The History of Our Tribe Hominini Textbook Part II Miocene Epoch Chapter 8 Ardipithecus ramidus, Ardipithecus kadabba

. GENUS ( ground ape ) Figure ' by Taylor . Deposits within the Afar of Ethiopia ( see Figure ) have yielded multiple species within the genera and . This hotbed of fossils is the northern limit of the East African Rift Zone , where the Arabian and African plates converge . The first species of to be discovered in the area was Ar . and the second and even older species was Ar . When Ar . was discovered by , he believed that it 66

EURASIAN PLATE A Gil A ARABIAN A . AFRICA , AFRICAN PLATE ) ATLANTIC , ocean INDIAN I PLATE ) I I ' All , Equator , AFRICAN Lake PLATE EXPLANATION Plato I East I am zom Figure The East African Rift Zone . The Afar triangle is featured in darker pink at the most northerly limit ( see Ale site ) EA rich in the is in the domain . was similar enough to Ar . that he included it in the same genus and species , thus species classification . Since Ar . was already named , its classification became Ar . in the same manner that we became Homo sapiens when it was decided that should be included in our species and they became Homo sapiens . The original name is always preserved for the original ( It becomes known as the type specimen or holotype and is used to describe the characteristics that define the species . The older subspecies then became Ar . Since that time , they have been split into two species within the genus . Each will be discussed below , Some have suggested that may be a better candidate for our ancestry than one or more of the . It has also been suggested that are descended from or that the are a separate but related branch . 67

( ground ape I at the root in Afar language ) Figure Map showing the fossil sites of the earliest . Map of the fossil sites of the earliest hominids by and Sting is licensed under . SITES , Ethiopia PEOPLE Tim White and colleagues PHYLOGENY The phylogeny of the is unknown . We do not know if they left any descendants , but it is thought that is likely descended from . 68 The History of Our Tribe

DISCOVERY AND GEOGRAPHIC RANGE During the early , fossils were unearthed at the site of in the Middle Awash region of the Afar Triangle of Ethiopia ( see Figure ) Since that time , material from more than 50 individuals has been ered , in particular the famous skeleton ( see Figures and ) that is complete , Prior to the discovery , all or most early African fossils were considered to be . Tim White and his colleagues determined that the material was distinctive enough to warrant new genus classification , Figure Digital reconstruction of specimen . by Michael is licensed under BY Fifteen years after its discovery , was presented to the world in a frenzy of media coverage . She shook the world , not just within paleoanthropology , but for anyone interested in our past , She was an upright ape ! Yes , we are all apes , but looked like what we think of as an ape . She had an ape face , small brain , long and strong arms and fingers , and feet . However , she stood upright with straight rather than flexed legs . The film Discovering ( 2009 , Discovery Communications ) showcases her discovery , fossil processing and analyses , the artists skeletal and reconstructions , biomechanical graphics , etc , for the modern student ! PHYSICAL CHARACTERISTICS were likely arboreal climbers , like the ancient basal . However , when they were on the ground , they walked , albeit with rather feet , Characteristics that were initially used to designate status were an anteriorly placed foramen magnum , aspects of the innominate and ulna , and especially the morphology of the humerus that suggested that it was not and therefore not involved in terrestrial locomotion . Primitive characteristics of can be seen in many body regions , Their brains were small , Depending on the source , their cranial base ( the inferior portion of the occipital bone ) was either flat like chimps and gorillas , or angled and tucked under the upper part of the cranium ( termed flexed cranial base or cranial flexion ) The enamel on their molars was thin like that of chimps and other extinct apes , They retained several primitive characteristics that are related to arboreal climbing Elevated for reaching up for branches , etc . 69

Figure Artist representation of . by is licensed under . Long arms and long , curved fingers . Mobile wrists . Poorly differentiated thumb , meaning that they had poor opposability . Orangutans are the only great ape with a similar thumb morphology and hence have poor manual dexterity . divergent hallux ( the big toe away from the lateral four digits , like our thumbs ) would also have been adaptive for climbing . Derived characteristics of are all in the hip and lower limb . While species had short legs and long arms ( ie . high intermembral index ) the morphology of their hip and leg bones reflect bipedality , according to Tim White , Owen Lovejoy , and other members of their team . The innominate and foot morphology combine adaptations for climbing and . They were capable of full extension at 70 The History of Our Tribe

the knee , unlike the flexed knee seen in extant apes . Their feet were stable and supported their body weight and the divergent hallux facilitated grasping and climbing . Body mass is estimated from skeleton and thus no estimate for males of the species is possible . is estimated to have been ( 120 ) tall and weighed about 110 ( 50 ) Gibbons 2009 ) The absence of both a honing complex and pronounced prognathism suggests to some researchers , such as Owen joy , that males were not competing for females and may have formed with them . Review of Primitive Characteristics Small brain and flat cranial base . Thin molar enamel . Climbing complex of upper limb Elevated shoulder joint . Long arms . Long and curved fingers . dexterity . Divergent hallux . Review of Derived Characteristics Anteriorly oriented foramen magnum . Bipedal hip , leg , and foot characteristics . ENVIRONMENT AND WAY OF LIFE The sites where fossils have been recovered were a mosaic environment consisting of and grasslands during the late and early . Those ancient apes likely on a combination of arboreal and terrestrial forest resources . Their thin molar enamel suggests that , like chimps and , their diet consisted of relatively soft food items , such as fruit , young leaves , and shoots and possibly ants and termites . They could locomote within and between trees when foraging , or climb down and travel between trees or forested areas . Since all great apes build nests , may have made a new arboreal nest every night . 71

Figure by Taylor . Some scientists see the lack of canine sexual dimorphism and honing complex as evidence for There is good evidence from the animal literature to relate sexual monomorphism ( no difference in size between males and females ) and . As mentioned in Chapter , while there are several groups of primates that exhibit that grouping and mating strategy , they are all arboreal . The lesser apes are real , primates that form territorial pairs . Their mode of locomotion is brachiation , swinging under branches . While that is a more efficient means by which to avoid predation relative to climbing around in the trees , the latter were larger and heavier and thus were likely fairly safe . When they descended to the ground , however , pairs would have been fair game for predators . 72 The History of Our Tribe

The idea that male provisioning , in combination with , was the evolutionary stimulus for is also problematic . As I discussed in Chapter , I do not understand why females would need to be provisioned unless their babies could no longer hang on . I just do not see males risking life and limb to bring food back to females . I know of no examples in nature of a mammalian male provisioning his mate . It is more likely that resources became fragmented to the point that upright locomotion was the most way to move between trees and forest patches . was an adaptation to enable continued reliance on forest resources while minimizing competition . could move to another forest patch when resources became scarce . I think of them as being apes like chimps and gorillas but , unlike those extant species , they had less of a stable resource base . They thus evolved a more efficient motor strategy for expanding their home range . Figure Parenting by Taylor . ground ape I oldest ancestor in Afar language ) discovered the second species in the Middle Awash region of the Afar Depression ( see Figure ) The species is thought to be ancestral to Ar . Dental characteristics are more than those of Ar . While the fossils are very fragmentary , a toe bone suggests bipedal . 73

Figure by Taylor . foot movement involving the motion , ie . when we push off with the toes of one foot as we plant our other foot following its swing phase . 74 The History of Our Tribe