Organisms are organized into suites of anatomical structures that typically covary when developmentally or functionally related, and this morphological integration plays a determinant role in ...evolutionary processes. Artificial selection on domestic species causes strong morphological changes over short time spans, frequently resulting in a wide and exaggerated phenotypic diversity. This raises the question of whether integration constrains the morphological diversification of domestic species and how natural and artificial selection may impact integration patterns. Here, we study the morphological integration in the appendicular skeleton of domestic horses and donkeys, using three-dimensional geometric morphometrics on 75 skeletons. Our results indicate that a strong integration is inherited from developmental mechanisms which interact with functional factors. This strong integration reveals a specialization in the locomotion of domestic equids, partly for running abilities. We show that the integration is stronger in horses than in donkeys, probably because of a greater degree of specialization and predictability of their locomotion. Thus, the constraints imposed by integration are weak enough to allow important morphological changes and the phenotypic diversification of domestic species.
Sexual dimorphism is challenging to detect among fossils due to a lack of statistical representativeness. The Angeac-Charente Lagerstätte (France) represents a remarkable 'snapshot' from a Berriasian ...(Early Cretaceous) ecosystem and offers a unique opportunity to study intraspecific variation among a herd of at least 61 coeval ornithomimosaurs. Herein, we investigated the hindlimb variation across the best-preserved specimens from the herd through 3D Geometric Morphometrics and Gaussian Mixture Modeling. Our results based on complete and fragmented femora evidenced a dimorphism characterized by variations in the shaft curvature and the distal epiphysis width. Since the same features vary between sexes among modern avian dinosaurs, crocodilians, and more distant amniotes, we attributed this bimodal variation to sexual dimorphism based on the extant phylogenetic bracketing approach. Documenting sexual dimorphism in fossil dinosaurs allows a better characterization and accounting of intraspecific variations, which is particularly relevant to address ongoing taxonomical and ecological questions relative to dinosaur evolution.
Limb long bones are essential to an animal's locomotion, and are thus expected to be heavily influenced by factors such as mass or habitat. Because they are often the only organs preserved in the ...fossil record, understanding their adaptive trends is key to reconstructing the paleobiology of fossil taxa. In this regard, the Bovidae has always been a prized group of study. This family is extremely diverse in terms of both mass and habitat, and it is expected that their bones will possess adaptations to both factors. Here, we present the first 3D geometric morphometric study focusing on bovid limb long bones. We used anatomical landmarks as well as curve and surface sliding semi‐landmarks to accurately describe the stylopod and zeugopod bones. We included 50 species from ten of the twelve currently recognized tribes of bovids, ranging from 4.6 to 725 kg, and living in open plains, forests, mountains, or anywhere in‐between. Shape data were correlated with the mean mass of the species and its habitat, even when taking into account the phylogenetic history of our sample. Bones pertaining to heavy species are more robust, adapted for a better repartition of stronger forces. Articulations are especially affected, being proportionally much larger in heavier species. Muscle insertion areas are unevenly affected. Insertion areas of muscles implied in body support and propulsion show a strong increase in their robustness when compared to insertion areas of muscles acting on the limb mostly when it is off the ground. Habitat influences the shape of the humerus, the radius‐ulna, and the femur, but not of the tibia, whether the phylogeny is taken into account or not. Specific habitats tend to be associated with particular features on the bones. Articulations are proportionally wider in open‐habitat species, and the insertion areas of muscles involved in limb extension and propulsion are wider, reflecting the fact that open habitat species are more cursorial and rely on fast running to avoid predators. Forest and mountain species generally present similar adaptations for increased manoeuvrability, such as a round femoral head, and generally have more gracile bones.
This work studies the influence of body mass and habitat on the shape of limb long bones in bovids in a phylogenetic framework using 3D geometric morphometrics. We found that an important body mass is associated with stronger bones, and especially stronger insertion areas for the extensor muscles. Open habitat species are characterized by adaptations for stability and resistance to the important forces involved in galloping, forest and mountain habitat species present adaptations for manoeuvrability.
Hybridization has been widely practiced in plant and animal breeding as a means to enhance the quality and fitness of the organisms. In domestic equids, this hybrid vigor takes the form of improved ...physical and physiological characteristics, notably for strength or endurance. Because the offspring of horse and donkey is generally sterile, this widely recognized vigor is expressed in the first generation (F1). However, in the absence of recombination between the two parental genomes, F1 hybrids can be expected to be phenotypically intermediate between their parents which could potentially restrict the possibilities of an increase in overall fitness. In this study, we examine the morphology of the main limb bones of domestic horses, donkeys and their hybrids to investigate the phenotypic impact of hybridization on the locomotor system. We explore bone shape variation and covariation to gain insights into the morphological and functional expressions of the hybrid vigor commonly described in domestic equids.
Our data reveal the occurrence of transgressive effects on several bones in the F1 generation. The patterns of morphological integration further demonstrate that the developmental processes producing covariation are not disrupted by hybridization, contrary to functional ones.
These results suggest that an increase in overall fitness could be related to more flexibility in shape change in hybrids, except for the main forelimb long bones of which the morphology is strongly driven by muscle interactions. More broadly, this study illustrates the interest of investigating not only bone shape variation but also underlying processes, in order to contribute to better understanding how developmental and functional mechanisms are affected by hybridization.
The appendicular skeleton of tetrapods is a particularly integrated structure due to the shared developmental origin or similar functional constraints exerted on its elements. Among these ...constraints, body mass is considered strongly to influence its integration but its effect on shape covariation has rarely been addressed in mammals, especially in heavy taxa. Here, we propose to explore the covariation patterns of the long bones in heavy animals and their link to body mass. We investigate the five modern rhinoceros species, which display an important range of bodyweight. We used a 3D geometric morphometric approach to describe the shape covariation of the six bones composing the stylopodium and zeugopodium both among and within species. Our results indicate that the appendicular skeleton of modern rhinos is a strongly integrated structure. At the interspecific level, the shape covariation is roughly similar between all pairs of bones and mainly concerns the muscular insertions related to powerful flexion and extension movements. The forelimb integration appears higher and more related to body mass than that of the hind limb, suggesting a specialization for weight support. The integration of the stylopodium elements does not seem to relate to body mass in our sample, which suggests a greater effect of shared developmental factors. Conversely, the covariation of the zeugopodium bones seems more associated with body mass, particularly for the radius‐ulna pair. The fibula appears poorly integrated with other bones, especially within non‐Rhinoceros species, which may represent a case of parcellation due to a functional dissociation between the hind limb bones. The exploration of the integration patterns at the intraspecific level also highlights a more prominent effect of age over individual body mass on shape covariation within C. simum. This study lends support to previous hypotheses indicating a link between high body mass and high integration level.
This study explores the patterns of covariation of the long bones among the five modern species of rhinos and the link between morphological integration and body mass. The appendicular skeleton of modern rhinos appears strongly integrated. The forelimb parts are more integrated than the hind limb ones due to differences of weight constraints. Integration patterns at the intraspecific level are more related to ontogeny than to body mass.
Abstract
In quadrupeds, limb bones are strongly affected by functional constraints linked to weight support, but few studies have addressed the complementary effects of mass, size and body ...proportions on limb bone shape. During their history, Rhinocerotoidea have displayed a great diversity of body masses and relative size and proportions of limb bones, from small tapir-like forms to giant species. Here, we explore the evolutionary variation of shapes in forelimb bones and its relationship with body mass in Rhinocerotoidea. Our results indicate a general increase in robustness and greater development of muscular insertions in heavier species, counteracting the higher weight loadings induced by an increased body mass. The shape of the humerus changes allometrically and exhibits a strong phylogenetic signal. Shapes of the radius and ulna display a stronger link with body mass repartition than with the absolute mass itself. Congruent shape variation between the humerus and the proximal part of the ulna suggests that the elbow joint is comprised of two strongly covariant structures. In addition, our work confirms the uniqueness of giant Paraceratheriidae among Rhinocerotoidea, whose shape variation is related to both a high body mass and a cursorial forelimb construction.
Objectives
Humans are known to possess more complex manual abilities than other primates. However, the manual abilities of primates have not been fully explored, and we still do not know if the ...manipulative abilities we attribute to humans are unique. The aim of this study was to compare the manual function and performance developed by humans, gorillas and orangutans while performing the same experimental tool use task.
Materials and Methods
The study was conducted on 20 humans, 6 gorillas, and 7 orangutans. Each individual had to use a tool to collect food from a maze during six experimental sessions while maintaining the same unconstrained body posture condition. We quantified the different manual techniques used and the manual performance.
Results
Each species used different techniques. Humans used bimanual grip techniques, pad‐to‐pad precision grasping postures, and in‐hand movements involving fingertips. Gorillas used unimanual grip techniques and simple in‐hand movements while orangutans used a variety of strategies (e.g., hand or mouth). With these techniques, humans performed the task better than both gorillas and orangutans (e.g., by being quicker to collect the food).
Discussion
This study highlights other ways in which humans’ manual dexterity differs from that of other species and emphasizes the distinct manipulative function of orangutans. The differences between the species could be due to the differing muscular anatomy and morphology of the hands, with hand proportion possibly placing particular biomechanical constraints on each species. The differences between gorillas and orangutans could result from their different locomotor behaviors, and we hypothesize terrestriality facilitates the development of complex manipulation.
Human-induced environmental changes have increased rapidly during the Holocene and have reached alarming levels today. Consequently, it is crucial to better understand the impact of humans and ...climate on the faunas and floras through time. Understanding the direct and underlying effect of past human activity not only contributes to improving our knowledge of human history but also provides insights for the future. We here investigate the effect of the human-induced environmental changes that took place during the modern era (14–19th century AD) on the mandible of a small mammal, Suncus etruscus, in Corsica. We detected rapid morphological changes in mandible shape over the relatively short period of time included in our study, suggesting a strong human impact on the island. The morphological changes observed had functional consequences as they are related to changes in the mechanical potential of the principal masticatory muscle, the temporalis that, in turn, reflects shifts in the animal's diet over time. These results highlight the effect that the 600-year human agricultural activity shifts had on the island and its fauna. The integration of the body and the ramus of the mandible appears to be related to the mechanical potential of the temporalis muscle but does not constitute an indicator of human-induced environmental change. Whether these morphological changes are the result of natural selection (genetic processes) or of phenotypic plasticity (epigenetic processes) remains to be elucidated.
•Jaw shape changed rapidly over time (14–19th century AD).•This led to changes in the mechanical potential of the the temporalis muscle.•The temporalis's negative correlation with the masseter, and their link with the anthropisation index suggest diet shifts linked to human activity.•The integration of the body and ramus is not an indicator of environmental changes.
Abstract
Many tetrapod lineages show extreme increases in body mass in their evolutionary history, associated with important osteological changes. The ankle joint, essential for foot movement, is ...assumed to be particularly affected in this regard. We investigated the morphological adaptations of the astragalus and the calcaneus in Rhinocerotidae, and analysed them in light of a comparative analysis with other Perissodactyla. We performed 3D geometric morphometrics and correlated shape with centroid size of the bone and body mass of the species. Our results show that mass has an influence on bone shape in Rhinocerotidae and in Perissodactyla, but this is not as strong as expected. In heavy animals the astragalus has a flatter trochlea, orientated more proximally, associated with a more upright posture of the limb. The calcaneus is more robust, possibly to sustain the greater tension force exerted by the muscles during plantarflexion. Both bones show wider articular facets, providing greater cohesion and better dissipation of the loading forces. The body plan of the animals also has an influence. Short-legged Teleoceratina have a flatter astragalus than the other rhinocerotids. Paraceratherium has a thinner calcaneus than expected. This study clarifies adaptations to high body weight among Rhinocerotidae and calls for similar investigations in other groups with massive forms.
PDF
