Article: The problematical Precambrian fossil Chuaria
Chuaria circularis from the late Precambrian of the Grand Canyon was regarded by Walcott as a primitive brachiopod. It has subsequently been referred to as an alga, a chitinous foraminiferid, a gastropod, a hyo-lithid operculum, a trilobite egg, and an acritarch. It is here suggested that Chuaria is a compressed, unusually large planktonic organism (generally 2 to 5 mm diameter). Chuaria wimani, Fermoria, and unnamed material from Canada, Sweden, France, Siberia, India, Iran, and Australia show no systematic differences from C. circularis and are considered synonymous. Chuaria is compared with Leiosphaeridia and classified with this as an sphaeromorphid acritarch. All recorded occurrences of Chuaria are in late Precambrian strata, less than 1000 m.y. old: it may be regarded as a new stratigraphic index fossil.