The Burgess Shale (Middle Cambrian) Fauna

Abstract

The preservation of soft parts in fossils is rare because fossilization usually occurs long after decay has destroyed soft tissues. A notable exception is the soft-bodied fauna from the Middle Cambrian Burgess Shale (about 530 million years old) located near Field in southern British Columbia, where both completely soft-bodied groups (e.g. polychaetes) and the soft parts of creatures with resistant skeletons (e.g. trilobites) are beautifully preserved. In addition, this fauna includes animals with fragile skeletons of thin cuticle that normally do not fossilize. The Burgess Shale fauna is of special impor­ tance because it permits a unique glimpse of the period shortly after the upper Precambrian-lowermost Cambrian radiation of the Metazoa (26). In 1909 Charles Doolittle Walcott (Secretary of the Smithsonian Institu­ tion), returning from a field season, stopped to split open a rock that blocked a trail on the western slopes between Wapta Mountain and Mount Field. The rock contained soft-bodied fossils. The following year Walcott and his two sons located the original stratum: the Burgess Shale. Quarrying contin­ ued for several seasons (1910--l3, 1917), and more than 40,000 specimens were shipped to the Smithsonian Institution (USNM). Subsequent expedi­ tions by Harvard University (MCZ) in 1930 (92, 94), the Geological Survey of Canada (GSC) in 1966 and 1967 (153), and the Royal Ontario Museum (Toronto) in 1975 collected more material. After Walcott's preliminary publications ( l35-l37, l39-146, 148), a much needed reinvestigation was undertaken by the GSC, with H. B. Whittington directing the paleontologi­ cal work.