Lecture 10-1 Early Fossil Hominids: Bipedal Anatomy & Pre- Australopithecines and Australopithecines

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Roderick Eaton
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1 Lecture 10-1 Early Fossil Hominids: Bipedal Anatomy & Pre- Australopithecines and Australopithecines Big Questions 1. What is a hominid? 2. Why did hominids evolve from an apelike primate? 3. Who were the first hominids? 4. What was the evolutionary fate of the first hominids? *Hominid characteristics (that all hominids share) include: -Bipedalism -Non-honing chewing *Non-honing chewing: refers to the way the mouth processes food: less slicing and more grinding. Lack of projecting canine, diastema. More pressure on front portion of chewing muscles *Bipedal locomotion: walking on 2 limbs, involved major skeletal changes. Evolved before large brain size *Anatomy of bipedality -Centered foramen magnum -Lumbar curve* -Broad, short pelvis -Longer legs -Long femur neck -Carrying angle* -Arches in the foot -Non-opposable big toe Costs and Benefits of Bipedalism *Benefits -Can see greater distances -Easier to transport food, children, etc. -Frees hands to use tools *Costs -More visible to predators (?) -Slower than quadrapedalism -Potential for back problems, and greater strain on circulatory system Hominid Evolution *Hominid evolution occurred in Africa in the late Miocene or very early Pliocene *Why did hominids emerge? -3 Major hypotheses: -Hunting hypothesis (Darwin) -Patchy forest hypothesis -Provisioning hypothesis Charles Darwin s Hunting Hypothesis

2 *Bipedalism had freed the hands for carrying weapons -Weapons relaxed canines -Size of canines diminished *Tool production and use essential for human intelligence and large brain *New evidence shows this not to be the case -Earliest tools date to 2.6mya -Brain expansion dates to after 2mya Patchy Forest Hypothesis (Rodman & McHenry) *Human origins and bipedalism related to the greeter efficiency in some habitats of moving on two limbs rather than four *Bipedalism arose in areas where forests were fragmented and food resources also became scattered *As forests fragmented, bipedalism freed the hands to pick up food allowing for both tree and ground food resources to be exploited Provisioning Hypothesis (Owen Lovejoy) *Freeing the hands was important in allowing males to assist females more efficiently in procuring food - provisioning acted as a form of seal competition among males for females *Birth spacing would also be reduced, since females would have to move around less and would have access to greater food resources *Lovejoy s hypothesis makes the argument for monogamous fathers Sexual Dimorphism and Human Behavior *Many primate species are highly sexually dimorphic, with males larger than females -this is linked to male-male competition *Some scientists see little sexual dimorphism in early hominids -therefore, males would have been more cooperative and less competitive -This would be consistent with the Provisioning Hypothesis *Evidence exists for both the patchy forest and the provisioning hypothesis *Considerable debate over which hypothesis is more likely *Because of the Miocene Gap, it is difficult to find a definitive answer Earliest Fossil Hominids Pre-Australopithecines *7-4.4mya *Bipedal but with small brains *3 genera -Sahelanthropus -Orrorin -Ardipithecus *Forrest dwellers Sahelanthropus tchadensis, 7-6mya *Tiny brain and massive browridge, but possibly bipedal and non-honing chewing -centered F.M

3 -no honing complex *Lived in a forest habitat Orrorin tugenensis, 6mya *Tugen Hills of Kenya *Likely bipedal, non-honing chewing -A long femoral neck and an obturator externs groove *Lived in a forest habitat Ardipithecus, mya *Awash River Valley of Ethiopia *Two species -Ar. Kadabba 5.8mya -Ar. Ramidus 4.4mya *Primitive dentition and phalanges, but fully bipedal *Lived in a wooded habitat Australopithecines *4-1mya, Africa *Bipedal, non-honing chewers with small brains *Two forms -Gracile form: anamensis, afarensis, africanus, garhi, sediba -Robust form: aethiopicus, boisei, robustus Australopithecus anamensis, 4mya *Lake Turkana (Kenya) and Ethiopia *Ape-like U-shaped tooth rows, but the knee shows bipedal morphology -A carrying angle Australopithecus afarensis, 3.6-3mya *Found by Donald Johanson, Maurice Taib and Tim White *Located in Laetoli, Tanzania and Hadar (and other places) in Ethiopia - Lucy is very complete for the age, 40% of skeleton found in Hadar -At Laetoli, assemblages include hominids as well as footprints of 3 hominids -Bipedal, may have had stride similar to modern humans *Long arms, curved finger bones, suggesting tree use *Cranial capacity of 430cc *Lived in varied habitats Hadar Specimens *Hadar, Ethiopia * mya, K/Ar dating *Riverine forest at the time * Lucy discovered in 1974 *A fossilized female afarensis, 40% complete

4 Laetoli Specimens *Laetoli, Tanzania *Hominid footprints preserved in a volcanic ash layer *3.5mya K/Ar dating *Likely made by afarensis *The area was semiarid woodland or grassland Australopithecus africanus, 3-2mya *Found by Raymond Dart *Taung, South Africa & other sites *Cranial capacity of 450cc *Possibly 3 species *Ancestor to Homo? South African Specimens *The fossil record in South Africa (from caves) is problematic *Cave specimens are difficult to date *Hominids didn t live in caves- likely they were dropped in by predators *Fossils are often embedded in rock- difficult to remove Australopithecus garhi, 2.5mya *Ethiopia *450cc *Stone tool use? *Ancestor to Homo? *Garhi is associated mammal bones with cut marks, leading to conclusion that they made Oldowan tools, the earliest stone tools (controversial). *Stone tools were long associated with meat consumption; some wear may indicate tools were also used for digging in the ground Robust Australopithecines *Significant evolution of craniums *Morphological adaptation to specialized diets in drying environment but later went extinct *Some argue that they should be put in their own genus: Paranthropus Australopithecus aethiopicus, 2.5mya *East Africa, e.g. Ethiopia *Cranial capacity of 410cc Australopithecus boisei, mya *East African sites *510cc Australopithecus robustus, 2mya *South Africa

5 *530cc Anatomy of the robust A. *Big, robust chewing teeth- molars and molarized premolars (smaller front teeth) *Thick enamel *Dietary focus on harder foods (Microscopic exams) *Heavy-build lower jaws *Flared zygomatic (cheek) bones -Masseter muscle attachments -Temporalis muscles pass *Sagittal crests

4/20/2008. Overview. Early Human Evolution. Chronology of Hominid Evolution. Overview of Species. Epochs of the Cenozoic Era

4/20/2008. Overview. Early Human Evolution. Chronology of Hominid Evolution. Overview of Species. Epochs of the Cenozoic Era Early Human Evolution Overview and Chronology What makes us human? Ardipithecus and early Australopithecus Robust and gracile australopithecines Oldowan tools Overview First hominins appeared late in the