山階鳥類研究所研究報告
Online ISSN : 1883-3659
Print ISSN : 0044-0183
ISSN-L : 0044-0183
全蹼目の適応三体型の分折及び胸筋
黒田 長久
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ジャーナル フリー

1961 年 3 巻 1 号 p. 54-66

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The Steganopodes are heterogenous Order comprising such distinctive adaptive groups as the Cormorant, the underwater swimmer, the Gannet, the deep diver from air, and the Frigate Bird, the extreme aerial flier. I could examine the samples of types which were brought back from the Galapagos Is. by Mr. Koichi Sekiguchi. They are Nannopterum harrisi (a well known flightless cormorant), Sula nebouxii and Fregata magnificens.
Various parts of their skinned body were measured and analysed by taking proportions, based on proposed 'Alphabetical measurements of bird body (carcass)' (See Table 1). Nannopterum, with degenerated wings, is characteristically long-bodied, with short, somewhat broad but shallow chest, extremely long belly, long and most massively muscled pelvic and tibial parts. The neck muscles, particularly basal part of m. collis anticus, are strongly developed for underwater use. Sula has the body of log-type, with long pectoral part, (although it was rather short and broad in an example of S. sula (juv.) examined), the pelvic-tibial part with medium amount of muscles, though much less than in Nannopterum, and the fairly thick and long neck. Fregata's body is of an unique short aerial type, with no sign of aquatic adaptation. The chest is extremely deep, broad and short, the pelvic-tibial part being poorly developed. The neck is relatively (for thoracic length) short and weakly muscled.
But, in spite of these adaptive peculiarities of each three type, the indexes in % of the 'Cervical length (ai)', the 'Dorso-pelvic length (ci)', the 'Thoracic length (fi)', the 'Pelvic length (qi)', the 'Pectoral length (ji)' and the 'Belly length (ei)' for the 'Basic total length (a+c)' are very constant among them, showing an Order-specific trend of the bodily proportions, except the deviations shown by Nannopterum in Pectoral and Belly length indexes owing to its special adaptation. Among other birds, a 'Standard-type trend of proportions' was noticed among taxonomically different Orders, while some others, such as the heron and the penguin, revealed very specific or aberrant proportional trends, as in the case of Steganopodes. Therefore, this method of analysis of morphological adaptive radiation way be of significance.
The peculiarities in the pectoral muscles in the three Steganopodes are also described which supplement the author's previous paper (Auk, 78 (2)). The possession by flightless Nannopterum of m. pect. major. profundus (though only 1mm. thick as are other parts) which is characteristic in large soaring birds, suggests the cormorant's soaring origin. The highly soaring habit of Anhinga related to cormorants is in support of this. Only in Fregata, the medius layer of the pect. major is developed, but the very massive proximal part of the pect. major lateralis in Sula, is well suggestive of the history of development of the medius layer of Fregata.

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