The earliest Foraminifera from southern Shaanxi, China

Vase-shaped microfossils (VSMs) described herein mainly occur as isolated individuals in thin bedded siltstone and silty carbonate of the Gaojiashan Member of the upper Ediacaran Dengying Formation (ca. 551–541 Ma). Although these fossils are abundant, chained tests or other types of colonial aggregates have not been observed. Specimens in the siltstones can easily be isolated from the host rocks by ultrasonic vibrators. Compared with the co-occurring fossils Gaojiashania and Conotubus , VSMs are rarely pyritized, yet they are always three-dimensionally persevered with little deformation, suggesting that their tests were sturdy and possibly mineralized. Petrological observation and elemental mapping reveal two types of tests that are respectively calcareous and siliceous in composition. Calcareous tests typically consist of two to three crypto-crystal laminae, somewhat resembling bilamellar walls of foraminifers. Siliceous tests consist of fine-grained particles agglutinated with siliceous cement, similar to agglutinated walls of foraminifers. The Gaojiashan VSMs are broadly similar, at least in gross morphology, to the testate amoebae-like VSMs, but their relative large sizes (600–2400 μm) and possibly mineralized (rather than organic) tests argue against this comparison. They also show some similarities to other protozoans, especially tintinnids. However, tintinnids have robust pesudochitinous loricae consisting of both secreted and agglutinated materials. Moreover, tintinnid loricae differ in shape from the Gaojiashan VSM tests in having a constricted aboral end (sometimes with a caudal appendix) and a flaring oral opening. If the Gaojiashan VSMs are indeed related to foraminifers, they indicate that foraminifers were important players in late Ediacaran communities.