A Curious Bug

To the best of my recollection, I have never seen this bug before:

And yet this morning, the Publix / Cheek & Scott parking lot was littered with them:

Basking in the predawn glow of the parking lot's artificial lighting, which you can see reflected on their hard-back shells.

They are nearly motionless, and as hard as a glass marble. About the size of two marbles side-by-side.

You can see here, I gently nudge one with my shoe (flipping it up-side-down) and it immediately (and quite frantically) rights itself, then becomes motionless again:

Does anyone know what kind of bug this is?