Latest early to early Middle Devonian trilobites from theErbenochileBed, Jbel Issoumour, Southeastern Morocco

Abstract

A bed on Jbel Issoumour, near Alnif in southeastern Morocco, contains numerous complete trilobites. The bed is located stratigraphically at the base of the El Otfal Formation, immediately above a cliff-forming resistant unit known to local trilobite miners as the ‘grand calcaire’, and is latest Emsian or early Eifelian in age. The fauna exhibits an alpha trilobite diversity of at least eight species, includingErbenochile issoumourensisn. sp.,Acanthopyge (Lobopyge) bassein. sp., andWalliserops lindoein. sp. The absence of lateral palpebral extensions inE. issoumourensisbut their presence in the type species ofErbenochile, E. erbeni, when considered with other differences in the exceptionally large eyes of both species, supports the hypothesis that these palpebral structures functioned as eyeshades inE. erbenibut not inE. issoumourensis. Walliserops lindoeihas a short, stout haft at the base of the trident anterior cephalic projection, which is the most characteristic feature ofWalliserops.This projection inWalliseropsprimarily functioned as a deterrent to predators.