Hominid Evolution in Context - BioAnthro - Home

Hominid Evolution in Context - BioAnthro - Home

Mid-Pliocene Hominids (4-3 mya) Australopithecines History of discovery influenced understanding of hominid evolution Obligate bipedalism established Climate & landscape changes acting as strong selective pressures A lot of variation in species: Aus. anamensis Aus. bahrelgazali Aus. Garhi

Kenyanthropus platyops You WILL NOT need to know these species for the exam! Adaptive Patterns of the Australopithecines Small bodied (avg. height 4-5 ft.) Small brains (approx. same as modern chimp) Tool use similar to modern chimps

NOT stone tool makers Foragers gathered fruits, nuts, seeds, roots, tubers, insects Mixed woodland/savannah environment Small, nomadic social groups Effects of genetic drift, mutation likely to be felt more strongly Resulting in more rapid genetic divergence & eventual speciation Australopithecus

africanus Discovered: 1924 in Taung limestone quarry in South Africa by Raymond Dart Age range: 3.0 2.2 mya Features: slightly projecting lower face, large molars, small front teeth & canines, short face Australopithecus africanus Cranial capacity: 440 cc (avg.) Type specimen: Taung Child (6 yo)

First Australopithecine EVER discovered Australopithecus robustus Discovered: 1936 by Robert Broom in South Africa Age range: 2 -1.5 mya Features: robust features = sagittal crest, large teeth, thick & wide cheekbones, large face, large jaw, small brain Diet of hard food items: nuts, seeds, tubers, roots, leaves

Cranial capacity: 530 cc Australopithecus boisei Discovered: 1959 by Mary Leakey in Tanzania (East Africa) Features: Hyper-robust massive jaw, huge molars & big teeth w/wear, prominent sagittal crest Cranial-dental features work as grinding machine; nicknamed Nutcracker Man; ate seeds, nuts, roots, tubers, leaves (NOT a tool maker---teeth are tools)

Australopithecus boisei Age range: 2.3 1.2 mya Cranial capacity: 530 cc Note: Originally named Zinjanthropus boisei Both A. robustus & A. boisei become extinct (an evolutionary dead end) Relatives not ancestors Distinct features/adaptations = Separate genus? Paranthropus Australopithecus afarensis

(aka Lucy) Discovered: 1974 in Hadar, Ethiopia (East Africa) by Don Johanson Age range: 3.9 3 mya Significance: Antiquity - 1 my older than any other hominid found at that time 40% complete nearly all bones represented Established bipedalism in earliest

known hominid (w/small brain) Australopithecus afarensis, cont. The First Family Discovered: 1975 by Don Johanson in Hadar, Ethiopia, E.Africa Features: Remains of 13 individuals (males, females, adults, juveniles) Highly sexually dimorphic (males much bigger than females; males have sagittal crest)

Significance: strong evidence of variation within the species & for Au. afarensis as a hominid Aus. afarensis, cont. The Laetoli Footprints

Discovered: 1978 in Tanzania by Mary Leakey Age: 3.7 3.5 mya Features: Prints reveal human-like stride; big toe in line with others; arch in foot Significance: Firmly establishes bipedality in earliest hominids Important Notes on Aus. afarensis Physical Features: Ape-like face, jaw Small brain

(375 -550 cc) Males w/sagittal crest But(unlike apes) Reduced canine Broader palate From neck down: Arms longer than legs Curved finger & toe bones Flexible ankle &

shoulder joints Wide but shortened pelvis Funnel shaped rib cage Important Notes on Aus. afarensis, cont. Behaviorally, Aus. Afarensis spent time in the trees AND on the ground

Centralized foramen magnum indicates obligate bipedalism Latest discovery - Lucys baby (Selam, 3 yr. old child skeleton) shows early hominid bipedalism not the same as modern bipeds Summary of Early Hominids Australopithecine ancestors are very ape-like in appearance & behavior Lots of variation for natural selection to work with (lots of selective pressures, esp. climate shocks operating

Exhibit a mix of traits but establishing a set of evolutionary trends that will define our genus, Homo Very challenging to determine relatives from ancestors Are not what we would consider human (so are not assigned to our genus)

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