A Phylogenetic Analysis of Geese and Swans (Anseriformes: Anserinae), Including Selected Fossil Species

Abstract

A phylogenetic analysis of modern and selected fossil geese and swans was performed using 165 characters of the skeleton, trachea, and natal and definitive integument. Five shortest trees were found (length = 318; consistency index for informative characters = 0.634), which differed only in details of relationships among three species of Branta. The trees supported (1) †Cnemiornis as sister group to other taxa analyzed; (2) a sister group relationship between the moa-nalos of Hawaii and other geese and swans; (3) Cereopsis as sister group of Anser, Branta, Coscoroba, and Cygnus (contra Livezey, 1986, Auk 103:737–754); (4) monophyly of Anser, Branta, and †Geochen and confirmation of generic monophyly of each; and (5) Coscoroba as sister group to Cygnus. Selective exclusion of fossil taxa from the analysis variably affected inferred relationships and had substantial impacts on computational efficiency. Some nodes were not robust to bootstrapping: (1) nodes relating species groups within Anser, Cygnus, and †Thambetochen and (2) the node uniting Anser, Branta, Coscoroba, and Cygnus relative to Cereopsis. Bremer (decay) indices indicated similar differences in relative support for nodes. Skeletal characters were comparatively important in establishing higher order relationships, whereas integumentary characters were critical for lower order inferences. Constrained analyses revealed that other proposed phylogenetic hypotheses entailed variable penalities in parsimony. The shortest tree(s) was considered with respect to selected ecomorphological attributes (e.g., body mass, sexual size dimorphism, clutch size) and biogeography, and a revised phylogenetic classification of the geese and swans is proposed.

Anseriformes, Anserinae, cladistics, comparative analysis, fossils, geese, morphology, swans, waterfowl