1Institute of Paleontology, Hebei Geo University, Shijiazhuang 050031, Hebei, China
2Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China.
3University of Chinese Academy of Sciences, Beijing 100049, China.
4Natural Resources Monitoring Institute of Henan Province.
*Corresponding author: Jianghx@hgu.edu.cn.
Abstract
The oldest known calcified green algae are the dasycladalean Vermiporella from the Middle Ordovician of North American and Scotland. Though several dasycladalean-like fossils were reported from the Cambrian, their affinity of green algae is not confirmed. Here we reported abundant small calcified fossils from the 520 Ma old dolostones of early Cambrian stage 3 in the Tarim Basin, NW China, which possess all critical characteristics of typical calcified dasycladaleans, such as a central cavity, numerous lateral pores and a microstructure of granular calcite. They are similar to Vermiporella in morphology and size, and to the extant calcified dasycladalean Bornetella in growth form, with a subspherical, mushroom-like, rod-shaped, or clavate thallus, and which should be assigned to a new genus, Tarimporella gen. nov. Discovery of these fossils reveal the morphology and internal structures of the ancestral calcified green algae, and represent an important evolutionary event following the rise and fall of small shelly fossils in the early time of the Cambrian.