Lecture 10 - Earliest Hominin Candidates Flashcards
Sahelanthropus tchadensis hominin synapomorphies
- relatively small canines w/apical wear
- non-honing CP3 complex
- more vertical face
- more anterior foramen magnum
- potential biped but no postcranial evidence
Sahelanthropus tchadensis hominoid synapomorphies
- large brow ridges
- small endocranial volume
Sahelanthropus tchadensis
Sahelanthropus tchadensis general info
- 7 ma
- Chad
- lacks postcranial evidence
- TM266 “Toumai” - squished reconstructed cranium
is Sahelanthropus tchadensis a crown hominin
- absence of CP3 honing complex
- other traits rely on reconstruction
Orrorin tugenesis
Orrorin tugenesis general info
- 6 Ma
- Tugen Hills, Kenya
- “Millenium Man”
- 13 specimens including femur, jaws, teeth
Orrorin tugenesis
Orrorin tugenesis fossil evidence
- dental evidence - more ape like
- bipedal evidence: strong
- large femoral head, similar to later hominins
- distribution of the cortical bone likely indicates facultative bipedalism
Orrorin tugenesis
Orrorin tugenesis hominin synapomorphies
- femur: facultative bipedalism
- thumb anatomy
- tip to side grip
- tip to tip
- pad to pad
- long thumb, similar to Homo
Orrorin tugenesis
Orrorin tugenesis hominoid symplesiomorphies
- curved phalanges
- dentition is ape-like: medium sized canines
Orrorin tugenesis
isOrrorin tugenesis a crown hominin
- dentition is still primitive
- postcranial evidence is debated (femur, fingers)
Ardipithecus kadabba
Ardipithecus kadabba general info
- 5.5 Ma
- Ethiopia
Ardipithecus kadabba
Ardipithecus kadabba fossil evidence
- fragmentary but teeth show small
- pedal phalangers suggest upright posture
Ardipithecus kadabba
Ardipithecus kadabba hominin synapomorphies
- shorter, more circular canine and slight CP3 wear
- reduced CP3 honing complex
Ardipithecus kadabba
Ardipithecus kadabba hominoid symplesiomorphies
- curved fingers and toes
Ardipithecus kadabba
is Ardipithecus kadabba a crown hominin
- still relatively ape-like dental morphology
- weak bipedalism for bipedalism/upright posture
Ardipithecus ramidus
Ardipithecus ramidus general info
- Middle Awash, Ethiopia
- 4.4. Ma
Ardipithecus ramidus
Ardipithecus ramidus hominin synapomorphies
- absence of honing complex
- foramen magum more anterior
- intermediate enamel thickness
- short pelvis
- metatarsophalangeal joint shape indicates dorsiflexion
- hand is consistent w/ predictions for Pan/Homo LCA
Ardipithecus ramidus
Ardipithecus ramidus pelvis evidence
- evidence for both bipedalism & climbing
- ischial surface primitive
- short broad ilia, greater sciatic notch that is absent in Pan
Ardipithecus ramidus
foot bipedalism?
- doming proximal pedal phalanx. in humans & Ardi
- ape-like curvature in phalanges
- opposable hallux
Ardipithecus ramidus
hand evidence
- primitive?
- reflects a more general grasping adaptation not related to suspensory locomotion
Ardipithecus ramidus
Ardipithecus ramidus hominoid symplesiomorphies
- small endocranial volume
- curved fingers & toes
- orientation of ischium
Ardipithecus ramidus
is Ardipithecus ramidus a crown hominin?
- pelvic, femoral, and foot anatomy compatible with incipient bipedalism
- ancestor-descendant relationship w/ australopiths unknown
bottom line
- candidates do not have to be panins, hominins, or common ancestor
- could belong to one (or more) extinct clades
why is it hard to be sure whether these are hominins or not?
- adaptations could be because of environmental pressures
> homoplasy/convergent evolution that could cause hominin-like adaptations - limited evidence - mostly fragmented, incomplete skeletons
> don’t know if species are the same or different based on the evidence we have - absence of a Pan fossil record
- species closer to Pan-Homo split will only have a few derived traits, similar populations, hard to know what lineage the species is on
