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

Samuel Zamora,Imran A Rahman,William I Ausich

doi:10.7717/peerj.1450

Samuel Zamora, Imran A Rahman + Show 1 more

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https://doi.org/10.7717/peerj.1450

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Abstract

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.

Highlights

Ordovician crinoids from west peri-Gondwana (North Africa and southwestern and central Europe) are relatively rare, with only a few species reported from Spain, France, Italy, Morocco, Portugal, and the Czech Republic (Ubaghs, 1969; Ubaghs, 1983; Prokop & Petr, 1999; Ausich, Gil Cid & Domınguez Alonso, 2002; Ausich, Sa & Gutierrez-Marco, 2007; Correia & Loureiro, 2009; Zamora, Colmenar & Ausich, 2014; Sumrall et al, 2015)
Crinoids from Morocco include an incomplete specimen assigned to Ramseyocrinus sp. by Donovan & Savill (1988) from the Upper Fezouata Formation, which is Floian (Early Ordovician) in age, and several well-preserved complete specimens of Rosfacrinus robustus (Le Menn & Spjeldnaes, 1996), from the Upper Tiouririne Formation (Lefebvre et al, 2007), which is Katian (Late Ordovician)
We report a new species of Iocrinus from the Ordovician of Morocco, thereby extending the range of this genus with certainty to encompass west peri-Gondwana and confirming its cosmopolitan distribution

Summary

INTRODUCTION

Ordovician crinoids from west peri-Gondwana (North Africa and southwestern and central Europe) are relatively rare, with only a few species reported from Spain, France, Italy, Morocco, Portugal, and the Czech Republic (Ubaghs, 1969; Ubaghs, 1983; Prokop & Petr, 1999; Ausich, Gil Cid & Domınguez Alonso, 2002; Ausich, Sa & Gutierrez-Marco, 2007; Correia & Loureiro, 2009; Zamora, Colmenar & Ausich, 2014; Sumrall et al, 2015). The Outer Feijas Shale Group includes the Lower and Upper Fezouta formations (Tremadocian–Floian) and the Tachilla Formation (Darriwilian) (Fig. 1) These units are characterized by siltstones that are rich in graptolites, with some thin sandstone interbeds, and contain exceptionally preserved Burgess Shale-type faunas in places (Van Roy et al, 2010; Van Roy, Briggs & Gaines, 2015; Martin et al, in press). The overlying First Bani Group spans the Darriwilian to Sandbian and is subdivided into five formations (Taddrist, Bou-Zeroual, Guezzart, Ouine-Inirne, and Izegguirene formations) that are comprised of sandstones with interbedded shales This group is the thickest, most constant, and most extensive sandstone group in the Anti-Atlas Mountains (Destombes, Hollard & Willefert, 1985).

A AFRICA

MATERIAL AND METHODS

RESULTS