I found this ischium myself while digging in the Hell Creek formation in Powderville, Montana.
You’re probably wondering: What the heck is an ischium?
The ischium forms the lower and back part of the pelvis, and mainly serves as an anchor point for muscle attachment. Humans have them too, but ours look nothing like those found in dinosaurs.
Here are a few more pictures of the fossil from the time it was found to the time I began prepping it.