Hominid Evolution in Context Ancient hominid fossils not accepted as ancestors Biases in fossil record (from 19th century): Fossil remains of species not that old (Homo erectus & Neanderthal) Found in Asia and Europe Had relatively large brains Cultural biases: Big brains, intelligence emphasized Resistance to ancestors with primitive features Resistance to Africa as cradle of humankind Humans viewed as unique (culturally & biologically)

Hominid Evolution in Context Occurs in a series of ADAPTIVE RADIATIONS The evolution & spreading out of related species into new environmental niches What “ingredients” are needed for natural selection/evolution to work?

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

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

Sahelanthropus tchadensis Found in central Africa, country of Chad 7 myo 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?

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

Orrorin tugenensis, cont. 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

Second Adaptive Radiation Early Pliocene (4-5 mya) New species & new genus evolves Dense forest environment All exhibit bipedalism – established hominids Represent a challenge to the established “Savanna Hypothesis”

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. Ape-like traits Grasping big toe (only biped w/ this feature) Long arms, short legs Small brain Human-like traits: Small canines Small molars Hand bones NOT adapted for knuckle-walking

Ardipithecus ramidus Diet: omnivorous - plants, fruits, insects, nuts, seeds Environment: lush woodlands, forests Significance: 1 my older than Lucy Closest established hominid to Last Common Ancestor with chimps Arboreal AND Bipedal Adaptations