Lecture 24 notes.docx

Introduction to Human Evolution: Monday November 6, 2023 Today: Pre-australopiths Australopith trends Finding Early Hominin Fossils East African sites along the Great Rift Valley where more than 2,000 hominin fossils have been found (Hominins are limited to the continent of African until abou...

Introduction to Human Evolution: Monday November 6, 2023 Today: Pre-australopiths Australopith trends Finding Early Hominin Fossils East African sites along the Great Rift Valley where more than 2,000 hominin fossils have been found (Hominins are limited to the continent of African until about 1.8 million years ago) South Africa sites with geological strat more complex than along the East African Rift Valley Earliest Hominins How early hominins fit into human evolution are much debated Significant early finds include Sahelanthropus tchadensis: 6-7 mya from chad in Central Africa Orrorin tungensis: 6 mya from kenya in eastern Africa Ardipithecus kadaba: 5.8-5.2 mya from Ethiopia in eastern Africa Ardipithecus ramidus: 5.8-4.4 mya from Ethiopia in eastern Africa Ardipithecus ramidus showed that some early hominins lived in wooded environments rather than open savanna Early Hominins from Africa Span of 5 million years (~7mya - 1mya) Three major groups: 1. Pre-australopiths (~6+ - 4.4 mya) 2. Australopiths (4.2 - 1.2 mya) 3. Early Homo (2 - 1.4 mya) Pre-Australopiths During the miocene-pliocene (~7-4.2 mya) East Africa, North-Central Africa Large (30-60 kg or 66-133lbs) Diurnal Terrestrial bipedalism; Arboreal ‘‘climbing’’? (i.e., opposable big toe) Earliest known hominins Lived in wooded savanna or woodland mosaic habitats Small brain (370-400 cc), like apes Small molars and premolars, thin enamel, like apes Somewhat reduced facial projection (prognathism) Protrusion of the face, in certain parts Foramen magnum faced inferiorly (toward the bottom) Pre-Australopiths (earliest and most primitive humans) Sahelanthropus tchadensis (~7-6 mya) Central Africa - Chad Oldest possible hominin Preserved cranium Possibly bipedal Orrorin tungenensis (~6 mya) Central Kenya and Middle Awash area of NE Ethiopia 1st Hominin with postcranial remains Possibly bipedal Ardipithecus (5.8-4.4 mya) - Ardi East Africa-Ethiopia Very complete skeleton Bowl shaped pelvis Bipedeal and quadrupedal Opposable big toe Honing Complex A shearing large upper canine / 1st premolar arrangement Typical in OWM and apes Absent in most hominins (this along with bipedalism represent mosaic evolution) Non-honing chewing complex (humans) The presence of this feature, is telling of what the individuals were eating and where they fit into Showing the slow changes that occurred based on the resources available in their environments Key Pre-Australopith Discoveries Dates Region Hominins Significance ~7.0 mya Central Africa Sahelanthropus Tchadensis oldest hominin; well preserved cranium; very small brained; likely bipedal ~6.0 mya East Africa Orrorin tungenensis First (hominin) with postcranial remains 5.2-5.8 East Africa Ardipithecus Fragmentary, but probably bipedal 4.4 mya East Africa Ardipithecus ramidus Large collection of fossils, partial skeletons; bipedal but derived Sahelanthropus Small braincase Vertical face Huge brow ridge Australopiths (4.2-1.2 mya) The best-known, most widely distributed, and most diverse of the arlth African Hominins Made up of two closely related genera Australopithecus and Paranthropus Gracile and robust groups