15 - Earliest Hominins Flashcards
1
Q
Fossil
A
Preserved remains or traces of plants, animals, and other organisms from the remote past
2
Q
Types of fossils
A
- Bones and teeth
- Trace fossils
- Wood, leaves
- Subfossils
3
Q
Continental drift
A
- Drift is a major engine of climate change
- Larger landmasses are colder
- Orientation of landmasses affects water circulation
4
Q
Global temps during Cenozoic period
A
Got cooler
5
Q
Epoch Homo sapiens appeared in
A
Pleistocene
6
Q
Absolute dating / radiometric methods
A
- Gives age estimate in years
- Elements in nature exist in unstable, radioactive isotopes (e.g. 12 C vs. 14 C)
- Decay at clock-like rate: spontaneously change to another isotope
- Know rate and proportion of isotopes = can get time
- e.g. potassium-argon dating
of volcanic layers (>500kya)
7
Q
Relative dating
A
- Gives fossils an age relative to something else
- Provides a sequence, and complements absolute dating methods
8
Q
Biostratigraphy
A
Date rocks by looking at the fossils and comparing with other dated sequences
9
Q
Closest living relative
A
Chimpanzees and bonobos
10
Q
Hominin
A
- Members of the ‘human clade’ that have evolved since the split with chimpanzees
- Everything more closely related to humans than chimps
11
Q
Hominid
A
All great apes
12
Q
5 new features that seperate humans from chimps
A
- Dental characteristics
- Larger brain/body size ratio
- Slow maturation and development
- Complex symbolic and material culture (Including language)
- Habitual (committed) bipedalism (Anatomical changes from head to toe)
13
Q
Dental changes
A
- Reduction in size of canines
- Canines don’t interlock
- Upper canine no longer sharpens on the 1 st lower premolar
- Honing characteristic of apes and monkeys
- Change in shape of the dental arcade (tooth row) from U- shape to parabola
- Enamel gets thicker
14
Q
Brain size
A
- Apes have large brains relative to body size (~ 2 x expected)
- Humans are 7-8x greater than expected
- Chimp brains ~ 320- 350 cc
- Human brains average 1350 cc
- Cognition, life history patterns are implicated, but not straightforward
15
Q
Slow Maturation
A
- Humans have slower life histories than apes
- Humans have longer gestation, juvenile period and growth, menopause etc.
- Can be measured to some extent in fossils (Tooth eruption and bone/enamel development)
16
Q
Life History
A
- Timing of key events in an organism’s life, shaped by ecology and natural selection
- Growth, sexual maturity, death etc
17
Q
Culture
A
- Apes do have complex cognition and some ability to use tools
- Increased reliance on technology
- Ability to inhabit almost all
environments - Tools, fire, symbolism, art, and language are major innovations
- Archaeological record tells us some aspects of culture
- Many thing would not preserve (e.g. wood tools, body decorations)
18
Q
Bipedalism
A
- The most defining feature of hominins
- Recognizable in the fossil record
- We know now that it comes first
- Before big brains
19
Q
Anatomical adaptations for walking
A
- Foramen magnum positioned at bottom of skull
- S spine instead of C spine
- Wide flared pelvis for hip adductor muscles
- Long neck of femur
- Femur angled so that knee joints are close together other nody
- Stiff ankle with limited side movement
- Not opposable big toe and arched foot
20
Q
Human pelvis
A
- Most altered bony anatomy in humans
- Trade offs between walking and need for birthing large brain babies
21
Q
Hip Abductor Muscles
A
- Attach to the iliac crest
- Wide short ilium with distinctive sciatic notch present in humans and hominins, not chimps
- Keep pelvis from slanting downwards with each step
- Minimize movement of center of gravity for efficient
walking
22
Q
Human bipedalism
A
- Extended knee and hip
- Lumbar curve
- Ventral foramen magnum
- Places center of gravity (COG) in line with major joints
- Compared to lying down, standing requires only 7%
more oxygen in humans - Stable, not much muscle
activity needed
23
Q
Chimp bipedalism
A
- Bent hip, bent knee(BHBK)
- COG further forward
- Chimps must use muscles
constantly to keep upright
(always falling forward)
24
Q
The Late Miocene of Africa
A
- Late Miocene marked by drying and cooling
- Poor fossil record
25
When did hominins and chimps split
6 - 8 Ma
26
Sahelanthropus tchadensis
- Found 2002 in Chad
- 6-7 Ma using relative dating
- Near complete cranium and mandible
- Woodland environment
- Bipedal
27
Primitive characteristics of S. tchadensis
Brain size (~350cc like chimp)
28
Derived characteristics of S. tchadensis
- Flat face like later hominids
- Thick enamel
- Small canines
29
Primitive characteristics of O. tugenensis
Curved proximal phalanx
29
Orrorin tugenensis
- Found 1999 Kenya
- 6 Ma
- Teeth and postcranial bones
- Woodland environment
30
Derived characteristics of O. tugenensis
- Teeth small w/ thick enamel
- Bipedal
31
Ardipithecus kadabba
- 5.2 – 5.8 Ma
- Ethiopia
- Limited material
32
Primitive characteristics of A. kadabba
- Upper canine sharpens against lower premolar
33
Derived characteristic A. kadabba
Bipedal?
34
Ardipithecus ramidus
- Ethiopia 4.4 Ma
- Woodland environment
- 1 Ma after A. kadabba
- 'Ardi' in 2009 (complete female skeleton)
35
Primitive characteristics of A. ramidus
- Opposable big toe
- Long fingers/short
thumb
- Thin enamel on molars
- Small brain (~300- 350cc)
36
Derived characteristics of A. ramidus
- Anterior foramen magnum
- Bipedal adaptations in pelvis
- Small canines
- Thick enamel
37
Controversy of earliest hominins / pre australopiths
- Are they really hominins?
- Is evidence for bipedalism ‘good enough’?
- If hominin, is it necessarily ancestral to later hominins,
or just a ‘dead end’?
- Many primitive features retained
- Likely still spending time in trees
38
What do first hominins tell us?
1. Early hominins more widespread than thought
2. Bipedalism, thicker tooth enamel and reduced canines are first key derived features of hominins (Not brain size, tool use etc)
3. Environment of earliest bipedal creatures was some kind of woodland (Previously assumed to be savannah environment)
