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The Pelagornithidae, commonly called pelagornithids, pseudodontorns, bony-toothed birds, false-toothed birds or pseudotooth birds, are a prehistoric family of large seabirds. Their fossil remains have been found all over the world in rocks dating between the Late Paleocene and the Pliocene-Pleistocene boundary.〔Bourdon (2005), Mayr (2008), Boessenecker and Smith (2011)〕 Most of the common names refer to these birds' most notable trait: tooth-like points on their beak's edges, which unlike true teeth contained Volkmann's canals and were outgrowths of the premaxillary and mandibular bones. Even "small" species of pseudotooth birds were the size of albatrosses; the largest ones were truly gigantic, and with wingspans estimated at 5–6 metres (15–20 ft) among the largest flying birds ever to live. They were the dominant seabirds of most oceans throughout most of the Cenozoic, and modern humans apparently missed encountering them only by a hair's breadth of evolutionary time: the last known pelagornithids were contemporaries of ''Homo habilis'' and the beginning of the history of technology.〔Hopson (1964), Olson (1985: pp. 199–201), Bourdon (2005), Geraads (2006), Mayr (2009: pp. 55,59), Mlíkovský (2009)〕 ==Description and ecology== Apart from the giant teratorn ''Argentavis magnificens'', the biggest of the pseudotooth birds were the largest flying birds known. Almost all〔''"Pseudodontornis" stirtoni'' is the only notable exception: Scarlett (1972) ''contra'' Mayr (2009: p. 59)〕 of their remains from the Neogene are immense, but in the Paleogene there were a number of pelagornithids that were around the size of a great albatross (genus ''Diomedea'') or even a bit smaller. The undescribed species provisionally called "Odontoptila inexpectata"〔Published in a thesis and hence a ''nomen nudum''. Also, ''Odontoptila'' is already used for a geometer moth genus: ICZN (1999), uBio (2005)〕 – from the Paleocene-Eocene boundary of Morocco – is the smallest pseudotooth bird discovered to date and was just a bit larger than a white-chinned petrel (''Procellaria aequinoctialis'').〔Scarlett (1972), Olson (1985: pp. 199–200), Bourdon (2005, 2006), Mayr (2008, 2009: pp. 57,59), Mayr ''et al.'' (2008)〕 The Pelagornithidae had extremely thin-walled bones widely pneumatized with the air sac extensions of the lungs. Most limb bone fossils are very much crushed for that reason. In life, the thin bones and extensive pneumatization enabled the birds to achieve large size while remaining below critical wing loadings. Though 25 kg/m2 (5 lb/ft2) is regarded as the maximum wing loading for powered bird flight, there is evidence that bony-toothed birds used dynamic soaring flight almost exclusively: the proximal end of the humerus had an elongated diagonal shape that could hardly have allowed for the movement necessary for the typical flapping flight of birds; their weight thus cannot be easily estimated. The attachment positions for the muscles responsible for holding the upper arm straightly outstretched were particularly well-developed, and altogether the anatomy seems to allow for an ability of holding the wings rigidly at the glenoid joint unmatched by any other known bird. This is especially prominent in the Neogene pelagornithids, and less developed in the older Paleogene forms. The sternum had the deep and short shape typical of dynamic soarers, and bony outgrowths at the keel's forward margin securely anchored the furcula.〔Meunier (1951), Hopson (1964), Olson (1985: p. 200) Mayr (2008, 2009: p. 58)〕 The legs were proportionally short, the feet probably webbed and the hallux was vestigial or entirely absent; the tarsometatarsi (anklebones) resembled those of albatrosses while the arrangement of the front toes was more like in fulmars. Typical for pseudotooth birds was a second toe that attached a bit kneewards from the others and was noticeably angled outwards. The "teeth" were probably covered by the rhamphotheca in life, and there are two furrows running along the underside of the upper bill just inside the ridges which bore the "teeth". Thus, when the bill was closed only the upper jaw's "teeth" were visible, with the lower ones hidden behind them. Inside the eye sockets of at least some pseudotooth birds – perhaps only in the younger species – were well-developed salt glands.〔Woodward (1909): pp. 86–87, Hopson (1964), Olson (1985: p. 142), Bourdon (2005), Mayr (2009: p. 58), Mayr ''et al.'' (2008)〕 Altogether, almost no major body part of pelagornithids is known from a well-preserved associated fossil and most well-preserved material consists of single bones only; on the other hand the long occurrence and large size makes for a few rather comprehensive (though much crushed and distorted) remains of individual birds that were entombed by as they lay dead, complete with some fossilized feathers. Large parts of the skull and some beak pieces are found not too infrequently. In February 2009, an almost-complete fossilized skull of a presumed ''Odontopteryx'' from around the Chasicoan-Huayquerian boundary c. 9 million years ago (Ma) was unveiled in Lima. It had been found a few months earlier in Ocucaje District of Ica Province, Peru. According to paleontologist Mario Urbina, who discovered the specimen, and his colleagues Rodolfo Salas, Ken Campbell and Daniel T. Ksepka, the Ocucaje skull is the best-preserved pelagornithid cranium known as of 2009.〔Olson (1985: pp. 194–195), Mayr (2008), GG ()〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pelagornithidae」の詳細全文を読む スポンサード リンク
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