如何使用可变参数模板定义不同类型的矢量矢量？

I would like to make a vector of vectors of different types. Suppose I have 4 classes; Dog, Cat, Pig, Cow. I would like a vector that contains vectors of each of these, and be able to access them by two indices so I can iterate over them, which would be the case if it was a vector of vectors.I would like to make a vector of vectors of dif