Article: Affinities of Miocene waterfowl (Anatidae: Manuherikia, Dunstanetta and Miotadorna) from the St Bathans Fauna, New Zealand
Trevor H. Worthy and Michael S. Y. Lee
The recently described St Bathans Fauna, from the Manuherikia Group, Early–Middle Miocene, 19–16 Ma, New Zealand, includes six anatid taxa. Here we present detailed morphological descriptions of all available skeletal elements of the three best represented anatids: Manuherikia lacustrina (551 specimens), Dunstanetta johnstoneorum (7 specimens), and Miotadorna sanctibathansi (115 specimens). The affinities of these taxa, and of the similar-aged European taxon Mionetta blanchardi, are evaluated with phylogenetic analyses using a dataset of 133 characters (128 osteological, 5 integumental) and 57 terminal taxa. Representatives of all main anatid groups were included, with dense sampling of Australasian taxa including the recently extinct New Zealand forms (Cnemiornis, Chenonetta finschi), and relatively primitive taxa (anserines, Dendrocygna, oxyurines, tadornines). Analyses were conducted with no constraints, and with certain taxa constrained to conform to arrangements supported by multiple independent genetic studies. In the preferred (constrained) analyses: (1) anserines were the most basal anatids; (2) the four Tertiary fossil taxa were more derived than anserines and Dendrocygna; and (3) the European Mionetta blanchardi was basal to an oxyurine clade. The New Zealand fossils Manuherikia and Dunstanetta either associated with this oxyurine clade or formed separate lineages of an approximately oxyurine evolutionary grade, depending on whether diving characters were included or excluded. Similarly, Biziura, Thalassornis, and a Stictonetta–Malacorhynchus clade either associated with oxyurines or formed independent lineages of approximately oxyurine grade. Above oxyurines, a well-supported clade groups Miotadorna with Tadorna species exclusive of T. radjah. These results cast doubt on the distinctiveness of Dendrocheninae Livezey and Martin, 1988, and instead suggest oxyurine affinities for the Miocene fossils Mionetta, Dendrochen, Manuherikia and Dunstanetta, and the modern Biziura, Thalassornis, Oxyura, Nomonyx, Stictonetta and Malacorhynchus. The association of Mionetta with oxyurines indicates that the divergence between oxyurines and higher anatids occurred around 25 Ma, while the position of Miotadorna within Tadorna indicates that the basal divergence between living Tadorna occurred by the Early–Middle Miocene; together, these two dates indicate that many basal splits within anatids occurred within a short interval during the Miocene.