Early primates and hominins

Transcription

1 Early primates and hominins 1

2 Wild Card slide part deux 2

3 Hominins ~7-6 mya split from chimpanzees and bonobos -emerged and stayed in Africa until later Homo Mosaic evolution - these characteristics evolved at significantly different rates (not at same time) 3

4 Derived Hominin traits 1. Bipedalism Larsen 2010 pp Distinct dental pattern 3. Tool-making behavior 4. Large brains 4

5 Australopiths ( mya) * Defining traits -Clearly bipedal -Smaller brains (compared to us) -Large teeth, thick enameled molars -Often called walking apes 5

6 Summary 6

7 Summary 7

8 This week Topics 1. Dating methods and geologic time 2. Early hominins 3. Early genus Homo 4. Homo erectus and contemporaries 5. Premodern humans

9 Today Topics 1. Dating methods 2. Early hominins 3. Early genus Homo (hopefully) 4. Homo erectus and contemporaries

10 1. Dating methods and geologic time Two types: relative and chronometric Relative Dating methods Main idea: gives an approx range relative to other established dates Stratigraphic dating Biostratigraphy Paleomagnetic Chronometric Dating methods Main idea: gives absolute date with chronological measurement (centuries, decades, years, etc.) Radiometric decay

11 1. Dating methods and geologic time Relative Dating methods Main idea: approx range relative to other established dates *Stratigraphic dating -Law of superposition - bottom strata (layers) are the oldest *Biostratigraphy: dates sites relative to fossil species dated elsewhere *Paleomagnetic: relative to shifts in geomagnetic pole over time

12 1. Dating methods and geologic time Chronometric Dating methods Main idea: gives absolute date with chronological measurement (centuries, decades, years, etc.) Radiometric decay: radioactive isotopes decay at a predictable rate *Potassium-Argon dating Half Life: 1.25 by (half of K-40 will have decayed to Ar-40 in 1.25 by) -Volcanic deposits Range: 5-1 mya -useful in dating early hominin sites from East Africa *Radiocarbon dating (C-14 dating) Half Life: 5,730 years -Organic materials (wood, charcoal, and plant fibers) Range: 40 k to a few thousand years ago Cross-correlation

13 2. Early hominins Pre-Australopiths (6-4.4 mya) Australopiths ( mya) Early Homo (2-1.4 mya) Mosaic evolution -different traits of a species evolved at different rates over time

14 2. Early hominins Pre-Australopiths (6-4.4 mya) Sahelanthropus tchadensis ~6 mya; Central Africa -earliest possible hominin ancestor -small brain (less than 400 cc which is average for chimpanzees) -flat face -bipedalism suggested by position of foramen magnum Orrorin ~6 mya; East Africa -human-like teeth and leg bones

15 2. Early hominins Pre-Australopiths (6-4.4 mya) Ardipithecus ramidus mya; East Africa -bipedal with ancestral adaptations to arboreal context -omnivorous

16 2. Early hominins Australopiths ( mya) Australopithecus afarensis mya; East Africa -more ape-like -omnivorous -Laetoli footprints dated 3.7 mya Australopithecus africanus mya; South Africa -first hominin found by Raymond Dart (Taung Child) -foraging omnivore

17 2. Early hominins Australopiths ( mya) Robust australopiths mya Australopithecus boisei mya; East Africa -dietary specialist ("nutcracker man") -sagittal crest, massive jaw, and teeth

18 2. Early hominins Australopiths ( mya) Australopithecus sediba 1.9 mya; East Africa -mixture of ancestral and derived traits Ancestral: small brain (420 cc) Derived: shorter fingers -transitional form to genus Homo?

19 Australopithecus garhi 2.5 mya East Africa Ancestral: small body size Derived: butchered bones discovered with Au garhi fossils

20 3. Early genus Homo Early Homo (2-1.4 mya) Homo habilis mya; East Africa -first associated with tool-use

21 Homo erectus -Emerged in East Africa ~1.7 mya * Evolutionary success due to: 1. Cultural technology 2. Larger body size -flourished from 1.8 mya to 100 kya (1.5 mya) -used sophisticated tools (Oldowan and Acheulian)

22 Homo erectus from Africa 22 Current view: Homo erectus evolved first in Africa -probably arose from earlier group of Homo in East Africa around mya Evidence for: -Earlier hominins are only found in Africa mya fossils at East Turkana, in Kenya, and not long after at other sites in East Africa.

23 General morphology of Homo erectus 23 Body size -adults weigh more than 110 pounds -average height 5'6" Brain size cc Cranium long, low, heavily built -distinctive shape: pentagonal cranium shape (viewed from behind)

24 Homo erectus Timeline 24