New Siluro-Devonian Anomalocystitids (Echinodermata, Stylophora) from Bolivia and Canada, and a Reevaluation of Skeletal Homologies in Mitrates

Two new mitrate stylophorans are described from the upper part of Santa Rosa Formation (Lochkovian) in Central Subandean Zone Bolivia and Jupiter (Cybèle Member, late Llandovery) Anticosti Island (Canada). Both identified as allanicytidiine anomalocystitids. The Bolivian mitrate, Perikefalea racheboeufi gen. sp. nov. is characterized by a strongly reduced number plates (five) on its thecal surface strong spike posterior median marginal. morphology P. suggests relatively affinities with Occultocystis, Lower Devonian Talacasto Argentina. Although incompletely preserved, Perikefalea? cybeleae nov., represents first stylophoran Silurian North America report post-Ordovician Allanicytidiinae outside (peri) Gondwanan regions. Skeletal homologies mitrates (marginals, infracentrals, spines, adorals, supracentrals) reevaluated, so to describe plate pattern Perikefalea. This revision was prompted fossil evidence Furongian–Tremadocian interval suggesting that (1) derive “Phyllocystis” jingxiensis-like cornutes wide marginals, posteriorly open marginal frame (loss M5 $${\text{M}}_{5}^{'}$$ ), zygal central position, confluent, sutured M3 G; (2) anomalocystitids Mitrocystites-like mitrocystitidans modification two marginals (digital glossal) into spines. distinct terminologies tentatively proposed for supracentrals Anomalocystitinae, because highly standardized patterns their Siluro-Devonian representatives were possibly acquired independently clades.