Paleontological studies on the placodermi and chondrichthyan remains from Japan

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1. Taxonomical, morphological and histological studies on the placodermi remains from Japan : The dermal armours which were discovered from the Hukuji Formation (Lower Devonian) in Hukuji, Kmitakara-mura, Gifu Prefecture, central Japan were described as spinal plates of Romundina sp., Acanthothoraci by the morphological and histological studies (Okura and Goto, 1992).2. Studies on the teeth of Mesozoic elasmobranchii : Tooth of Hybodus sp. from the Middle Triassic, Acrodus sp. from the Upper Triassic and Asteracanthus sp. from the Lower Jurassic of Japan were described (Goto et al., 1991).3. Evolutionary study on the form and structure of chondrichthyes : The morpology and histology of teeth in fossil and extant chondrichthyes were investigated. It can be considered that the tooth structure of Chondrichthyes is not dependent on their evolutionary level, but the result of an adaptation to their food habits (Goto, 1991).4. Palaeozoic and Early Mesozoic fish fauna in Japan : Based on the present data, the fossil fishes of the Palaeozoic and Early Mesozoic of Japan are classified into twenty-two genera and thirty-one species, that is, one species of placodermi (Lower Devonian), fifteen species of elasmobranchs (Permian-Jurassic), two species of cochliodonts (Permian), eleven species of petalodonts and two species of osteichthyes (Triassic) (Goto, 1992).5. Origin and evolution of skeletal tissues in vertebrates : The dermal armor (exoskeleton) of primitive agnathians which was formed as a mechanism for removing excess calcium from the blood changed to an organized functional support (endoskeleton) for the body of terrestrial vertebrates (Goto, 1991 ; 1992).