Pentremites robustus
Blastoid
Late Mississippian
Glen Dean Formation
Perry County, Missouri, USA

Big 54mm blastoid. Good for display or as a spare golf ball.

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

Kid: What is that?

Scientist: It’s a blastoid.

Kid: That sounds cool.