The specific name (second part) of a species is somewhat subjective, and is used to describe behaviour or properties a given species has that can be used to differentiate it from another related species.
That mostly works ok, but in some parts of the animal kingdom there are some areas where it really doesn't. If you discovered fossils of both a poodle and a mastiff would you categorise them both as canis familiaris?
Not just the name, but the whole biological species concept can break down at times. I mean look at the wholphin https://en.m.wikipedia.org/wiki/Wholphin which is a fertile hybrid between parents of different genera but it doesn't make much sense to call false killer whales and bottlenose dolphins the same species.
That mostly works ok, but in some parts of the animal kingdom there are some areas where it really doesn't. If you discovered fossils of both a poodle and a mastiff would you categorise them both as canis familiaris?