古盘虫类有孔虫是维宪早期到谢尔普霍夫早期最有用的生物地层标志微体化石之一, 广泛分布于正常浅海底栖环境。古盘虫超科里的平古盘虫亚科从早维宪中期开始出现, 具有最原始的壳壁结构。它将古盘虫类与其祖先假砂盘虫类联系起来。平古盘虫亚科壳壁主要是黑色微粒状。透明放射层局限在脐部或延伸覆盖到内部壳圈的壳缘。平古盘虫从何而来? 即古盘虫类的祖先问题, 一直存在争议。本文通过研究华南马栏边剖面石磴子组连续演化的Lapparentidiscus和Viseidiscus, 证实了Lapparentidiscus是古盘虫类的祖先, 早期演化序列为 Lapparentidiscus talasicus–Viseidiscus eospirillinoides–Viseidiscus monstratus, 古盘虫类的透明放射层是以替代而非填充的形式出现的, 透明放射层逐渐替代黑色微粒层, 并从脐部逐步扩展到壳缘。
Archaediscacean foraminifers are perhaps one of the most useful biostratigraphic marker microfossils from the early Visean to early Serpukhovian. They are widespread in normal marine, benthic, shallow-shelf carbonate environments. The subfamily Planoarchaediscinae of the superfamily Archaediscacea appeared in the middle early Visean. The wall structure of the planoarchaediscins is the most primitive in this superfamily, which provides an evolutionary link between the Archaediscidae and the ancestral pseudoammodiscids. The wall of the archaediscaceans is predominantly dark and microgranular. The hyaline-radial layer is either limited to the umbilical area, or it forms a thin covering over the sides, or sometimes it covers the periphery of the interior volutions. Regarding the ancestor of the archaediscids, this topic is still open to debate. This study focuses on the specimens of Lapparentidiscus and Viseidiscus with continuous stratigraphic appearances from the Shidengzi Formation at the Malanbian section in South China. The result suggests that Lapparentidiscus is a unique pseudoamrnodiscid that gives rise to the archaediscids. The evolution trend of primitive archaedis cacean foraminifers is: Lapparentidiscus talasicus–Viseidiscus eospirillinoides–Viseidiscus monstratus. The hyalin-radial layer of the archaediscids appears as a replacement instead of a filling. It replaces the dark, microgranular layer gradually, and extends from the umbilical area to the sides.