The fourth international symposium of IGCP507, “Paleoclimates of the Cretaceous in Asia and their global correlation” was held in Kumamoto, on December 1-6, 2009. The purpose of the symposium, which was organized by the Scientific Committee of the IGCP507 Symposium, was to investigate Cretaceous biodiversity, faunal changes, environments, and climate in Asia through geological analyses of rock and fossil records. Seventy participants registered to attend the conference from 10 countries, and gave 28 oral and 28 poster presentations, two keynote speeches, one workshop “Cretaceous to Recent bryozoans”, and five sessions addressing (1) Vertebrate evolution in Asia during the Cretaceous (thematic session), (2) Paleontology, (3) Paleoclimate, (4) Sedimentology, and (5) Tectonics, on December 4-5. There was a pre-symposium field excursion, “Cretaceous non-marine and shallow marine facies and fossils in western Kumamoto, Kyushu, Japan”, to northern parts of Amakusa Islands (December 1-3). The excursion focused on sedimentary processes, faunal changes in benthic molluscan fossils, and biostratigraphy in the mid-Cretaceous Goshoura and the Upper Cretaceous Himenoura groups. During the post-symposium field excursion, “Mifune Dinosaur Museum and Upper Cretaceous Dinosaur site in the Mifune Group, Kumamoto (December 6)”, participants visited a typical terrestrial vertebrate site and museum exhibitions.
Fission-track (FT) dating was carried out on zircon crystals from four vitric tuff beds in the Mifune Group, middle Kyushu. FT ages of 93.1±4.4 Ma, 89.8±4.0 Ma for the lower part of the Lower formation, 83.6±3.1 Ma for the lower part of the Upper formation and 82.1±11.1 Ma for the upper part of the Upper formation were obtained. These data suggest that the Mifune Group ranges in age from Late Cenomanian to Early Campanian, though the upper age limit remains uncertain. The age of the vertebrate fauna from the middle part of the Upper formation is assigned to Coniacian to Campanian. This age is younger than previously estimated age obtained from paleontological studies. The Mifune Group is possibly correlated with the Onogawa Group on the basis of the present FT ages.
Ornithomimosaurs have unusual characters among theropod dinosaurs, and many records of these animals have been reported previously from Asia and North America. However, the fossil record of ornithomimosaurs is limited and was not known from the Upper Cretaceous in Japan despite its many dinosaur discoveries. Here, the first fossil of an ornithomimosaurian dinosaur from the Upper Cretaceous in Japan is described from the Upper Formation of the Mifune Group in Kumamoto Prefecture, Southwest Japan. This new discovery indicates the existence of ornithomimosaurs in the Late Cretaceous coastal areas of East Asia under a semi-arid climate. The occurrences of ornithomimosaur fossils described here are consistent with the presence of many fossil records from a dry climate rather than the humid conditions in the Cretaceous deposits of Asian mainland today.
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