Zamora S et al. (2015), Palaeogeographic implications of a new iocrinid...

ECB-ART-50020

PeerJ 2015 Jan 01;3:e1450. doi: 10.7717/peerj.1450.

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Palaeogeographic implications of a new iocrinid crinoid (Disparida) from the Ordovician (Darriwillian) of Morocco.

Zamora S , Rahman IA , Ausich WI .

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Complete, articulated crinoids from the Ordovician peri-Gondwanan margin are rare. Here, we describe a new species, Iocrinus africanus sp. nov., from the Darriwilian-age Taddrist Formation of Morocco. The anatomy of this species was studied using a combination of traditional palaeontological methods and non-destructive X-ray micro-tomography (micro-CT). This revealed critical features of the column, distal arms, and aboral cup, which were hidden in the surrounding rock and would have been inaccessible without the application of micro-CT. Iocrinus africanus sp. nov. is characterized by the presence of seven to thirteen tertibrachials, three in-line bifurcations per ray, and an anal sac that is predominantly unplated or very lightly plated. Iocrinus is a common genus in North America (Laurentia) and has also been reported from the United Kingdom (Avalonia) and Oman (middle east Gondwana). Together with Merocrinus, it represents one of the few geographically widespread crinoids during the Ordovician and serves to demonstrate that faunal exchanges between Laurentia and Gondwana occurred at this time. This study highlights the advantages of using both conventional and cutting-edge techniques (such as micro-CT) to describe the morphology of new fossil specimens.

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	Figure 1. Chronostratigraphical chart for the Ordovician, indicating the levels that provided the studied specimen.Correlations between stratigraphical units in the Anti-Atlas (after Destombes, Hollard & Willefert, 1985; Gutiérrez-Marco et al., 2003; Villas et al., 2006), the British regional time scale (Fortey et al., 1995), North American graptolite zonal sequences (Webby et al., 2004), Mediterranean regional stages (Gutiérrez-Marco et al., 2003), and global stages are shown. Modified from Sumrall & Zamora (2011). Abbreviations: Kral, Kralodvorian; pars., partial; Tr., Tremadocian.
	Figure 2. Geographical and geological setting of the eastern Anti-Atlas Mountains, Morocco, showing the type locality of the new species (indicated by a star) close to the village of Battou.After Rábano, Gutiérrez-Marco & García-Bellido (2014). (A) Map of Africa. (B) Detailed map of west Africa showing the position of the Anti-Atlas Mountains. (C) Simplified geological map of Morocco with the position of the studied locality; a: Precambrian and Palaeozoic rocks, b: Ordovician rocks, c: post-Palaeozoic cover. (D) Geographic map indicating the position of the studied locality.
	Figure 3. Field photographs showing the Taddrist Formation and the levels yielding fossiliferous concretions.(A) General view of the Taddrist Formation in the studied area. (B) Detail of the trench providing the fossiliferous concretions.
	Figure 4. Iocrinus africanus sp. nov. (MGM 6754) from the Darriwilian (Middle Ordovician) of Morocco.(A), (B) General morphology including the complete crown showing the E-ray (A) and BC-interray (B), the proximal column, and part of the arms. (C) Detail of the cup showing the E-ray. (D) Detail of the cup showing the A-ray. (E) Detail of the cup showing the D-ray. All images are photographs of latex casts of the specimen whitened with ammonium chloride sublimate.
	Figure 5. Iocrinus africanus sp. nov. (MGM 6754) from the Darriwilian (Middle Ordovician) of Morocco.Digital reconstructions of the specimen. (A) General morphology showing the AE-interray. (B) Detail of the theca showing the C-ray. (C) Detail of the cup showing the BC-interray. (D) Detail of the cup showing the D-ray. (E) Detail of the column showing pentastellate shape and holomeric construction. (F) Detail of the proximal arms showing the E-ray. (G) Column in an open coil. Abbreviations: A–E, ambulacra.
	Figure 6. Distribution of the major paleocontinents during the Middle Ordovician, showing the known geographical distribution of Iocrinus and Merocrinus.Locality markers indicate the presence of a taxon on a palaeocontinent; multiple localities are not noted on a single palaeocontinent. Modified from Cocks & Torsvik (2006).

References :

Van Roy, Ordovician faunas of Burgess Shale type. 2010, Pubmed