Sphenoid Bone Length

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Human Uniqueness Compared to "Great Apes": 
Absolute Difference
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The sphenoid, along with the ethmoid and the right and left temporal bones, provides the skeletal link between the face and neurocranium. As the central bone of the cranial base from which the face grows forward, growth in the anterior sphenoid body during early ontogeny determines the spatial relationships between the face, neurocranium, and cranial base. Humans experience less growth in the anterior sphenoid body early in development than do other apes, and accordingly have shorter sphenoid lengths (in the sagittal plane) and reduced facial projection. Sphenoid shortening may be an adaptation for speech, as it results in reduced oropharynx length and contributes to the uniquely human proportions of the vocal tract, allowing humans to make distinct speech sounds.


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: 
100 thousand years ago
Background Information: 

Lieberman, 1998.  Sphenoid shortening and the evolution of modern human cranial shape. Nature 393: 158-162. Spoor et al., 1999.  Anterior sphenoid in modern humans. Nature 397: 572. Lieberman et al., 2000.  Basicranial influence on overall cranial shape. J Hum Evol 38: 291-315.  

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Topic Certainty
Foramen Magnum Placement Speculative
Prognathism Likely
Upper Facial Height Likely


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