Size, shape and structural versatility of the skull of the subterranean rodent Ctenomys (Rodentia, Caviomorpha): functional and morphological analysis

Abstract

Morphological analysis of the skull of the subterranean rodent Ctenomys , a highly speciose genus which uses both claws and teeth when digging, shows that for a broad range of species size, scaling was associated with both variation and maintenance of shape. Our results show that the angle of incisor procumbency (AIP), a character largely viewed as an adaptation to digging with teeth, is highly variable. We found a non‐significant relationship between AIP and basicranial axis (basioccipital + basisphenoid) length, a measure of overall skull size. Accordingly, both small and large Ctenomys species possess either high or low AIP. A significant relationship between AIP and diastema length, given the rostral allometry seen in Ctenomys , suggests that hypermorphosis to a certain extent influences AIP. However, the roots of the incisor are lateral to those of the cheek teeth and their position may thus shift freely. This observation supports the notion that skull structural design, and to a certain extent rostral allometry, underlies variation in AIP. On the other hand, the positive allometry of incisor width and thickness indicates that, in larger species, proportionately powerful incisors are able to resist greater bending forces. We found that the out‐lever arm of the jaw adductor muscles scales with positive allometry against basicranial axis length. However, we found an isometric relationship between in‐ and out‐lever arms. In this case, conservation of skull proportions, regardless of variation in size, is a feature possibly related to the maintenance of an effective tooth digging capability. Functional and ecological data are discussed when assessing the implications of size and shape variation in the skull of Ctenomys . © 2003 The Linnean Society of London. Biological Journal of the Linnean Society , 2003, 78, 85−96.

Forelimb indicators of prey‐size preference in the Felidae

“…Measurements follow von den Dreisch, 1976;Merriam and Stock, 1932;and Van Valkenburgh, 1987. discriminant function analysis (DFA). These statistical techniques were chosen because they are often used to examine ecomorphological differences among taxa ( Van Valkenburgh, 1987;Van Valkenburgh and Koepfli, 1993;Mora et al, 2003). The MANOVA tested for significant differences in morphology among both the prey size and locomotor categories, respectively.…”

Morphometric variation in island and mainland populations of two lizard species from the Pacific Coast of Mexico

“…According to PCA and its variance-covariance matrix, we identified those variables that explain most of the variation in the shape (dimensions of the head and limbs) of both males and females from each species and population. We excluded the SVL of PC1 from hypothesis testing, since our goal was to isolate the overall effect of body size (SVL) and represent the components that show changes in body shape (Mora et al 2003), factors that should be subject to natural selection. To meet criteria of normality and homogeneity of variances prior to each analysis, all data were transformed to log 10 to fit a normal distribution (Zar 1999).…”

“…This analysis was performed as suggested by Jolicoeur (1963) and Mora et al (2003), which is based on testing whether the variation explained by principal component 1 (PC1; SVL in this case) is greater than the other components or morphometric variables, because the analysis expresses the relationship between coefficients of each variable with respect to PC1. Depending on the value of the allometric coefficient of each combination (SVL vs. morphometric character), we determined whether there was an isometric or allometric relationship between morphometric variables and body size.…”

Incisor morphology reflects diet in caviomorph rodents

“…Most recent studies that have examined rodent incisors in an ecological context have attempted to correlate their morphology with digging behavior rather than diet (e.g., Fernández et al. 2000;Hopkins and Davis 2009;Millien and Jaeger 2001;Millien-Parra 2000;Mora et al 2003;Rybczynski 1999). Other studies have focused on size evolution and guild partitioning among a small number of sympatric species using incisor data and have demonstrated character displacement indicative of dietary resource partitioning (Ben-Moshe et al 2001; Dayan and Simberloff 1994;Parra et al 1999).…”