Reich et al.—First Ordovician cyclocystoid (Echinodermata) from Gondwana


737


Figure 1. Geographic and geologic setting of eastern Anti-Atlas Mountains, Morocco, showing type locality of our new cyclocystoid close to the village of Battou. (1) Map of Africa. (2) Detailed map of northwest Africa showing position of Anti-Atlas Mountains. (3) Simplified geological map of Morocco with position of the cyclocystoid locality: (a) Precambrian and Paleozoic rocks; (b) Ordovician rocks; (c) post-Paleozoic cover. (4) Detailed geographic map indicating location of the cyclocystoid locality (after Rábano et al., 2014, modified).


Geological setting and stratigraphy


The Ordovician succession is particularly thick and well exposed in the Anti-Atlas Mountains of southern Morocco (Destombes et al., 1985; Fig. 1). It is traditionally subdivided into four main lithostratigraphic units: the Outer Feijas Group; the First Bani Group; the Ktaoua Group; and the Second Bani Group (Choubert, 1942; Choubert and Termier, 1947; Destombes, 1971; Destombes et al., 1985; Marante, 2008). The Outer Feijas Group includes the Lower and Upper


Fezouata formations (Tremadocian–Floian), the Zini Formation (late Floian), and the Tachilla Formation (Darriwilian) (Fig. 2). The Zini Formation corresponds to a diachronistic facies con- sisting of sandstones and massive quartzites, which is laterally equivalent to part of the Upper Fezouata Formation (Destombes, 1962, 1971; Destombes et al., 1985). The Zini Formation is absent in the western Maïder area (Tazzarine-Alnif area), where the cyclocystoids were collected. The three other units belonging to the Outer Feijas Group are characterized by fine-grained sili- ciclastic deposits (shales, siltstones), with some thin sandstone interbeds (Destombes, 1962, 1971; Destombes et al., 1985). In the Zagora area (central Anti-Atlas), the Lower and Upper Fezouata formations have yielded exceptionally preserved Bur- gess Shale-type faunas including anomalocaridids, demosponges, and marrellomorphs (Fezouata Biota; Botting, 2007; Van Roy et al., 2010, 2015; Lefebvre et al., 2016a; Martin et al., 2016). The overlying First Bani Group (Darriwilian–earliest


Sandbian) is the thickest, most constant, and most extensive sandstone group in the Anti-Atlas (Choubert, 1942; Destombes, 1971; Destombes et al., 1985). It is subdivided into five sand- stone units with interbedded shales: the Taddrist, Bou-Zeroual, Guezzart, Ouine-Inirne, and Izegguirene formations (Fig. 2). The biostratigraphy and fossil taxa recovered from the First Bani Group were both thoroughly reviewed by Gutiérrez-Marco


et al. (2003), while its sedimentology and sequential strati- graphy were investigated by Marante (2008). In the eastern Anti-Atlas, the uppermost part of the First Bani Group has yielded exceptionally preserved assemblages comprising cheloniellid arthropods, eldonioids, and palaeoscolecid worms (Tafilalt Biota; Samuelsson et al., 2001; Alessandrello and Bracchi, 2003; Van Roy, 2006; Lefebvre et al., 2008; Gutiérrez- Marco and Garcia-Bellido, 2015). The First Bani Group is conformably overlain by the


Ktaoua Group (Sandbian–Katian), which is predominantly composed of siltstones, with a variable number of interbedded sandstone units (Destombes, 1962, 1971; Destombes et al., 1985). It is traditionally subdivided into the Lower Ktaoua (early Sandbian–early Katian), Upper Tiouririne (middle Katian), and Upper Ktaoua (late Katian) formations (Fig. 2). Several occurrences of exceptional preservation have been reported from various levels of the Ktaoua Group, including fully articulated specimens of machaeridian annelids (Vinther et al., 2008) and dense beds of exquisitely preserved echino- derms (Hunter et al., 2010; Lefebvre et al., 2010). In the Anti-Atlas, the Ordovician succession is topped by


the sandstones of the Second Bani Group (Hirnantian), which is generally subdivided into the Lower and Upper Second Bani formations (Destombes, 1971; Destombes et al., 1985; Loi et al., 2010). The Lower Second Bani Formation corresponds to shallow shelf deposits lying conformably over the underlying Upper Ktaoua Formation (Destombes et al., 1985; Loi et al., 2010). The Upper Second Bani Formation represents fluvio- glacial sandstones filling large subglacial tunnel valleys, more or less deeply excavated through the underlying deposits of the Ktaoua and First Bani groups (Destombes et al., 1985; Le Héron, 2007; Loi et al., 2010). Echinoderm remains were first reported in the Ordovician succession of the Anti-Atlas by Ségaud and Termier (1933),


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