Abstract

A lineage of latest Jurassic-Early Cretaceous dinoflagellate cysts possessing arcuate process clusters from Madagascar is described. The lineage has helped to reveal the true identity of a group of skolochorate dinoflagellate cysts, bearing numerous long processes and process clusters, which have been reported as species of Systematophora. The revelation is that that group does not belong to Systematophora, but affiliates with the Madagascan lineage. A new genus, Palaecysta, is proposed. Seven new species: P. integra (type species), P. crispabaculata, P. foveoreticulata, P. melakyensis, P. morondavaensis, P. pectita and P. virgae; eight new subspecies: P. integra subsp. digitata, P. integra subsp. mahajangaensis, P. crispabaculata subsp. delicata, P. foveoreticulata subsp. madagascarensis, P. palmula subsp. ankamotraensis, P. pectita subsp. merinai, P. virgae subsp. externa and P. virgae subsp. lanceolata; and three new combinations: P. complicata (Neale & Sarjeant, 1962), P. palmula (Davey, 1982) and P. silyba (Davey, 1979a) are described. Palaecysta shares some morphological features with Systematophora, including being skolochorate, having intra- to penitabular features, and having sexiform paratabulation and an apical archeopyle. It differs in having arcuate process clusters and two unlinked isolated paracingular processes in each paracingular paraplate, as opposed to nearly penitabular, annulate process clusters and two linked (by a low basal ridge) paracingular processes in each paracingular paraplate in the latter genus. Palaecysta occurred globally from the Tithonian to the Hauterivian. Its rapid evolution provides useful timelines for biostratigraphy; six assemblage zones are established. The zonation is compared with that from neighbouring regions in Australia and Papua New Guinea. The morphological differences and similarities between Palaecysta and the related genera, Systematophora, Kilwacysta and Amphorulacysta gen. nov., are discussed. The significance of the arcuate dinoflagellate cyst group and the interrelationship amongst their member genera, reflected in the geological record, are commented upon. The genus Amphorula is emended.

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