Journal of Systematic Palaeontology, Vol. 9, Issue 3, September 2011, 425–454 Ordovician edrioasteroids from Morocco: faunal exchanges across the Rheic Ocean Colin D. Sumrall a∗ and Samuel Zamora b a Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA; b ´ Area y Museo de Paleontolog´ ıa-IUCA, Departamento de Ciencias de la Tierra, Universidad de Zaragoza, E-500009, Zaragoza, Spain (Received 9 November 2009; accepted 21 May 2010; printed 15 September 2011) A new edrioasteroid fauna from the Ordovician of Morocco, North Africa includes eight new isorophid species placed in six genera of which three are new. A phylogenetic analysis of Moroccan genera and other taxa places these new edrioasteroids into a phylogenetic framework. Pyrgocystidae is redefined to include plesiomorphic isorophids with hood plates underlying the cover plates. New pyrgocystid taxa include Streptaster nodosus sp. nov., Belochthus? chauveli sp. nov., Argodiscus espilezorum sp. nov. and Moroccopyrgus matacarros gen. et sp. nov. Isorophinid taxa include Isorophus africanus sp. nov., Isorophusella gutii sp. nov., Euryeschatia reboulorum gen. et sp. nov. and the morphological aberrant Anedriophus moroccoensis gen. et sp. nov. These taxa are attached either epibiotically on conulariids or echinosphaeritid rhombiferans, or encrust large bioclasts such as cephalopods and trilobites in a siliciclastic environment that is otherwise devoid of suitable hard substrates. The presence of close relatives of North American taxa in this Perigondwanan section indicates a high degree of communication between North America and North Africa in Ordovician time. Also described are two species of an unusual eocrinoid? Hexedriocystis gen. nov., the type species H . inexpectatus sp. nov. and H. mimus sp. nov., that is a close mimic of isorophid taxa. Keywords: Echinodermata; palaeobiogeography; Edrioasteroidea; Perigondwana; Ordovician; Palaeozoic Introduction Isorophid edrioasteroids are a clade of small echinoderms that are an uncommon element in Palaeozoic faunas world- wide. These organisms are sessile encrusters and are char- acterized by having a globular to discoidal theca with five straight to curved ambulacra that lack accessory feed- ing appendages such as brachioles or arms. Most reports of Ordovician edrioasteroids are of North American taxa (Bassler 1935, 1936; Bell 1976b; Guensburg 1988; Guens- burg & Sprinkle 1994). Ordovician reports from outside North America are few and scattered (Barrande 1887; Prokop 1965; Chauvel 1966, 1978; Plass & Prokop 1979). Furthermore, scattered reports of edrioasteroids outside North America and Europe at other times in Earth history include only Australia (Holloway & Jell 1983; Jell et al. 1985; Smith & Jell 1990) and Siberia (Arendt 1983; Sumrall 2009) and a few other species that have yet to be described from the Middle Cambrian of China (Zhao et al. 2010) and the Silurian of Argentina, South America (Sumrall et al. 2008). Here we describe a series of edrioasteroids recently discovered in the Ordovician of Morocco, North Africa. These eight new taxa include two species from the Arenig Upper Fezouata Formation, two species from the lower- most Caradoc Izegguirene Formation, and four species ∗ Corresponding author. Email: csumrall@utk.edu from the Caradoc–Ashgill Lower Ktaoua–Upper Tiouririne formations. In addition, a review of specimens previously described by Chauvel (1966, 1978) is presented. Also described are two species of the unusual edrioasteroid-like eocrinoid? Hexedriocystis gen. nov. from the Izegguirene and Tiouririne formations. A phylogenetic analysis of these taxa was performed to place the Moroccan edrioasteroid fauna into an evolu- tionary framework. This analysis shows that four of the edrioasteroid taxa are pyrgocystids and the remaining four are isorophids. Four of the genera – Streptaster Hall, Belochthus Bell, Isorophus Foerste and Isorophusella Bassler – show close affinities with North America. Three taxa – Argodiscus Prokop, Isorophusella Bassler and Euryeschatia gen. nov. – show affinities with taxa from Perigondwannan basins in Europe. This suggests an unusu- ally strong connection in the Upper Ordovician between edrioasteroid faunas from North America and Morocco. Previous investigations In recent years, echinoderm faunas from the Ordovi- cian of Morocco have been found to be richly diverse, bearing numerous echinoderm clades: homalozoans, asterozoans, blastozoans, crinoids and edrioastreroids ISSN 1477-2019 print / 1478-0941 online Copyright C  2011 The Natural History Museum DOI: 10.1080/14772019.2010.499137 http://www.informaworld.com Downloaded by [University of Tennessee, Knoxville] at 05:48 13 September 2011