Morphology of the Brow Ridge

Certainty Style Key
Hover over keys for definitions:
True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
No Difference
MOCA Topic Authors: 

Considerable variation exists between hominoid species in the morphology of the supraorbital region. Gorillas and chimpanzees (and most fossil hominins) possess a prominent supraorbital torus, or brow ridge, presenting as a continuous projecting ridge above the orbits and nose (although continuous, the torus is anatomically divisible into three regions: laterally positioned supraorbital trigones, medially positioned supercillary arches, and a midline glabellar prominence). In these species with prominent brow ridges, a supratoral sulcus is generally present as a shallow groove just posterior to the torus. Humans and orangutans lack prominent brow ridges. Brow ridges may develop as an architectural or biomechanical by-product of hafting a prognathic (projecting) face onto the low frontal bone characteristic of apes and earlier humans, such that the lack of a brow ridge in modern humans is a consequence of their having an orthognathic (vertical) face and vertical frontal (high forehead). Orangutans possess a supraorbital rim (a thin, non-projecting ridge across the orbits) rather than a torus, which may be a function of the airorynchy (backwards rotation of the face towards the neurocranium) that characterizes these apes.

Related MOCA Topics
Related Topics (hover over title for reason):
Referenced By:
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

Possible Appearance: 
100 thousand years ago
Probable Appearance: 
100 thousand years ago
Definite Appearance: 
100 thousand years ago
Background Information: 

Lieberman, 1995. Testing hypotheses about recent human evolution from skulls. Curr Anthropol 36:159-197. Lieberman, 2000. Ontogeny, homology, and phylogeny in the hominid craniofacial skeleton: The problem of the browridge. In O'Higgins & Cohn (eds.) Development, Growth and Evolution.  London, Academic Press. pp. 85-122. Lieberman, 2008. Speculations about the selective basis for modern craniofacial form. Ev Anthropol 17:55-68.

References

No related publications have been added for this topic