Life had been good for a certain class of tetrapods. They evolved two layers graphene in a specialized collagen creating a relatively thin yet seemingly impenetrable hide. All of their natural predators moved on to other prey without such tough skin, but soon over competition for plants struck. Many of them remained herbivores, but in order for many members of this class to survive, carnivory had to evolve again. It would be difficult, but probably not impossible, as no creature could truly make perfect graphene. Perhaps small flaws in the collagen itself could be exploited.
The collagen not only contains graphene, but also copper to support its structure. Both copper and carbon are a major and plentiful part of the diet for these tetrapods.
I am mainly concerned about the required materials to damage the graphene. Would they be biologically attainable and maintainable? I omit to go in depth about the structure of the collagen so that liberties can be taken. After all, if the graphene collagen were too difficult to damage, the tetrapods would have faced mass extinction due to overpopulation. As a basis, currently, the creatures are constructed with the same elements animal life on Earth is, but in different concentrations. There is more copper than there is on Earth, but many animals use hemoglobin in their blood, plus iron in their bones.
I am always interested in hearing about new elements to incorporate in their biology, so if anything else would be helpful, it would be great to know. So far, I have pictured mostly teeth and/or claws, as those weapons seem to work very well for predators on Earth. In the end it comes down to whatever can get the job done (as long as the predator still has a good chance of being alive afterwards.)