[M-IS13] 遠洋域の進化

[MIS13-07] ジュラ紀中世のStriatojaponocapsaおよび白亜紀中期のTurbocapsula属の系統進化と信頼性の高い放散虫生層序区分

*松岡 篤¹、Li Xin² (1.新潟大学理学部地質科学科、2.新潟大学大学院自然科学研究科)

キーワード：放散虫、系統進化、生層序区分

The four-segmented Stichocapsa tegiminis Yao group gave rise to three-segmented Striatojaponocapsa plicarum (Yao). The evolutionary first appearance biohorizon defines the base of the Striatojaponocapsa plicarum Zone of Bajocian-early Bathonian age. In turn, Striatojaponocapsa plicarum (Yao) evolved into Striatojaponocapsa conexa (Matsuoka) through Striatojaponocapsa synconexa O’Dogerty, Gorican and Dumitrica. The evolutionary first appearance biohorizon of Striatojaponocapsa conexa defines the base of Striatojaponocapsa conexa Zone of late Bathonian-early Callovian age. This is a well-known evolutionary lineage of Middle Jurassic radiolarians and contributes to offer a reliable chronological framework. An evolutionary trend similar to the Striatojaponocapsa lineage is recognized in middle Cretaceous radiolarians belonging to the genus Turbocapsula. Four-segmented forms of Turbocapsula evolved into three-segmented Turbocapsula figitiva O’Dogerty by reducing segment number. Turbocapsula figitiva gave rise to Turbocapsula costata (Wu) by acquiring widely-spaced costae. This speciation is characterized by cladogenesis. The Turbocapsula lineage has a potential to produce a reliable radiolarian zonal scheme for the middle Cretaceous (Barremian-Aptian).