Lecture: Primitive and Modern Traits in Chimpanzee and Human Skulls

Primitive Traits in Chimpanzees

• Teeth and Jaw
  • Large upper canines and large teeth are primitive traits.
  • Larger mandible compared to humans.
• Sagittal Crest
  • Crest of bone on top of the cranium for muscle attachment.
  • Large crest implies large jaw muscles for heavy chewing.
• Brow Ridges
  • Prominent brow ridges above eye sockets.
  • Result of cranial structure accommodating large jaw muscles.
• Prognathism
  • High degree of prognathism (projected snout area).
• Cranial Shape
  • Oval or oblong cranium.
  • Large nasal cavity.
  • Flattened cranial base due to quadrupedality.

Modern Traits in Humans

• Cranial and Facial Structure
  • Globular, rounded cranium.
  • Large cranial capacity for bigger brains.
  • Small mandible and teeth, no sagittal crest.
  • Vertical face with little to no prognathism.
  • Smaller nasal cavity.
  • Little to no brow ridges, with features absorbed into the forehead.
• Cranial Base and Shape
  • Rounded cranial base, supporting bipedal posture.
  • Occipital bone involved in cranial shape.

Comparison: Primitive vs. Modern

• Primitive Traits
  • High prognathism, large brow ridges.
  • Sagittal crest, large mandible, and teeth.
  • Small cranial capacity.
  • Large nasal cavity and flattened cranial base.
• Modern Traits
  • Little prognathism, small brow ridges.
  • Small mandibles and teeth.
  • Large cranial capacity, globular cranium shape.
  • Presence of a chin due to reduced prognathism.

Fossil Evidence

• Earliest Hominid: Sahelanthropus tchadensis
  • Discovered in 2001 at Toros Menalla, Chad.
  • Dated to about 7 million years ago.
  • Unusual morphology with a mix of traits not found in other early hominids.

Conclusion

• Primitive traits relate to common ancestors, while modern traits are unique to humans.
• Further discussion on Sahelanthropus will continue in the next segment.