Obruchevella and other microfossils in the Burgess Shale: preservation and affinity

Abstract

Charles D. Walcott's thin sections of the Middle Cambrian Burgess Shale of British Columbia, Canada, have yielded many specimens of the helically coiled microfossil Obruchevella delicata, as well as fragments of the cyanobacteria Marpolia and Morania, sphaeromorph acritarchs, and sclerites of the enigmatic metazoan Wiwaxia. Obruchevella of the Burgess Shale displays a spectrum of preservation styles ranging from tangled masses to well-developed helixes. All Obruchevella specimens are preserved in three dimensions, which suggests original skeletalization or early post-mortem mineralization of the organism. Morphologic analysis of Obruchevella supports an affinity with modern helical cyanobacteria. Study of all reported occurrences of Obruchevella indicates that: 1) the genus has been overly split into seventeen species; 2) no correlation between size and age of Obruchevella exists; and 3) most Obruchevella specimens are tightly coiled and have helix diameters four to six times their filament diameters.