Length of Cervical Vertebral Spinous Processes

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Human Uniqueness Compared to "Great Apes": 
Absolute Difference
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The seven cervical vertebrae, as well as the thoracic and lumbar vertebrae, have dorsal projections known as spinous processes. In the cervical region these processes provide attachment for nuchal muscles that insert on the posterior cranial vault and that function to support and move the head. In pronograde (that is, with a body more parallel to the ground), quadrupeal apes, the cranium projects anterior of the vertebral column, and large nuchal muscles are required to counteract gravitational forces that act to rotate the face downwards. Accordingly, chimpanzees, gorillas and orangutans possess enlarged spinous processes, which are some two- to five-times larger relative to their vertebral bodies than are those of humans. In these apes the fifth or sixth cervical vertebra tends to have the longest and most robust spinous processes. The orthograde (upright) body posture and bipedal locomotion of humans results in a cranium that is balanced atop the vertebral column and does not require much in the way of counterbalancing tension from the nuchal muscles. Thus in humans the nuchal musculature is slight and the spinous processes of the cervical vertebrae are relatively short and gracile. In humans the seventh cervical vertebra tends to have the longest spinous processes (and is therefore often called the “vertebra prominens”).

Timing

Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Probable Appearance: 
6,000 thousand years ago
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Occipital Bone Morphology Likely
Striding Bipedalism Likely

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