Annakacygna, a new genus for two remarkable flightless swans (Aves, Anatidae, Cygnini) from the Miocene of Gunma, central Japan: With a note on the birds’food niche shift and specialization of wings for parental care

By MATSUOKA Hiroshige (Department of Geology and Mineralogy, Kyoto University) and HASEGAWA Yoshikazu (Gunma Museum of Natural History)

The article describes a new genus, Annakacygna (Aves, Anatidae, Cygnini) and two species of flightless swan, Annakacygna hajimei and A.yoshiiensis from fossil specimens found in the Miocene Haraichi Formation, Gunma, central Japan from around 11.5 Ma.

(c) Gunma Museum of Natural History

Osteological features of A. hajimei indicate that this large anatid bird belongs to tribe Cygnini as it possesses the diagnostic features of the tribe such as the long neck and long pelvis with dorsally swelling ala postacetabularis illi.

The skeleton of Annakacygna hajimei. In standing and wing folded posture. The white elements/parts were not found in the fossil.

(c) Gunma Museum of Natural History

Annakacygna were a genus of flightless birds characterized by distally small wing elements, a large body, and pachyostotic bones. In addition, the autapomorphies of Annakacygna indicate that this bird was an animal with a body plan that specialised in breeding behavior, sex appeal and parental care. Musculoskeletal systems also indicate that it was a highly adapted filter feeder that had a planktonic diet, feeding in the seas of Miocene Japan.

The image of size difference between Annakacygna yoshiiensis (black bird in back) and A. hajimei (grey one in front).

(c) Gunma Museum of Natural History

A. hajimei was similar in size to the modern day black swan but with a larger head and wider, heavy body. A. yoshiiensis, known only from the distal end of tibiotarsus (GMNH-PV-1685), was larger than a mute swan but weighed considerably more due to its pachyostotic bones.

The full article can be found here.