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THE SPECIES PROBLEM WITH FOSSIL ANIMALS 



Fig. 3. Tabular summary of some characteristics of typological, biologi- 

 cal, transient, and successional species. Operational taxonomic criteria asso- 

 ciated with each of these concepts are indicated. 



Figure 3 summarizes aspects of the species concept which 

 have been emphasized in the preceding discussion. 



Problems in Applying Biological Species Concepts to Fossils 



Transient Species. In the foregoing discussion attention has 

 been focused on the theoretical model of the biological species 

 in use today by a majority of paleontologists. We shall now exam- 

 ine some of the practical problems which arise when this model 

 is applied to real paleontological data. Most of these problems 

 arise from three sources: the inadequacy of morphological data, 

 the prevalence of biased frequency distributions, and the incom- 

 pleteness of the available fossil record. 



1. Inadequacy of inorphological data. The most obvious 

 shortcoming of paleontological data is that fossils normally pre- 

 serve only hard skeletal parts. To a student of soft-bodied living 

 animals (say Euglena) this difficulty might appear insuperable. 

 Indeed, some taxonomists assume for this reason alone that clas- 



