Radiolarian evolution during the Permian and Triassic transition in South and Southwest China

Abstract

This article presents the results of a recent study on the radiolarian faunas spanning the Paleozoic-Mesozoic transition in South and Southwest China. Some radiolarians from the uppermost Changxingian in the area can be compared closely with their Mesozoic counterparts, including Paurinella Kozur & Mostler and Orbiculiforma Pessagno, but their exact identity with these Mesozoic forms cannot be confirmed at present because their internal structures are unknown. The Changxingian Paurinella ? is thought to be the progenitor of the Triassic Oertlispongidae Kozur and Mostler and Intermediellidae Lahm. However, the evolutionary relationship between the Changxingian Orbiculiforma ? and Jurassic Orbiculiforma Pessagno is poorly understood. The survivors in the Lower Triassic of the study area, consisting of at least five genera ( Entactinia Foreman, Entactinosphaera Foreman, Latentifistula Nazarov and Ormiston, Follicucullus Ormiston and Babcock and Hegleria Nazarov and Ormiston) are characterized by wide adaptability to varied ecological habitats. The recovery of the Triassic radiolarian faunas in the area occurred in the early Anisian and is characterized by moderately diverse multicyrtid nassellarians with slender shells and lacking obvious constriction among segments, and by the spumellarian species with round main spines. In the middle and late Anisian, the shells of the multicyrtid nassellarians became strong and had developed constriction between segments; and the spumellarians with both round spines and three-bladed spines were also common. In addition, some possible evolutionary relationships among the Anisian radiolarians in the area are also suggested.