The History of Our Tribe Hominini Textbook Part IV Pleistocene Epoch Chapter 17 Australopithecus Paranthropus aethiopicus

17 . southern ape I beside human I Ethiopia ) Figure Model of . by is licensed under . SITES Ethiopia Deposits Kenya West Lake PEOPLE Yves , Camille , and Alan Walker INTRODUCTION is the most primitive of the robust species . I use genus because it is thought to be descended from Au . In addition , was the genus name 118

assigned to the South African robust form , and questions remain as to whether the two species are related . PHYLOGENY There are multiple lines of evidence to support Au . as a descendent species of Au . While some believe that Au . gave rise to , others link with in a ent , with Au . as their common ancestor . More recently discovered material within the graphic range of Au . supports the Au . evolutionary scenario . The dates of the new fossils fall between the two species , and they possess intermediate or transitional characteristics . Figure shows one schema that illustrates how some researchers suggest these species were related . This particular scenario shows the authors belief that Au . is a robust form . HOMO Figure analysis of early . anal sis earl by Charles Clarke is licensed under . DISCOVERY AND GEOGRAPHIC RANGE In 1967 , the earliest Au . fossils were discovered by Yves and Camille in the deposits at the site of in southern Ethiopia . They assigned them to a new genus and species , While it was debatable as to whether they actually had a new species , the discovery of the Black Skull ( see Figure ) in the West Lake region of Kenya by Alan Walker in 1985 put any doubts to rest . At that time , the species was added to genus because it was thought to be descended from Au . There were then three recognized species of robust in Africa , and efforts to determine their phylogenetic relationships began . The Black Skull or ( Kenya National Museum West ) 15000 was a magnificent find . The almost complete skull was stained from manganese , but it is always fun to sing scary movie music to my students when introducing THE BLACK SKULL ! Figure for fun ! 17 . 119

Figure Skull and Crossbones . Crossbones ( by Pearson Scott is in the public domain . PHYSICAL CHARACTERISTICS A unique characteristic that ties Au . to is a foramen magnum , as opposed to the more ovoid form seen in Au . and . Primitive characteristics shared with Au . are the flat cranial base , small brain ( long molars ( mesiodistally , front to back versus side to side ) and the degree of prognathism in the lower face . Because their faces were so broad and their brains so small , they exhibit a high degree of postorbital constriction ( also known as waisting ) the area between the face and is narrow . Derived robust characteristics are of the skull , face , and mandible . Their muscles of mastication were incredibly strong , as evidenced by the sagittal crest ning down the midline of their skull where the muscle originated . The sagittal crest was higher and more posteriorly placed than in the two more derived robust species . The were large and flared to allow for passage of the muscle from the sagittal crest to insert on the mandible and to expand the attachment site for the masseter muscle , the other large muscle of mastication ( see Figure ) The were more forwardly flared than in the other two robust species . They also had heavy nuchal ( posterior neck ) muscles to support the weight of their heavy face and skull , and the attachment sites of those muscles on the posterior skull was also an expanded crest that converged with the sagittal crest , a compound crest . Large brow ridges in the robust species offset the stress by biting down on hard foods . However , Au . brows were smaller than the other two species . Their third maxillary molars were convergent , meaning they were positioned more medially than the first and second . While some researchers disagree , others find evidence for a more derived venous sinus system in the crania of the robust forms . The system consists of large collecting veins that ultimately empty into the jugular veins , allowing for rapid , blood drain from the brain , in order to keep fresh blood pumping in via several arterial systems . The largest and most superficial of those sinuses ( see Figure ) leave impressions on the inside of the skull vault . Dean Fall Radiator Theory argues that our ancestors needed to keep their brains cool as they increased in size in a hot , open environment . The system became more complex after the time of the . 120 The History of Our Tribe

Review of Primitive Characteristics . Small brain . Prognathic . Review of Derived Characteristics foramen magnum . Robust skull , face , and mandible . Large , compound crest . Large brow ridges . Pronounced postorbital constriction . Large , powerful muscles of mastication . Large forwardly flared with a large zygomatic arch . Convergent maxillary third molars . Possible derived venous sinus system . ENVIRONMENT AND WAY OF LIFE As mentioned , there is evidence that Au . was more terrestrial than the southern , suggesting that the classic ape environment had diminished . We know that grasslands were expanding and woodlands were shrinking . Since it is assumed that Au . is descended from Au . the environment was favoring species with dietary adaptations that allowed them to survive . 17 . 121

Figure Muscles of mastication ( and ) Illustration by Taylor ' SUP . Figure Cranial sinus system ( SIN . sinus ) Based on Grays Anatomy Plate 488 . blue by is in the public domain . 122 The History of Our Tribe Figure tool use by Taylor . 17 . 123