Smew

The Smew (Mergellus albellus) is a small duck which is somewhat intermediate between the typical mergansers (Mergus) and the goldeneyes (Bucephala). It is the only member of the genus Mergellus; sometimes included in Mergus, this genus is well distinct (though closely related) and might actually be a bit closer to the goldeneyes^[1]. The Smew has interbred with the Common Goldeneye (B. clangula).

An unnamed fossil seaduck, known from a humerus found in the Middle Miocene Sajóvölgyi Formation (Late Badenian, 13-12 million years ago) of Mátraszõlõs, Hungary, was assigned to Mergus. However, the authors included the Smew therein, and consequently, the bone is more properly assigned to Mergellus – especially as it was more similar to a Smew’s than to Bucephala remains also found at the site. It is sometimes^[2] argued that the Mátraszõlõs fossil is too old to represent any of the modern seaduck genera, but apparently these were all well-distinct even back then.^[3]

The living species is known to exist since about 2 to 1.5 million years, as attested by fossils from the earliest Pleistocene found in England.