Description

Pentremites pyriformis
Late Mississippian
Indian Springs Shale Formation
Crawford County, IN, USA

Fine 0.55 inch pathologic blastoid– it only has 4 sides! Rare and unusual!

Blastoid,

Pentremites is a genus of blastoid that lived across the Mississippian and Pennsylvanian Periods.  It is known from various parts of North America from northern Canada to Arizona and east to Virginia.

Blastoids are an extinct group of echinoderms that appeared during the Ordovician and survived to the end of the Permian, dying out during the end-Permian mass extinction, the most devastating mass extinction in the history of life on earth.

Occasionally, someone finds a pathologic blastoid.  As a rule adult echinoderms show fivefold (pentaradial) symmetry, the body branches out from a central point as five identical divisions.  This specimen shows fourfold symmetry which indicates a genetic disorder.