Tools for quantitative form description : an evaluation of different software packages for semi-landmark analysis

The challenging complexity of biological structures has led to the development of several methods for quantitative analyses of form. Bones are shaped by the interaction of historical (phylogenetic), structural, and functional constrains. Consequently, bone shape has been investigated intensively in an evolutionary context. Geometric morphometric approaches allow the description of the shape of an object in all of its biological complexity. However, when biological objects present only few anatomical landmarks, sliding semi-landmarks may provide good descriptors of shape. The sliding procedure, mandatory for sliding semi-landmarks, requires several steps that may be time-consuming. We here compare the time required by two different software packages ('Edgewarp' and 'Morpho') for the same sliding task, and investigate potential differences in the results and biological interpretation. 'Morpho' is much faster than 'Edgewarp,' notably as a result of the greater computational power of the 'Morpho' software routines and the complexity of the 'Edgewarp' workflow. Morphospaces obtained using both software packages are similar and provide a consistent description of the biological variability. The principal differences between the two software packages are observed in areas characterized by abrupt changes in the bone topography. In summary, both software packages perform equally well in terms of the description of biological structures, yet differ in the simplicity of the workflow and time needed to performthe analyses

Interspecific variation in the limb long bones among modern rhinoceroses—extent and drivers

International audienceAmong amniotes, numerous lineages are subject to an evolutionary trend toward body mass and size increases. Large terrestrial species may face important constraints linked to weight bearing, and the limb segments are particularly affected by such constraints due to their role in body support and locomotion. Such groups showing important limb modifications related to high body mass have been called "graviportal." Often considered graviportal, rhinoceroses are among the heaviest terrestrial mammals and are thus of particular interest to understand the limb modifications related to body mass and size increase. Here, we present a morphofunctional study of the shape variation of the limb long bones among the five living rhinos to understand how the shape may vary between these species in relation with body size, body mass and phylogeny. We used three dimensional geometric morphometrics and comparative analyses to quantify the shape variation. Our results indicate that the five species display important morphological differences depending on the considered bones. The humerus and the femur exhibit noticeable interspecific differences between African and Asiatic rhinos, associated with a significant effect of body mass. The radius and ulna are more strongly correlated with body mass. While the tibia exhibits shape variation both linked with phylogeny and body mass, the fibula displays the greatest intraspecific variation. We highlight three distinct morphotypes of bone shape, which appear in accordance with the phylogeny. The influence of body mass also appears unequally expressed on the different bones. Body mass increase among the five extant species is marked by an increase of the general robustness, more pronounced attachments for muscles and a development of medial parts of the bones. Our study underlines that the morphological features linked to body mass increase are not similar between rhinos and other heavy mammals such as elephants and hippos, suggesting that the weight bearing constraint can lead to different morphological responses

Biomechanical evolution of solid bones in large animals: a microanatomical investigation

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Can growth in captivity alter the calcaneal microanatomy of a wild ungulate?

Reduced mobility associated with captivity induces changes in biomechanical stress on the skeleton of domesticated animals. Due to bone plasticity, bone’s morphology and internal structure can respond to these new biomechanical stresses over individuals’ lifetime. In a context where documenting early process of animal domestication is challenging, this study will test the hypothesis that change in mobility patterns during a wild ungulate’s life will alter the internal structure of its limb bones and provide a proof of concept for the application of this knowledge in Zooarchaeology. Using the calcaneus as a phenotypic marker through qualitative and quantitative 3D microanatomical analyses, we relied on a comparative study across wild boars (Sus scrofa) populations from controlled experimental conditions with different mobility patterns (natural habitat, large pen, and stall) and archaeological specimens collected from middle and late Mesolithic as surrogate for the norm of reaction in European wild boar phenotype before the spread of agriculture and domestic pigs. Results provide evidence for compressive and tensile forces as the main elements affecting the variation in the cortical thickness along the calcaneus. Furthermore, changes in the internal structure of the calcaneus between mobility patterns are observed but their intensity is not directly associated with the degree of mobility restriction and only weakly impacted by the size or weight of the individuals. Despite having greater bone volume, the calcaneus of the Mesolithic wild boars displays a very similar microanatomy compared to the present-day hunted or captive wild boars. These results suggest that calcaneal microanatomy is more affected by population differences than by locomotor variation. For all these reasons, this preliminary study doesn’t support the use of microanatomy of the calcaneus as an indicator of change in locomotor behaviour induced by captivity in the archaeological record

Disentangling isolated dental remains of Asian Pleistocene hominins and pongines

International audienceScholars have debated the taxonomic identity of isolated primate teeth from the Asian Pleis-tocene for over a century, which is complicated by morphological and metric convergence between orangutan (Pongo) and hominin (Homo) molariform teeth. Like Homo erectus, Pongo once showed considerable dental variation and a wide distribution throughout mainland and insular Asia. In order to clarify the utility of isolated dental remains to document the presence of hominins during Asian prehistory, we examined enamel thickness, enamel-den-tine junction shape, and crown development in 33 molars from G. H. R. von Koenigswald's Chinese Apothecary collection (11 Sinanthropus officinalis [= Homo erectus], 21 "Heman-thropus peii," and 1 "Hemanthropus peii" or Pongo) and 7 molars from Sangiran dome (either Homo erectus or Pongo). All fossil teeth were imaged with non-destructive conventional and/or synchrotron micro-computed tomography. These were compared to H. erectus teeth from Zhoukoudian, Sangiran and Trinil, and a large comparative sample of fossil Pongo, recent Pongo, and recent human teeth. We find that Homo and Pongo molars overlap substantially in relative enamel thickness; molar enamel-dentine junction shape is more distinctive, with Pongo showing relatively shorter dentine horns and wider crowns than Homo. Long-period line periodicity values are significantly greater in Pongo than in H. erec-tus, leading to longer crown formation times in the former. Most of the sample originally assigned to S. officinalis and H. erectus shows greater affinity to Pongo than to the hominin comparative sample. Moreover, enamel thickness, enamel-dentine junction shape, and a long-period line periodicity value in the "Hemanthropus peii" sample are indistinguishable from fossil Pongo. These results underscore the need for additional recovery and study of associated dentitions prior to erecting new taxa from isolated teeth

Advances in vertebrate palaeohistology: recent progress, discoveries, and new approaches

International audienceThis special issue of the Biological Journal of the Linnean Society (2014, volume 112: issue 4) focuses on advances in vertebrate palaeohistology, a dynamic area of research that relies on an understanding of the constraints acting on vertebrate mineralized tissues, and enables, through comparison with living organisms, access to biological data for fossil taxa. Substantial advances have been made in recent years and the special issue presents new discoveries from some rapidly developing fields of investigation. This introduction briefly reviews the discipline of palaeohistology and then introduces the twelve contribution

Bone histology of aquatic reptiles: what does it tell us about secondary adaptation to an aquatic life?

International audienceAquatic reptiles are very diversified in the fossil record. The description and pooling of certain bone histological features (collagenous weave and vascular network) of the various groups of aquatic reptiles highlight what this histological information can tell us about the process of secondary adaptation to an aquatic life. Notably, they show the absence of interaction between these histological features on the one hand and body size, mode of swimming, type of microanatomical specialization and phylogeny on the other. These histological features in aquatic reptiles seem to essentially provide information about the growth rate and basal metabolic rate of these taxa. The growth rate seems to have been rather high in most marine reptiles, when compared with terrestrial ectotherms. Moreover, distinct metabolic abilities are suggested. Indeed, various groups probably displayed a peculiarly high body temperature, and some show trends towards endothermy. This study also emphasizes the crucial need for homologous comparisons in histology and shows that much remains to be done to better understand the relationship between histological features, growth rate and metabolism in extant taxa in order to make inferences in the fossil groups

Pachyostosis in aquatic amniotes: a review

International audienceDuring the course of amniote evolution, numerous taxa secondarily adapted to an aquatic life. It appears that many of these taxa primitively display "pachyostosis," an osseous specialization characterized by an increase in bone compactness and/or volume. The term "pachyostosis" is used in morphological and histological descriptions to describe what in fact corresponds to different patterns. The aim of this paper is to present the current state of knowledge relative to this adaptation among aquatic amniotes. All the taxa that have returned to an aquatic environment are listed. Moreover, their degree of adaptation to the marine environment, their life environment, and the nature of their "pachyostotic" pattern, when present, are described. This inventory enables the evaluation of the current quality of the data relative to this specialization and provides an indication of the work that remains to be done. The functional consequences of "pachyostosis," and notably its importance for buoyancy control in the context of hydrostatic regulation of the body trim, are discussed and opposed to the requirement of improved swimming abilities in the case of a hydrodynamic mode of trim regulation. Questions are posed about the significa-tion of the polymorphism displayed by this specialization between different taxa, different specimens of the same taxon and different bones of the same specimen, and the problem of quantification of pachyostosis is discussed

Palaeoecological and morphofunctional interpretation of bone mass increase: an example in Late Cretaceous shallow marine squamates

International audienceBone mass increase (BMI; i.e. osteosclerosis with possible additional pachyostosis) is characteristically displayed by many Late Cretaceous squamates that adapted to shallow marine environments-plesiopelvic mosasauroids, stem-ophidians and pachyophiids. A combined morphological and microanatomical analysis of vertebrae and, to a lesser extent, ribs of these fossil squamates provides new data about the distribution and variability of this osseous specialization in these taxa. Classical thin sections and third generation synchrotron microtomography and laminography were used for the microanatomical analysis. Following the explanation of the likely involvement of this specialization in the control of buoyancy, body trim and Carrier's constraint, new palaeoecological inferences and new hypotheses about the locomotor abilities and life environment of these organisms are produced. The taxa displaying BMI are considered to have undertaken long dives, hovering slowly and maintaining a horizontal trim, in shallow and protected water environments. Conversely, marine stem-ophidians deprived of this specialization are regarded as slow surface swimmers able to live in more open marine environments. This study highlights the importance of microanatomical data for palaeoecological studies. It also discusses the significance of the use of this specialization as a character in phylogenetic studies