Palaecysta gen. nov., the greatest Systematophora imposter no more: introducing a lineage of latest Jurassic to Early Cretaceous (Tithonian-Hauterivian) dinoflagellate cysts from Madagascar

Abstract

A lineage of 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 Madagascar 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 and Sarjeant, 1962), P. palmula (Davey, 1982), and P. silyba (Davey, 1979a) are described. Palaecysta shares some morphological features with Systematophora, including skolochorate cyst, intra- to penitabular paratabulation, and gonyaulacacean, sexiform and apical archeopyle, but differs in having arcuate process clusters and two unlinked isolated paracingular processes in each paracingular paraplate, as oppose 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 other related genera, Systematophora, Kilwacysta, and Amphorulacysta gen. nov., are discussed. The significance of the arcuate dinoflagellate cysts group and the interrelationship amongst their member genera, reflected in the geological record, are commented upon. The genus Amphorula is emended.

Keywords:

• Amphorula
• Amphorulacysta
• arcuate
• biochronostratigraphy
• dinoflagellate
• Hauterivian
• Kilwacysta
• Madagascar
• Palaecysta
• Systematophora
• Tithonian

Acknowledgements

This study is part of the contribution of a research project of ExxonMobil Exploration Company Biostratigraphy Group, to which this author is grateful for all their assistance. The permission to publish this paper granted by ExxonMobil Exploration Company management is appreciated. This author is thankful to Drs. John Backhouse and Daniel Mantle for their extensive and careful review of the manuscript and constructive suggestions.

Notes

Note: conf'd–confirmed ?–inadequate data