Observations on the Jurassic dinoflagellate cyst &amp;lt;i&amp;gt;Nannoceratopsis ambonis&amp;lt;/i&amp;gt; Drugg, 1978

J B Riding

doi:10.1144/jm.3.1.75

Abstract

Abstract. The Lower to Middle Jurassic dinoflagellate cyst Nannoceratopsis ambonis Drugg, 1978 is here divided into two species, Nannoceratopsis ambonis Drugg, 1978 emend. nov. and N. dictyambonis sp. nov. on the basis of differing saggital band morphologies. The two species do not appear to intergrade morphologically and have differing stratigraphical ranges, N. ambonis emend. nov. being found from the Upper Pliensbachian (spinatum Zone) to the Upper Bajocian and N. dictyambonis sp. nov. being restricted to the uppermost Toarcian (moorei Subzone: levesquei Zone) – Lower Bajocian (laeviuscula Zone) interval.

Highlights

Drugg (1978) described three species of the Jurassic dinoflagellate cyst genus Nannoceratopsis Deflandre from material collected in Europe - N . ambonis, N .plegas and N . triceras
N . plegas is similar in overall morphology to N . gracilis Alberti, 1961 but has a more elongate dorsal antapical horn which imparts a deep, sickle-shaped concavity to the antapex
N . triceras is a distinctive taxon because it is the only species of Nannoceratopsis known to possess three antapical horns

Summary

INTRODUCTION

Drugg (1978) described three species of the Jurassic dinoflagellate cyst genus Nannoceratopsis Deflandre from material collected in Europe - N . ambonis, N. Gracilis Alberti, 1961 but has a more elongate dorsal antapical horn which imparts a deep, sickle-shaped concavity to the antapex It is a rare species which seems to be confined to the Aalenian of Europe Triceras is a distinctive taxon because it is the only species of Nannoceratopsis known to possess three antapical horns It is never found in large numbers, ye?is persistent from the Lower Toarcian (tenuicostatum Zone) to the Lower Bajocian (laeviuscufa Zone) in England (Riding, 1983; Woollam & Riding, 1983). Gracilis, but differing in having smooth to very finely granulate autophragm and prominently thickened saggital bands, the original description included forms with both solid and reticulate saggital areas Ambonis and it has become clear that the species, as described by Drugg, includes two distinct forms; those with thickened solid saggital bands, and forms with distinctly reticulate thickened saggital areas.

Jurassic dinoflagellate cyst Nannoceratopsis ambonis

DISCUSSION