三葉虫 : 研究の総説および多様性の変遷

概要

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This paper reviews researches on trilobites and history of trilobite diversity under the Paleozoic environment. First, the studies on exoskeletal morphology, its chemical compositions and internal organs are reviewed. Second, a systematic outline of classification on the Trilobita and its bearing taxonomic problems such as these of agnostids and naraoids are discussed based on previous studies focused into the aspect of functional morphology. The life history of trilobites are divided into three major periods of the initial (early Cambrian), radiative (Cambrian to Ordovician) and declining stages (Silulian to Permian), respectively. Dominated carbonate ramp-settings under the condition of sea-level fluctuation are favored to be one of the most important factors that influenced the history of the morphological and the taxonomic diversity in the initial stage. Increased morphological diversity occurred in the radiative stage, corresponding to the period of widely expanded carbonate depositional settings, especially of reefal facies. In case of the declined stage, sea-level lowering during the mid Silurian to the earliest Devonian and the late Devonian extinction event is favored as the main factors to explain the trend of the declined and low morphological diversity. An additional factor to this may be the switch of the aragonite/calcite sea water which happened in the middle Carboniferous.
日本古生物学会の論文
2002-09-20