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Chapter 10 From Hominoid to Hominin

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Jon Stone

Chapter 10 From Hominoid to Hominin I) The first Hominins appear in the fossil record about 6 mya. Between 4 and 2 mya, a diverse community of hominin species ranged through eastern and southern Africa. a. Creatures were difft from other Miocene apes in two ways: i. Walked upright ii. Began to exploit new savanna and woodland habitats, and new kinds of foods became availablethe hominin chewing apparatus changed II) A number of shared derived characters distinguish modern humans from other living hominoids: a. Bipedal locomotion b. Dentition and jaw musculature are very different c. We have much larger brains in relation to body size d. Slower development e. Dependence on highly variable material and symbolic culture, transmitted in part through spoken language I) At the beginning Last common ancestor of humans and chimps ~ 7-5 mya a. Sahelanthropus tchadensis 7-6 i. Surprising mix of derived and primitive features ii. Foramen magnum (spine hole) located in bottom of skull = bipedal iii. Small brains b. Orrorin tugensis 6 mya i. Mix of characteristics c. Ardipithecus  from Awash region of Ethiopia (was woods and grassland) i. Ar. Kabadda 5.8-5.2 mya 1. Mix of primitive and derived dental features ii. Ar. Ramidus 4.4 mya 1. Ardi – similar to Sahelanthropus and Orrorin 2. Provides a preview of a distinctive suite of dental traits that characterize later hominins. These include thicker molar enamel, general reduction in the size and extent of sexual dimorphism in canines 3. Characteristics of feet and pelvis in postcranial anatomy suggest walked upright II) The Adaptive Advantages of Bipedalism a. The shift from quadrupedal to bipedal locomotion is a defining feature of the hominins. However, it is not entirely clear why bipedality was favoured by natural selection i. Bipedalism first evolved among arboreal Miocene apes as a feeding adaptation and was retained in hominins. 1. Bipedal posture allows efficient harvesting of fruit from trees. 2. Erect posture keeps hominins cool (less Surface area for solar radiation and more contact with the wind to remove heat from perspiration) 3. Bipedal locomotion leaves hands free to carry things III) The Hominin community diversifies a. Beginning about 4 mya the hominin lineage proliferated i. Australopithecus: small bipeds with teeth, skull and jaws adapted to a generalized diet 1. anamensis – 4.2-3.9 mya, more apelike than later Austs (small ear holes, U-shaped dental arcade, more sharply r
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