Lost part of my rally center cap

Anyone ever had this happen to them? Going about 40 MPH, I heard the sound of metal hitting concrete, so I pulled over to see if I lost an emblem or something. I didn't see anything at first, until I was walking around to get back in the car. The passenger front wheel is missing the very center of the center cap. I didn't even know these came off? I searched the area for a good 30 minutes with no luck.