図版−1．ペリカン目カツオドリ科カツオドリ属の1種Sula (Microsula) sp.の母岩を 真上から見たところ．中央に上顎・頭蓋・上腕骨・叉骨が認められる． (母岩の大きさは，左右18.5cm)

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Discovery of five Miocene birds from Chichibu Basin, central Japan

Keiichi ONO
National Science Museum, Tokyo. 169 Japan.
and
Osamu SAKAMOTO
Saitama Museum of Natural History. Nagatoro, Chcichibu-gun, 369-13 Japan.

Abstract The Miocene strata in the Chichibu Basin are well known by abundant fossils of fishes, reptiles, birds and mammals. Some important fossil materials we obtained from the Nagura Formation are remains of shearwaters (Puffinus spp.), a gannet (Sula (Microsula) sp.), a bony-toothed bird (Osteodontornis sp.). And an anhinga (Anhinga sp.) was collected from the lower Tomita Mudstone Formation. The gannet is represented by 2 skeletons and 10 bone fragments. Fossils identified as Anhinga sp. is a distal half of the humerus and a distal portion of the deltoid crest. The bony-toothed bird we obtained is a complete quadrate.
　　A lage sized shearwater and a small sized one were unearthed : a large species is represented by a skeleton with a skull, and smaller species is represented by an almost complete humerus. These fossils are significant to understand the evolutions of Neogene avifauna in Japan.
　　Recent anhinga is distributed around freshwaters habitats of the tropics, and the Tomita Mudstone Formation yields abundant terrestrial plant fossils.
　　From the formation, we discovered a leaf of Quercus miovariabillis which is common in Daijima fossil flora. This indicates that the fossil yielding bed belongs to the latest Early Miocene to earliest Middle Miocene. The occurrences of Quercus miovariabillis leaf and anhinga indicate that the paleoclimate was relatively warmer than present. The presence of shearwaters, a gannet, and a bony-toothed bird in the the Nagura Formation is also indicative of warmer environment.