albertonykus
Well-known member
Matsuoka, H., R. Seoka, and Y. Hasegawa (2024)
Reexamination of the prepelvic vertebrae found in the holotype of Annakacygna hajimei (Aves, Anseriformes, Cygnini) revealed the adaptive morphology of vertebral column linked to the mode of life of the "ultimate bird"
Bulletin of Gunma Museum of Natural History 28: 15–44
Annakacygna hajimei is an extinct flightless bird described from the marine Miocene (11.5 Ma) of Annaka, Gunma, Japan. Totally 17 prepelvic vertebrae, 12 cervical and 5 free thoracic, included in the holotype of A. hajimei were reexamined here. As a result, the number of cervical vertebrae of Annakacygna in life totaled 23, and provides a strong reason to identify this genus as a member of Cygnini. The body length (bill-to-tail length) of A. hajimei was reconstructed to about 150 cm. The original description estimated that A. hajimei was about the same length as the black swan (120-130 cm), but this must be corrected. As a result of this simple calculation A. yoshiiensis was found to be a giant bird with a total body length of nearly 2 meters.
Morphological examination of the prepelvic vertebrae of Annakacygna revealed that the neck of this bird had a unique curve at its base, with a strong kyphosis at the cervical-thoracic boundary (CTB). Because of this kyphotic curve, the clavicular air sac at the base of the neck and the cervical air sac developed in and around the cervical vertebrae may be pushed ventrally below the water surface when the bird was on water. This "floating ring" found at the base of the bird’s neck acts as the fulcrum on the body axis to give the buoyancy and stability to the bird’s body when on the water surface. The thoracic vertebral column is regarded as a flexible "suspension bridge" that absorbed the weight of the chicks on the back. One of the diagnostic features of Annakacygna, "ribs with unfused uncinate processes'', was interpreted as an adaptation that ensured flexibility of the entire ribcage. Annakacygna is a good example of "kin selection". We wholeheartedly agree with the recognition of Annakacygna as the "ultimate birds'' to have ever existed.
Reexamination of the prepelvic vertebrae found in the holotype of Annakacygna hajimei (Aves, Anseriformes, Cygnini) revealed the adaptive morphology of vertebral column linked to the mode of life of the "ultimate bird"
Bulletin of Gunma Museum of Natural History 28: 15–44
Annakacygna hajimei is an extinct flightless bird described from the marine Miocene (11.5 Ma) of Annaka, Gunma, Japan. Totally 17 prepelvic vertebrae, 12 cervical and 5 free thoracic, included in the holotype of A. hajimei were reexamined here. As a result, the number of cervical vertebrae of Annakacygna in life totaled 23, and provides a strong reason to identify this genus as a member of Cygnini. The body length (bill-to-tail length) of A. hajimei was reconstructed to about 150 cm. The original description estimated that A. hajimei was about the same length as the black swan (120-130 cm), but this must be corrected. As a result of this simple calculation A. yoshiiensis was found to be a giant bird with a total body length of nearly 2 meters.
Morphological examination of the prepelvic vertebrae of Annakacygna revealed that the neck of this bird had a unique curve at its base, with a strong kyphosis at the cervical-thoracic boundary (CTB). Because of this kyphotic curve, the clavicular air sac at the base of the neck and the cervical air sac developed in and around the cervical vertebrae may be pushed ventrally below the water surface when the bird was on water. This "floating ring" found at the base of the bird’s neck acts as the fulcrum on the body axis to give the buoyancy and stability to the bird’s body when on the water surface. The thoracic vertebral column is regarded as a flexible "suspension bridge" that absorbed the weight of the chicks on the back. One of the diagnostic features of Annakacygna, "ribs with unfused uncinate processes'', was interpreted as an adaptation that ensured flexibility of the entire ribcage. Annakacygna is a good example of "kin selection". We wholeheartedly agree with the recognition of Annakacygna as the "ultimate birds'' to have ever existed.
