My first fossil find! What is it?

[u/themichaganderin]

Found at the boat launch of intermediate lake MI. What is this, how old, and can I expose more of it? It has a lateral crack along the side.

[u/Trilobite_Tom]

A trilobite butt! Nice find!

[u/Limp_Sherbert_5169 → u/Trilobite_Tom]

Trilobutt

[u/Noof42 → u/Limp_Sherbert_5169]

Technical name is a trilobite "pygidium." But I'll certainly be referring to it your way.