Paleobiogeographic implications of the earliest echinoderms from western Gondwana

Abstract

Since their first appearance in the fossil record (Cambrian Stage 3, ~520 Ma), echinoderms were already relatively diverse (classes Edrioasteroidea, Eocrinoidea, Helicoplacoidea) and cosmopolitan. Herein, we describe the gogiid Atlaseocrinus new genus—the oldest echinoderm known so far from the African continent (Issafen Formation, Cambrian Series 2, Stage 3; Morocco). The discovery of the oldest articulated specimens from the Iberian Chains (northeastern Spain) clarifies the systematic position of ‘ Rhopalocystis ’ mesonesensis (Clausen, 2004), which is assigned to the new genus Atlaseocrinus. Atlaseocrinus issafenensis new genus new species has a weakly differentiated stem composed of small, irregularly arranged circular plates. The theca is made of a mosaic of irregularly polygonal plates in five regular circlets, each ornamented with fine granulation and numerous respiratory structures (epispires). The aboral end consists of a single basal plate, which is a trait unique among gogiids. The brachioles comprise two series of alternating floor plates and two series of alternating cover plates. These long appendages branch as bundles of generally three from elevated spouts around the oral frame. Atlaseocrinus mesonesensis new combination from Spain, is included in the new genus based on a single cup-shaped basal plate. Its basal plate has a single through-going canal leading from theca to stem.

UUID: http://zoobank.org/c86c40de-8733-4cfa-b1e3-1593a409f6b5