A New Giant Asaphid Trilobite from the Lower Ordovician of Morocco

Abstract

A giant asaphid trilobite from the Fezouata Formation (Lower Ordovician, Tremadocian) is distinguished by its extraordinary genal spines, which project outwards before curving backwards. Asaphellus stubbsi sp. nov. is in other respects a conservative asaphid. The preservation of giant trilobites in the coarser 'couches' of the Fezouata Formation is discussed, noting the absence of smaller growth stages in the intervening graptolite shales. The majority of examples represent the catastrophic killing of an assemblage of large individuals. The absence of smaller moults is attributed to solution of their calcite exoskeletons prior to their preservation peculiar to high latitude shelf environments close to the Ordovician pole. Two of the specimens are fakes constructed from more than one individual.