Description

Proplina cornutaformis
Other Mollusc
Lower Ordovician
Gasconade Dolomite
Ozarks, Sullivan, Missouri, USA

16mm monoplacophoran on 37mm matrix.

Proplina is a genus of early mollusc (Class Monoplacophora) with a cap-like shell known primarily from Late Cambrian to Early Ordovician sites in North America with occurrences in South Korea and Antarctica.  It lived during a time when monoplacophorans and other molluscs were diversifying.

Monoplacophorans disappeared from the fossil record by the end of the Ordovician and were therefore thought to have perished in the mass extinction event at the end of the period so it was quite a surprise when scientists discovered modern forms living in deepwater environments in 1952.