This is the hypothetical common ancestor to the Kenyanthropus and Homo lineages. There is a continued reduction in the anteromedial incursion of the temporal lines, and the temporal squama is variable in its pneumatization. The external cranial base is more flexed and the articular tubercle is small. The digastric muscle insertion region is deep and narrow, and the basioccipital is short. There is a continued increase in cranial capacity. Occipitomarginal sinus frequency is low and the cerebellar is tucked under. The zygomatic is now in a near vertical orientation, and the masseter origin is low. Nasal bones are not projected and the nasal cavity entrance is stepped. The subnasal region is increased in height. The upper molars are reduced in size. Molar lingual cusps do not crowd occlusal surface, buccal cusps do. Mandibular tori are undeveloped, while the corpus is robust. Mandibular extramolar sulcus is narrow. The evolutionary trend at this point is for the brain to increase in size, while conversely the face and dental complex are reducing in overall size and robusticity.

0 0

Post a comment