Mergus
The Brazilian merganser (M. octosetaceus) is a South American duck, and one of the six most threatened waterfowl in the world, with possibly fewer than 250 birds in the wild.In other traits, however, the genera Mergus, Lophodytes, Mergellus, and Bucephala are very similar: uniquely among all Anseriformes, they do not have notches at the hind margin of their sternum, but holes surrounded by bone.[6] The genus name is the Latin word for an unidentified waterbird mentioned by Pliny the Elder and other authors; some sources have identified the original mergus as referring to either a cormorant or Scopoli's shearwater.[20] A Late Serravallian (13–12 million years ago) fossil sometimes attributed to Mergus, found in the Sajóvölgyi Formation of Mátraszőlős, Hungary, probably belongs to Mergellus.[21] The affiliations of the mysterious "Anas" albae from the Messinian (c. 7–5 million years ago) of Hungary are undetermined; it was initially believed to be a typical merganser too.