The Paradoxides puzzle resolved: the appearance of the oldest paradoxidines and its bearing on the Cambrian Series 3 lower boundary

Abstract

The Moroccan Atlas ranges provide sections that help reconstruct the earliest evolution of Paradoxides s.l. A fine-scale analysis of the basal part of the Jbel Wawrmast Formation in the eastern Anti-Atlas and comparisons with other sections in southern Morocco not only shows the abrupt appearance of Acadoparadoxides in nearly monofacial successions, but also illustrates a rapid diversification of the genus. This remarkable evolution of the clade includes material that can be assigned provisionally to the frequently described species Acadoparadoxides mureroensis (Sdzuy, 1958), to A. nobilis (Geyer, 1998) and also to the new species A. pampalius, A. levisettii and A. ovatopyge, of which A. pampalius can be shown to be the oldest described species of Paradoxides s.l. presently known. A fine-scale biostratigraphic and depositional development analysis permits a precise evaluation of suggested correlations within West Gondwana and into other Cambrian continents, and shows that attempts at precise correlations based on Acadoparadoxides species, and particularly A. mureroensis as a key taxon for global correlation, suffer from deficiencies that become obvious. In addition, the often subtle differences between species of the A. mureroensis clade illustrate that a confident identification of these species is only possible for well-preserved and largely undistorted specimens. Thus, many reports of A. mureroensis may be based, in part, on unfavourably preserved specimens of other species. The concept of a fairly variable species and even the idea of a dimorphism seem to have led to problematic identifications. In this context, material from the Taurus Mountains, southern Turkey, identified as A. mureroensis is identified herein as Acadoparadoxides deani n. sp. Paradoxides s.l. species appear to have been quite provincial in their palaeogeographic distribution, and an analysis of early appearing species shows that A. harlani (Green, 1834) was restricted to the Avalonia palaeocontinent, is incorrectly reported from West Gondwana and cannot be used as a basis for lower Series 3 correlation or chronostratigraphy. Finally, the so-called Valdemiedes Event described from the Iberian Chains in Spain obviously is a regional feature based on the abrupt appearance of an early, but not the earliest, Series 3 trilobite assemblage above a barren interval. This “event” appears to be a local stratigraphic artefact and does not reflect regional West Gondwanan or global geological history.