THE PHYLOGENETIC POSITION OF CAYAOA BRUNETI (ANSERIFORMES, ANATIDAE), FLIGHT LOSS AND LARGE SIZE EVOLUTION IN COASTAL MARINE ANATIDAE

DE MENDOZA, R.; TAMBUSSI C.P.

DIAMANTE

Congreso; 9th International Meeting of the Society of Avian Paleontology and Evolution; 2016

Cayaoa bruneti was a large flightless diving Anatidae from early Miocene of Gaiman Formation, Chubut, Argentina. Without any phylogenetic analysis, in its original description (Tonni, el Hornero, 1980, XII:11-15) was related with Tachyeres. A cladistics analysis using parsimony was made with 157 osteological characters from the literature and original observations, aiming to resolve the phylogenetic position of Cayaoa bruneti. Cayaoa resulted part of a diving duck clade, sustained by nine unambiguous synapomorphies nested within Anatinae-Tadorninae, while Tachyeres is in other clade with Lophonetta within Anatinae, sustained by four unambiguous synapomorphies. Analyzing only parts of the matrix considering each bone in independent cladistics analysis, characters of the femur and humerus are those that have more relevance. In contrast the results obtained using skull characters are more similar to those of molecular analysis, where Oxyurinae is out of Tadorninae-Anatinae and there is no diving ducks clade. By running the analysis again with a backbone phylogeny derived from molecular analysis for extant species, Cayaoa results in a basal position within Oxyurinae, sustained by ten unambiguous synapomorphies (e.g. the incisura capitis opens to the fossa pneumotricipitalis dorsalis in an elevated groove, the tuberculum ventrale partially occludes the fossa pneumotricipitalis ventralis and the attachment of musculus scapulo humeralis cranealis is elongated and robust). According with this hypothesis, Cayaoa is an Oxyurinae. Represents an early example in a basal Anatidae of a secondary loss of flight capacity and a tendency toward large sizes related to coastal marine environments, as it is also documented by Tachyeres within Anatinae and fossil Pleistocene examples within Merginae (Chendytes Miller, Condor, 1925, 27:145-147 y Shiriyanetta Watanabe y Matsuoka, Journal of Vertebrate Paleontology, 2015, e994745, 22 pages).