Why is my weimaraner getting dark spots on her chest?

My 3 year old weimaraner has never had any health problems. But I've noticed over the past couple of days that she has a large reddish-brownish spot on her chest (about 6 inches or so) and another on her inner thigh. It's not swollen, it's not bleeding, and it doesn't seem to bother her at all. Should I be worried about this? She refuses to sleep on her bed, and often sleeps on the hard linoleum floor in the kitchen - could this be a callus of some sort? Any other ideas? I'm going to call the vet tomorrow, but it doesn't seem like an emergency, and I was curious about whether anyone else had experienced this.