Hominid Evolution in Context Ancient hominid fossils not

Hominid Evolution in Context • Ancient hominid fossils not accepted as ancestors – Biases in fossil record (from 19 th 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 East African Sites • Volcanic ash/sediments • Can be dated by Argon/Argon (chronometric) dating, relative dating techniques (stratigraphy) & paleomagnetism South African Sites • Mostly limestone (no volcanic sediments) • Cave sites with bone accumulations • Dated with biostratigraphy & 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