Novel evidence for the youngest Naraoia and a reassessment of naraoiid paleobiogeography

Naraoiids are nektaspidid arthropods that display two exoskeletal shields, typically lack thoracic tergites, and have an exceptional Cambrian diversity. Despite their predominantly Cambrian fossil record, Naraoia species have been documented in deposits as young as the late Silurian (Pridoli). At present, only one specimen of the Silurian taxon— Naraoia bertiensis —has been documented. Here we report the second known Silurian Naraoia specimen assigned to N. cf. bertiensis from the Phelps Member of the Fiddlers Green Formation, extending the fossil record from the Williamsville Member. We use paleo-elevation models to explore naraoiid paleobiogeography, illustrating a striking decrease in naraoiid distribution from the Cambrian into the Ordovician and Silurian. These models allow us to explore the proposal that geologically younger naraoiids migrated to deep water, off shelf environments, inhabiting these refugia-like conditions after the Cambrian.