480 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



The evidence for erect posture in the prehominines is good. The 

 pelvis is known from one almost complete specimen as well as a 

 number of incomplete ones, and it differs markedly, in structure and 

 function, from the pongid or monkey type but only insignificantly 

 from the hominine type. The lumbar region of the spinal column, 

 the proximal and distal ends of the femur, and the nature and orienta- 

 tion of the occiput all add to the evidence which shows that the aus- 

 tralopithecines were structurally and functionally well adapted to 

 erect posture and locomotion. 



The dentition provides considerable evidence of hominid affinity. 

 The anterior teeth are small, compact, and built closely on the homi- 

 nine pattern. Even the canines are within the size range of homi- 

 nines. Other teeth that are especially diagnostic are the first lower 

 premolar (P3) , first lower deciduous molar (dmi) , and lower deciduous 

 canine (dc). In pongids the first two are semisectorial teeth usually 

 having one prominent cusp, though a second may be partially devel- 

 oped. In the prehominines and hominines P3 is bicuspid and dmi well 

 molarized, having five cusps as in the permanent molars. Sophis- 

 ticated statistical analysis of the lower deciduous canines has shown 

 that the prehominine teeth are easily and sharply distinguished from 

 the pongid form while they closely resemble, and in some cases are 

 indistinguishable from, the modern hominine form (Bronowski and 

 Long, 1952). 



These and other telling morphological features clearly indicate 

 close affinity with hominines, but the small brain indicates a more 

 primitive condition. The endocranial volume appears to be about 

 500 cm.^ only — I know of no sound evidence at present indicating a 

 brain significantly larger than this. The range was evidently about 

 450 to 550 cm.^ and therefore well below the pongid maximum of 

 750 cm.^ found by Schultz. The early hominines appear to have had 

 endocranial volumes averaging about 900 to 1,100 cm.^, although 

 estimated volumes as low as 7'55 cm.^ have been given. 



Along with this small endocranial volume in the prehominines, 

 the braincase is relatively small and the face relatively prognathous. 

 It is therefore evident that an important feature of hominines — the 

 enlarged brain and the modifications of skull architecture conse- 

 quent upon this — was not yet significantly developed in the known 

 prehominines. 



TAXONOMIC DIFFERENTIATION WITHIN THE PREHOMININES 



The prehominines are at present commonly regarded as comprising 

 a morphologically variable group without any significant taxonomic 

 differentiation within it (e.g., Le Gros Clark, 1955). A considerable 

 volume of evidence exists which shows that this is not the case — so 



