Although the species is one of the fundamental units of biological classification, there is remarkably little consensus among biologists about what defines a species, even within distinct sub-disciplines. The literature of paleobiology, in particular, is littered with qualifiers and cautions about applying the term to the fossil record or equating such species with those recognized among living organisms. In Species and Speciation in the Fossil Record, experts in the field examine how they conceive of species of fossil animals and consider the implications these different approaches...