Protaspid larvae are unique to trilobites

Trilobites represent a model for 'evo-devo' studies in fossil euarthropods, owing to a rare developmental trait: the biomineralization of the dorsal exoskeleton soon after hatching. Many fossilized trilobite on-togenies thus feature early stages -the protaspides -characterized by non-articulated, calcified dorsal exoskeletons. The recent discovery of a protaspid-like fossil occurring with aglaspidid remains in Middle Ordovician strata of Siberia has been interpreted as evidence for the presence of protaspides in these distant relatives of trilobites. In this contribution, we demonstrate that this Siberian protaspis actually belongs to the asaphid trilobite Isotelus (or a related taxon), a genus likely present in the same bed. We conclude that protaspid larvae still represent a developmental trait unique to Trilobita. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Trilobites possess a unique developmental trait of biomineralization on the dorsal exoskeleton soon after hatching, with their protaspid larvae characterized by non-articulated, calcified structures. A recent discovery of a protaspid-like fossil occurring with aglaspidid remains in Siberia was found to actually belong to the trilobite Isotelus, indicating that protaspid larvae are still a unique developmental trait of trilobites.