size being the key
To find a mammal large enough to contain an identifiable fossels seems to be the big surprize. No surprize that smaller animals would scavenge on dinos any more than ants on an elephant or that a larger mammal predator would be higher on the food chain than a tiny dino.
In the pre-extinction period it is remarkable to find a mammal this large. In addition to perhaps being predators they must have also been very good at hiding. :)