THE SPECIES PROBLEM WITH FOSSIL ANIMALS 



5 populations is a necessary prerequisite for the definition and 

 lelineation of fossil species. Disagreement exists not only on the 

 nature of species but also on the inevitable question of their 

 proper scope. Thus Burma (1948) would distinguish as species 

 the smallest statistically recognizable grouping of populations, 

 whereas Imbrie ( 1956) argues that consistent application of such 

 a criterion would lead to useless multiplication of species names. 

 Since all the problems alluded to in the preceding paragraph 

 have their exact counterparts in neontology, it would be pointless 

 to make of this paper a compendium of paleontological disagree- 

 ment. Instead, we shall focus on those aspects of the species 

 problem which are unique, or are at least uniquely developed, 

 in dealing with fossil materials. 



Species Concepts 



In dealing with sexual organisms, whether fossil or living, two 

 fundamentally different species concepts can be employed. The 

 typological concept defines species as a group of individuals 

 essentially indistinguishable from some specimen selected as a 

 standard of reference. The biological species concept, on the 

 other hand, considers the species to be made up of one or more 

 variable, interbreeding populations. Both of these concepts serve 

 as theoretical bases for taxonomic work in paleontology today. 



Different criteria may be emphasized in delimiting biological 

 species. For many students the criterion of interbreeding is de- 

 cisive, and species so defined may be referred to as genetic 

 species. In order to emphasize the fact that most modern and all 

 fossil species are distinguished more on the basis of morpholog) 

 than on breeding habits, some taxonomists recognize a morpho- 

 logical species concept as distinct from the genetical concept. But 

 this is really a trivial distinction. Morphological data are never 

 really considered by themselves; their interpretation is always 

 colored to some degree by prevailing theories on population 

 structure. Moreover, descriptions of species, like descriptions of 

 molecules and genes, arc inferences drawn from various sorts of 

 data, including observations on geographic distribution and ecol- 

 ogy as well as morphology and genetics. 



