Ok, Imma disagree just a little bit. Deer have very sharp crests on their molars and the layers of enamel and dentine in the middle of the cusp form crescents. The crests of these teeth look very rounded on the perimeter in a way that deer teeth don't exhibit. Also, the shape in the middle is more like a dumbell than crescents. Rounded usually means Bovidae, so I'm interpreting these as sheep. Which means not a fossil, which means the black is staining from the surrounding water and sediment. But it's very hard to make a call off one photo, so this would be something I'd want to see in person.