The definition of a species is something we can demonstrate very clearly: if two individuals can have grandkids, then they're part of the same species. With fossils it's tricky to test this. If you bang two fossils together, they don't make baby fossils. In the next section on paleoanthropology, we will lump fossils into groups and label them with an official looking genus and species designation written in Latin and in italics, but it's really important for you to remember that this designation is not a concrete fact, it's just a hypothesis that will continue to be tested (and often contested). Understanding that paleospecies are hypotheses will help you to understand the context for many of the debates in paleontology and especially paleoanthropology.
*Lygers, Zonkeys, Jaglions… skim examples of hybrids