The giant emucaridid Tafilocaris ordovicica gen. et sp. nov. (Euarthropoda, Nektaspida), a peri-Gondwanan ‘Cambrian’ survivor in the Upper Ordovician Tafilalt Biota of Morocco

Abstract

Emucaridids are small, non-biomineralised, nektaspid trilobitomorph arthropods so far only known for the Cambrian. Their bodies are made up of a cephalic shield, a small number of thoracic segments and an elongate pygidium, larger than the cephalon. Here we describe a new emucaridid, Tafilocaris ordovicica gen. et sp. nov. from the early Late Ordovician (Sandbian 1), Bou Nemrou locality (Jbel Tijarfaïouine) of the Tafilalt Lagerstäte of Morocco. The two specimens of this new fossil arthropod are preserved in medium-grained sandstones and are about 150 mm long and 100 mm wide, making it almost twice the size of the largest nektaspid known to date, Naraoia magna from the Burgess Shale (British Columbia), and 5–25 times larger than other species in the Family Emucarididae. This concurs with observations made in other high palaeolatitude Ordovician taxa, where polar gigantism has been described in some radiodonts, trilobites and palaescolecid worms from different Ordovician biotas of Morocco and Portugal. The stratigraphical range of the new taxon is also compared with other Nektaspida of Cambrian and Ordovician age and reveals the survival of the Family Emucarididae beyond the Cambrian, and its expansion from Eastern Gondwanan and South China tropical waters to Southwestern Gondwanan polar environments.