The unexpected occurrence of enigmatic ‘percevalicrinids’ (Echinodermata, Crinoidea) in the Lower Jurassic strata of North Africa — Implications for their stratigraphic and palaeogeographic distribution and discussion on their belonging to the subfamily Balanocrininae

Abstract

The marl and limestone alternations of the Lower Jurassic Ain Ouarka and Ain Rhezala formations (Pliensbachian–Toarcian) in the western Saharan Atlas, Northwest Algeria, yield a diverse micro- and macrofauna, including moderately numerous crinoids, which are represented by remains of isocrinids, i.e., Balanocrinus ticinensis Hess and columnals of the genus Percevalicrinus. So far, the latter genus has been observed from the Upper Jurassic–Lower Cretaceous strata of Eurasia, North America, and the African continent. Thus, the present find is the oldest record of this crinoid genus, and the second one from the southern Tethyan margin. In this paper, it is shown that Percevalicrinus, which is traditionally regarded as a representative of the subfamily Balanocrininae, displays several features of the subfamily Isocrininae. The crinoid assemblage and associated facies and invertebrate fauna are typical of a low-energy deep outer shelf/ramp (below the storm wave-base) setting.