134 



THE SPECIES PROBLEM WITH FOSSIL ANIMALS 



echinoids, and mammals. For such groups differences in the 

 classification of fossil and living organisms at the species level 

 are rarely attributable to the inadequacy of morphological data. 

 Students of some of the groups just listed may argue that 

 many important specific taxonomic characters are not preserved 

 in fossils — pelage characteristics in mammals, for example. This 

 view, however, violates one of the basic tenets of taxonomy: that 

 the nature of a unit biological character is not so important in 



Fig. 5. Ratio diagram comparing range of size variation in the fossil 

 bamboo rat (Rhizomys sinensis troglodytes) and three modern subspecies of 

 R. sinensis. A, Rhizomys sinensis troglodytes; Bd, R. s. clacicli; Bv, R. s. 

 lestitus; Bw, R. s. wardi. Diagram constructed in the same manner as 

 Fig. 4 (Colbert and Hooijer, 1953). 



taxonomy as its statistical distribution within and between 

 populations (Simpson, 1943). This point is so fundamental to 

 an understanding of the paleontologist's approach to classification 

 on the species level that it will be illustrated with three examples 

 drawn from diverse sorts of animals. 



In a study of Chinese Pleistocene mammals, Colbert and 

 Hooijer (1953) analyzed skeletal data on several species of 

 modern Asiatic mammals and made comparisons with similar 

 data on fossils. A ratio diagram (Fig. 4) based on skeletal meas- 



