| Research Abstract |
In the Japanese Carboniferous, the following archaediscacean genera are recognized : Viseidiscus, Planoarchaediscus, Archaediscus, Paraarchaediscus, Planospirodiscus, Neoarchaediscus, and Asteroarchaediscus. Archaediscacean faunal changes have been observed at two horizons close to the V3b/V3c and Mid-Carboniferous boundaries. Another faunal change among aechaediscaceans is presumed at the Middle/Upper Visean boundary according to the data from central Iran and several references. The first aechaediscacean fauna which was flourished during the Early and Middle Visean includes the subfamilies planoarchaediscinae and kasachstanodiscinae such as Viseidiscus, Planoarchaediscus, Glomodiscus, and Uralodiscus ; the second one observed in the Upper Visean is composed mainly of Archaediscus and Paraarchaediscus as well as several earlier archaediscascan genera mentioned above ; the third one thriving in the latest Visean and Serpukhovian consists of Neoarchaediscus and Asteroarchaediscus togeth
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er with Paraarchaediscus, Archaediscus, and Planospirodiscus. In Bashkirian and Moscovian time, few archaediscaceans belonging to Archaediscus, Neoarchaediscus, Asteroarchaediscus, and others were observed.
Most of the archaedicacean genera were cosmopolitan during Visean and early Serpukhovian time. In late Serpulhovian and later, some genera such as Eosigmoilina and Brenckleina having sigmoidal coiling tend to have paleobiogeographically restricted distribution. These genera are very rare in the Eastem Tethys and Panthalassa provinces (no representative of these genera has been reported in the Japanese Carboniferous). Moreover, archaediscacean occurrence becomes sparse in Bashkirian and later. During that time, their distribution tend to be restricted in and around the Russian Platform. These are caused by the reduction and closure of the Circum-equatrial Seaway between Laurasia and Gondwana Continents occurred. in the late Serpukhovian time (formation of the Pangea), which enabled free interchange among the shallow-marine tropical and subtropical faunas in the equatrial zone. It has resulted in controlling the distribution and migration of the shallow-marine, equatrial faunas, and in increasing their provincialism. Less
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