Chapter 10 Early Hominins and Australopithecus

Becoming a Biped Anatomical Changes Constructing the Bipedal Body Plan balancing the body’s weight over two limbs Constructing the Bipedal Body Plan Why Bipeds?

The Transition to Human Behavior What Made Humans Human? the anatomical shift from quadrupedalism came after a behavioral shift began at every stage of the process, natural selection favored the form the evolving protohominin took at the earliest stages of hominin evolution, brain size and intelligence were quite apelike

Will you Know a Hominin When You See One? Bipedality Dentition Parabolic arch Size of anterior and posterior teeth Prognathism CP3 Enamel Cranial Features

The First Hominins Sahelanthropus tchadensis (7.0-6.0 MYA) Chad Less prognathic face Large brow-ridge Smaller canines Anterior foramen magnum Small brain U-shaped arcade Thin enamel

The First Hominins (cont’d) Orrorin Tugenensis (6.0 MYA) Kenya 6 mya Arm and femoral fragments may suggest bipedalism Thick enamel Small teeth Large upper canines

The First Hominins (cont’d) Ardipithecus ramidus (4.4 MYA) and Ardipithecus kadabba (5.8-5.2 MYA) ramidus 4.4 mya Smaller canine Anterior foramen magnum Apelike molars kadabba 5.8 - 5.2 mya More apelike dentition Originally considered a variant of ramidus

Australopithecus and Kin Australopithecus anamensis (4.2-3.9 MYA) Thickened tibia Primitive dentition Lumped with afarensis? Lived in forested region

Australopithecus and Kin (cont’d) Australopithecus afarensis 3.9-2.9 mya Lucy Short, broad pelvis Tilted femurs In-line big toe Sagittal crest Small brain Sexually dimorphic

Australopithecus and Kin (cont’d) Australopithecus bahrelghazali (3.5-3.0 MYA) Western Africa Mandible fragment with seven teeth A specimen of afarensis?

Australopithecus and Kin (cont’d) Kenyanthropus platyops (3.5 MYA) Flat face Small molar teeth afarensis?

Australopithecus and Kin (cont’d) Australopithecus garhi (2.5 MYA) Small brain Prognathic face Large canines Sagittal crest More human-like postcranial proportions? Tool use?

Australopithecus and Kin (cont’d) Australopithecus africanus (3.5-<2.0 MYA) Slight brain increase Rounded vault No crests Less projecting face Bipedal postcranial anatomy

Australopithecus and Kin (cont’d) Australopithecus sediba (1.97-1.78MYA) Discovered 2010 in South Africa Slight brain increase (420-435 cc) Characteristics similar to Homo dental anatomy derived face features of the pelvis

Australopithecus and Kin (cont’d) 'Robust' Australopithecus (or Paranthropus) Hard object feeding Sagittal crest Large cheek teeth Flared zygomatic arch Dished face Extreme postorbital construction Woodland and open woodland habitat

Australopithecus and Kin (cont’d) Robust Australopithecines (cont’d) Australopithecus (p.) aethiopicus 2.7-2.5 mya Australopithecus (p.) boisei 2.3-1.2 mya Australopithecus (p.) robustus 2.0-1.5 mya