抄録
Charophyte gyrogonites, isolated teeth of crocodylomorphs, ornithopods and sauropods, and theropod eggshells, found from the Lower Cretaceous (lower to middle Albian) Ohyamashimo Formation of the Sasayama Group at Tambasasayama and Tamba cities, Hyogo Prefecture, Japan, were newly described, classified, and discussed, and their taxonomic diversity in this formation was examined. Charophyte gyrogonites were identified as Characeae based on their five spiral cells converging at the tips and the absence of an utricle. Crocodylomorph teeth were classified in seven morphotypes based on the size, shape, and surface structure. Morphotypes I-III were assigned to Atoposauridae, whereas morphotypes IV-VI belong to Neosuchia, and morphotype VII belongs to Metasuchia. Ornithopod teeth include two dental types, styracosternan maxillary and ankylopollexian dentary teeth. If these teeth belong to a single taxon, derived styracosternan iguanodontians, which are more basal than Xuwulong, are possible candidates for these teeth. Sauropod teeth were classified into two distinct taxa: one resembling Tambatitanis and another earlier diverging taxon. Eggshells were classified into three ootaxa: Nipponoolithus ramosus, Elongatoolithus oosp., and indeterminate theropods. These results expand our knowledge of the spatial and chronological distributions of terrestrial taxa in the Ohyamashimo Formation, which partly sheds light on ecosystem transitions in the region.
