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
*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
-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, 5.8-4.4mya *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 *3.4-2.9mya, K/Ar dating *Riverine forest at the time * Lucy discovered in 1974 *A fossilized female afarensis, 40% complete
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, 2.3-1.2mya *East African sites *510cc Australopithecus robustus, 2mya *South Africa
*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