THE HIDDEN DIVERSITY OF THE FEZOUATA SHALE BIOTA: NEW SPECIES AND DISPARATE BODY PLANS

The fossils of the Fezouata Shale (~475 mya) represent one of the most significant Paleozoic fossil discoveries. By providing a window of exceptional preservation into the early Ordovician, these animals bridge the critical gap between the establishment of modern phyla during the Cambrian Explosion and the ecological expansion of the Great Ordovician Biodiversification Event. However, relatively few taxa have been described from this biota, with most of the focus on taxa that cross the Cambro-Ordovician boundary like marellomorphs and radiodonts.

Here, we provide an overview of over several new taxa from the Fezouata Shale which, due to their almost entirely soft-tissue anatomy, fall into groups unlikely to fossilize under non-lagerstätte conditions. These specimens are based at the Harvard University Museum of Comparative Zoology and Yale Peabody Museum. First are the annelids, body fossils for which are exceedingly rare in the fossil record generally. The first new species appears similar to modern phyllodocids, with expansive, paddle-shaped parapodia. The second is a segmented worm with minimal external elaboration, superficially similar to modern lugworms or oligochaetes. Both of these species are morphologically and phylogenetically disparate from the only other described annelids from Fezouata, the machaeridians, which are related to modern scale worms.

Two new species of undescribed echinoderm are also present in Fezouata. The first is an asterozoan, which can be distinguished from the coeval Cantabrigiaster through its lack of prominent virgal ossicles. The second is an ophiocistioid-like animal similar in morphology to Volchovia. Both of these new forms are ecologically distinct from the most common Fezouata echinoderms such as the stylophorans and blastozoans.

A new mollusc bears some resemblance to the recently described Calvapilosa kroegeri, with a prominent anterior shell plate. Unlike C. kroegeri, however, this shell plate is proportionately much larger and the body of the animal is more elongate. Long, corrugated tubes appear similar to recently described tubicolous hemichordates from Cambrian lagerstatte such as the Burgess Shale. Finally, a large, segmented, soft-tissue organism defies any confident placement among any modern group, highlighting the persistent enigmatic nature of the Fezouata biota.