Molluscan protoconchs from the Early Silurian anoxic strata of Severnaya Zemlya, Arctic Russia

Though early ontogenetic development (embryonic and larval shell) is very important for the classification and systematics of molluscan high taxa, well-preserved protoconchs are very rare in geological record. The oldest finds of embryonic shell are known as isolated protoconchs, thus their taxonomic affinity is unclear.

Here we report well-preserved molluscan protoconchs of various affinities as well as adult shells from the early Silurian of Severnaya Zemlya Archipelago (Arctic Russia). They occur in black limestone nodules within graptolitic shales. Good preservation and high concentration of protoconchs is probably due to an anoxic environment of strata formation.