Will the Earliest Hominid Please Stand Up? Earliest representatives of our lineage lived at end of Miocene & beginning of Pliocene epoch 6 – 4.5 mya

Geological Context of Hominid Sites South African Sites Mostly limestone (no volcanic sediments) Cave sites with bone accumulations Dated with biostratigraphy & paleomagnetism East African Sites Volcanic ash/sediments Can be dated by Argon/Argon (chronometric) dating, relative dating techniques (stratigraphy) & paleomagnetism

Mid-Pliocene Hominids (4-3 mya) Australopithecines 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

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 Features: slightly projecting lower face, large molars, small front teeth & canines, short face

Australopithecus africanus Age range: 3.0 – 2.2 mya Type specimen: Taung Child (6 yo) First Australopithecine EVER discovered Cranial capacity: 440 cc (avg.)

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)

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 (male, female, adults, juveniles) Highly sexually dimorphic (males much bigger than females) 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 Features: Prints reveal human-like stride; big toe in line with others; arch in foot Age: 3.7 – 3.5 mya 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 pelvis, 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

Adaptive Patterns of Early African Hominids Gracile australopiths More omnivorous More arboreal Reflected in foot, ankle, hand, wrist bones A. afarensis, A. africanus

Adaptive Patterns of Early African Hominids Robust australopiths Diet of hard food items Less arboreal Due to food sources Extinct 1 mya A. robustus, A. boisei Different Genus? - Paranthropus

Second Adaptive Radiation Early Pliocene (4-5 mya) New species & new genus evolves All exhibit bipedalism – established hominids

Ardipithecus ramidus Discovered: 1994 in Ethiopia by various research teams Age range: 5.8- 4.4 mya Features: most complete ancient hominid skeleton – bones of hand, feet, limbs, pelvis, most of skull & teeth; remains of males, females, juveniles

A. ramidus, cont. Mix of ape & human traits: Small canines Grasping big toe (only biped w/ this feature) Long arms, short legs Small brain Hand bones NOT adapted for knuckle-walking Small molars Diet: omnivorous - plants, fruits, insects, nuts, seeds Environment: lush woodlands, forests

Ardipithecus ramidus Significance: 1 my older than Lucy Closest established hominid to Last Common Ancestor with chimps Evidence of bipedalism arising in a more arboreal context than previously thought

Ardipithecus ramidus, cont.

Ardipithecus ramidus

First Adaptive Radiation Late Miocene (6-7 mya) Produced potential/possible LAST COMMON ANCESTORS These are the earliest (possible) Hominids Forest adapted

Orrorin tugenensis aka “Millenium Man” Discovered: 2001 in western Kenya Age range: 6 mya Remains: Fragmentary arm & thigh bones; lower jaws & teeth Features: Limb bones larger than later hominid species Cranial capacity: Not yet determined Notes: Some evidence of bipedality & tree climbing; dental & some skeletal features more human than ape like Significance: More evidence that bipedalism may have originated in the trees

Sahelanthropus tchadensis Found in central Africa, country of Chad Nearly complete cranium Mix of human & ape-like traits Small braincase: 370-380 cc Massively built, heavy browridges, crest in back, large muscle attachments Reduced upper canine Small, vertical face Cannot determine bipedality OLDEST possible hominid Common ancestor?

Summary of Early Hominids Australopithecine ancestors & relatives are very ape-like in appearance & behavior Lots of variation for natural selection to work with Exhibit a mix of traits but establishing a set of evolutionary trends that will define our genus, Homo Are not what we would consider “human” (Thus, are not assigned to our genus)