484 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



Australopithecus is of the same type as is found in all known homi- 

 nines, having a characteristic specialization of the anterior half of the 

 crown. Paranthropus is unique in the primates in having a com- 

 pletely molarized deciduous first lower molar without any trace of the 

 specialization seen in Australopithecus and all hominines. The decid- 

 uous lower canines also differ considerably in the two forms. 



The differences in skull architecture can be explained primarily in 

 terms of differences of dental and dietary specialization. Paranthro- 

 pus has very heavy crushing and grinding cheek teeth, but the an- 

 terior teeth were clearly less important since they not only are much 

 reduced in size, but also wear less rapidly than the cheek teeth in 

 spite of their smaller size. Strong reliance on crushing and grinding 

 implies a vegetarian diet in which considerable bulk is required to 

 provide the necessary nutritive value. Much chewing is necessary to 

 comminute the often tough plant material. Enlargement of the cheek 

 teeth with specialization for crushing and grinding are common 

 features of creatures adapted to vegetarian diet. Paranthropus ap- 

 parently also ate roots and bulbs, since there is clear evidence of grit 

 in the diet, in the form of small chips and flakes of enamel which have 

 broken off from the occlusal margins of the crowns through strong 

 pressure being applied over a small area. The powerful chewing 

 forces which must have been generated in this robust masticatory 

 mechanism have resulted in substantial thickening of the bone in 

 which the cheek teeth are set and along the avenues through which 

 the chewing forces are dissipated. These include the palate, cheek 

 bones and jugal arches, lateral parts of the supraorbital tori, and the 

 pterygoids. The heavy jaws needed powerful muscles; hence there 

 is further robustness in such areas as the origin and insertion of the 

 masseter and pterygoid muscles. The relation of large temporal 

 muscles to relatively small braincase was such that even females ap- 

 parently normally had a sagittal crest. On the other hand, the very 

 small anterior teeth resulted in a face which did not protrude forward 

 at all markedly. 



Australopithecus^ on the other hand, has none of these extreme modi- 

 fications. Both skull shape and structure and especially dental mor- 

 phology, are closely comparable to the early hominine condition. It 

 therefore seems reasonable to conclude that the diet of this form was 

 basically the same as that of early hominines ; i.e., they were omnivores 

 eating both flesh and vegetable matter. This was probably the sort 

 of diet still found in hunters and food gatherers of today. 



The adaptive difference between these two forms is thus consider- 

 able. Their ecological requirements and direction of evolution were 

 quite different. The degree of difference between them in these 

 respects was of a distinctly greater order than between any two of 



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