Late Ordovician solutan echinoderms from the Western Tafilalt, Morocco

Abstract

In the western Tafilalt area, eastern Anti-Atlas (Morocco), solutan echinoderms are a major faunal element of most echinoderm Lagerstätten occurring within the Lower Ktaoua Formation (late Sandbian-early Katian). For the first time, members of the class Soluta are formally described from Morocco and Africa. All solutans from the Lower Ktaoua Formation are identified as Dendrocystites aff. sedgwicki. Three size-related morphotypes, probably corresponding to successive growth stages (‘juvenile’, ‘adult’ and ‘gerontic’), could be distinguished within the abundant and well-preserved material from Morocco. The occurrence of the genus Dendrocystites in the western Tafilalt confirms the strong faunal affinities between Morocco and other regions of the Mediterranean Province (Czech Republic and Spain) in Late Ordovician times. In high palaeolatitude (peri-)Gondwanan areas, Dendrocystites was a gregarious solutan living in shallow, siliciclastic settings at or above storm-wave base.

The Late Ordovician Tafilalt Biota, Anti-Atlas, Morocco: a high-latitude perspective on the GOBE

“…aulacophore in extended position, with slightly ajar cover plates; Lefebvre et al 2022a, b) and also of ophiuroids literally 'frozen in the act' of capturing, and presumably feeding on, young individuals of eocrinoids (Lefebvre et al 2008) Comprising representatives of ten distinct classes (Asteroidea, Coronoidea, Crinoidea, Diploporita, Edrioasteroidea, Eocrinoidea, Ophiuroidea, Rhombifera, Soluta, and Stylophora), the Tafilalt Biota yielded not only one of the best preserved, but also one of the most diverse Late Ordovician echinoderm faunas from the Mediterranean Province. Although their composition varies from locality to locality, possibly reflecting subtle differences in environmental conditions, such as hydrodynamics and bathymetry, starfish beds from the eastern and western Tafilalt yielded comparable Sandbian-early Katian assemblages generally dominated by ophiuroids, solutans and/or stylophorans, with sometimes locally abundant edrioasteroids, eocrinoids and/or rhombiferans, and more occasional occurrences of asteroids, coronoids, diploporites and/or crinoids (Lefebvre et al 2007(Lefebvre et al , 2008(Lefebvre et al , 2010(Lefebvre et al , 2022aNardin 2007;Régnault 2007;Hunter et al 2010;Sumrall & Zamora 2011Nardin & Régnault 2015;Botting 2018;, 2019Nohejlová & Lefebvre 2021). These assemblages display strong palaeobiogeographical affinities with coeval faunas from Bohemia (Czech Republic) and, to a lesser extent, with the Armorican Massif (France) and the Iberian Peninsula (Portugal and Spain).…”

“…9b) occurring in association with the solutan Dendrocystites aff. sedgwicki (Nohejlová & Lefebvre 2021). At Isthlou, the youngest assemblages (mid-Katian, Upper Tiouririne Formation) mark the first appearance of asteroids in the Tafilalt, while also heralding the return of protasterid faunas with affinities to Bohemia (Czech Republic).…”

“…Recent excavations in the locality of Tizi n'Mouri provided articulated specimens of the rare diploporite Asterocystis associated with ophiuroids, the solutan Dendrocystites aff. sedgwicki (Nohejlová & Lefebvre 2021) and the glyptocystitid rhombiferan Homocystites adidiensis .…”

“…Solutans. This small clade includes free-living echinoderms characterized by a moderately flattened theca, a short feeding appendage (brachiole), and a much longer stem-like structure (homoiostele) used for locomotion on soft, siliciclastic substrates (Noailles et al 2014;Nohejlová & Lefebvre 2021).…”

“…Jbel Taklimt, piste de Jorf, Tarafin Signit; Nohejlová & Lefebvre 2021). One locality (Tizi n'Mourghi) yielded impressive accumulations of thousands of fully articulated, current-orientated dendrocystitid solutans (Lefebvre et al 2007(Lefebvre et al , 2010Hunter et al 2010;Nohejlová & Lefebvre 2021).…”