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 A105 Human Origins and Prehistory
Lecture 9

Lecture 9: Early Hominids and their Lifeways

I. Earliest Hominids
  A. Orrorin tugenensis, 6 mya. Tugen Hills, Kenya.  Assorted skeletal parts claimed to be hominid, but could also be chimpanzee ancestor. 
 
 
 
 

   B. Lothagam, 5.6 mya, is a site with another early fossil, consisting of part of a jaw and a tooth.  Molars are square, enamel thick.
 
 
 

   C. Ardipithecus ramidus, 4.2 mya. Afar, Ethiopia.  Earliest widely recognized species. 
    Skull pieces, pelvic fragments, some teeth.  Lower deciduous molar is chimplike (unlike Lothagam), molars are intermediate in size between chimp and later hominids'; position uncertain, but may be root ancestor to all hominids or a sister species to that ancestor.  Pelvis and foramen magnum are said to indicate bipedalism.
 

   D. Australopithecus anamensis, 4.1 mya, Allia Bay and Kanapoi, Kenya.
   Palate, mandible, tibia, small piece of temporal.  Teeth are square and enamel thick like Lothagam and A. afarensis.  Tibia has a thick proximal end, large articular surfaces relative to shaft dimensions --> bipedalism.
 
 
 

II.  Australopithecus afarensis, 3.6-2.8 mya Hadar, Ethiopia; Laetoli, Tanzania. 

  • Laetoli footprints, Tanzania, 3.6 mya.  A number of animals, including two or three hominids, walked across wet volcanic ash and their tracks were preserved.  69 hominid prints, in two sets (38 small, and 31 large).  There may be a third set of prints inside the large ones. The two main tracks are side by side.  Prints are reasonably humanlike EXCEPT:
        Ball of foot smaller, arch less pronounced, big toe may be splayed (divergent); this last not agreed by all scientists. Laetoli also has teeth.
  • For A. afarensis we have the parts of at least 35 individuals, including the 40% complete "Lucy" skeleton.
  • There is also the "First Family," site A.L. 333, which contains the remains of 13 individuals (4 male, 1 female, 4 juvenile, 4 not able to be sexed) that may have come from a single social group.
  • Cranial characteristics:  Browridge present.  Brain averages 400 cc (compare with chimp, 350cc avg.).  Occipital rather apelike, with large nuchal area for neck muscle attachment, but foramen magnum in human position.  Zygomatics robust and flared.
  • Teeth: canine larger than later hominids', smaller than chimps', honed against lower premolar (can indicate males fighting).  Incisors smaller than chimps' but still relatively large.  Molars large with thick enamel.
  • High amount of sexual dimorphism: height range 3'3"-5'7", weight range 60-150 lbs.  Similar amount of dimorphism to gorilla.
  • Postcrania mix of chimplike, humanlike, unique traits.
          Chimplike: Fingers, toes intermediate length but curved, with flexor sheath ridges; distal humerus ridged; cone-shaped torso; glenoid fossa tilted upward.
 
 
 
 

           Humanlike: Valgus femur; large calcaneus; may have had arches in feet.
 

   

          Unique: Short legs (despite bipedal features); pelvis wider than necessary for childbirth (bad for bipedal walking).
 
 

  • Chimplike above the waist, humanlike below (even the joint surfaces follow this -- larger than ours above waist, smaller below).
  • Anatomy suggests some suspensory (arboreal) activity, with habitual bipedalism.  Less locomotor component than today.  Possibly for stability in trees.

 
  • Behavior: Able to exploit arboreal and terrestrial areas.  Engaged in bipedal behavior, probably feeding in small trees, with some amount of arm-hanging.  Able to climb trees, especially smaller individuals (females, juveniles; similar pattern to chimps).  Not adapted to carrying things or walking efficiently.  Probably frugivorous, specializing in small woodland fruits.
  • Social life: Dimorphism suggests males fought by themselves, but they may occasionally have banded together to defend, maybe with fists as seen in chimps (canines probably too small to do much damage), maybe with simple weapons like clubs. From modern primate social systems, female choice is the most logical given the amount of dimorphism and terrestriality, but A. afarensis would not have acted just like a gorilla.
  • Breeding male, females probably traveled together, with females bonding more to the male than to each other (though female friendships certainly could develop).  Females could be related to each other or not.  Some time spent grooming, but not as much as in some primates like monkeys.  In single-male societies, there tends to be little sexual activity, and estrus tends to be concealed (not visible).
  • Groups were likely nomadic, stopping where they happened to be at night rather than returning to a home base.  Wandering among resource patches.  Some terrestrial primates have siblings sticking together, helping each other, which could have happened here, been the basis for larger groupings.  They probably slept in trees for safety, and may have scavenged meat on the savannas, but if this happened, it was not a major part of the diet.
III. A. africanus, 3.5-2 mya.  South Africa: Taung, Sterkfontein, Makapansgat.  Some disputed claims for East Africa.  Faunal dates only.
 
  • Teeth: Incisors smaller, molars larger than afarensis.
  • Cranial anatomy (vs. afarensis): Reduced nuchal area; face more robust (flared zygomatics) and drawn under braincase more; browridge less pronounced; brain ~450cc; skull more globular.
  • Postcrania: Little published, but may be more chimplike than afarensis.
At about 2.5 mya, another cooling pulse further shrank forests, expanded savannas.

IV. Robust Australopithecines.
                                     Gracile vs. Robust
A. afarensis, A. africanus are considered gracile.  Generally lived before 2 mya (3.8-2.5 mya); brains <500cc; small brow ridge; some prognathism; face flat  with squared zygomatics.  

The three robust australopithecines were different: very large zygomatics, extreme prognathism, very large molars; microwear on teeth (scratches and pits) indicates diet of nuts, hard seeds, hard-husked fruits; nuchal area and incisors reduced.  They are considered to be an extinct side branch (not our direct ancestors).
 

  • A. aethiopicus, 2.5 mya, Lake Turkana, Kenya.  KNM-WT 17000 (the "black skull").  Mix of afarensis, new features:  New: Larger sagittal crest, huge face, larger molars & premolars, larger body size.  Old: small brain (404 cc), prognathic, large nuchal area and relatively large incisors; high dimorphism.  Bipeds who still climbed trees, increasing chewing/crushing capacity but still relying on incisors.
  • A. boisei, 2-1 mya.  Olduvai, Lake Turkana.  OH5 ("Zinj"), made Leakeys' careers.  Incisors smaller than ours, molars 3-4x ours.  Nuchal area smaller than afarensis.  Dished face (zygomatics in front of nose) but less prognathic; sagittal crest forward; brain 500cc.  Dimorphic; descendant of A. aethiopicus.

 
 
  • A. robustus, 2-1.5 mya, South Africa: Swartkrans, Kromdraai.  Large faces, molars slightly larger than africanus; dished face, smaller incisors, forward sagittal crest, less prognathism, less nuchal area than aethiopicus.  Brain ~500 cc.  Broad fingertips; bipedalism.  Often seen at same sites as early Homo.  Could be descended from africanus or aethiopicus.
 V. Other pre-Homo Hominids.
  • A. garhi, Bouri, Ethiopia, 2.5 mya.  Brain 450 cc; prognathic jaw like afarensis; molars larger than robustus; teeth also have Homo features. Postcrania -- upper limb segments relative length is humanlike, but lower arm long.  Found with cutmarked fauna.
  • Kenyanthropus platyops, 3.5 mya, Kenya.  Just announced 2001.