Fig 1.
TL, total length of skull; BCL, brain case length; BCW, brain case width; ZW, zygoma width; FL, face length; IOD, inter-ocular distance; ZFW, zygomatic fossa width, ZFL, zygomatic fossa width, GSW, greatest skull (squamosal) width; MW, width at mastoids; PW, palate width; RWM, rostral width at molars; PL, palate length; RWC, rostral width at canines; PL, palate length; CBL, condylobasal length; OSA, occlusal surface area of premolar and molar teeth; ZH, zygoma height; ZL, zygoma length; MRW, mandibular ramus width; MRH, mandibular ramus height; MAT, moment arm of the temporalis; OLC, out lever at the condyle; MAM, moment arm of masseter; JW, jaw width; JL, jaw length. Trait definitions are given in Table 1.
Table 1.
Definitions of morphometric variables.
Fig 2.
Multivariate regression ordination of skull shape based on feeding mode.
Symbols reflect feeding mode for each species (circles, hand-oriented; squares, mouth-oriented). Ellipses depict standard errors for regression scores. Vectors give partial regression coefficients (trait abbreviations as in Table 1). Individuals (data points color-coded by species) and species to the right in this space have elongate skulls, especially for relative palate and jaw length, and have narrow palate width, small intra-ocular distance and shallow mandibular rami.
Table 2.
MANOVA results for otter cranial form and shape.
Fig 3.
Canonical ordination of sea otter (E. lutris) skull form by subspecies.
Symbols reflect feeding mode, which varies from relative piscivory (circles) to greater inclusion of invertebrates (diamonds), to durophagy (triangles). Vectors give covariance structure coefficients and only major vectors are labeled (trait abbreviations as in Table 1). The vector for OSA½ proceeds approximately three-fold more than shown. Ellipses depict 95% confidence intervals for subspecies centroids. The horizontal axis generally reflects the classic morphological suite of traits for durophagy: individuals to the right in this space have greatly increased occlusal surface area, long zygomas, short outlever at the level of the carnassials, short faces, a relatively short moment arm of the masseter, and relatively narrow zygomatic fossa in the center of the fossa. Plot aspect ratio (1.4:1) reflects the square root of the eigenvalue ratio for the major (horizontal) and minor (vertical) axes of skull form.