The Ordovician cornute Flabellicystis rushtoni n. gen. n. sp. (Stylophora, Echinodermata) and its phylogenetic position within the group Cornuta

Abstract

The new Tremadoc cornute,Flabellicystis rushtoni n. gen. n. sp., from the Shineton Shale Formation of Shropshire is described and reconstructed. The description is based on three articulated individuals preserved as moulds. The oldest cornutes are Middle Cambrian in age but only few species are known from sediments older than Arenig; the description of the new cornute is therefore a significant contribution to our knowledge of the early diversity and evolution of the group. BecauseFlabellicystis rushtoni is the second cornute described from Tremadoc sediments, it constitutes as well an important link between the Cambrian and the Arenig forms. A new cladistic analysis of the group Cornuta placesFlabellicystis between the Cambrian speciesPonticulocarpus robisoni and the Arenig genusChauvelicystis. The three genera share a similar basic design, almost identical marginal plating, a flat lower surface and an expanded, fan-like plate surrounding the anal lobe.