Enigmatic encrusting fossils from the middle Devonian of Morocco: A new epibiont or peculiarly preserved ascodictyid microproblematica?

Abstract

Devonian was a special time during which the sea floors were covered by numerous hard substrates, which provided the settlement of various encrusting and boring organisms. Although many of them are well-recognized and have their representatives in younger systems, some have still unresolved taxonomic affinities and thus represent problematic taxa. Here we present intriguing microfossils encrusting a brachiopod shell derived from the Middle Devonian carbonates of the Mader Basin, eastern Anti-Atlas, Morocco, which haven't been reported so far. The fossils have elongated, ribbon-like morphologies with characteristic lateral, tubular branches and are preserved as Fe-oxides/hydroxides casts after pyrite. The best-preserved specimens alone could have easily been taken as some completely new encrusting taxa. However, their association with some ascodictyids, a group of incertae sedis encrusters, and the presence of similar, but much less well-preserved branches located nearby on the same shell or occurring on other shells may indicate that the fossils described, may in fact only represent a differently preserved ascodictyid. If so, the fossils described suggest, that the same encrusting taxon may produce different taphomorphs even on the same small-sized substrate. Thus, finding such fossils alone may unnecessarily increase the diversity of the hard substrate community unless detailed and critical comparisons are made.