THE PROBLEM OF THE ORIGIN OF THE EARLY CAMBRIAN FAUNA

Abstract

Review of reported occurrences of Precambrian fossils fails to reveal substantial evidence of metazoan life other than the impressions of soft-bodied organisms of the Ediacaria fauna (S. Australia) and the similar fossils at Charnwood Forest (England) and in the Nama Series of Southwest Africa. Skeletal organisms appear gradually in the Early Cambrian, represented first by the archeocyathids, later by trilobites, but the earliest forms occur at only a few points throughout the world. Many explanations for the development of hard parts based on physical, chemical or biological factors fail of inconsistency with important facts, and all assume the sudden appearance of a diversified skeletal fauna. The local appearance of the few earliest forms indicates that at first they were confined to a narrow range of environments from which they spread as did terrestrial animals later in the Devonian. That such complex animals as trilobites were among the earliest skeletal forms has remained puzzling. The evolution of Proterozoic annelid worms toward trilobites is now confirmed by the discovery of Spriggina floundersi Glaessner in the Ediacaria fauna with its horseshoe- shaped head. R. B. Neuman