A critical interval in blastoid evolution: the respiratory transition and palaeogeographic dispersion of the spiraculate blastoids in the Devonian

Abstract

Blastoids underwent a revolution in respiration in the Devonian. Emsian blastoid faunas were dominated by fissiculates such as Pentremitidea, giving rise to a transitional spiraculate, Conuloblastus. Hyperoblastus and a mosaic of spiraculates followed; they featured a more advanced respiratory system and were dominant until the Permian. This diversification occurred just prior to or during the Stony Point and Kačák Events, major ecological disruptions of marine ecosystems. Most new spiraculate blastoids were endemic and short lived, but Hyperoblastus survived the major extinction events, lasting into the Famennian. Material from Germany, Spain and North America enables us to trace the diversification of the spiraculates during the Devonian. We erect the new family Conuloblastidae, including Hreggoblastus differentialis gen. et sp. nov.; also Altusoblastus (type species Pentatrematites eifeliensis) with new species A. eremitus, A. palliolatus, A. sp. 1 and A. sp. 2 in the Hyperoblastidae. Pentremitidea roemeri and Hyperoblastus schultzei are assigned to Altusoblastus. Hyperoblastus batheri is declared the type species of Absensoblastus gen. nov.; H. ludwigi sp. nov. is assigned to Hyperoblastus. Pentahedronoblastus gen. nov. (type species P. giesdorfensis sp. nov.) is described. The fissiculate nymphaeoblastid genus Pentremitella (including P. osoleae and ?P. sp. 1) is redescibed. We recognize the eleutherozoic Freisoblastus gen. nov. (type species F. hemisphaericus sp. nov.), Dissimiloblastus gen. nov. (type species D. inequalis sp. nov.) and non‐eleutherozoic Lotusoblastus gen. nov. (type species Pentremitidea medusa) (order and family incertae sedis). We recognize 13 American species of Hyperoblastus.