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.•

The first Ordovician cyclocystoid (Echinodermata) from Gondwana and its morphology, paleoecology, taphonomy, and paleogeography

“…This report was based on a single specimen, then belonging to the private collection of Laurent Lacombe that is now registered and deposited in the University Lyon 1 collections as UCBL-FSL 712001. However, more precise information obtained in late 2013 from Laurent Lacombe and Patrick Catto (who together collected this specimen and another one, UCBL-FSL 712000, in the mid 2000s) did not confirm this age and geographic origin, but pointed out that the two specimens were indeed collected from the same locality (Battou) and level (Taddrist Formation) described in Rábano et al (2014).…”

“…Unfortunately, original top or bottom of our cyclocystoid concretions from this layer has not been recorded by any of the collectors, perhaps because many concretions were already weathered out and lying on the surface of this sloping outcrop. Rábano et al (2014) suggested that the levels containing fossiliferous concretions belong to the Didymograptus murchisoni graptolite Biozone (Gutiérrez-Marco et al, 2003), which Figure 2. Chronostratigraphical chart for the Ordovician, indicating the level that provided the studied specimens.…”

“…According to Rábano et al (2014, p. 367), the fossiliferous concretions have yielded the trilobites Caudillaenus nicolasi Rábano et al, 2014, Morgatia? rochi (Destombes, 1972, Placoparia (Coplacoparia) n.…”

“…1, 2). This locality was described by Rábano et al (2014), who provided detailed information about the faunal content and age based on the presence of key graptolites and trilobites. In this area, the Taddrist Formation has been excavated predominantly by local collectors and has yielded a rich faunal assemblage preserved in carbonate concretions.…”

“…Alnif, eastern Anti-Atlas Mountains, southeastern Morocco, North Africa (see Rábano et al, 2014;Zamora et al, 2015 Description.-Most specimens nearly circular, holotype very slightly subpentagonal, axially compressed, many specimens slightly convex on one side, nearly flat or slightly concave on the other side. Most of relief in studied molds located in ring of thick marginal ossicles.…”