Yes, I also thought that was strange. Maybe they are inside the "drag" and got filled in?
This area is a horseback riding arena, and I regularly drag it with a chain harrow.
I'm not sure why people are saying "no footprints" because I sure see enough of them in that picture.If it was on snow I would say an otter, they like to lay on their bellies and push along with their hind legs. How far apart are the footprints, both lateral and along the drag marks?