Judging an acritarch by its cover: the taxonomic implications of Introvertocystis rangiaotea gen. et sp. nov. from the Late Cretaceous (Cenomanian–Turonian) of the Chatham Islands, New Zealand

Abstract

Described here is a small acritarch with a fine reticulation on the internal surface of the cyst wall which provides a new criterion for future acritarch taxonomy. Sixty-six specimens of Introvertocystis rangiaotea gen. et sp. nov. have been identified from sediments of Ngaterian to Arowhanan age (Cenomanian to early Turonian; c. 99–92 Ma) within the Tupuangi Formation, Chatham Islands, New Zealand. The diagnostic feature of this fossil cyst is internal reticulation. This requires the emendment of the genus Palaeostomocystis. Some specimens may show waist constriction; this constriction is more common in larger specimens where it is suggestive of a paracingulum. However, the absence of a definite paracingulum, parasulcus or definable archeopyle precludes its assignment within the dinoflagellates. The wall structure is unusual in that the sculptural ornamentation is present on the internal surface, a feature that distinguishes it from all known acritarch genera.

Keywords:

• acritarchs
• Introvertocystis rangiaotea gen. et sp. nov.
• internal ornamentation
• Cretaceous
• Zealandia
• Chatham Islands, Palaeostomocystis

Acknowledgements

The authors would like to thank the following people: D. Mantle, Geoscience Australia (Canberra, Australia) for his mentoring and assistance with the practical side of palynology; I. Raine, Geological and Nuclear Sciences (Lower Hutt, New Zealand) for kindly processing the sediment samples from which these specimens were found; A. Partridge for inspiration and advice; the residents of Pitt Island, especially J. Preece, B. Gregory-Hunt and D. Gregory-Hunt for allowing access to the outcrops on their land, as well as K. Lanauze and J. Lanauze for their assistance and support on Pitt Island; S. Poropat for assistance in the field and for editing; L. Sorrentino-Mariconda, D. Thompson and C. Rodriguez for their advice and encouragement. This investigation was funded by the Monash University Bridging and Research Initiatives Grant awarded to JDS and an Australian Postgraduate Award Scholarship awarded to CMM.