Exotic trilobites from the Lower–Middle Cambrian boundary interval in Morocco and their bearing on the Cambrian Series 3 lower boundary

Abstract

The Moroccan Atlas ranges provide sections which not only permit fine-scale biostratigraphic analysis of the basal part of the Middle Cambrian by means of typical West Gondwanan faunal elements, but also include exotic trilobites well known from other Cambrian continents or at least extremely rare in West Gondwana. Such trilobites often permit intercontinental correlation that significantly improves the framework for the traditional Lower–Middle Cambrian boundary interval and leads to a fairly robust correlation table. Other “exotic” trilobites are rare findings of new taxa with mosaic patterns of morphological characters, which therefore remain problematic in consideration of their systematic position. This case study illustrates and (re)describes the trilobites Granularaspis bommeli n. sp., Shergoldiella vincenti Geyer, Palaeoworld 15: 348–359, 2006, Onchocephalites permingeati (Termier and Termier, Paleontologie marocaine. Tome 2. Invertebres de l'Ere primaire. Fasc. 4: Annelides, Arthropodes, Echinodermes, Conularides et Graptolithes. Notes et Memoirs de la Service geologique du Maroc 79, and Coll. Actualites scientifiques vol 1095 Hermann & Cie, Paris, pp 282, 1950), Eoptychoparia tafilaltensis n. sp., Oreisator tichkaensis Geyer and Malinky, J Paleontol 71(4): 620–637, 1997 and Cambroproteus lemdadensis n. gen., n. sp. from the Moroccan Atlas ranges. These species partly belong to genera previously known from outside West Gondwana only, and all of them provide new and unexpected clues for faunistic relationships from West Gondwana into other Cambrian continents and distinctly supplement the picture of the organismic diversity for the basal Middle Cambrian in the region.