Recently developmental mechanisms of vertebrates have been understood from the viewpoint of cellular biology in detail. In this paper, evolutionary changes in vertebrate history were recognized as changes of the developmental processes and discussed on the basis of cellular biology.

抄録全体を表示

 Recent and fossil rock-boring bivalves were obtained from the Kamiiso area, southwestern Hokkaido, Japan. Recent rock-boring assemblage is composed of five bivalves, Penitella gabbii, Irus mitis, Pseudoirus mirabilis, Zirfaea subconstricta and Nettastomella japonica. The assemblage is characterized by the warm-water species such as I. mitis and P. mirabilis due to the influence of warm Tsugaru current. From the Pleistocene Tomikawa Formation, fossil rock-boring bivalves and their burrows were occurred. Pleistocene rock-boring assemblage consists of two cold-water species, Nettastomella japonica and Hiatella arctica. The assemblage is associated with molluscan fossils of the cold-water Setana Fauna. Occurrence of the Nettastomella assemblage is ascribed to the cooler climate in Pleistocene age than in the modern.

抄録全体を表示

 In this study, a large lacuna at the summit of the cusp of human premolar is demonstrated by the observation of a ground section. This specimen probably was upper premolar and had large round swelling with marginal rim at the tip of lingual cusp. On a longitudinal ground section, this specimen had many incremental lines (striae of Retzius) in the enamel. A remarkable striae of Retzius among them was observed and divided the enamel into inner and outer layer. The inner enamel formed the central swelling at the tip of the cusp. This intense incremental line reached the bottom of the central swelling. The outer enamel formed the marginal rim and incremental lines of this layer converged at the base of the swelling.
 Desmostylus, lived in the Miocene in the North Pacific region, had a large lacuna like a crater with a central cone on each molar cusp. Ijiri (1939) suggested that a large lacuna like a crater with a central cone of Desmostylus molar was a crestal pit.
 Crestal pit (foveola apicis tuberculi dentis), reported and named by Tokoro in 1937, is a small pit on the cuspal and/or marginal ridge of tooth crown in human and some other mammalian teeth. Since then, there has been argument about relation between these two features. Suzuki et al. (1999) offered a hypothesis on the developmental process of the crestal pit of Desmostylus molar by histological studies. This specimen of human premolar had histological similarity to the crestal pit of Desmostylus. It seems that this specimen suggests that human teeth have capability to form the Desmostylus like crestal pit. It is needed to study about factors influencing changes of metabolism related to amelogenesis.

抄録全体を表示

 A selachian fossil tooth is discovered from the Eocene Hiwada-toge Formation in Kuma Town, Shikoku. This specimen is identified as Odontaspididae gen. et sp. indet. The first discovery of this taxon from Kuma area has important meaning to elucidate the temporal and spatial distribution of selachian fossils in Southwest Japan.
 Living selachians of Odontaspididae commonly inhabit in open sea, where warm current flows. The discovery of this specimen also indicates that Kuma area in the Eocene did not have inlet palaeogeography, but faced to open sea.

抄録全体を表示