Skull Shape Evolution in Durophagous Carnivorans

Abstract

In this article, we investigate convergent evolution toward durophagy in carnivoran skull shape using geometric morphometrics in a sample of living and extinct species. Principal components analysis indicate that, in spite of the different dietary resources consumed by durophages-that is, bone-crackers and bamboo-feeders-both groups of carnivorans share portions of skull phenotypic spaces.We identify by discriminant analyses a shared set of adaptations toward durophagy in the skull of carnivores. However, ancestral states indicate that although durophages reached similar phenotypes, the evolutionary pathways that they followed are different depending upon the family to which they belong. Furthermore, while the carnivoran cranium more closely reflects the nature of the resources consumed-that is, soft or hard and tough items-the mandible shows particular feeding adaptations-that is, bamboo or bone. This finding supports the interpretation that the mandible has more evolutionary plasticity than the cranium, which is more limited to evolve toward a particular feeding adaptation. However, we find that the shapes of the cranium and the mandible are highly integrated for the whole order Carnivora. Published studies of teratological cats and dogs indicate that the role of internal constraints in shaping this pattern of integration is absent or weak and malleable by selection. K E Y W O R D S :Carnivore, durophagy, evolutionary convergence, morphometrics, phenotype.

Directional selection can drive the evolution of modularity in complex traits

“…Correlated stabilizing selection can have many different causes, such as the necessity for cohesion among parts within an organism that impose selection on the associations between traits (3, 25, 26) or environmental and functional restrictions that also lead to stabilizing selection on the relations between traits. For example, the upper jaw and lower jaw must be the same size to allow proper mastication (26,27). Directional selection acts on the variation maintained by these internal and external processes.…”

Habitat changes and changing predatory habits in North American fossil canids

“…As we are only interested in quantifying the presence of phylogenetic signal, instead of the strength of the phylogenetic signal, we used the permutation approach developed by Laurin 46 , extended for multivariate analysis by Klingenberg and Gidaszewski 47 , and applied to shape data by other authors (for example, refs [48][49][50][51][52][53][54], to simulate the null hypothesis of complete absence of phylogenetic signal in elbow shape. The mean species shapes are randomly distributed as the tips of the phylogeny in 10,000 permutations, and for each permutation, the tree length was computed.…”

“…The association between environmental change and canid predatory behaviour was investigated using the arrangement of the enamel prism bands-known as bands of HunterSchreger (HSB)-as a proxy. The reason is because carnivores that live in open environments consume more intrinsic (bones from carcasses) and extrinsic (grit) hard food items, which relates to heavily folded HSB 28,51,[68][69][70] . Studies of carnivorans demonstrate a link between bone and carcass consumption and increased kleptoparasitism in open habitats because of increased carcass detectability [30][31][32] .…”

Studying morphological integration and modularity at multiple levels: concepts and analysis

“…Genetic integration has mostly been compared to static phenotypic integration, reflecting the importance of the genetic and phenotypic covariance matrices in quantitative genetic theory [67,71,73]. Evolutionary integration has been compared to static within-taxon integration [16,25,95] and ontogenetic variation [35,85,87,88], and through links to ecological variables such as diet or direct biomechanical arguments, functional considerations have also been incorporated [63,113]. Systematic multilevel studies incorporating more than two levels simultaneously are rare.…”