Reich et al.—First Ordovician cyclocystoid (Echinodermata) from Gondwana
ranges from the late middle Darriwilian (Dw2) to the early late Darriwilian (Dw3) stage slices of the global chronostratigraphic scale (Gutiérrez-Marco et al., 2008; Bergström et al., 2009). However, the Taddrist Formation also yielded palynomorphs typical of the Laufeldochitina clavata chitinozoan Biozone (Marante, 2008; Videt et al., 2010). The stratigraphic range of this biozone is generally considered to be restricted to the base of the late Darriwilian (Dw3) stage slice (Videt et al., 2010; Gendry et al., 2013). Consequently, both graptolites and chitinozoans provide congruent stratigraphic data, supporting an early late Darriwilian age (base of Dw3) for the cyclocystoid level (Fig. 2). The Taddrist Formation is about 80 meters thick in the
western Maïder area (Tazzarine-Alnif area; Marante, 2008; Destombes, 2006). This unit was interpreted as the regressive part of a fourth-order sequence (Marante, 2008). The regressive trend was deduced from the transition from fine shales to bioturbated siltstones and finally bioturbated fine sandstones at the top of the Taddrist Formation. Sedimentary structures indi- cate the influence of distal storms in an otherwise relatively calm, distal setting, on an almost flat and wide continental shelf. 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. sp., Colpocoryphe sp., Parabarrandia aff. crassa (Barrande, 1872), and an un- determined cheirurid (Eccoptochile? sp.). Other non-trilobite fossils include palynomorphs, mollusks (e.g., a cyrtonellid tergomyan, bivalves such as Praenucula sp., and orthoconic nautiloids), hyolithids (Elegantilites
sp.), echinoderms
(Diploporita and Asterozoa indet.), conulariids (Exoconularia sp.), and rare graptolites (Didymograptus sp.). The sandy shales above and below the fossiliferous trench contain abundant trace fossils such as Teichichnus isp. and Palaeophycus isp. In addition to the new cyclocystoid described herein, a new crinoid species, Iocrinus africanus, was recently described by Zamora et al. (2015). The occurrence of putative remains of cyclocystoids in the
early Sandbian Izegguirène Formation (Late Ordovician) of the eastern Anti-Atlas was mentioned by Lefebvre et al. (2008, 2010, 2013). 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).
Preservation and taphonomy
Most of the known specimens of this new cyclocystoid were preserved in siderite-encrusted (iron carbonate) concretions (Figs. 3.3–3.15, 4, 5) with a fine clastic internal matrix (siltstone?). The concretions probably formed around the
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specimens during early diagenesis because of decay of soft tissues and movement of Fe and CO3 ions through the porous matrix. At least one specimen (Fig. 3.1, 3.2; UCBL-FSL 712001) was found on a slab with similar matrix that may have been a hardground. Both occurrences probably represent repe- ated storm or slump deposits that buried the specimens alive in a clastic seafloor environment that was near storm wave base on a deep shelf in high-latitude Gondwana. Many of our cyclocystoid specimens are slightly to mod-
erately damaged, including injuries that occurred during life, damage from catastrophic events that killed, partly or com- pletely buried, and eventually entombed them in their siderite concretions, or damage that occurred during present-day weathering or when the exposed or dug-up concretions were split open. A few specimens, such as our very large holotype (Fig. 3.1, 3.2), are complete and very well preserved, except for some loss of detail because of weathering or later casting on the inferred top mold surface, and some loss of the outer fringe region on the bottom mold that extends to the edge of its smaller slab. Another paratype is nearly complete but may be upside down in its concretion, which apparently occurred at the time of death. Other nearly complete specimens show small or large stunted areas in their marginal rings (Fig. 4.1, 4.2, 4.6, 4.7), probably from nonlethal injuries or predation during life. Others are missing parts of their ossicle ring, frontal plates, and peripheral fringe from breakage when they were killed, or disarticulated plates are strewn over the adjacent mold surface because the carcass was lying partly exposed on the seafloor. Two paratypes are mostly complete and fairly well preserved but folded over in their concretions, with their top and bottom mold layers nearly superimposed (Figs. 3.5, 3.6, 3.12, 3.13, 4.3–4.5), probably because of high currents or seafloor slumps that tumbled and perhaps broke these folded specimens. Many additional specimens in concretions are poorly preserved or incomplete (e.g., Fig. 3.10, 3.11, 3.14, 3.15). This may have occurred at the time of death, during diagenetic concretion growth, during recent weathering, or when the concretions broke up while being split open and not all the mold pieces were recovered.
Materials and methods
Specimens, repositories, and institutional abbreviations.— About 20 specimens of this new cyclocystoid from the Ordo- vician of SE Morocco are known; this study is based on eight type specimens (and their casts; Fig. 3.1–3.15) now housed at the Collections de Paléontologie, Laboratoire de Géologie, Lyon 1 University, Villeurbanne, France (UCBL-FSL), the Natural History Museum, London, U.K. (NHMUK), the Non-vertebrate Paleontology Laboratory, University of Texas, Austin, USA (NPL), and the Bavarian State Collection of Palaeontology and Geology, Munich, Germany (SNSB-BSPG). These cyclocystoids were collected during several field cam- paigns (NHMUK-EE 15409, 15413, 16220), donated (UCBL- FSL 712000, 712001; NPL 74385, 74386), or purchased (NPL 62451). The materials we have assembled for this study (holo- type, seven paratypes, and additional photographed specimens) are listed with abbreviated stratigraphic locality information.
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