The History of Our Tribe Hominini Textbook Part IV Pleistocene Epoch Chapter 21 Australopithecus sediba

21 . Southern ape I fountain or in the language ) Figure holotype . by Brett is licensed under . SITES , South Africa PEOPLE Lee and Matthew Berger and subsequent colleagues INTRODUCTION My research on this interesting species showed me how little I knew ! Since ( many biological who teach human evolution are not , Au . is a fairly recent discovery , and ( many textbooks have not as yet included much information about it , I have provided a more overview of this species . 136

Six individuals of a new species of were discovered , beginning in 2008 , at the cave site of , South Africa . Lee Berger crew is credited with the discovery after Berger son Matthew ( see Figure ) happened upon the fossils of a juvenile male ( that became the holotype for the species ( see Figure ) The other five individuals were an adult male , an adult female ( and , remarkably , an infant . It is of great utility in terms of interpreting morphology that much of the fossil material was found in situ ( where the body settled versus missing or scattered about ) that they became buried and began fairly rapidly . It is thought that they fell into a cavern , possibly lured by the presence of water in that then dry ' Figure Matthew Berger with fossil discovery . Matthew Berger with I by Lee Berger is licensed under . PHYLOGENY Since Au . shares characteristics with both Au . and Homo , it is thought to possibly be mediate between the two species . That scenario , of course , disagrees with Au . as being our direct ancestor , with Au . as a side branch . According to Berger et al . 2010 ) Au . is more distinct from Au . than the latter is from Au . in hand , pelvis , foot , and ankle morphology . However , the team working with the material believe it should stay within the genus because it lacks the Home trend . Surprisingly , Au . is more similar to Homo erectus in some respects than to Early Homo ( habilis or ) There has also been speculation that Au . is a derived form of Au . but it is problematic in that the specimens are only 100 kya more recent than the youngest Au . material . Furthermore , because the material is contemporary with Early Homo material ( habilis and ) some insist that they can not be ancestral to those species . ever , Pickering et al . 2011 ) dispute that claim , since Early Homo material is still problematic , both and . Berger et al . 2010 ) have proposed four phylogenetic Au . was the ancestor of Homo habilis , Homo , or Home erectus , or was a sister species to the ancestor of the Homo lineage . 137

Figure Mala 41 site . fossil site August 2011 site of discovery of view North by Lee Berger is licensed under . DISCOVERY AND GEOGRAPHIC RANGE Because the Party ( my term ) discovery is such a great story , I used it to introduce the species and will not repeat it here . see Figure ) is northeast of and 45 west of in the Cradle of Humankind World Heritage Site ( see Figure ) Wikipedia ) No fossil material has been found elsewhere . Figure . area indicated on map of South African provinces . Map of South Africa with shaded and districts numbered ( 2011 ) by is licensed under 138 The History of Our Tribe

PHYSICAL CHARACTERISTICS In general , the species morphology is a mosaic of ( especially Au . and characteristics , but there are multiple lines of evidence to support its classification as a separate species ( Berger et al . 2010 ) Since the material provides some of the best in situ evidence for many body parts , relative to other contemporary and previous species , I will spend more time discussing the physical and biomechanical significance . The brain of Au . was in its size and convolutional patterns ( et al . 2011 ) However , derived aspects of the frontal lobe show that reorganization preceded pronounced ( et al . 2011 ) This is an exciting discovery , in that we do not see so much of a gradual increase in size but rather that the brain evolved in a mosaic fashion and that an increase in the association region was favored at the time . If cranial capacity alone was all that was available to infer in Au . that important fact would be missed . Figure Lee Berger with . Lee Berger and the Cranium of by Brett is licensed under . Like most areas of the body , the cranial morphology reflects ( especially Au . and characteristics ( Berger et al . 2010 ) Relative to Au . Au . had smaller teeth and a less robust face ( see Figure ) Of interest is that they are described as having an incipient nose , ie . the beginnings of a protruding nose ( Berger et al . 2010 ) They share various mandibular and dental tics with Au . Early Homo , and Homo erectus ( Irish et al . 2013 de et al . 2013 ) Mandibular size and shape and tooth size most closely resemble Early Homo , and while some tooth measures and growth pattern are most similar to erectus , the overall growth trajectory is unique compared to other fossil ( de et al . 2013 ) Analysis of tooth shape , molar cusp patterns , and root number of the ious teeth shows that Au . and Au . share five ( shared traits among related species ) thus supporting a South African . In addition , Au . shares five with , suggesting a South African ancestry for our lineage ( Irish et al . 2013 ) 139

Au . retained relatively long arms and elevated shoulder joints for climbing ( see Figure ) et al . 2011 et al . 2013 ) Except for three wrist bones and the distal phalanges of the four fingers , the right distal forearm , wrist , and hand have been recovered intact for the adult female . While the of the hand is unique in some ways and they were still capable of strong flexion for climbing , some traits are associated with tool production in Homo species , especially the longer , more dexterous thumb and shorter fingers that facilitate our strong precision pinching . The only other hand that is well preserved from the late is that of OH , attributed to Homo habilis . However , the hand was better suited to tool production and there is still speculation that OH was actually , a robust not in our lineage . Thus , Au . may have been responsible for the tools that have been recovered at South African sites ( et al . 2011 ) Figure compared with Lucy . From left to right , Lucy , and Lucy by Peter is licensed under . While determining the thoracic shape of fossil has been a problem due to the lack of intact mens , it is generally thought that had a conical thorax like extant great apes . A conical thorax is involved with arboreal locomotion , whereas our thorax is ( adapted for endurance ing and running , related to shoulder breadth and to counter trunk rotation and facilitate our greater respiratory abilities , and ( facilitated by a decrease in gut volume related to and a less herbaceous diet ( first reviewed in Bramble and 2004 and later in et al . 2013 ) The Au . specimens support the notion of a conical shape to the upper thorax , but surprisingly , the lower thorax is not as as was previously thought , being more . et al . 2013 ) assert that the uncoupling of the upper and lower trunk morphology in Au . argues against a physiological response , in favor of a biomechanical one . The conical upper thorax would have been useful for climbing but would not have allowed for effective or heavy breathing and thus they were likely not capable of exertive walking and running . Their gut must have been smaller than a typical ape , suggesting a less herbaceous diet and setting the stage for the expensive tissue allowing for in our lineage ( et al . 2013 ) Au . likely possessed the modern number of regional vertebrae . While the vertebrae of all increase in size from superior to inferior , earlier lacked enlarged lumbar and sacral vertebral bodies and our pronounced sacral curve ( see Williams et al . 2013 for references ) Au . is the earliest to exhibit those characteristics , which are present in Home erectus and all subsequent species . While the vertebrae in the five regions of our vertebral column have distinctive characteristics , they grade into one another so that there are transitional vertebrae , the seventh cervical bra resembles the first thoracic vertebra and so on . Unlike humans , the transitional thoracolumbar vertebra 140 The History of Our Tribe

in Au . erectus ( based on the specimen ) and possibly Au . is 11 versus 12 . Thus while vertebra 12 is , it also likely functioned to elongate the lumbar region , increasing lower back flexibility ( Williams et al . 2013 ) The were in dimensions involved with childbirth but exhibited and other characteristics of Homo , such as iliac shape and vertical positioning , shortened ischium , and so forth ( et al . 2011 ) The proximal femur was with a small head and long neck , but the angle and insertion of the gluteus maximus were humanlike . The knee exhibits both and characteristics . Like us , they were capable of fully extending their knees ing the swing phase of walking ( et al . 2013 ) The partially articulated ankle and foot elements present a unique combination of primitive and derived traits . Humanlike characteristics include the morphology of the distal tibia , Achilles tendon insertion ( tuberosity ) possible valgus ( medially inverted ) knee indicative of the bicondylar angle , probable arched foot , etc . Some aspects of the bones are more , eg . more gracile calcaneus and some are more , robust medial malleolus ( distal fibula , what we think of as our medial ankle bone ) and some joints and muscle attachment sites ( et al . 2011 ) Like in apes , initial ground contact was via the heel and lateral aspect of the foot , so that the foot was inverted . They then the foot by transferring weight medially so that the ankle was inverted and the plantar surface of the foot rolled medially and became . Modern humans with tion have problems with increased stress and wear on the joints , and the same is evident in Au . remains ( et al . 2013 ) along with a robust medial malleolus , flexible , and upper limb adaptations , was apparently an adaptive response to bipedal terrestrial locomotion and tion of arboreal climbing abilities ( personal communication with author , 2014 ) As in the , the divergent hallux likely aided in climbing and would have given them more of a tripod foundation to stabilize their upright stance when standing and walking ( Lovejoy et al . 2009 ) Taken together , the mosaic of lower limb characteristics suggest that Au . may have practiced a form of unique from , or that they were descended from a more terrestrial ancestor and they then reverted to a more lifestyle ( et al . 2013 ) Review of Primitive Characteristics Brain size and convolutions . growth trajectory of teeth and jaws . Climbing adaptations elevated shoulder joint , long arms , and strong hand flexion . Conical upper thorax . femoral head and neck . Some primitive aspects of ankle and foot . Retention of hallux . 141

Review of Derived Characteristics Reorganization of the frontal cortex . Small teeth and jaws and less robust face . tooth shape and growth pattern . Humanlike lower thorax . Increased manual dexterity and precision grip . Longer , more dexterous thumb . Shorter fingers . Enlarged lumbar and sacral bodies and sacral curve . and more vertical ilium . carrying angle and gluteus maximus insertion . Full knee extension . Humanlike aspects of tibia , ankle , and foot . Possibly unique form of , ENVIRONMENT AND WAY OF LIFE The habitat of Au . is thought to have been a mosaic environment of and grasslands . from their tooth enamel indicate that they had access to forest products . are silica bodies in plants that can be used to identify what plant species were consumed . Fruit , leaves , wood , and bark were identified , with the latter being a first for fossil ( Henry et al . 2012 ) Unlike other and , the diet of Au . most closely resembled dwelling chimps and secondarily Ar . in that they specialized on plants , such as herbaceous plants , shrub and tree plant products , and grasses , and possibly animals that consumed those items . We know that plants were available at the time because remains of those more open , plants have been recovered in the same layers within which the material was found . In addition , rodents , horses , and were resident at the time . Their diet was thus less ( I made that up for fun ! varied than contemporary species inhabiting similar environments , such as Au . and , as well as Homo species that had an even broader diet . analyses show that the two individuals ( and ) under study ate a greater percentage of hard food items relative to other , being more similar to or erectus ( Henry et al . 2012 ) Being specialists in a environment may have involved more time invested in foraging , or they may have favored a more closed environment for feeding . It is thus likely that there were enough woodland or riverine environments to have supported the population . Additionally , they could have hard items when available or as fallback foods . 142 The History of Our Tribe