A 3D geometric morphometric analysis of the bovid distal humerus, with special reference to Rusingoryx atopocranion (Pleistocene, Eastern Africa)

The family Bovidae [Mammalia: Artiodactyla] is speciose and has extant representatives on every continent, forming key components of mammal communities. For these reasons, bovids are ideal candidates for studies of ecomorphology. In particular, the morphology of the bovid humerus has been identified as highly related to functional variables such as body mass and habitat. This study investigates the functional morphology of the bovid distal humerus in isolation due to its increased likelihood of preservation in the fossil record, and the resulting opportunity for a better understanding of the ecomorphology of extinct bovids. A landmark scheme of 30 landmarks was used to capture the 3D distal humerus morphology in 111 extant bovid specimens. We find that the distal humerus has identifiable morphologies associated with body mass, habitat preference and tribe affiliation and that some characteristics are shared between high body mass bovids and those living on hard, flat terrain which is likely due to the high stress on the bone in both cases. We directly apply our findings regarding extant bovids to the extinct alcelaphine bovid, Rusingoryx atopocranion from the mid to late Pleistocene (>33-45 ka) Lake Victoria region of Kenya. This species is known for some peculiar morphologies including a domed cranium with hollow nasal crests, and having small hooves for a bovid of its size. Another interesting aspect of Rusingoryx's skeletal morphology which has not been addressed is an unusual protrusion on the lateral epicondyle of the distal humerus. Despite considerable individual variation in the Rusingoryx specimens, we find evidence to support its historical assignment to the tribe Alcelaphini, and that it likely preferred open grassland habitats, which is consistent with independent reconstructions of the palaeoenvironment. We also provide the most accurate body mass estimate for Rusingoryx to date, based on distal humerus centroid size. Overall, we are able to conclude that the distal humerus in extant bovids is highly informative regarding body mass, habitat preference and tribe, and that this can be applied directly to a fossil taxon with promising results.

Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch Ptychodus

The fossil fish Ptychodus Agassiz, 1834, characterized by a highly distinctive grinding dentition and an estimated gigantic body size (up to around 10 m), has remained one of the most enigmatic extinct elasmobranchs (i.e. sharks, skates and rays) for nearly two centuries. This widespread Cretaceous taxon is common in Albian to Campanian deposits from almost all continents. However, specimens mostly consist of isolated teeth or more or less complete dentitions, whereas cranial and post-cranial skeletal elements are very rare. Here we describe newly discovered material from the early Late Cretaceous of Mexico, including complete articulated specimens with preserved body outline, which reveals crucial information on the anatomy and systematic position of Ptychodus. Our phylogenetic and ecomorphological analyses indicate that ptychodontids were high-speed (tachypelagic) durophagous lamniforms (mackerel sharks), which occupied a specialized predatory niche previously unknown in fossil and extant elasmobranchs. Our results support the view that lamniforms were ecomorphologically highly diverse and represented the dominant group of sharks in Cretaceous marine ecosystems. Ptychodus may have fed predominantly on nektonic hard-shelled prey items such as ammonites and sea turtles rather than on benthic invertebrates, and its extinction during the Campanian, well before the end-Cretaceous crisis, might have been related to competition with emerging blunt-toothed globidensine and prognathodontine mosasaurs.

Who was the real sabertooth predator: Thylacosmilus or Thylacoleo?

Sabertoothed mammalian predators, all now extinct, were almost exclusively feloid carnivorans (Eutheria, Placentalia): here a couple of extinct metatherian predators are considered in comparison with the placental sabertooths. Thylacosmilus (the "marsupial sabertooth") and Thylacoleo (the "marsupial lion") were both relatively large (puma-sized) carnivores of the Plio-Pleistocene in the Southern Hemisphere (Argentina and Australia, respectively). Both carnivores have captured the public imagination, especially as predators that were somehow analogous to northern placental forms. But a more detailed consideration of their morphology shows that neither can be simply analogized with its supposed placental counterpart. While Thylacosmilus did indeed have saber-like canines, many aspects of its anatomy show that it could not have killed prey in the manner proposed for the sabertoothed felids such as Smilodon. Rather than being an active predator, it may have been a specialized scavenger, using the hypertrophied canines to open carcasses, and perhaps deployed a large tongue to extract the innards. Thylacoleo lacked canines, and its supposedly "caniniform" incisors could not have acted like a felid's canines. Nevertheless, while its mode of dispatching its prey remains a subject for debate, it was clearly a powerful predator, likely to be capable of bringing down prey bigger than itself while hunting alone. In that regard, it may have filled the ecomorphological role proposed for placental sabertooths, and so despite the lack of canines can be nominated as the true "marsupial sabertooth" out of the two extinct taxa.

Genomic underpinnings of head and body shape in Arctic charr ecomorph pairs

Across its Holarctic range, Arctic charr (Salvelinus alpinus) populations have diverged into distinct trophic specialists across independent replicate lakes. The major aspect of divergence between ecomorphs is in head shape and body shape, which are ecomorphological traits reflecting niche use. However, whether the genomic underpinnings of these parallel divergences are consistent across replicates was unknown but key for resolving the substrate of parallel evolution. We investigated the genomic basis of head shape and body shape morphology across four benthivore-planktivore ecomorph pairs of Arctic charr in Scotland. Through genome-wide association analyses, we found genomic regions associated with head shape (89 SNPs) or body shape (180 SNPs) separately and 50 of these SNPs were strongly associated with both body and head shape morphology. For each trait separately, only a small number of SNPs were shared across all ecomorph pairs (3 SNPs for head shape and 10 SNPs for body shape). Signs of selection on the associated genomic regions varied across pairs, consistent with evolutionary demography differing considerably across lakes. Using a comprehensive database of salmonid QTLs newly augmented and mapped to a charr genome, we found several of the head- and body-shape-associated SNPs were within or near morphology QTLs from other salmonid species, reflecting a shared genetic basis for these phenotypes across species. Overall, our results demonstrate how parallel ecotype divergences can have both population-specific and deeply shared genomic underpinnings across replicates, influenced by differences in their environments and demographic histories.

Riverine flow rate drives widespread convergence in the shell morphology of imperiled freshwater mussels

Frequent and strong morphological convergence suggests that determinism tends to supersede historical contingencies in evolutionary radiations. For many lineages living within the water column of rivers and streams, hydrodynamic forces drive widespread morphological convergence. Living below the sediment-water interface may release organisms from these hydrodynamic pressures, permitting a broad array of morphologies, and thus less convergence. However, we show here that the semi-infaunal freshwater mussels have environmentally determined convergence in shell morphology. Using 3D morphometric data from 715 individuals among 164 Nearctic species, we find that species occurring in rivers with high flow rates have evolved traits that resist dislodgement from their burrowed position in the streambed: thicker shells for their body size, with the thickest sector of the shell being the most deeply buried. Species occurring in low flow environments have evolved thinner and more uniformly thickened shells, corresponding to an alternative adaptation to dislodgement: increased burrowing efficiency. Within species, individuals also show increased shell thickness for their body size at higher flow rates, suggesting that ecophenotypy may, in part, be an important mechanism for establishing populations in new environments and thus evolutionary divergence in this highly imperiledinvertebrate group.

Uncovering the mosaic evolution of the carnivoran skeletal system

The diversity of vertebrate skeletons is often attributed to adaptations to distinct ecological factors such as diet, locomotion, and sensory environment. Although the adaptive evolution of skull, appendicular skeleton, and vertebral column is well studied in vertebrates, comprehensive investigations of all skeletal components simultaneously are rarely performed. Consequently, we know little of how modes of evolution differ among skeletal components. Here, we tested if ecological and phylogenetic effects led to distinct modes of evolution among the cranial, appendicular and vertebral regions in extant carnivoran skeletons. Using multivariate evolutionary models, we found mosaic evolution in which only the mandible, hindlimb and posterior (i.e. last thoracic and lumbar) vertebrae showed evidence of adaptation towards ecological regimes whereas the remaining skeletal components reflect clade-specific evolutionary shifts. We hypothesize that the decoupled evolution of individual skeletal components may have led to the origination of distinct adaptive zones and morphologies among extant carnivoran families that reflect phylogenetic hierarchies. Overall, our work highlights the importance of examining multiple skeletal components simultaneously in ecomorphological analyses. Ongoing work integrating the fossil and palaeoenvironmental record will further clarify deep-time drivers that govern the carnivoran diversity we see today and reveal the complexity of evolutionary processes in multicomponent systems.

Craniodental ecomorphology of the large Jurassic ichthyosaurian Temnodontosaurus

Marine amniotes have played many crucial roles in ocean ecosystems since the Triassic, including predation at the highest trophic levels. One genus often placed into this guild is the large Early Jurassic neoichthyosaurian Temnodontosaurus, the only post-Triassic ichthyosaurian known with teeth which bear a distinct cutting edge or carina. This taxonomically problematic genus is currently composed of seven species which show a wide variety of skull and tooth morphologies. Here we assess the craniodental disparity in Temnodontosaurus using a series of functionally informative traits. We describe the range of tooth morphologies in the genus in detail, including the first examples of serrated carinae in ichthyosaurians. These consist of false denticles created by the interaction of enamel ridgelets with the carinal keel, as well as possible cryptic true denticles only visible using scanning electron microscopy. We also find evidence for heterodonty in the species T. platyodon, with unicarinate mesial teeth likely playing a role in prey capture and labiolingually compressed, bicarinate distal teeth likely involved in prey processing. This type of heterodonty appears to be convergent with a series of other marine amniotes including early cetaceans. Overall, the species currently referred to as the genus Temnodontosaurus show a range of craniodental configurations allowing prey to be captured and processed in different ways - for example, T. eurycephalus has a deep snout and relatively small bicarinate teeth likely specialised for increased wound infliction and grip-and-tear feeding, whereas T. platyodon has a more elongate yet robust snout and larger teeth and may be more adapted for grip-and-shear feeding. These results suggest the existence of niche partitioning at higher trophic levels in Early Jurassic ichthyosaurians and have implications for future work on the taxonomy of this wastebasket genus, as well as for research into the ecology of other extinct megapredatory marine tetrapods.

Multiple performance peaks for scale-biting in an adaptive radiation of pupfishes

The physical interactions between organisms and their environment ultimately shape their rate of speciation and adaptive radiation, but the contributions of biomechanics to evolutionary divergence are frequently overlooked. Here we investigated an adaptive radiation of Cyprinodon pupfishes to measure the relationship between feeding kinematics and performance during adaptation to a novel trophic niche, lepidophagy, in which a predator removes only the scales, mucus, and sometimes tissue from their prey using scraping and biting attacks. We used high-speed video to film scale-biting strikes on gelatin cubes by scale-eater, molluscivore, generalist, and hybrid pupfishes and subsequently measured the dimensions of each bite. We then trained the SLEAP machine-learning animal tracking model to measure kinematic landmarks and automatically scored over 100,000 frames from 227 recorded strikes. Scale-eaters exhibited increased peak gape and greater bite length; however, substantial within-individual kinematic variation resulted in poor discrimination of strikes by species or strike type. Nonetheless, a complex performance landscape with two distinct peaks best predicted gel-biting performance, corresponding to a significant nonlinear interaction between peak gape and peak jaw protrusion in which scale-eaters and their hybrids occupied a second performance peak requiring larger peak gape and greater jaw protrusion. A bite performance valley separating scale-eaters from other species may have contributed to their rapid evolution and is consistent with multiple estimates of a multi-peak fitness landscape in the wild. We thus present an efficient deep-learning automated pipeline for kinematic analyses of feeding strikes and a new biomechanical model for understanding the performance and rapid evolution of a rare trophic niche.

The topological organization of the turtle cranium is constrained and conserved over long evolutionary timescales

The cranium of turtles (Testudines) is characterized by the secondary reduction of temporal fenestrae and loss of cranial joints (i.e., characteristics of anapsid, akinetic skulls). Evolution and ontogeny of the turtle cranium are associated with shape changes. Cranial shape variation among Testudines can partially be explained by dietary and functional adaptations (neck retraction), but it is unclear if cranial topology shows similar ecomorphological signal, or if it is decoupled from shape evolution. We assess the topological arrangement of cranial bones (i.e., number, relative positioning, connections), using anatomical network analysis. Non-shelled stem turtles have similar cranial arrangements to archosauromorph outgroups. Shelled turtles (Testudinata) evolve a unique cranial organization that is associated with bone losses (e.g., supratemporal, lacrimal, ectopterygoid) and an increase in complexity (i.e., densely and highly interconnected skulls with low path lengths between bones), resulting from the closure of skull openings and establishment of unusual connections such as a parietal-pterygoid contact in the secondary braincase. Topological changes evolutionarily predate many shape changes. Topological variation and taxonomic morphospace discrimination among crown turtles are low, indicating that cranial topology may be constrained. Observed variation results from repeated losses of nonintegral bones (i.e., premaxilla, nasal, epipterygoid, quadratojugal), and changes in temporal emarginations and palate construction. We observe only minor ontogenetic changes. Topology is not influenced by diet and habitat, contrasting cranial shape. Our results indicate that turtles have a unique cranial topology among reptiles that is conserved after its initial establishment, and shows that cranial topology and shape have different evolutionary histories.

Diadromy Drives Elevated Rates of Trait Evolution and Ecomorphological Convergence in Clupeiformes (Herring, Shad, and Anchovies)

AbstractMigration can have a profound influence on rates and patterns of phenotypic evolution. Diadromy is the migration between marine and freshwater habitats for feeding and reproduction that can require individuals to travel tens to thousands of kilometers. The high energetic demands of diadromy are predicted to select for ecomorphological traits that maximize swimming and locomotor efficiency. Intraspecific studies have shown repeated instances of divergence among diadromous and nondiadromous populations in locomotor and foraging traits, which suggests that at a macroevolutionary scale diadromous lineages may experience convergent evolution onto one or multiple adaptive optima. We tested for differences in rates and patterns of phenotypic evolution among diadromous and nondiadromous lineages in Clupeiformes, a clade that has evolved diadromy more than 10 times. Our results show that diadromous clupeiforms show convergent evolution for some locomotor traits and faster rates of evolution, which we propose are adaptive responses to the locomotor demands of migration. We also find evidence that diadromous lineages show convergence into multiple regions of multivariate trait space and suggest that these respective trait spaces are associated with differences in migration and trophic ecology. However, not all locomotor traits and no trophic traits show evidence of convergence or elevated rates of evolution associated with diadromy. Our results show that long-distance migration influences the tempo and patterns of phenotypic evolution at macroevolutionary scales, but there is not a single diadromous syndrome.

Evolutionary ecomorphology for the twenty-first century: examples from mammalian carnivores

Carnivores (cats, dogs and kin) are a diverse group of mammals that inhabit a remarkable range of ecological niches. While the relationship between ecology and morphology has long been of interest in carnivorans, the application of quantitative techniques has resulted in a recent explosion of work in the field. Therefore, they provide a case study of how quantitative techniques, such as geometric morphometrics (GMM), have impacted our ability to tease apart complex ecological signals from skeletal anatomy, and the implications for our understanding of the relationships between form, function and ecological specialization. This review provides a synthesis of current research on carnivoran ecomorphology, with the goal of illustrating the complex interaction between ecology and morphology in the skeleton. We explore the ecomorphological diversity across major carnivoran lineages and anatomical systems. We examine cranial elements (skull, sensory systems) and postcranial elements (limbs, vertebral column) to reveal mosaic patterns of adaptation related to feeding and hunting strategies, locomotion and habitat preference. We highlight the crucial role that new approaches have played in advancing our understanding of carnivoran ecomorphology, while addressing challenges that remain in the field, such as ecological classifications, form-function relationships and multi-element analysis, offering new avenues for future research.

Xenorhinos bhatnagari sp. nov., a new, nasal-emitting trident bat (Rhinonycteridae, Rhinolophoidea) from early Miocene forests in northern Australia

A new Old World trident bat (Rhinonycteridae) is described from an early Miocene cave deposit in the Riversleigh World Heritage Area, northwestern Queensland, Australia. Living rhinonycterids comprise a small family of insect-eating, nasal-emitting rhinolophoid bats from Africa, Madagascar, Seychelles, the Middle East, and northern Australia. The new fossil species is one of at least 12 rhinonycterid species known from the Oligo-Miocene cave deposits at Riversleigh. We refer the new species to the genus Xenorhinos (Hand, Journal of Vertebrate Paleontology, 18, 430-439, 1998a) because it shares a number of unusual cranial features with the type and only other species of the genus, X. halli, including a broad rostrum, very wide interorbital region, pronounced ventral flexion of the rostrum, very constricted sphenoidal bridge, and, within the nasal fossa, reduced bony division, and relatively well developed turbinals. Xenorhinos species lived in northern Australia during the global Miocene Climatic Optimum, in closed wet forests, unlike the drier habitats that trident bats largely inhabit today. Our phylogenetic analysis suggests that more than one dispersal event gave rise to the Australian rhinonycterid radiation, with two lineages having sister-group relationships with non-Australian taxa.

Phenotypic plasticity of a generalist fish species resident to lotic environments: Insights from the Great Lakes region

Fish morphology is incredibly plastic and local/resident morphology can be influenced by factors including habitat, predation, resource availability, and water velocity. Through analysis of body shape using geometric morphometrics, we describe the degree of phenotypic plasticity within a generalist fish species resident to low-order tributaries of Green Bay and Lake Michigan. We predicted that isolated populations of creek chub (Semotilus atromaculatus) would display plastic responses in body shape due to differences in selective pressures imposed by stream environments. We show that body shape of creek chub was significantly different between streams which are considered to be isolated populations, and while we expected body shape variation to remain constant between study years, we found that shape was not fixed and changed over time in the same manner among focal streams. The diversity of creek chub diet and degree of agricultural land use in the watershed were significant predictors of body morphology. The effect of resource availability and land use within the watershed demonstrates how selective pressures influence phenotypes at the population level. Our study provides insight into morphological changes of stream fish populations, which may be important in the context of changing ecosystems and novel conditions.

Exploring the relationship between bats (Mammalia, Chiroptera) and ectoparasitic flies (Diptera, Hippoboscoidea) of the Orinoquia Region in South America

Bat flies (Nycteribiidae and Streblidae) have been used to study co-evolutionary patterns between ectoparasites and bats. In the world, Nycteribiidae and Streblidae are represented by approximately 276 and 237 species, respectively. In regions such as the Orinoquia located in the north of South America (Colombia and Venezuela), the richness of bats is high (more than 100 documented species), but studies on Nycteribiidae and Streblidae are scarce and discontinuous. To contribute to the knowledge of ectoparasitic flies in the Orinoquia, records of flies and their interactions with bats were reviewed, including new records and associations using interaction networks. We documented 124 species of Streblidae and only 12 of Nycteribiidae for the Orinoquia in approximately 102 bat species reported in Colombia and Venezuela. New records for six species of bat flies in Colombia were found (Mastopteraguimaraesi, Noctiliostreblamaai, Paradyschiriaparvuloides, Trichobiusjubatus, Trichobiusparasiticus, and Basiliaferrisi) associated with six species of bats (Cynomopsplanirostris, Desmodusrotundus, Myotishandleyi, Molossusrufus, Noctilioalbiventris, and Phyllostomushastatus). The bat-ectoparasite interaction networks in the Orinoquia revealed a pattern of antagonistic relationships, with high specialization, modularity, and low connectivity and nesting. The identified networks are between bat fly species belonging to different ecomorphological groups with unique host species. This supports the idea of ecological niche partitioning among ectoparasitic bat flies and hosts. Our study expanded the knowledge of the distribution of some fly species and the associations with bat hosts in Colombia, by presenting morphological descriptions and new observations, which are key to understanding the ecology, diversity, and distribution of these species.

Ontogenetic morphometry of the brown smoothhound shark Mustelus henlei with implications for ecology and evolution

The central tenet of ecomorphology links ecological and morphological variation through the process of selection. Traditionally used to rationalise morphological differences between taxa, an ecomorphological approach is increasingly being utilised to study morphological differences expressed through ontogeny. Elasmobranchii (sharks, rays and skates) is one clade in which such ontogenetic shifts in body form have been reported. Such studies are limited to a relatively small proportion of total elasmobranch ecological and morphological diversity, and questions remain regarding the extent to which ecological selection are driving observed morphometric trends. In this study, we report ontogenetic growth trajectories obtained via traditional linear morphometrics from a large data set of the brown smoothhound shark (Mustelus henlei). We consider various morphological structures including the caudal, dorsal and pectoral fins, as well as several girth measurements. We use an ecomorphological approach to infer the broad ecological characteristics of this population and refine understanding of the selective forces underlying the evolution of specific morphological structures. We suggest that observed scaling trends in M. henlei are inconsistent with migratory behaviour, but do not contradict a putative trophic niche shift. We also highlight the role of predation pressure and sex-based ecological differences in driving observed trends in morphometry, a factor which has previously been neglected when considering the evolution of body form in sharks.

Neuroanatomy of the crocodylian Tomistoma dowsoni from the Miocene of North Africa provides insights into the evolutionary history of gavialoids

The interrelationships of the extant crocodylians Gavialis gangeticus and Tomistoma schlegelii have been historically disputed. Whereas molecular analyses indicate a sister taxon relationship between these two gavialoid species, morphological datasets typically place Gavialis as the outgroup to all other extant crocodylians. Recent morphological-based phylogenetic analyses have begun to resolve this discrepancy, recovering Gavialis as the closest living relative of Tomistoma; however, several stratigraphically early fossil taxa are recovered as closer to Gavialis than Tomistoma, resulting in anomalously early divergence timings. As such, additional morphological data might be required to resolve these remaining discrepancies. 'Tomistoma' dowsoni is an extinct species of gavialoid from the Miocene of North Africa. Utilising CT scans of a near-complete, referred skull, we reconstruct the neuroanatomy and neurosensory apparatus of 'Tomistoma' dowsoni. Based on qualitative and quantitative morphometric comparisons with other crocodyliforms, the neuroanatomy of 'Tomistoma' dowsoni is characterised by an intermediate morphology between the two extant gavialoids, more closely resembling Gavialis. This mirrors the results of recent studies based on the external anatomy of these three species and other fossil gavialoids. Several neuroanatomical features of these species appear to reflect ecological and/or phylogenetic signals. For example, the 'simple' morphology of their neurosensory apparatus is broadly similar to that of other long and narrow-snouted (longirostrine), aquatic crocodyliforms. A dorsoventrally short, anteroposteriorly long endosseous labyrinth is also associated with longirostry. These features indicate that snout and skull morphology, which are themselves partly constrained by ecology, exert an influence on neuroanatomical morphology, as has also been recognised in birds and turtles. Conversely, the presence of a pterygoid bulla in Gavialis and several extinct gavialoids, and its absence in Tomistoma schlegelii, could be interpreted as a phylogenetic signal of crocodylians more closely related to Gavialis than to Tomistoma. Evaluation of additional fossil gavialoids will be needed to further test whether these and other neuroanatomical features primarily reflect a phylogenetic or ecological signal. By incorporating such previously inaccessible information of extinct and extant gavialoids into phylogenetic and macroecological studies, we can potentially further constrain the clade's interrelationships, as well as evaluate the timing and ecological association of the evolution of these neuroanatomical features. Finally, our study supports recent phylogenetic analyses that place 'Tomistoma' dowsoni as being phylogenetically closer to Gavialis gangeticus than to Tomistoma schlegelii, indicating the necessity of a taxonomic revision of this fossil species.

The genetics-morphology-behavior trifecta: Unraveling the single greatest limitation affecting our understanding of chondrichthyan evolution

Sharks, rays, and chimaera form the clade Chondrichthyes, an ancient group of morphologically and ecologically diverse vertebrates that has played an important role in our understanding of gnathostome evolution. Increasingly, studies seek to investigate evolutionary processes operating within the chondrichthyan crown group, with the broad aim of understanding the driving forces behind the vast phenotypic diversity observed among its constituent taxa. Genetic, morphological, and behavioral studies have all contributed to our understanding of phenotypic evolution yet are typically considered in isolation in the context of Chondrichthyes. In this viewpoint, I discuss why such isolation is prevalent in the literature, how it constrains our understanding of evolution, and how it might be overcome. I argue that integrating these core fields of organismal biology is vital if we are to understand the evolutionary processes operating in contemporary chondrichthyan taxa and how such processes have contributed to past phenotypic evolution. Despite this, the necessary tools to overcome this major limitation already exist and have been applied to other taxa.

Upper beak depression instead of elevation dominates cranial kinesis in woodpeckers

The value of birds' ability to move the upper beak relative to the braincase has been shown in vital tasks like feeding and singing. In woodpeckers, such cranial kinesis has been thought to hinder pecking as delivering forceful blows calls for a head functioning as a rigid unit. Here, we tested whether cranial kinesis is constrained in woodpeckers by comparing upper beak rotation during their daily activities such as food handling, calling and gaping with those from closely related species that also have a largely insectivorous diet but do not peck at wood. Both woodpeckers and non-woodpecker insectivores displayed upper beak rotations of up to 8 degrees. However, the direction of upper beak rotation differed significantly between the two groups, with woodpeckers displaying primarily depressions and non-woodpeckers displaying elevations. The divergent upper beak rotation of woodpeckers may be caused either by anatomical modifications to the craniofacial hinge that reduce elevation, by the caudal orientation of the mandible depressor muscle forcing beak depressions, or by both. Our results suggest that pecking does not result in plain rigidification at the upper beak's basis of woodpeckers, but it nevertheless significantly influences the way cranial kinesis is manifested.

Lacustrine speciation associated with chromosomal inversion in a lineage of riverine fishes

Geographic isolation is the primary driver of speciation in many vertebrate lineages. This trend is exemplified by North American darters, a clade of freshwater fishes where nearly all sister species pairs are allopatric and separated by millions of years of divergence. One of the only exceptions is the Lake Waccamaw endemic Etheostoma perlongum and its riverine sister species E. maculaticeps, which have no physical barriers to gene flow. Here we show that lacustrine speciation of E. perlongum is characterized by morphological and ecological divergence likely facilitated by a large chromosomal inversion. While Etheostoma perlongum is phylogenetically nested within the geographically widespread E. maculaticeps, there is a sharp genetic and morphological break coinciding with the lake-river boundary in the Waccamaw River system. Despite recent divergence, an active hybrid zone, and ongoing gene flow, analyses using a de novo reference genome reveal a 9 Mb chromosomal inversion with elevated divergence between E. perlongum and E. maculaticeps. This region exhibits striking synteny with known inversion supergenes in two distantly related fish lineages, suggesting deep evolutionary convergence of genomic architecture. Our results illustrate that rapid, ecological speciation with gene flow is possible even in lineages where geographic isolation is the dominant mechanism of speciation.

Armed to the teeth: The underestimated diversity in tooth shape in snakes and its relation to feeding behavior and diet

The structure, composition, and shape of teeth have been related to dietary specialization in many vertebrate species, but comparative studies on snakes' teeth are lacking. Yet, snakes have diverse dietary habits that may impact the shape of their teeth. We hypothesize that prey properties, such as hardness and shape, as well as feeding behavior, such as aquatic or arboreal predation, or holding vigorous prey, impose constraints on the evolution of tooth shape in snakes. We compared the morphology of the dentary teeth of 63 species that cover the phylogenetic and dietary diversity of snakes, using 3D geometric morphometrics and linear measurements. Our results show that prey hardness, foraging substrate, and the main feeding mechanical challenge are important drivers of tooth shape, size, and curvature. Overall, long, slender, curved teeth with a thin layer of hard tissue are observed in species that need to maintain a grip on their prey. Short, stout, less curved teeth are associated with species that undergo high or repeated loads. Our study demonstrates the diversity of tooth morphology in snakes and the need to investigate its underlying functional implications to better understand the evolution of teeth in vertebrates.

Reconstructing locomotor ecology of extinct avialans: a case study of Ichthyornis comparing sternum morphology and skeletal proportions

Avian skeletal morphology is associated with locomotor function, including flight style, swimming and terrestrial locomotion, and permits informed inferences on locomotion in extinct taxa. The fossil taxon Ichthyornis (Avialae: Ornithurae) has long been regarded as highly aerial, with flight similar to terns or gulls (Laridae), and skeletal features resembling foot-propelled diving adaptations. However, rigorous testing of locomotor hypotheses has yet to be performed on Ichthyornis, despite its notable phylogenetic position as one of the most crownward stem birds. We analysed separate datasets of three-dimensional sternal shape (geometric morphometrics) and skeletal proportions (linear measurements across the skeleton), to examine how well these data types predict locomotor traits in Neornithes. We then used this information to infer locomotor capabilities of Ichthyornis. We find strong support for both soaring and foot-propelled swimming capabilities in Ichthyornis. Further, sternal shape and skeletal proportions provide complementary information on avian locomotion: skeletal proportions allow better predictions of the capacity for flight, whereas sternal shape predicts variation in more specific locomotor abilities such as soaring, foot-propelled swimming and escape burst flight. These results have important implications for future studies of extinct avialan ecology and underscore the importance of closely considering sternum morphology in investigations of fossil bird locomotion.

Determinants of natal dispersal distances in North American birds

Natal dispersal-the movement from birth site to first breeding site-determines demographic and population genetic dynamics and has important consequences for ecological and evolutionary processes. Recent work suggested that one of the main factors determining natal dispersal distances is the cost of locomotion. We evaluated this hypothesis using band recovery data to estimate natal dispersal distances for 50 North American bird species. We then analyzed the relationships between dispersal distances and a suite of morphological and ecological predictors, including proxies for the cost of locomotion (flight efficiency), using phylogenetic regression models. We found that flight efficiency, population size, and habitat influence natal dispersal distances. We discuss how the effects of population size and habitat can also be related to mobility and locomotion. Our findings are consistent with a predominant effect of adaptations for mobility on dispersal distances.

Initiation of speciation across multiple dimensions in a rock-restricted, tropical lizard

Population isolation and concomitant genetic divergence, resulting in strong phylogeographical structure, is a core aspect of speciation initiation. If and how speciation then proceeds and ultimately completes depends on multiple factors that mediate reproductive isolation, including divergence in genomes, ecology and mating traits. Here we explored these multiple dimensions in two young (Plio-Pleistocene) species complexes of gekkonid lizards (Heteronotia) from the Kimberley-Victoria River regions of tropical Australia. Using mitochondrial DNA screening and exon capture phylogenomics, we show that the rock-restricted Heteronotia planiceps exhibits exceptional fine-scale phylogeographical structure compared to the codistributed habitat generalist Heteronotia binoei. This indicates pervasive population isolation and persistence in the rock-specialist, and thus a high rate of speciation initiation across this geographically complex region, with levels of genomic divergence spanning the "grey zone" of speciation. Proximal lineages of H. planiceps were often separated by different rock substrates, suggesting a potential role for ecological isolation; however, phylogenetic incongruence and historical introgression were inferred between one such pair. Ecomorphological divergence among lineages within both H. planiceps and H. binoei was limited, except that limestone-restricted lineages of H. planiceps tended to be larger than rock-generalists. By contrast, among-lineage divergence in the chemical composition of epidermal pore secretions (putative mating trait) exceeded ecomorphology in both complexes, but with less trait overlap among lineages in H. planiceps. This system-particularly the rock-specialist H. planiceps-highlights the role of multidimensional divergence during incipient speciation, with divergence in genomes, ecomorphology and chemical signals all at play at very fine spatial scales.

Diet and habit explain head-shape convergences in natricine snakes

The concept of ecomorphs, whereby species with similar ecologies have similar phenotypes regardless of their phylogenetic relatedness, is often central to discussions regarding the relationship between ecology and phenotype. However, some aspects of the concept have been questioned, and sometimes species have been grouped as ecomorphs based on phenotypic similarity without demonstrating ecological similarity. Within snakes, similar head shapes have convergently evolved in species living in comparable environments and/or with similar diets. Therefore, ecomorphs could exist in some snake lineages, but this assertion has rarely been tested for a wide-ranging group within a single framework. Natricine snakes (Natricinae) are ecomorphologically diverse and currently distributed in Asia, Africa, Europe and north-central America. They are primarily semiaquatic or ground-dwelling terrestrial snakes, but some are aquatic, burrowing or aquatic and burrowing in habit and may be generalist or specialist in diet. Thus, natricines present an interesting system to test whether snakes from different major habit categories represent ecomorphs. We quantify morphological similarity and disparity in head shape among 191 of the ca. 250 currently recognized natricine species and apply phylogenetic comparative methods to test for convergence. Natricine head shape is largely correlated with habit, but in some burrowers is better explained by dietary specialism. Convergence in head shape is especially strong for aquatic burrowing, semiaquatic and terrestrial ecomorphs and less strong for aquatic and burrowing ecomorphs. The ecomorph concept is useful for understanding natricine diversity and evolution, though would benefit from further refinement, especially for aquatic and burrowing taxa.

Darter fishes exhibit variable intraspecific head shape allometry and modularity

Allometry, the relationship between anatomical proportions and body size, may either limit or facilitate the diversification of morphology. We examined the impact of allometry in darter fish morphology, which displays a variety of trophic morphologies. This study aimed to address (a) whether there was significant variation in darter head allometry, (b) if allometry contributed to head shape diversity in adults, and (c) if darters show head shape modularity associated with allometry. We used geometric morphometrics to quantify head shape across 10 different species and test for heterogeneity in allometric slopes. In addition, we quantified the degree of modularity between the preorbital and postorbital regions of the darter head, both before and after correction for body size. We found that different species have unique allometric slopes, particularly among the Simoperca subgenus, and that closely related darter species tend to show ontogenetic divergence, contributing to the diversity of head shapes observed in adults. We suggest that such a pattern may result from the similarity of juvenile diets due to gape limitation. We also found that several species show significant modularity in head shape but that modularity was evolutionarily labile and only sometimes impacted by head shape allometry. Overall, our work suggests that ontogenetic shape development may have been important to the evolution of head shape in darters, particularly in the evolution of foraging traits and microhabitat.

Diet versatility and functional trade-offs shape tooth morphology in squirrels

Identifying the drivers of adaptation is key to understanding the origin and evolution of diversity. Here we study the morphological evolution of tooth morphology, a classic example of a conserved structure, to gain insights into the conditions that can overcome resistance to evolutionary change. We use geometric morphometrics of the occlusal surface outline of the fourth lower premolar (p4) of squirrels, a paradigm of a stable tooth morphology, to explore morphological adaptations to diet. Although a versatile generalist dental morphology favors the retention of the ancestral shape, the acquisition of diets that require strong mechanical processing drives morphological change. In particular, species that eat both grass and dry fruits evolved disparate tooth shape morphologies, related to trade-offs between feeding performance that lead to a more or less pronounced change depending on the proportion of those items in their diet. Also, some folivores develop relatively large p4s, and most bark gleaners have relatively small p4s. Ultimately, despite the role of diet shaping these patterns, we showed that diet is not the only factor driving the evolution of tooth morphology.

Ecomorphological patterns in trigeminal canal branching among sauropsids reveal sensory shift in suchians

The vertebrate trigeminal nerve is the primary mediator of somatosensory information from nerve endings across the face, extending nerve branches through bony canals in the face and mandibles, terminating in sensory receptors. Reptiles evolved several extreme forms of cranial somatosensation in which enhanced trigeminal tissues are present in species engaging in unique mechanosensory behaviors. However, morphology varies by clade and ecology among reptiles. Few lineages approach the extreme degree of tactile somatosensation possessed by crocodylians, the only remaining members of a clade that underwent an ecological transition from the terrestrial to semiaquatic habitat, also evolving a specialized trigeminal system. It remains to be understood how trigeminal osteological correlates inform how adaptations for enhanced cranial sensation evolved in crocodylians. Here we identify an increase in sensory abilities in Early Jurassic crocodylomorphs, preceding the transitions to a semiaquatic habitat. Through quantification of trigeminal neurovascular canal branching patterns in an extant phylogenetic bracket we quantify and identify morphologies associated with sensory behaviors in representative fossil taxa, we find stepwise progression of increasing neurovascular canal density, complexity, and distribution from the primitive archosaurian to the derived crocodilian condition. Model-based inferences of sensory ecologies tested on quantified morphologies of extant taxa with known sensory behaviors indicate a parallel increase in sensory abilities among pseudosuchians. These findings establish patterns of reptile trigeminal ecomorphology, revealing evolutionary patterns of somatosensory ecology.

Phylomorphometrics reveal ecomorphological convergence in pea crab carapace shapes (Brachyura, Pinnotheridae)

Most members of the speciose pea crab family (Decapoda: Brachyura: Pinnotheridae) are characterized by their symbioses with marine invertebrates in various host phyla. The ecology of pea crabs is, however, understudied, and the degree of host dependency of most species is still unclear. With the exception of one lineage of ectosymbiotic echinoid-associated crabs, species within the subfamily Pinnotherinae are endosymbionts, living within the body cavities of mollusks, ascidians, echinoderms, and brachiopods. By contrast, most members of the two other subfamilies are considered to have an ectosymbiotic lifestyle, sharing burrows and tubes with various types of worms and burrowing crustaceans (inquilism). The body shapes within the family are extremely variable, mainly in the width and length of the carapace. The variation of carapace shapes in the family, focusing on pinnotherines, is mapped using landmark-based morphometrics. Mean carapace shapes of species groups (based on their host preference) are statistically compared. In addition, a phylomorphometric approach is used to study three different convergence events (across subfamilies; between three genera; and within one genus), and link these events with the associated hosts.

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

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

Ecomorphology and Morphological Disparity of Caquetaia Kraussii (Perciformes: Cichlidae) in Colombia

Understanding the interspecific morphological variability of Caquetaia kraussii (Perciformes: Cichlidae) between different localities in its distribution range is becoming essential, as this species constitutes a valuable resource for the economy and subsistence of the local human communities where it is endemic in Colombia and Venezuela. In order to develop efficient farming and handling plans for this species, a deep understanding of the factors and mechanisms generating morphological variability is crucial. This study analyzes the morphological variability of C. kraussii by using geometric morphometrics in four localities distributed between the Dique and North channels, which are part of the Bolívar department in Colombia. Likewise, the effect of environmental variables such as temperature (T°), dissolved oxygen (OD) and pH on morphological variability was analyzed using a partial least squares approach. The results show that environmental stress has an influence on ~10% of the body shape of C. kraussii, whereas ~90% of the body shape is not directly influenced by environmental parameters, suggesting an effect from stress related to sexual dimorphism. Similarly, the analyses show shape variation among localities, mainly between populations of lotic environments and those of lentic environments. This morphological disparity seems to be subject to environmental and sexual stresses in the different localities.

Louse flies holding on mammals' hair: Comparative functional morphology of specialized attachment devices of ectoparasites (Diptera: Hippoboscoidea)

Hippoboscidae and Nycteribiidae of the dipteran superfamily Hippoboscoidea are obligate ectoparasites, which feed on the blood of different mammals. Due to their limited flight capability, the attachment system on all tarsi is of great importance for a secure grasp onto their host and thus for their survival. In this study, the functional morphology of the attachment system of two hippoboscid species and two nycteribiid species was compared in their specificity to the host substrate. Based on data from scanning electron microscopy and confocal laser scanning microscopy, it was shown that the attachment systems of both Hippoboscidae and Nycteribiidae (Hippoboscoidea) differ greatly from that of other calyptrate flies and are uniform within the respective families. All studied species have an attachment system with two monodentate claws and two pulvilli. The claws and pulvilli of the Hippoboscidae are asymmetric, which is an adaptation to the fur of even-toed ungulates (Artiodactyla). The fur of these mammals possesses both, thinner woolen and thicker coat hair; thus, the asymmetry of the attachment system of the hippoboscid species enables a secure attachment to all surfaces of their hosts. The claws and pulvilli of the nyceribiid species do not show an asymmetry, since the fur of their bat (Chiroptera) hosts consists of hairs with the same thickness. The claws are important for the attachment to mammals' fur, because they enable a secure grip by mechanical interlocking of the hairs through the claws. Additionally, well-developed pulvilli are able to attach on thicker hairs of Artiodactyla or on smooth substrates such as the skin.

Deep ecomorphological and genetic divergence in Steller's Jays (Cyanocitta stelleri, Aves: Corvidae)

The relationship between ecology and morphology is a cornerstone of evolutionary biology, and quantifying variation across environments can shed light on processes that give rise to biodiversity. Three morphotypes of the Steller's Jay (Cyanocitta stelleri) occupy different ecoregions in western North America, which vary in climate and landcover. These morphotypes (Coastal, Interior, Rocky Mountain) differ in size, plumage coloration, and head pattern. We sampled 1080 Steller's Jays from 68 populations (plus 11 outgroups) to address three main questions using data on morphology, plumage, genetics (mtDNA, microsatellites), and ecological niches: (1) How do phenotypic and genetic traits vary within and among populations, morphotypes, and ecoregions? (2) How do population‐level differences in Steller's Jays compare with other sister species pairs of North American birds? (3) What can we infer about the population history of Steller's Jays in relation to past climates, paleoecology, and niche evolution? We found substantial morphological, genetic, and ecological differentiation among morphotypes. The greatest genetic divergence separated Coastal and Interior morphotypes from the Rocky Mountain morphotype, which was associated with warmer, drier, and more open habitats. Microsatellites revealed additional structure between Coastal and Interior groups. The deep mtDNA split between Coastal/Interior and Rocky Mountain lineages of Steller's Jay (ND2 ~ 7.8%) is older than most North American avian sister species and dates to approximately 4.3 mya. Interior and Rocky Mountain morphotypes contact across a narrow zone with steep clines in traits and reduced gene flow. The distribution of the three morphotypes coincides with divergent varieties of ponderosa pine and Douglas fir. Species distribution models support multiple glacial refugia for Steller's Jays. Our integrative dataset combined with extensive geographic sampling provides compelling evidence for recognizing at least two species of Steller's Jay.

Cranial ecomorphology of turtles and neck retraction as a possible trigger of ecological diversification

Turtles have a highly modified body plan, including a rigid shell that constrains postcranial anatomy. Skull morphology and neck mobility may therefore be key to ecological specialization in turtles. However, the ecological signal of turtle skull morphologies has not been rigorously evaluated, leaving uncertainties about the roles of ecological adaptation and convergence. We evaluate turtle cranial ecomorphology using three-dimensional geometric morphometrics and phylogenetic comparative methods. Skull shape correlates with allometry, neck retraction capability, and different aquatic feeding ecologies. We find that ecological variables influence skull shape only, whereas a key functional variable (the capacity for neck retraction) influences both shape and size. Ecology and functional predictions from three-dimensional shape are validated by high success rates for extant species, outperforming previous two-dimensional approaches. We use this to infer ecological and functional traits of extinct species. Neck retraction evolved among crownward stem-turtles by the Late Jurassic, signaling functional decoupling of the skull and neck from the shell, possibly linked to a major episode of ecomorphological diversification. We also find strong evidence for convergent ecological adaptations among marine groups. This includes parallel loss of neck retraction, evidence for active hunting, possible grazing, and suction feeding in extinct marine groups. Our large-scale assessment of dietary and functional adaptation throughout turtle evolution reveals the timing and origin of their distinct ecomorphologies, and highlights the potential for ecology and function to have distinct effects on skull form.

Polar bear paw pad surface roughness and its relevance to contact mechanics on snow

Microscopic papillae on polar bear paw pads are considered adaptations for increased friction on ice/snow, yet this assertion is based on a single study of one species. The lack of comparative data from species that exploit different habitats renders the ecomorphological associations of papillae unclear. Here, we quantify the surface roughness of the paw pads of four species of bear over five orders of magnitude by calculating their surface roughness power spectral density. We find that interspecific variation in papillae base diameter can be explained by paw pad width, but that polar bear paw pads have 1.5 times taller papillae and 1.3 times more true surface area than paw pads of the American black bear and brown bear. Based on friction experiments with three-dimensional printed model surfaces and snow, we conclude that these factors increase the frictional shear stress of the polar bear paw pad on snow by a factor of 1.3-1.5 compared with the other species. Absolute frictional forces, however, are estimated to be similar among species once paw pad area is accounted for, suggesting that taller papillae may compensate for frictional losses resulting from the relatively smaller paw pads of polar bears compared with their close relatives.

Attachment Performance of Stick Insects (Phasmatodea) on Plant Leaves with Different Surface Characteristics

Herbivorous insects and plants exemplify a longstanding antagonistic coevolution, resulting in the development of a variety of adaptations on both sides. Some plant surfaces evolved features that negatively influence the performance of the attachment systems of insects, which adapted accordingly as a response. Stick insects (Phasmatodea) have a well-adapted attachment system with paired claws, pretarsal arolium and tarsal euplantulae. We measured the attachment ability of Medauroidea extradentata with smooth surface on the euplantulae and Sungaya inexpectata with nubby microstructures of the euplantulae on different plant substrates, and their pull-off and traction forces were determined. These species represent the two most common euplantulae microstructures, which are also the main difference between their respective attachment systems. The measurements were performed on selected plant leaves with different properties (smooth, trichome-covered, hydrophilic and covered with crystalline waxes) representing different types among the high diversity of plant surfaces. Wax-crystal-covered substrates with fine roughness revealed the lowest, whereas strongly structured substrates showed the highest attachment ability of the Phasmatodea species studied. Removal of the claws caused lower attachment due to loss of mechanical interlocking. Interestingly, the two species showed significant differences without claws on wax-crystal-covered leaves, where the individuals with nubby euplantulae revealed stronger attachment. Long-lasting effects of the leaves on the attachment ability were briefly investigated, but not confirmed.

Comparative morphology and soft tissue histology of the remote-touch bill-tip organ in three ibis species of differing foraging ecology

Ibises (order: Pelecaniformes, family: Threskiornithidae) are probe-foraging birds that use 'remote-touch' to locate prey items hidden in opaque substrates. This sensory capability allows them to locate their prey using high-frequency vibrations in the substrate in the absence of other sensory cues. Remote-touch is facilitated by a specialised bill-tip organ, comprising high densities of mechanoreceptors (Herbst corpuscles) embedded in numerous foramina in the beak bones. Each foramen and its associated Herbst corpuscles make up a sensory unit, called a 'sensory pit'. These sensory pits are densely clustered in the distal portion of the beak. Previous research has indicated that interspecific differences in the extent of sensory pitting in the beak bones correlate with aquatic habitat use of ibises, and have been suggested to reflect different levels of remote-touch sensitivity. Our study investigates the interspecific differences in the bone and soft tissue histology of the bill-tip organs of three species of southern African ibises from different habitats (mainly terrestrial to mainly aquatic). We analysed the external pitting pattern on the bones, as well as internal structure of the beak using micro-CT scans and soft tissue histological sections of each species' bill-tip organs. The beaks of all three species contain remote-touch bill-tip organs and are described here in detail. Clear interspecific differences are evident between the species' bill-tip organs, both in terms of bone morphology and soft tissue histology. Glossy Ibises, which forage exclusively in wetter substrates, have a greater extent of pitting but lower numbers of Herbst corpuscles in each pit, while species foraging in drier substrates (Hadeda and Sacred Ibises) have more robust beaks, fewer pits and higher densities of Herbst corpuscles. Our data, together with previously published histological descriptions of the bill-tip organs of other remote-touch foraging bird species, indicate that species foraging in drier habitats have more sensitive bill-tip organs (based on their anatomy). The vibrations produced by prey (e.g., burrowing invertebrates) travel poorly in dry substrates compared with wetter ones (i.e., dry soil vs. mud or water), and thus we hypothesise that a more sensitive bill-tip organ may be required to successfully locate prey in dry substrates. Furthermore, our results indicate that the differences in bill-tip organ anatomy between the species reflect complex trade-offs between morphological constraints of beak shape and remote-touch sensitivity requirements, both of which are likely related to each species' foraging behaviour and substrate usage. Our study suggests that structures in the bone of the bill-tip organ could provide valuable osteological correlates for the associated soft tissues, and consequently may provide information on the sensory ecology and habitat usage of the birds in the absence of soft tissues.

Diet, habitat and flight characteristics correlate with intestine length in birds

A link between diet and avian intestinal anatomy is generally assumed. We collated the length of intestinal sections and body mass of 390 bird species and tested relationships with diet, climate and locomotion. There was a strong phylogenetic signal in all datasets. The total and small intestine scaled more-than-geometrically (95%CI of the scaling exponent > 0.33). The traditional dietary classification (faunivore, omnivore and herbivore) had no significant effect on total intestine (TI) length. Significant dietary proxies included %folivory, %frugi-nectarivory and categories (frugi-nectarivory, granivory, folivory, omnivory, insectivory and vertivory). Individual intestinal sections were affected by different dietary proxies. The best model indicates that higher consumption of fruit and nectar, drier habitats, and a high degree of flightedness are linked to shorter TI length. Notably, the length of the avian intestine depends on other biological factors as much as on diet. Given the weak dietary signal in our datasets, the diet intestinal length relationships lend themselves to narratives of flexibility (morphology is not destiny) rather than of distinct adaptations that facilitate using one character (intestine length) as proxy for another (diet). Birds have TIs of about 85% that of similar-sized mammals, corroborating systematic differences in intestinal macroanatomy between vertebrate clades.

Community science reveals links between migration arrival timing advance, migration distance, and wing shape

Substantial global data show that many taxa are shifting their phenologies in response to climate change. For birds, migration arrival dates in breeding regions have been shifting earlier, and there is evidence that both evolutionary adaptation and behavioural flexibility influence these shifts. As more efficient flyers may be able to demonstrate more flexibility to respond to changing conditions during migratory flight, we hypothesize that differences among passerine species in flight efficiency, as reflected by morphology, may be associated with the magnitude of shifts in arrival date in response to climate warming. We applied a logistic model to eighteen years of eBird data to estimate mean arrival date for 44 common passerines migrating to northeast North America. We then used linear mixed-effects models to estimate changes in mean arrival date and compared these changes to morphological proxies for flight efficiency and migratory distance using phylogenetic generalized least squares models. On average, passerine species shifted their arrival dates 0.120 days earlier each year, with 27 of the 44 species shifting to significantly earlier arrival times, and two shifting to significantly later ones. Of the 15 species with non-significant shifts, 13 trended toward earlier arrivals. Longer migration distances and higher wing aspect ratios were associated with greater shifts towards earlier arrivals. Migration distance and aspect ratio were also significantly correlated to each other. This suggests that changes in arrival date are affected by factors pertaining to migratory flight over long distances namely, flight efficiency and migration distance. These traits may be able predict the magnitude of arrival date shift, and by extension identify species that are most at risk to climate change due to inflexible arrival timing.

Global ecomorphological restructuring of dominant marine reptiles prior to the Cretaceous-Palaeogene mass extinction

Mosasaurid squamates were the dominant amniote predators in marine ecosystems during most of the Late Cretaceous. Here, we use a suite of biomechanically rooted, functionally descriptive ratios in a framework adapted from population ecology to investigate how the morphofunctional disparity of mosasaurids evolved prior to the Cretaceous-Palaeogene (K/Pg) mass extinction. Our results suggest that taxonomic turnover in mosasaurid community composition from Campanian to Maastrichtian is reflected by a notable global increase in morphofunctional disparity, especially driving the North American record. Ecomorphospace occupation becomes polarized during the Late Maastrichtian, with morphofunctional disparity plateauing in the Southern Hemisphere and decreasing in the Northern Hemisphere. We show that these changes are not strongly associated with mosasaurid size, but rather with the functional capacities of their skulls. Our novel approach indicates that mosasaurid morphofunctional disparity was in decline in multiple provincial communities before the K/Pg mass extinction, highlighting region-specific patterns of disparity evolution and the importance of assessing vertebrate extinctions both globally and locally. Ecomorphological differentiation in mosasaurid communities, coupled with declines in other formerly abundant marine reptile groups, indicates widespread restructuring of higher trophic levels in marine food webs was well underway when the K/Pg mass extinction took place.

Geometric morphometrics of mandibles for dietary differentiation of Bovidae (Mammalia: Artiodactyla)

The mammalian family Bovidae has been widely studied in ecomorphological research, with important applications to paleoecological and paleohabitat reconstructions. Most studies of bovid craniomandibular features in relation to diet have used linear measurements. In this study, we conduct landmark-based geometric-morphometric analyses to evaluate whether different dietary groups can be distinguished by mandibular morphology. Our analysis includes data for 100 species of extant bovids, covering all bovid tribes and 2 dietary classifications. For the first classification with 3 feeding categories, we found that browsers (including frugivores), mixed feeders, and grazers are moderately well separated using mandibular shape. A finer dietary classification (frugivore, browser, browser-grazer intermediate, generalist, variable grazer, and obligate grazer) proved to be more useful for differentiating dietary extremes (frugivores and obligate grazers) but performed equally or less well for other groups. Notably, frugivorous bovids, which belong in tribe Cephalophini, have a distinct mandibular shape that is readily distinguished from all other dietary groups, yielding a 100% correct classification rate from jackknife cross-validation. The main differences in mandibular shape found among dietary groups are related to the functional needs of species during forage prehension and mastication. Compared with browsers, both frugivores and grazers have mandibles that are adapted for higher biomechanical demand of chewing. Additionally, frugivore mandibles are adapted for selective cropping. Our results call for more work on the feeding ecology and functional morphology of frugivores and offer an approach for reconstructing the diet of extinct bovids.

Plicidentine in the oral fangs of parrotfish (Scarinae, Labriformes)

Parrotfish play important ecological roles in coral reef and seagrass communities across the globe. Their dentition is a fascinating object of study from an anatomical, functional and evolutionary point of view. Several species maintained non-interlocked dentition and browse on fleshy algae, while others evolved a characteristic beak-like structure made of a mass of coalesced teeth that they use to scrape or excavate food off hard limestone substrates. While parrotfish use their highly specialized marginal teeth to procure their food, they can also develop a series of large fangs that protrude from the upper jaw, and more rarely from the lower jaw. These peculiar fangs do not participate in the marginal dentition and their function remains unclear. Here we describe the morphology of these fangs and their developmental relationship to the rest of the oral dentition in the marbled parrotfish (Leptoscarus vaigiensis), the star-eye parrotfish (Calotomus carolinus), and the palenose parrotfish (Scarus psittacus). Through microtomographic and histological analyses, we show that some of these fangs display loosely folded plicidentine along their bases, a feature that has never been reported in parrotfish. Plicidentine is absent from the marginal teeth and is therefore exclusive to the fangs. Parrotfish fangs develop a particular type of simplexodont plicidentine with a pulpal infilling of alveolar bone at later stages of dental ontogeny. The occurrence of plicidentine and evidence of extensive tooth wear, and even breakage, lead us to conclude that the fangs undergo frequent mechanical stress, despite not being used to acquire food. This strong mechanical stress undergone by fangs could be linked either to forced contact with congeners or with the limestone substrate during feeding. Finally, we hypothesize that the presence of plicidentine in parrotfish is not derived from a labrid ancestor, but is probably a recently evolved trait in some parrotfish taxa, which may even have evolved convergently within this subfamily.

Multiscale analysis on otolith structural features reveals differences in ontogenesis and sex in Merluccius merluccius in the western Adriatic Sea

Otolith biomineralization results from biochemical processes regulated by the interaction of internal (physiological) and external (environmental) factors which lead to morphological and ultrastructural variability at intra- and interspecific levels. The aim of this study was to conduct a multi-scale analysis of the sagittal otoliths of the Merlucius merlucius (European hake) from the western Adriatic Sea in order to correlate otolith features with fish ontogeny and sex. We show that otoliths of sexually undifferentiated (non-sexed) individuals having a fish body total length (TL) less than 15 cm had faster growth in length, width, area, perimeter, volume and weight and a higher amount of organic matrix compared with otoliths of sexually differentiated individuals (females and males) having a fish size range of 15-50 cm. Most importantly, with increasing fish TL, female saccular otoliths contained a higher number of protuberances and rougher surface compared with male specimens, which showed more uniform mean curvature density. The differences between females and males discovered in this study could be associated with fish hearing adaptation to reproductive behavioural strategies during the spawning season. The outcomes of this research provide insights on how size and sex-related variations in otolith features may be affected by fish ecological and behavioural patterns.

Transfer of Anolis locomotor behavior across environments and species

Arboreal animals must learn to modulate their movements to overcome the challenges posed by the complexity of their heterogeneous environment, reduce performance failure, and survive. Anolis lizards are remarkable in the apparent ease with which they conquer this heterogeneity, demonstrating an impressive ability to modulate their locomotor behavior to maintain stable locomotion on widely disparate surfaces. Significant progress has been made towards understanding the impact of substrate structure on the behavioral plasticity of arboreal species, but it is unclear whether the same strategies employed to shift between substrates in one context can be employed to shift between those same substrates in a new context. Is the kinematic shift between broad and narrow perches achieved in a similar way on different inclines? Do all species within an ecomorph make similar adjustments? Here, we analyze the limb movements of two trunk-crown Anolis ecomorphs, A. carolinensis and A. evermanni, running on 6 different surfaces (3 inclinations × 2 perch diameters), from the perspective of Transfer Learning. Transfer learning is that field of machine learning which aims at exploiting the knowledge gained from one task to improve generalization about another, related task. In our setting, we use transfer learning to show that the strategies employed to improve locomotor stability on narrow perches are transferred across environments with different inclines. Further, behaviors used on vertical inclines are shared, and thus transfer well, across perch diameters whereas the relationship between horizontal and intermediate inclines change on different perch diameters, leading to lower transfer learning of shallow inclines across perch diameters. Interestingly, the best incline for transfer of behavior differs between limbs: forelimb models learn best from the vertical incline and hind limb models learn best from horizontal and intermediate inclines. Finally, our results suggest both that subtle differences exist in how A. carolinensis and A. evermanni adjust their behaviors in typical trunk-crown environments and that they may have converged on similar strategies for modulating forelimb behavior on vertical surfaces and hind limb behavior on shallow surfaces. The transfer of behavior is analogous to phenotypic plasticity, which likely plays a key role in the rapid adaptive evolution characteristic of Anolis lizards. This work is an example of how modern statistical methodology can provide an interesting perspective on new biological questions, such as on the role and nuances of behavioral plasticity and the key behaviors that help shape the versatility and rapid evolution of Anolis lizards.

AVONET: morphological, ecological and geographical data for all birds

Functional traits offer a rich quantitative framework for developing and testing theories in evolutionary biology, ecology and ecosystem science. However, the potential of functional traits to drive theoretical advances and refine models of global change can only be fully realised when species-level information is complete. Here we present the AVONET dataset containing comprehensive functional trait data for all birds, including six ecological variables, 11 continuous morphological traits, and information on range size and location. Raw morphological measurements are presented from 90,020 individuals of 11,009 extant bird species sampled from 181 countries. These data are also summarised as species averages in three taxonomic formats, allowing integration with a global phylogeny, geographical range maps, IUCN Red List data and the eBird citizen science database. The AVONET dataset provides the most detailed picture of continuous trait variation for any major radiation of organisms, offering a global template for testing hypotheses and exploring the evolutionary origins, structure and functioning of biodiversity.

Geometric Morphometric Analysis of the Humerus in New and Old World Vultures

The vulture guild is composed of two distinct groups, Old and New World, that provide a unique insight into how morphology varies among convergent species. All vultures are considered to be large birds of prey that utilize a style of flight called thermal soaring to search and feed primarily on carrion. Even though this flight style is exhibited among all 23 species, slight variations in their skeletal morphology may relate to their differences in ecology. We hypothesized that vulture humeral morphology varies in relation to these organisms' habitat, average body mass, courtship displays, and migratory behavior. To address this hypothesis, we used three-dimensional geometric morphometrics to measure the overall shape differences of vulture humeri. Humeral morphology was found to vary most by habitat association and migratory tendency. The humeri of vultures that inhabit forested areas exhibit features that suggest increased flapping flight compared to those in open and mountainous regions. Migratory species were found to possess more robust features near the glenohumeral joint. We found these (and other features) have some utility for predicting ecology and behavior, but we suggest that further investigation into skeletal and muscular wing elements may reveal greater understanding of the habits of extinct vulture species. This article is protected by copyright. All rights reserved.

A new model of forelimb ecomorphology for predicting the ancient habitats of fossil turtles

Various morphological proxies have been used to infer habitat preferences among fossil turtles and their early ancestors, but most are tightly linked to phylogeny, thereby minimizing their predictive power. One particularly widely used model incorporates linear measurements of the forelimb (humerus + ulna + manus), but in addition to the issue of phylogenetic correlation, it does not estimate the likelihood of habitat assignment. Here, we introduce a new model that uses intramanual measurements (digit III metacarpal + non-ungual phalanges + ungual) to statistically estimate habitat likelihood and that has greater predictive strength than prior estimators. Application of the model supports the hypothesis that stem-turtles were primarily terrestrial in nature and recovers the nanhsiungchelyid Basilemys (a fossil crown-group turtle) as having lived primarily on land, despite some prior claims to the contrary.

Ecomorphology of the cervid calcaneus as a proxy for paleoenvironmental reconstruction

This study presents new ecomorphological models for the cervid calcaneus that can be used to make predictions about the nature of ancient environments. Using geometric morphometrics to quantitatively assess the length of the articular surface supporting the malleolus, the length and orientation of the tuber calcanei, and the position of the articular facets, we aimed to establish correlations between morphological traits, locomotor behavior, and environmental parameters in extant cervids. The morphology of the calcaneus was found to primarily vary with locomotor strategy and habitat, along a continuum from habitats with an open vegetation structure to habitats with a closed vegetation structure. Confounding factors, including sexual dimorphism, allometry, and phylogeny were accounted for using Principal Component Analysis, regressions and phylogenetic comparative methods. The results of our analyses suggested that these factors did not substantially obscure habitat predictions. As such, the calcaneus provides a valuable proxy for paleoenvironmental reconstruction that is broadly applicable to Quaternary fossil assemblages with a sufficiently large sample of cervids.

Foraging strategies, craniodental traits, and interaction in the bite force of Neotropical frugivorous bats (Phyllostomidae: Stenodermatinae)

Bats in the family Phyllostomidae exhibit great diversity in skull size and morphology that reflects the degree of resource division and ecological overlap in the group. In particular, the subfamily Stenodermatinae has high morphological diversification associated with cranial and mandibular traits that are associated with the ability to consume the full range of available fruits (soft and hard).We analyzed craniodental traits and their relationship to the bite force in 343 specimens distributed in seven species of stenodermatine bats with two foraging strategies: nomadic and sedentary frugivory. We evaluated 19 traits related to feeding and bite force in live animals by correcting bite force with body size.We used a generalized linear model (GLM) and post hoc tests to determine possible relationships and differences between cranial traits, species, and sex. We also used Blomberg's K to measure the phylogenetic signal and phylogenetic generalized least-squares (PGLS) to ensure the phylogenetic independence of the traits.We found that smaller nomadic species, A. anderseni and A. phaeotis , have a similar bite force to the large species A. planirostris and A. lituratus; furthermore, P. helleri registered a bite force similar to that of the sedentary bat, S. giannae. Our study determined that all the features of the mandible and most of the traits of the skull have a low phylogenetic signal. Through the PGLS, we found that the diet and several cranial features (mandibular toothrow length, dentary length, braincase breadth, mastoid breadth, greatest length of skull, condylo-incisive length, and condylo-canine length) determined bite force performance among Stenodermatiane.Our results reinforce that skull size is a determining factor in the bite force, but also emphasize the importance of its relationships with morphology, ecology, and phylogeny of the species, which gives us a better understanding of the evolutionary adaptions of this highly diverse Neotropical bat group.

Feeding ecology has shaped the evolution of modern sharks

Sharks are iconic predators in today's oceans, yet their modern diversity has ancient origins. In particular, present hypotheses suggest that a combination of mass extinction, global climate change, and competition has regulated the community structure of dominant mackerel (Lamniformes) and ground (Carcharhiniformes) sharks over the last 66 million years. However, while these scenarios advocate an interplay of major abiotic and biotic events, the precise drivers remain obscure. Here, we focus on the role of feeding ecology using a geometric morphometric analysis of 3,837 fossil and extant shark teeth. Our results reveal that morphological segregation rather than competition has characterized lamniform and carcharhiniform evolution. Moreover, although lamniforms suffered a long-term disparity decline potentially linked to dietary "specialization," their recent disparity rivals that of "generalist" carcharhiniforms. We further confirm that low eustatic sea levels impacted lamniform disparity across the end-Cretaceous mass extinction. Adaptations to changing prey availability and the proliferation of coral reef habitats during the Paleogene also likely facilitated carcharhiniform dispersals and cladogenesis, underpinning their current taxonomic dominance. Ultimately, we posit that trophic partitioning and resource utilization shaped past shark ecology and represent critical determinants for their future species survivorship.