21096 - Museum Grade Soft Bodied Aglaspid (Tremaglaspis vanroyi) Lower Ordovician Fezouata Fm

Aglaspidida is an extinct order of aquatic arthropods that were once regarded as primitive chelicerates. However, anatomical comparisons demonstrate that the aglaspidids cannot be accommodated within the chelicerates, and that they lie instead within the Artiopoda, thus placing them closer to the trilobites. Aglaspidida contains the subgroups Aglaspididae and Tremaglaspididae, which are distinguished by the presence of acute/spinose genal angles and a long spiniform tailspine in the Aglaspididae.

Aglaspidida, Walcott (1912) represents a major and diverse –
yet historically problematic – group of early Palaeozoic euarthropods typified by a biomineralized phosphatic exoskeleton (Briggs & Fortey, 1982). Although
aglaspidids are relatively poorly understood, recent studies have produced significant insights into their morphology (e.g. Van Roy, 2006), biostratigraphic range (e.g. Fortey & Rushton, 2003, 2009; Lerosey-Aubril et al. 2013), palaeobiogeographic distribution and phylogenetic position
within the evolutionary context of Artiopoda, and even the entire phylum Euarthropoda.

The conservation of soft parts in the fossil record is somewhat exceptional and only occurs under certain and exclusive taphonomic conditions. For example, anoxic substrates without oxygen, where the organic matter has difficulty decomposing.

The Fezouata Formation occurs in the lower part of the Lower to lower Middle Ordovician Outer Feijas Group, in the western, central and eastern Anti-Atlas
Mountains, southern Morocco (Destombes et al.1985; Gutierrez-Marco & Martin 2016).

It comes from The Konservat-Lagerstätten of Lower Fezouata Fm that spans the entire Tremadoc stage of the Ordovician system and is only present in the Moroccan Anti-Atlas. The discovery of the Fezouata biota in the latest Tremadocian of southeastern Morocco has significantly changed our understanding of the early Phanerozoic radiation. The shelly fossil record shows a well-recognized pattern of macroevolutionary stasis between the Cambrian Explosion and the Great Ordovician Biodiversification Event, but the rich soft-bodied Fezouata biota paints a different evolutionary picture. The Fezouata assemblage includes a considerable component of Cambrian holdovers alongside a surprising number of crown group taxa previously unknown to have evolved by the Early Ordovician. Study of the Fezouata biota is in its early stages, and future discoveries will continue to enrich our view of the dynamics of the early Phanerozoic radiation and of the nature of the fossil record.