A remarkable illaenid trilobite from the Middle Ordovician of Morocco

Abstract

Illaenid trilobites were relatively scarce in south-polar peri-Gondwanan areas during the Ordovician, with all their African occurrences restricted to the Middle and Upper Ordovician of Morocco. At a specific level, only the Bohemian form Ectillaenus benignensis (Novák) has been positively identified from the Middle Ordovician of that region. In the present work we add the discovery of the new form Caudillaenus nicolasi gen. et sp. nov., occurring in a single bed of late Darriwilian 2 age within the Taddrist Formation of the Rahiat region (south of Alnif), in the central Moroccan Anti-Atlas. The new genus is characterized by a large and subtriangular pygidium, a cephalon with relatively large eyes, a broad rostral plate with a short upwardly and forwardly turned posterior flange, and a globose hypostome. It shows a spheroidal enrolment type previously unknown in illaenids, with the pygidium protruding beyond the cephalon, and the cephalic margin fitting into a shallow and wide coaptative furrow on the pygidial doublure.