Further observations on the Jurassic dinoflagellate cyst Gonyaulacysta dentata (Raynaud 1978) Lentin & Vozzhennikova 1990 emended Riding 2012

Gonyaulacysta dentata is a large and morphologically distinctive dinoflagellate cyst. It is confined to the Late Callovian to earliest Oxfordian (Peltoceras athleta to Quenstedtoceras mariae zones) interval of the Boreal Realm and the Subboreal Province in the northern hemisphere, and has therefore been interpreted as a cold water species. The holotype of G. dentata is from the Staffin Shale Formation of Staffin Bay, Isle of Skye, northwest Scotland and has been lost. Consequently another well-preserved specimen from the Staffin Shale Formation of the Isle of Skye is proposed as a neotype. The ventral and apical areas of G. dentata are characterised by discontinuous, low, smooth sutural ridges. However, the 5″/6″, 4′/6″ and 4′/1′ sutures on the ventral side of the epicyst are frequently indicated by relatively high denticulate crests. The 2″′/1p suture and the cingular sutures may also be developed on the ventral face. Conversely, the dorsal and lateral sutural crests, except in the apical area, are prominent and denticulate. G. dentata is present in East Greenland. Two specimens were recorded, as Gonyaulacysta eisenackii subsp. oligodentata, from the Late Callovian of Jameson Land. These are probably from the Olympen Formation, and not the Upper Vardekløft Formation as was originally stated. This occurrence is entirely consistent with the Boreal distribution of G. dentata. The range of G. dentata, the Callovian–Oxfordian transition, was characterised by significantly lowered palaeotemperatures. Several other dinoflagellate cyst species are also believed to be cold water taxa, and migrated south from the Boreal Realm into Europe at this time.