Virgatasporites and Attritasporites: the oldest land plant derived spores, cryptospores or acritarchs?

ABSTRACT

The oldest reported occurrence of cryptospores supposed to derive from land plants (embryophytes) is currently considered to be in the Middle Ordovician. The two genera Virgatasporites and Attritasporites, described in the 1960ʹs from the Early Ordovician (Tremadocian) of Algeria, are morphologically close to the miospores, and therefore pose a dilemma, because these spore-like microfossils are recorded before the first appearance of the oldest land plant derived spores. Here the taxonomy, biostratigraphy and palaeobiogeography of the two genera and their species are revised. Both genera are found in many localities on the Gondwanan border between the late Cambrian and the Middle Ordovician. They have not been found at the margins of other palaeocontinents so far. The biological affinity of the taxa remains uncertain. Several authors considered the two genera to be spore-like microfossils, whereas other authors classified them as acritarchs, i.e. organic-walled microfossils of unknown biological affinity. As the relationship to the embryophyte lineage cannot be established clearly to date, the biological affiliation remains enigmatic. Therefore, in the absence of other evidence, the taxa Virgatasporites and Attritasporites should be temporarily classified as incertae sedis, i.e. as acritarchs, before their true biological affinity is known and they can be adequately placed into a biological group.

KEYWORDS:

• Acritarchs
• cryptospores
• embryophyte origin
• Gondwana
• Cambrian
• Ordovician

Acknowledgments

We thank Sylvie Régnier (Lille University) for sample treatment and Jessie Cuvelier (CNRS, Lille University) for helping finding references and literature. Yan Kui (Nanjing, China) is acknowledged for discussing Chinese occurrences. We thank the editor Paul Kenrick and two anonymous referees for their valuable comments that improved the manuscript. This is a contribution to IGCP no. 653 ‘The onset of the Great Ordovician Biodiversification Event’ and no. 735 ‘Rocks and the Rise of Ordovician Life.’

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

PS and TS designed the research program and the paper concept. HB, NNI, DMK, PS and TS carried out palynological studies and provided data. HB, NNI and DMK designed the figures, all authors participated in writing the manuscript.

Additional information

Funding

HB benefited from a mobility grant in the frame of the Programme National Exceptionnel (PNE) of the Algerian Ministry of Higher Education and Scientifical Research for a scientific stay at Lille University. NNI acknowledges financial support received from the Iranian Ministry of Science, Research and Technology (MSRT). DMK benefited from the support of Lille University (PhD research project). This paper is part of research funded by the ANR project EARTHGREEN (ANR-20-CE01-0002-01). PS is a NFSR Senior Permanent investigator.