Geometric morphometric analysis of skull shape in the Accipitridae

Abstract

Morphological adaptations for feeding are a conspicuous feature of avian evolution. Accipitrids exhibit a wide range of prey preferences. Skulls of 97 species which were assigned to seven dietary groups in the present study, were compared from the dorsal, lateral, and ventral views using geometric morphometrics. Landmarks were placed on the overall shape of cranium, bill, orbit, nostril, and attachment area for different jaw muscles. The results suggested considerable variations on the shape of bill and cranium, as well as the size of jaw closing muscles, by which can distinguish most of the groups. Scavengers were found to have a more slender and shallower skull, smaller orbits and longer maxilla whereas piscivores have a larger palatine. Mammalivores are characterized by reduced attachment area for the M. adductor mandibular externus superficialis, a relatively large palatine, long maxilla, and caudally positioned quadrate. Insectivores tend to have larger and more anteriorly oriented orbits, a relatively large attachment area for the M. adductor mandibular externus superficialis, and relatively broad and thin bills. Avivores are distinctive in their broad and protrudent caudal cranium. These morphological characteristics have some functional implications, and shed light on further biomechanical research. Moreover, phylogeny and size significantly contribute to skull shape variation.