16 - The Australopiths Flashcards
Australopithecines date
Found from ~ 4 Ma to ~ 1 Ma
Two genera of Australopithecines
- Australopithecus
- Paranthropus
Two main geographic areas of Australopithecines
- East Africa
- South Africa
Australopithecus best known species
Australopithecus afarensis
Kenyanthropus platyops
- 3.5-3.2 Ma
- Weird mixture of Australopithecus and Paranthropus features
Australopithecus species
- anamensis
- afarensis
- africanus
- garhi
- sediba
Australopithecus anamensis
- The oldest australopith
- Kenya/Ethiopia
- 4.2-3.9 Ma
- Woodlands/grasslands
Derived traits of A. anamensis
- Small(er) canines, thick enamel, large molars
- Bipedal
Primitive traits of A. anamensis
- Box-shaped jaw like apes
(parallel tooth rows), larger canines than later australopithecines - Upper limb features for arboreality
Australopithecus afarensis
- East Africa
- 3.6 - 3 Ma
- Forest, woodland and savannah
- Lucy (40% complete skeleton)
- Dikika child
- Laetoli footprint
Why is A. afarensis so interesting
- Best known, and largely representative of all australopiths
- Mixture of primitive and derived traits, many are intermediate
A. afarensis traits
- Face prognathic, medium canines, somewhat curved tooth rows, large molars and premolars with thick enamel
- Large neck and chewing muscles
- Highly sexually body size
- Ape like brain size
A. afarensis body
- Major shift in adaptations related to locomotion
- Shows clear evidence of habitual bipedalism
- Changes in pelvis, femur/knee, foor
Bipedal adaptations of the hip
- Ilium flared & rotated allows hip abductors to keep body over midline
- Enlarged sacrum-ilium joint allows more capacity for weight-bearing
Bipedal adaptations of the knee
- Valgus kne: femur angled medially places body weight
closer to midline - Minimizes side-to- side motion when you walk
- Puts support structure (knee) directly under trunk
Bipedal adaptations of the foot
- Enlarged heel (absorbs forces at heel strike)
- Longitudinal arch (stiffens foot into propulsive lever and absorbs forces during stance)
- Big toe in line with the other toes
Arboreal retentions
- Relatively long arms
- Mobile shoulder joint oriented superiorly
- Slender, curved fingers & toes
- May have spent time in the trees (safe from predators)
Disadvantages of A. afarensis bipedalism
- Compromised “bent hip bent knee” gait
- Short legs = more steps to move same distance
Laetoli footprints
- Tanzania, 3.4 Ma
- Formed by 3 individuals walking in wet volcanic ash
- Analyses show pattern of footfalls similar to modern humans
Australopithecus africanus
- First ever hominin found in Africa (south africa)
- Taung baby
- 3 - 2.2 Ma
- Postcrania similar to A. afarensis
- Dentition different: smaller canines and incisors, larger molars
Taung baby
- Raymond Dart, first discovery in 1924!
- Said hominin because of foramen magnum position
- Rejected by most scientists as too primitive and brain too small
Growth and Development
in Australopiths
- Taung Baby and Dikika Child are both ~ 3 years old
- Help us to understand life history patterns
- Both grew fast, like apes
Australopithecus garhi
- Ethiopia
- 2.5 Ma
- Means surprise in local language
- Even larger molars and premolars than A. africanus
- Found in association with cut- marked animal bones (evidence of butchery by hominins)
Australopithecus sediba
- Recent find (2010)
- South Africa, 2- 1.8 Ma
- Maybe descended from A. africanus and claimed ancestor of genus Homo
- Two partial skeletons
- Fully bipedal but still somewhat arboreal (long arms)
- “Transitional species”
Paranthropus
- The “robust” Australopithecines
- Separate line that diverged from early hominids
- same bipedal adaptations as A. africanus and A. afarensis
Paranthropus species
- Paranthropus aethiopicus (3.0-2.3 Ma)
- Paranthropus boisei (2.3 - 1.3 Ma)
- Paranthropus robustus (2-1 Ma)
Skull/teeth adaptations of Paranthropus
- Specialised dietary adaptations
- Massive molars (with molariform premolars)
- Large sagittal crests & wide flaring zygomatic arches (leaves room for large temporalis muscle)
- Thick lower jaw
- Diet likely of very hard or tough foods `(seeds, nuts, tubers)
Australopith Diets
- Are varied
- Trend over time for increase in premolar and molar size (post-canine dentition) coupled with thicker enamel
- Faces and mandibles get larger
- Bony attachments for chewing muscles get larger
- Most extreme in Paranthropus
Sexial dimorphism in australopiths
- Body size dimorphism: similar to modern gorillas and orangutans (a lot!)
- Canine dimorphism: Less than chimpanzees but more than humans
- Male-male competition, but not aggression?
Early Hominin Phylogeny
Lots of uncertainty as to
how species are related
- Not sure how if/how any of the ‘earliest hominins’ is related to australopiths
- Some australopith led to the genus Homo but we don’t know which one
