Species and Speciation in the Fossil Record Warren D. Allmon (Editor), Margaret M. Yacobucci (Editor)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