What does the presence of dinosaur footprints in an area where no dinosaur bones were found suggest?
Strongly suggests that even though bones have not been found, dinosaurs most certainly were around at the time the rock with the footprints were found.
Most dinosaurs or any land animal for that matter that dies on land is very rarely preserved as fossils. The remains tend to be scavenged by other animals and the bones break-up to dust. It takes a swampy, or ocean environment, or lake for bones to be preserved as fossils.
Here is a pic of some dinosaur trackways my friend and I first discovered at a coal mine in Alberta, Canada. We never did find any dino bones though.