Cranial osteology and taxonomy of albatrosses of genus Dimedea linneaus, 1758 and Thalassarche reichenbach, 1853 (procellariformes: Diomeidae)

Abstract

The currently accepted albatross taxonomy, based on characters of external morphology, plumage patterns, tail shape, bill size and coloration, organization of the plates of the bill, and, more recently, molecular data such as cytochrome-b gene sequences, resulted in a division of the family Diomedeidae into four genera: Diomedea, comprising the great albatrosses; Phoebastria, the North Pacific albatrosses; Thalassarche, the mollymawks; and Phoebetria, the sooty mollymawks. However, there are only a few, old studies on albatross osteology, which focused mostly on supra-generic relationships. Research on the group's taxonomy and anatomy is important in order to establish a secure basis for the identification of each species, including the differences between males, females and specimens of different ages, and also to verify anatomic characters which might be found useful for phylogenetic analysis based on morphological markers. In the present study, 63 skulls of Diomedea and Thalassarche albatrosses were analyzed and compared, thus establishing topographic correspondences and determining primary homologies, these resulting in: (a) the finding of no pattern of anatomical variation related to sex and age for both T. melanophris and for T. chlororhynchos; (b) the assessment of eight cranial landmarks separating the genera Diomedea and Thalassarche; (c) the recognition of 13 cranial landmarks differing among T. melanophris, T. chlororhynchos and T. cauta; (d) the re-identification of several specimens based on skull characters. The characters here presented for the genera and species, along with further anatomical research on the skull of the Diomedeidae, including the genera Phoebetria and Phoebastria, may help to enlighten relationships within the family.