Early Hominins: Evolution, Traits, and Tool Use

Posted on Jan 12, 2025 in Geography

**Difference Between Hominins and Hominids**

  • Humans and human ancestors only are referred to as hominins.
  • African-derived great apes (chimpanzees, bonobos, gorillas) and humans, along with their ancestors, are referred to as hominids.

**Hominin Traits**

  • Modifications in the pelvic girdle (hip bones) and lower limbs that make them capable of bipedal locomotion (bipedalism).
  • Changes in the upper arm and vertebral column indicate that weight is supported only by the legs.
  • Smaller canine teeth (canines are larger and sharper in carnivores: meat-eaters).
  • Forward-placed foramen magnum.
  • Reduced shearing complex: a shearing complex is when the lower first premolars are sharpened or flattened from rubbing against the large upper canines as the mouth closes (sectorial premolar).

**Orrorin tugenensis**

  • Dated to about 6 million years ago and found in Kenya.
  • It is debated if these fossils are hominin: only a few postcranial (below the cranium) bones were found besides a few teeth.
  • The molars found have thick enamel: found in hominins but not in chimpanzees or gorillas.
  • However, a canine was found that appears more apelike.
  • The femur fragments suggest Orrorin might have been bipedal, and that it could be a direct ancestor of modern humans.
  • More fossils are needed in order to better evaluate this species.

**Genus Ardipithecus**

  • Many fossils of Ardipithecus ramidus were found representing multiple individuals that lived 4.4 million years ago in Ethiopia (east Africa).
  • Earlier species Ardipithecus kadabba lived there about 5.5 to 5.8 million years ago (thought to be the earliest-known hominin).
  • Both show late Miocene hominid (both ape and human ancestor) traits such as a flat cranial base, thin molar enamel, large canine teeth, and facial prognathism (projecting jaw).
  • The pelvis shows adaptations for bipedalism, but still retains a shape suited for arboreal climbing (transitional).
  • Forward-placed foramen magnum and more gracile humerus like in hominins (thinner: not using the arms to bear weight when walking like quadrupeds do).
  • Pollen and other evidence suggests that Ardipithecus lived in a forested environment, so they might not have been fully bipedal.

**The Australopithecines**

  • Dating to about 4.2 million years ago in eastern and southern Africa.
  • Species of this genus were undoubtedly bipedal.
  • Australopithecus fossils provide us with the majority of the information we have on how early hominins lived.

**Gracile vs. Robust Australopithecines**

  • A robust group with stout mandibles, massive teeth, and large adaptations for chewing.
  • A gracile (smaller or thinner bones) group whose teeth are large but who do not have massive skulls and jaw adaptations of the robust group.
  • A. garhi fossils were found in direct association with primitive stone tool use and meat eating: mammal bone fossils found with tool marks on them.
    • Evidence suggests that A. garhi made and used stone tools to butcher animals that were hunted or scavenged from carnivore kills.
    • First evidence of tool use, manufacture, and meat-eating in hominins.