Unusual spheroidal inclusions in Late Permian gymnosperm pollen grains from southern India revisited: evidence of a fungal nature

Abstract

Conspicuous spheroidal inclusions are infrequently encountered in saccate gymnosperm pollen grains (e.g. Striatopodocarpites subcircularis, Striatopodocarpites multistriatus, Faunipollenites varius, Ibisporites diplosaccus, Scheuringipollenites maximus, Barakarites indicus) from the Upper Permian (±253–275 Ma) of the Godavari Graben, Andhra Pradesh, India. These structures, which occur singly or in clusters of two to eight in the corpus of the pollen grain, are 15–45 µm in diameter, smooth-walled, and usually translucent; ~30% of the specimens show a pre-formed circular opening in the wall. The biological affinities of the inclusions remain elusive. The interpretation of similar structures from the Raniganj Coalfield (Upper Permian, India) as components of the microgametophyte is implausible for several reasons. Rather, these pollen grains represent highly likely host substrates and habitats for microorganisms, and it is, therefore, probable that the inclusions are the remains of a pollen-colonising organism, perhaps the endobiotic zoosporangia of a chytrid or member in the Hyphochytridiomycota.

Keywords:

• fossil fungi
• palynology
• zoosporangium
• Lopingian
• Guadalupian
• Godavari Graben
• Chytridiomycota
• Hyphochytridiomycota

Acknowledgements

The authors thank Sunil Bajpai, the Director of the Birbal Sahni Institute of Palaeobotany, Lucknow, India, for giving permission to publish the paper and for his kind support of the research. NA and NJ are grateful to Sri M. Basava Chari, former Chief General Manager, Singareni Collieries Company Limited (SCCL), Andhra Pradesh, India, for granting access to the bore core, and providing all necessary information and assistance during the fieldwork. TNT and MK acknowledge the support of their research by the National Science Foundation (EAR-0949947) and the Alexander von Humboldt-Foundation (V-3.FLF-DEU/1064359). The paper benefited from the constructive comments and suggestions of two anonymous referees and Grana handling editor Christian Pott, Stockholm, Sweden.