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.