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Abstract
Coprolites (fossil feces) are important sources of evidence of ancient food webs and ecosystems. Actinomycetes are a fundamental component in the decay of organic matter, and serve as catalysts for nutrient cycles. Recently, gas vesicles filled with numerous verrucose colonies of substrate mycelium of an actinomycete were discovered inside a fossilized spiral amphipolar fish coprolite recovered from mid–Permian deposits of Brazil. These colonies are composed of masses of substrate hyphae, some of which are undergoing segmentation. Arising from the colonies are chains of spores separated by narrow, elongate connectives. The fossil actinomycete is described below as Palaeostromatus diairetus gen. et sp. nov. and represents the oldest known actinomycete associated with vertebrate deposits. Since the colonies occur only inside the coprolite, either Palaeostromatus diairetus gen. et sp. nov. was part of the gut flora or it was acquired from a food source. The only other remains in the coprolite are eighteen paleoniscoid fish scales, which suggests that the producer was a carnivorous/omnivorous fish. This is the oldest record of a direct interaction between vertebrates and actinomycetes.
Acknowledgements
We thank Yi Jiang, Yunnan Institute of Microbiology, for providing the names of extant genera with features of the fossil. We greatly acknowledge MSc. Adriana Strapasson (UFRGS) and Dr. Felipe Pinheiro (Unipampa) for field work support; Keila Marine for Figure and Catherine Fitzpatrick for english improvement. We specially thank the CEME–SUL (FURG) team for SEM analyses; Dr. G. Dike, Dr. G. Niedzwiedzki and Dr. M. Zaton for their helpful comments on earlier version of the manuscript.