Abstract
BackgroundThe shape of the appendicular bones in mammals usually reflects adaptations towards different locomotor abilities. However, other aspects such as body size and phylogeny also play an important role in shaping bone design.We used 3D landmark-based geometric morphometrics to analyse the shape of the hind limb bones (i.e., femur, tibia, and pelvic girdle bones) of living and extinct terrestrial carnivorans (Mammalia, Carnivora) to quantitatively investigate the influence of body size, phylogeny, and locomotor behaviour in shaping the morphology of these bones. We also investigated the main patterns of morphological variation within a phylogenetic context.ResultsSize and phylogeny strongly influence the shape of the hind limb bones. In contrast, adaptations towards different modes of locomotion seem to have little influence. Principal Components Analysis and the study of phylomorphospaces suggest that the main source of variation in bone shape is a gradient of slenderness-robustness.ConclusionThe shape of the hind limb bones is strongly influenced by body size and phylogeny, but not to a similar degree by locomotor behaviour. The slender-robust “morphological bipolarity” found in bone shape variability is probably related to a trade-off between maintaining energetic efficiency and withstanding resistance to stresses. The balance involved in this trade-off impedes the evolution of high phenotypic variability. In fact, both morphological extremes (slender/robust) are adaptive in different selective contexts and lead to a convergence in shape among taxa with extremely different ecologies but with similar biomechanical demands. Strikingly, this “one-to-many mapping” pattern of evolution between morphology and ecology in hind limb bones is in complete contrast to the “many-to-one mapping” pattern found in the evolution of carnivoran skull shape. The results suggest that there are more constraints in the evolution of the shape of the appendicular skeleton than in that of skull shape because of the strong biomechanical constraints imposed by terrestrial locomotion.
Highlights
The shape of the appendicular bones in mammals usually reflects adaptations towards different locomotor abilities
This study investigated the influence of phylogeny, allometry, and locomotor behaviour in shaping the morphology of the hind limb bones in mammalian carnivores
Phylogeny and size The permutation tests performed to investigate the presence of a phylogenetic structure in shape (Procrustes coordinates, Pco) and size (Log-transformed centroid size, Log-Centroid size (Cs)) showed statistically significant results for all the bones (Table 1)
Summary
The shape of the appendicular bones in mammals usually reflects adaptations towards different locomotor abilities Other aspects such as body size and phylogeny play an important role in shaping bone design. We used 3D landmark-based geometric morphometrics to analyse the shape of the hind limb bones (i.e., femur, tibia, and pelvic girdle bones) of living and extinct terrestrial carnivorans (Mammalia, Carnivora) to quantitatively investigate the influence of body size, phylogeny, and locomotor behaviour in shaping the morphology of these bones. This study investigated the influence of phylogeny, allometry, and locomotor behaviour in shaping the morphology of the hind limb bones (i.e., femur, tibia, and pelvic girdle bones) in mammalian carnivores (extant and extinct taxa from the order Carnivora plus some taxa from the closelyrelated order Creodonta). This study will lead to a complete picture of the morphological evolution of all major limb bones of the carnivoran appendicular skeleton as a whole
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