A PHYLOGENETIC ANALYSIS OF GEESE AND SWANS (ANSERIFORMES, ANSERINAE),INCLUDING SELECTED FOSSIL SPECIES

A phylogenetic analysis of modem and selected fossil geese and swans w as performed using 165 characters of the skeleton, trachea, and natal and definitive integument. Five shortest trees were found (length = 31 8; consistency index for informative characters = 0.634), which differ ed only in details of relationships among three species of Branta. The trees supported (1) dagger Cnemiornis as sister group to other taxa a nalyzed; (2) a sister group relationship between the moa-nalos of Hawa ii 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 dagger Geochen and confirmation o f generic monophyly of each; and (5) Coscoroba as sister group to Cygn us. Selective exclusion of fossil taxa from the analysis variably affe cted inferred relationships and had substantial impacts on computation al efficiency. Some nodes were not robust to bootstrapping: (1) nodes relating species groups within Anser, Cygnus, and dagger 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 im portant in establishing higher order relationships, whereas integument ary characters were critical for lower order inferences. Constrained a nalyses 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.