Among 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.

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.

their diet from a regime consisting mainly of endotherms with endoskeleton to ectotherms bearing a hard exoskeleton. Maxilla, palatine, pterygoid and dentary teeth were examined in an adult and a juvenile of Dolichophis schmidti, one Eirenis punctolineatus and one Eirenis persicus. 3D Geometric Morphometrics comparison revealed maxilla and palatine teeth of the E. persicus are blunt and conical shape while those teeth are sharp and elongated in E. punctatolineatus as well as the adult and juvenile D. schmidti. A similar difference could be noted for the pterygoid teeth. In contrast, the dentary teeth are not as different among the examined snakes. Blunt and conically shaped teeth, as observed in E. persicus, seem to be more adapted for biting hard bodied, arthropod prey, while sharp and elongated teeth in Dolichophis and E. punctatolineatus, are specialized for puncturing endotherm prey. The results of a finite element analysis confirms that during biting a hard bodied prey, the generated stresses in E. persicus tooth is mostly confined to the tip of the tooth and mostly well below the von Mises yield criterion the tooth. In contrary, D. schmidti tooth appears less well suited for biting a hard prey since the generated stresses widely distribute across the tooth with values roughly 2 to 3 times higher than the von Mises yield criterion of the tooth. A lower degree of specialization that was observed among the dentary teeth in the examined snakes suggest a similar functional constraint in pushing the prey against the upper tooth rows.

Abstract To date there are few quantitative studies investigating the evolution of tooth shape and function in aglyphous snakes in relation to diet. A considerable evolutionary decrease in body size is observed in whip snakes of the genus Dolichophis and their sister-group Eirenis. This was coupled with a considerable shift in diet from a regime consisting mainly of prey with endoskeleton to prey bearing a hard exoskeleton. Three-dimensional (3D) geometric morphometrics revealed that the maxillary and palatine teeth of E. persicus are blunt and conical in shape, while the same teeth are sharp and elongated in E. punctatolineatus and D. schmidti. Blunt and conically shaped teeth, as observed in E. persicus, seem to be more adapted for biting hard-bodied, arthropod prey. In contrast, the sharp and elongated teeth in Dolichophis and E. punctatolineatus, are likely specialized for puncturing prey with an endoskeleton. The results of a finite element analysis confirms that during the biting of a hard-bodied prey, the generated stresses in E. persicus teeth are well below the von Mises yield criterion, while in D. schmidti the value is roughly two to three times higher, indicating that E. persicus teeth are better suited for biting hard-bodied prey such as arthropods.