Species names
always comprised of (at least) two words: genus (capitalized) and species
(not capitalized); both words in italics e.g. Homo sapiens
Basal hominins
Sahelanthropus tchadensis
Orrorin tugenensis
Ardipithecus kadabba
Ardipithecus ramidus
Archaic hominins
Australopithecus afarensis
Australopithecus anamensis
Australopithecus bahrelghazali
Australopithecus garhi
Australopithecus sediba
Megadont archaic hominins
Paranthropus aethiopicus
Paranthropus robustus
Paranthropus boisei
Transitional hominins
Homo rudolfensis
Homo habilis
Pre-modern hominins
Homo georgicus
Homo ergaster
Homo erectus
Homo antecessor
Homo heidelbergensis
Homo naledi
Homo neanderthalensis
Denisovans
Sahelanthropus tchadensis facts
*7-6mya
* Found (unexpectedly) in Chad, central Africa
*Six specimens, including a complete cranium (Toumai)
and fragmentary lower jaws
* Dated by biostratigraphy: associated with fauna dated
*mixture of derived and primitive features
Orrorin tugenensis facts
*6.6-5.7mya
* Found in the Tugen hills in
Kenya, East Africa in 2000
* Found in sediments dated to
c6mya
* Femur is of a young adult
* Carnivore marks on femur
* Femur suggests bipedalism
* But humerus suggests some
retained arboreality!
* Ape or hominin? Confusing
teeth…
What are the two Ardipithecus species
- Ardipithecus ramidus from 4.4mya
- Ardipithecus kadabba 5.8-5.2mya
Sahelanthropus tchadensis cranium
- Long, narrow basicranium
- Small, ape-size braincase (estimated at 320-380cm3)
- Small, posteriorly located sagittal crest
- Large nuchal crest
- Flat and relatively long nuchal plane with large external occipital crest
- Triangular occipital shape
- Foramen magnum longer than wide, unlike rounded shape of Pan
Sahelanthropus tchadensis face
- Face relatively flat (similar to later hominins)
- Upper part of face wide relative to narrow, short lower face
- Orbits/eye sockets widely set separated by wide interorbital pillar
- Continuous, thick supraorbital torus/browridge (sexual selection?) Similar to later hominins
- Flat frontal squama with no supratoral sulcus but marked postorbital constriction more
pronounced than Pan or Gorilla) - Rear of skull rather ape-like
Sahelanthropus tchadensis jaw/teeth
- Canines relatively small, wear at tips
- large canine fossa
- Small, narrow u-shaped dental arch
- Enamel thickness intermediate between Pan and Australopithecus
- Small cheek teeth – similar to Ardipithecus and australopithecus
Sahelanthropus tchadensis
controversy
Dating:
* The skull was a surface find, out of context: association with dated sediments
unclear
* May have been exposed for some time – found in a grave oriented towards
Mecca?!
* Possibly previously found and re-buried by local pastoral peoples?
Hominin….
* Or Panin (early member of the chimpanzee lineage?)
* Or Gorilline (early member of Gorilla lineage?)
Bipedal?!
* Based on position of foramen magnum under the skull
* Original publication didn’t mention limb bones but a femur was apparently
found and only formally described in 2020 (18 years later?)
* Femur is thought to be ‘inconsistent with habitual bipedalism’
Orrorin tugenensis: bipedal?
Femur: has a few ape-like
features but many more derived features:
* Elongated femoral neck
* Anteriorly twisted head (vs
posterior twist in
australopithecines)
* Thicker cortex bone in the upper
part
* Well-developed gluteal
tuberosity (gluteus muscle
attachment area)
* Shallow superior notch
* Antero-posteriorly compressed
femoral neck
Ardipithecus kadabba facts
- c.5.8 – 5.2mya
- Central Awash complex and the Western margin,
Middle Awash, Ethiopia - Very little known
- About the size of a chimpanzee – more apelike than A.
ramidus - Bones from perhaps 5 individuals including from hand,
arm and clavicle(collar bone) - Orientation and shape of toe bone suggests a grasping
foot but also bipedal characteristics - Dimensions of arm suggest similar body size to
australopithecines - Forested environment? Mixed woodland, grassland
with springs, swamps and small lakes
Ardipithecus kadabba teeth
*Canines quite large and projecting
*Molar enamel thinner than chimpanzees but thicker than
later hominins
*Ate fruit and soft leaves
Ardipithecus ramidus facts
- C 4.5 – 4.3mya
- Dated via absolute dating of volcanic rocks above and below the finds
- Aramis, Middle Awash, Ethiopia
- At least 17 individuals, mainly teeth but including …
- A remarkably complete skeleton (c45% preserved?)
- Weighed c 50kg, height c 3ft 11in/1.2m
Ardipithecus ramidus skull
*Poorly preserved but quite similar to Sahelanthropus
* Quite ape-like but with slightly flatter face
* Brain size 300-370cm3
* cf. chimpanzee 282-500cm3
Ardipithecus ramidus teeth
- Reduced canines and little sexual dimorphism – implications for social
organization? - Relatively thin enamel (modern feature)
- Small molars and premolars; powerful front biting and gripping (leaf stripping)
- Varied diet, similar to a modern chimpanzee?
Ardipithecus ramidus feet
- Divergent big toe for good grasping (more apelike)
- Supportive mid-foot and heel to allow better
‘pushing off’ while walking bipedally
Ardipithecus ramidus pelvis
- Upper part of pelvis is more human-like, lower
part more ape-like
Ardipithecus ramidus hands
- Long, ape-like fingers
- But palm is short and robust
- Wrist is flexible
- NOT adapted to knuckle-walking or brachiation
but some arboreality
Ardipithecus ramidus limb proportion
- Relatively long arms
- More like old world monkeys, not great apes!
