Protaspid and early meraspid growth stages of the eodiscoid trilobitePagetia ocellataJell, and their implications for classification

Abstract

During recent investigations of the Middle Cambrian phosphate deposits south of Duchess in the Burke River Structural Belt, Georgina Basin, western Queensland, large numbers of the early growth stages of trilobites have been recovered by acid etching of samples from the Monastery Creek Phosphorite Member of the Beetle Creek Formation. Among these a late protaspid growth stage is recognised as belonging to Pagetia ocellata Jell 1970, described earlier from the same formation. The morphogenesis of this and the earliest meraspid growth stage are described, and their development compared to that of an associated agnostoid referred to Peronopsis. The differences between eodiscoid and agnostoid trilobites are reviewed in the light of much recently published information. A taxonomic separation of at least ordinal magnitude is advocated. If miomeran arthropods are related to polymeroid trilobites, then the eodiscoids are the closer of the two groups.