changes in complexity throughout the phylogeny are biased towards increases and whether there is evidence of driven trends. Third, we ask whether evolutionary shifts in complexity depart from a uniform Brownian motion model. Vertebral counts, but not complexity indices, differ significantly between major groups and exhibit greater within-group variation than recognized hitherto. We find strong evidence of a trend towards increasing complexity, where higher values propagate further increases in descendant lineages. Several increases are inferred to have coincided with major ecological or environmental shifts. We find support for multiple-rate models of evolution for all complexity metrics, suggesting that increases in complexity occurred in stepwise shifts, with evidence for widespread episodes of recent rapid divergence. Different subclades evolve more complex vertebral columns in different configurations and probably under different selective pressures and constraints, with widespread convergence on the same formulae. Further work should therefore focus on the ecological relevance of differences in complexity and a more detailed understanding of historical patterns.

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.

Is species richness mediated by functional and genetic divergence? A global analysis in birds

Unravelling why species richness shows such dramatic spatial variation is an ongoing challenge. Common to many theories is that increasing species richness (e.g. with latitude) requires a compensatory trade-off on an axis of species' ecology. Spatial variation in species richness may also affect genetic diversity if large numbers of coexisting, related species result in smaller population sizes.Here, we test whether increasing species richness results in differential occupation of morphospace by the constituent species, or decreases species' genetic diversity. We test for two potential mechanisms of morphological accommodation: denser packing in ecomorphological space, and expansion of the space. We then test whether species differ in their nucleotide diversity depending on allopatry or sympatry with relatives, indicative of potential genetic consequences of coexistence that would reduce genetic diversity in sympatry. We ask these questions in a spatially explicit framework, using a global database of avian functional trait measurements in combination with >120,000 sequences downloaded from GenBank.We find that higher species richness within families is not systematically correlated with either packing in morphological space or overdispersion but, at the Class level, we find a general positive relationship between packing and species richness, but that points sampled in the tropics have comparatively greater packing than temperate ones relative to their species richness. We find limited evidence that geographical co-occurrence with closely related species or tropical distributions decreases nucleotide diversity of nuclear genes; however, this requires further analysis.Our results suggest that avian families can accumulate species regionally with minimal tradeoffs or cost, implying that external biotic factors do not limit species richness. Read the free Plain Language Summary for this article on the Journal blog.

The Vitruvian spider: Segmenting and integrating over different body parts to describe ecophenotypic variation

Understanding what drives the existing phenotypic variability has been a major topic of interest for biologists for generations. However, the study of the phenotype may not be straightforward. Indeed, organisms may be interpreted as composite objects, comprising different ecophenotypic traits, which are neither necessarily independent from each other nor do they respond to the same evolutionary pressures. For this reason, a deep biological understanding of the focal organism is essential for any morphological analysis. The spider genus Dysdera provides a particularly well-suited system for setting up protocols for morphological analyses that encompass a suit of morphological structures in any nonmodel system. This genus has undergone a remarkable diversification in the Canary Islands, where different species perform different ecological roles, exhibiting different levels of trophic specialization or troglomorphic adaptations, which translate into a remarkable interspecific morphological variability. Here, we seek to develop a broad guide, of which morphological characters must be considered, to study the effect of different ecological pressures in spiders and propose a general workflow that will be useful whenever researchers set out to investigate variation in the body plans of different organisms, with data sets comprising a set of morphological traits. We use geometric morphometric methods to quantify variation in different body structures, all of them with diverse phenotypic modifications in their chelicera, prosoma, and legs. We explore the effect of analyzing different combined landmark (LM) configurations of these characters and the degree of morphological integration that they exhibit. Our results suggest that different LM configurations of each of these body parts exhibit a higher degree of integration compared to LM configurations from different structures and that the analysis of each of these body parts captures different aspects of morphological variation, potentially related to different ecological factors.

Evolution of fungal phenotypic disparity

Organismal-grade multicellularity has been achieved only in animals, plants and fungi. All three kingdoms manifest phenotypically disparate body plans but their evolution has only been considered in detail for animals. Here we tested the general relevance of hypotheses on the evolutionary assembly of animal body plans by characterizing the evolution of fungal phenotypic variety (disparity). The distribution of living fungal form is defined by four distinct morphotypes: flagellated; zygomycetous; sac-bearing; and club-bearing. The discontinuity between morphotypes is a consequence of extinction, indicating that a complete record of fungal disparity would present a more homogeneous distribution of form. Fungal disparity expands episodically through time, punctuated by a sharp increase associated with the emergence of multicellular body plans. Simulations show these temporal trends to be non-random and at least partially shaped by hierarchical contingency. These trends are decoupled from changes in gene number, genome size and taxonomic diversity. Only differences in organismal complexity, characterized as the number of traits that constitute an organism, exhibit a meaningful relationship with fungal disparity. Both animals and fungi exhibit episodic increases in disparity through time, resulting in distributions of form made discontinuous by extinction. These congruences suggest a common mode of multicellular body plan evolution.

Thirty years of geometric morphometrics: Achievements, challenges, and the ongoing quest for biological meaningfulness

The foundations of geometric morphometrics were worked out about 30 years ago and have continually been refined and extended. What has remained as a central thrust and source of debate in the morphometrics community is the shared goal of meaningful biological inference through a tight connection between biological theory, measurement, multivariate biostatistics, and geometry. Here we review the building blocks of modern geometric morphometrics: the representation of organismal geometry by landmarks and semilandmarks, the computation of shape or form variables via superimposition, the visualization of statistical results as actual shapes or forms, the decomposition of shape variation into symmetric and asymmetric components and into different spatial scales, the interpretation of various geometries in shape or form space, and models of the association between shape or form and other variables, such as environmental, genetic, or behavioral data. We focus on recent developments and current methodological challenges, especially those arising from the increasing number of landmarks and semilandmarks, and emphasize the importance of thorough exploratory multivariate analyses rather than single scalar summary statistics. We outline promising directions for further research and for the evaluation of new developments, such as "landmark-free" approaches. To illustrate these methods, we analyze three-dimensional human face shape based on data from the Avon Longitudinal Study of Parents and Children (ALSPAC).

Ecomorphological variation of the Triatoma guasayana wing shape in semi-arid Chaco region

Triatoma guasayana (Hemiptera, Reduviidae), considered a secondary vector of Chagas disease, invades rural dwellings through flight dispersal during the warm season in semi-arid Chaco of Argentina. The objective of this study was to define and compare morphometrics features in the relative body size and wing shape of T. guasayana related to temperature and rainfall between spring, summer and end of summer. A total of 188 adults were collected in rural communities in the northwest of the province of Córdoba (central Argentina). Relative body size [body length (mm) / wing length (mm)] and 11 landmarks on the right wing were recorded. The temperature ( °C) and precipitation (mm) data were extracted from the MODIS sensor and Terra Climate dataset, respectively. Correlations between climatic variables and morphological variation were analyzed using Partial Least Square (PLS). Males at the end of summer were smaller than those at spring or summer (F = 4.48; df = 2; p = 0.01), whereas females were similar in relative body size at all seasons (F = 0.76; df = 2; p = 0.47). The PLS in males showed a correlation between wing shape and temperature (r = 0.48; p = 0.03) and precipitation (r = 0.50; p = 0.02) while in females only the temperature was the correlation significant (r = 0.35; p = 0.03). Triatoma guasayana has elongated and thin wings in spring that become short and wide at the end of summer. The morphotype of early summer could allow sustained long-duration flights, while the morphotype of end of summer would be related to short flights, correlated with the dispersive behavior of the species. The results in this study suggest that wing morphology of T. guasayana has phenotypic plasticity, and that temperature and rainfall could be considered modulator factors during the developmental stage.

Evolvability and Macroevolution: Overview and Synthesis

Evolvability is best addressed from a multi-level, macroevolutionary perspective through a comparative approach that tests for among-clade differences in phenotypic diversification in response to an opportunity, such as encountered after a mass extinction, entering a new adaptive zone, or entering a new geographic area. Analyzing the dynamics of clades under similar environmental conditions can (partially) factor out shared external drivers to recognize intrinsic differences in evolvability, aiming for a macroevolutionary analog of a common-garden experiment. Analyses will be most powerful when integrating neontological and paleontological data: determining differences among extant populations that can be hypothesized to generate large-scale, long-term contrasts in evolvability among clades; or observing large-scale differences among clade histories that can by hypothesized to reflect contrasts in genetics and development observed directly in extant populations. However, many comparative analyses can be informative on their own, as explored in this overview. Differences in clade-level evolvability can be visualized in diversity-disparity plots, which can quantify positive and negative departures of phenotypic productivity from stochastic expectations scaled to taxonomic diversification. Factors that evidently can promote evolvability include modularity—when selection aligns with modular structure or with morphological integration patterns; pronounced ontogenetic changes in morphology, as in allometry or multiphase life cycles; genome size; and a variety of evolutionary novelties, which can also be evaluated using macroevolutionary lags between the acquisition of a trait and phenotypic diversification, and dead-clade-walking patterns that may signal a loss of evolvability when extrinsic factors can be excluded. High speciation rates may indirectly foster phenotypic evolvability, and vice versa. Mechanisms are controversial, but clade evolvability may be higher in the Cambrian, and possibly early in the history of clades at other times; in the tropics; and, for marine organisms, in shallow-water disturbed habitats.

Patterns in schizomid flagellum shape from elliptical Fourier analysis

The arachnid order Schizomida is a relatively understudied group of soil-dwelling predators found on all continents except Antarctica. While efforts to understand their biology are growing, there is still much to know about them. A curious aspect of their morphology is the male flagellum, a sexually dimorphic, tail-like structure which differs in shape across the order and functions in their courtship rituals. The flagellar shape is important for taxonomic classification, yet few efforts have been made to examine shape diversity across the group. Using elliptical Fourier analysis, a type of geometric morphometrics based on shape outline, we quantified shape differences across a combined nearly 550 outlines in the dorsal and lateral views, categorizing them based on genus, family, biogeographic realm, and habitat, with special emphasis on Caribbean and Cuban fauna. We tested for allometric relationships, differences in disparity based on locations and sizes in morphospace among these categories, and for clusters of shapes in morphospace. We found multiple differences in all categories despite apparent overlaps in morphospace, evolutionary allometry, and evidence for discrete clusters in some flagellum shapes. This study can serve as a foundation for further study on the evolution, diversification, and taxonomic utility of the male flagellum.

Morphological volatility precedes ecological innovation in early echinoderms

Origins of higher taxonomic groups entail dramatic and nearly simultaneous changes in morphology and ecological function, limiting our ability to disentangle the drivers of evolutionary diversification. Here we phylogenetically compare the anatomy and life habits of Cambrian-Ordovician echinoderms to test which facet better facilitates future success. Rates of morphological evolution are faster and involve more volatile trait changes, allowing morphological disparity to accrue faster and earlier in the Cambrian. However, persistent life-habit evolution throughout the early Palaeozoic, combined with iterative functional convergence within adaptive strategies, results in major expansion of ecospace and functional diversity. The interactions between tempo, divergence and convergence demonstrate not only that anatomical novelty precedes ecological success, but also that ecological innovation is constrained, even during a phylum's origin.

Phenotypic plasticity guides Moricandia arvensis divergence and convergence across the Brassicaceae floral morphospace

Many flowers exhibit phenotypic plasticity. By inducing the production of several phenotypes, plasticity may favour the rapid exploration of different regions of the floral morphospace. We investigated how plasticity drives Moricandia arvensis, a species displaying within-individual floral polyphenism, across the floral morphospace of the entire Brassicaceae family. We compiled the multidimensional floral phenotype, the phylogenetic relationships, and the pollination niche of over 3000 species to construct a family-wide floral morphospace. We assessed the disparity between the two M. arvensis floral morphs (as the distance between the phenotypic spaces occupied by each morph) and compared it with the family-wide disparity. We measured floral divergence by comparing disparity with the most common ancestor, and estimated the convergence of each floral morph with other species belonging to the same pollination niches. Moricandia arvensis exhibits a plasticity-mediated floral disparity greater than that found between species, genera and tribes. The novel phenotype of M. arvensis moves outside the region occupied by its ancestors and relatives, crosses into a new region where it encounters a different pollination niche, and converges with distant Brassicaceae lineages. Our study suggests that phenotypic plasticity favours floral divergence and rapid appearance of convergent flowers, a process which facilitates the evolution of generalist pollination systems.

Morphological disparity and evolutionary transformations in the primate hyoid apparatus

The hyoid apparatus plays an integral role in swallowing, respiration, and vocalization in mammals. Most placental mammals have a rod-shaped basihyal connected to the basicranium via both soft tissues and a mobile bony chain-the anterior cornu-whereas anthropoid primates have broad, shield-like or even cup-shaped basihyals suspended from the basicranium by soft tissues only. How the unique anthropoid hyoid morphology evolved is unknown, and hyoid morphology of nonanthropoid primates is poorly documented. Here we use phylogenetic comparative methods and linear morphometrics to address knowledge gaps in hyoid evolution among primates and their euarchontan outgroups. We find that dermopterans have variable reduction of cornu elements. Cynocephalus volans are sexually dimorphic in hyoid morphology. Tupaia and all lemuroids except Daubentonia have a fully ossified anterior cornu connecting a rod-shaped basihyal to the basicranium; this is the ancestral mammalian pattern that is also characteristic of the last common ancestor of Primates. Haplorhines exhibit a reduced anterior cornu, and anthropoids underwent further increase in basihyal aspect ratio values and in relative basihyal volume. Convergent with haplorhines, lorisoid strepsirrhines independently evolved a broad basihyal and reduced anterior cornua. While a reduced anterior cornu is hypothesized to facilitate vocal tract lengthening and lower formant frequencies in some mammals, our results suggest vocalization adaptations alone are unlikely to drive the iterative reduction of anterior cornua within Primates. Our new data on euarchontan hyoid evolution provide an anatomical basis for further exploring the form-function relationships of the hyoid across different behaviors, including vocalization, chewing, and swallowing.

Comparative analysis of morphospace of Neotropical Sericini (Coleoptera: Scarabaeidae): disparity in the light of species diversity and activity patterns

The striking diversity among herbivorous Scarabaeoidea is still poorly understood. Therefore, we compare in these work linear measurements of body features of Neotropical and Old World linages of Sericini chafers to uncover patterns possibly linked to foraging behavior (day or night activity) or to the success of their diversification in terms of diversity. If diversity in Sericini chafers would be linked to morphological disparity, we would expect in the much less diverse Neotropical lineage a very clear drop of morphological disparity. Comparing the two major sister clades, Old World and Neotropical Sericini, in terms of their disparity and diversity, the here elaborated distance data do not support the hypothesis that morphological disparity could be a driver for the diversity of Sericini in the Old World. The influence of the metacoxal length on morphological disparity appears to represent a possible key for a better understanding of the evolution of Sericini in the Neotropical region (including their lower diversity) and answers the question of why they are so much less diverse than their sister lineage in the Old World. The increasing length of the metacoxal plate appears to be a result of the presence of a secondary metacoxal joint in Old World Sericini, which has a crucial impact on hind leg mobility and digging behavior. General body shape and single morphological characters appear under similar general evolutionary pressure: high morphometric disparity between nocturnal and diurnal Neotropical species was also corroborated by disparity estimated from discrete morphological characters.

The diet of early birds based on modern and fossil evidence and a new framework for its reconstruction

Birds are some of the most diverse organisms on Earth, with species inhabiting a wide variety of niches across every major biome. As such, birds are vital to our understanding of modern ecosystems. Unfortunately, our understanding of the evolutionary history of modern ecosystems is hampered by knowledge gaps in the origin of modern bird diversity and ecosystem ecology. A crucial part of addressing these shortcomings is improving our understanding of the earliest birds, the non-avian avialans (i.e. non-crown birds), particularly of their diet. The diet of non-avian avialans has been a matter of debate, in large part because of the ambiguous qualitative approaches that have been used to reconstruct it. Here we review methods for determining diet in modern and fossil avians (i.e. crown birds) as well as non-avian theropods, and comment on their usefulness when applied to non-avian avialans. We use this to propose a set of comparable, quantitative approaches to ascertain fossil bird diet and on this basis provide a consensus of what we currently know about fossil bird diet. While no single approach can precisely predict diet in birds, each can exclude some diets and narrow the dietary possibilities. We recommend combining (i) dental microwear, (ii) landmark-based muscular reconstruction, (iii) stable isotope geochemistry, (iv) body mass estimations, (v) traditional and/or geometric morphometric analysis, (vi) lever modelling, and (vii) finite element analysis to reconstruct fossil bird diet accurately. Our review provides specific methodologies to implement each approach and discusses complications future researchers should keep in mind. We note that current forms of assessment of dental mesowear, skull traditional morphometrics, geometric morphometrics, and certain stable isotope systems have yet to be proven effective at discerning fossil bird diet. On this basis we report the current state of knowledge of non-avian avialan diet which remains very incomplete. The ancestral dietary condition in non-avian avialans remains unclear due to scarce data and contradictory evidence in Archaeopteryx. Among early non-avian pygostylians, Confuciusornis has finite element analysis and mechanical advantage evidence pointing to herbivory, whilst Sapeornis only has mechanical advantage evidence indicating granivory, agreeing with fossilised ingested material known for this taxon. The enantiornithine ornithothoracine Shenqiornis has mechanical advantage and pedal morphometric evidence pointing to carnivory. In the hongshanornithid ornithuromorph Hongshanornis only mechanical advantage evidence indicates granivory, but this agrees with evidence of gastrolith ingestion in this taxon. Mechanical advantage and ingested fish support carnivory in the songlingornithid ornithuromorph Yanornis. Due to the sparsity of robust dietary assignments, no clear trends in non-avian avialan dietary evolution have yet emerged. Dietary diversity seems to increase through time, but this is a preservational bias associated with a predominance of data from the Early Cretaceous Jehol Lagerstätte. With this new framework and our synthesis of the current knowledge of non-avian avialan diet, we expect dietary knowledge and evolutionary trends to become much clearer in the coming years, especially as fossils from other locations and climates are found. This will allow for a deeper and more robust understanding of the role birds played in Mesozoic ecosystems and how this developed into their pivotal role in modern ecosystems.

Evolutionary and biogeographical support for species-specific proteins in lizard chemical signals

The species-specific components of animal signals can facilitate species recognition and reduce the risks of mismatching and interbreeding. Nonetheless, empirical evidence for species-specific components in chemical signals is scarce and mostly limited to insect pheromones. Based on the proteinaceous femoral gland secretions of 36 lizard species (Lacertidae), we examine the species-specific component potential of proteins in lizard chemical signals. By quantitative comparison of the one-dimensional electrophoretic patterns of the protein fraction from femoral gland secretions, we first reveal that the protein composition is species specific, accounting for a large part of the observed raw variation and allowing us to discriminate species on this basis. Secondly, we find increased protein pattern divergence in sympatric, closely related species. Thirdly, lizard protein profiles show a low phylogenetic signal, a recent and steep increase in relative disparity and a high rate of evolutionary change compared with non-specifically signal traits (i.e. body size and shape). Together, these findings provide support for the species specificity of proteins in the chemical signals of a vertebrate lineage.

The patterns and modes of the evolution of disparity in Mesozoic birds

The origin of birds from non-avian theropod dinosaurs is one of the greatest transitions in evolution. Shortly after diverging from other theropods in the Late Jurassic, Mesozoic birds diversified into two major clades-the Enantiornithes and Ornithuromorpha-acquiring many features previously considered unique to the crown group along the way. Here, we present a comparative phylogenetic study of the patterns and modes of Mesozoic bird skeletal morphology and limb proportions. Our results show that the major Mesozoic avian groups are distinctive in discrete character space, but constrained in a morphospace defined by limb proportions. The Enantiornithines, despite being the most speciose group of Mesozoic birds, are much less morphologically disparate than their sister clade, the Ornithuromorpha-the clade that gave rise to living birds, showing disparity and diversity were decoupled in avian history. This relatively low disparity suggests that diversification of enantiornithines was characterized in exhausting fine morphologies, whereas ornithuromorphs continuously explored a broader array of morphologies and ecological opportunities. We suggest this clade-specific evolutionary versatility contributed to their sole survival of the end-Cretaceous mass extinction.

The complex effects of mass extinctions on morphological disparity

Studies of biodiversity through deep time have been a staple for biologists and paleontologists for over 60 years. Investigations of species richness (diversity) revealed that at least five mass extinctions punctuated the last half billion years, each seeing the rapid demise of a large proportion of contemporary taxa. In contrast to diversity, the response of morphological diversity (disparity) to mass extinctions is unclear. Generally, diversity and disparity are decoupled, such that diversity may decline as morphological disparity increases, and vice versa. Here, we develop simulations to model disparity changes across mass extinctions using continuous traits and birth-death trees. We find no simple null for disparity change following a mass extinction but do observe general patterns. The range of trait values decreases following either random or trait-selective mass extinctions, whereas variance and the density of morphospace occupation only decline following trait-selective events. General trends may differentiate random and trait-selective mass extinctions, but methods struggle to identify trait selectivity. Long-term effects of mass extinction trait selectivity change support for phylogenetic comparative methods away from the simulated Brownian motion toward Ornstein-Uhlenbeck and Early Burst models. We find that morphological change over mass extinction is best studied by quantifying multiple aspects of morphospace occupation.