If you say that a ground squirrel has greater evolutionary fitness than another ground squirrel in the same population, you mean that the animal

Has more offspring that have the ability to survive and reproduce themselves.

Explanation:

Evolution fitness can be defined as a characteristic or quality possessed by living organisms and determines their adaptability, as well as level of success in terms of reproduction i.e giving birth to offsprings.

Hence, if you say that a ground squirrel has greater evolutionary fitness than another ground squirrel in the same population, you mean that the animal has more offspring that have the ability to survive and reproduce themselves.

the fossil record provides evidence of a common ancestor to many species.