The oldest African echinoderms (Morocco): Morphology and implications for the diversification of blastozoans in the early Cambrian - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2023

The oldest African echinoderms (Morocco): Morphology and implications for the diversification of blastozoans in the early Cambrian

Martina Nohejlová
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Samuel Zamora
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Résumé

Since their first appearance in the fossil record (Cambrian Stage 3, ~520 Ma ago), echinoderms were already relatively diverse (classes Edrioasteroidea, Eocrinoidea, Helicoplacoidea, and Lepidocystoidea) and cosmopolitan. This suggests a possible earlier origin of the phylum, although no evidence for this has been found due to the absence of Lagerstätten able to preserve non-mineralized ancestral forms. The major diversification of echinoderms during the Cambrian and Ordovician (about twenty classes, so four times the number of extant classes) renders particularly difficult the identification of homologous structures and the construction of a phylogeny encompassing the whole phylum. The goal of this study is to clarify whether feeding appendages of blastozoans (brachioles) and crinoids (arms) are homologous (or not) and thus if those two groups belong (or not) to a same clade Pelmatozoa. In this context, the gogiid genus Alanisicystis -the oldest echinoderm known so far from the African continent, situated in Western Gondwana- is of particular interest. Its morphology was analyzed based on abundant and remarkably preserved specimens from the Issafen Formation (Cambrian Series 2, Stage 3; Morocco). This eocrinoid has a short stem composed of small, irregularly arranged circular plates. The theca is made of a mosaic of irregularly polygonal plates, ornamented with a fine granulation and numerous respiratory structures (epispires). Its aboral end consists of a single basal plate. The brachioles consist of two series of alternating flooring plates and two series of alternating cover plates. Those long appendages branch from the adoral end of the theca, at the edges of the oral frame
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Dates et versions

hal-04271130 , version 1 (05-11-2023)

Identifiants

  • HAL Id : hal-04271130 , version 1

Citer

Christophe Dupichaud, Bertrand Lefebvre, Martina Nohejlová, Samuel Zamora. The oldest African echinoderms (Morocco): Morphology and implications for the diversification of blastozoans in the early Cambrian. 11th European Conference on Echinoderms, Bertrand Lefebvre; Thomas Saucède, Oct 2023, Villeurbanne, France. ⟨hal-04271130⟩
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