Post-orbital constriction

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Top view of Australopithecus africanus skull with post-orbital constriction (left) and modern human skull without (right)

In

supraorbital torus, divided by the maximum upper facial breadth (BFM), bifrontomalare temporale, or as the maximum width behind the orbit of the skull.[1][2][3]

Cranial Evolution

Post-orbital constriction for various hominids[1]
Increased constriction
Gorilla
 0.57
P. aethiopicus
(KNM WT 17000)		 0.57
P. boisei
(KNM-ER 406)		 0.57
Intermediate
Dryopithecus
(RUD 77)		 0.73
Sahelanthropus
(TM 266-01-060-1)		 0.59
Australopithecus 0.66
P. robustus 0.70
Homo habilis
(OH 24, KNM-ER 1813)		 0.72
H. rudolfensis 0.70
H. ergaster 0.75
Orangutan
 0.66
Chimpanzee
 0.70
Reduced constriction
Praeanthropus
 0.80
Absolutely reduced constriction
Homo sapiens
 0.92

Measurement of cranial capacity in hominis has been long used to examine the evolutionary development of increased brain size, allowing for comparing and contrasting among hominin skulls and between primates and hominins. Similarly, the post-orbital constriction index has become a form to compare and contrast craniums with the possibility of determining the relative age and evolutionary place of a new found hominin. Cranial capacity and post-orbital constriction index can demonstrate a correlation between increased brain size and reduced post-orbital constriction.

Homo sapiens manifests a absolutely reduced post-orbital constriction (post-orbital constriction disappears) and a post-orbital constriction index of 0.92 due to increase in cranial capacity, about 1,350 cc.[1][6] From the Australopithecines to the Homo genus, along with an increase in cranial capacity, a transition from intermediate constriction to reduced constriction is visible, and eventually disappearance. Brain growth has changed both the appearance of the sagittal crest and post-orbital constriction.[4] KNM-ER 406, the skull of a Paranthropus, brain volume estimated to 410 cm3 with a visible sagittal crest and mild or intermediate post-orbital constriction but KNM-ER 37333, the skull of a Homo erectus, brain volume of 850 cm3 with no visual sagittal crest and an almost not present or reduced post-orbital constriction.[4]

Minatogawa I and IV and Dali

Minatogawa I-IV cranium were discovered in Okinawa Island in 1970-1971.[7] The skulls and other fossils found associated were dated to be 15,000-20,000 years old, with a chance of being slightly older.[7] In a study led by Daisuke Kubo, Reiko T. Kono, and Gen Suwa, the craniums for Minatogawa I and IV were further examined to identify cranial capacity and concluded that Minatogawa I's estimated cranial size is 1335 cc and Minatogawa IV's is 1170 cc,[7] very close to the average cranial size of modern Homo sapiens. Kubo, et al. identify two possible forms of measuring post-orbital constriction, established by measuring the anterior, closer to the face, and posterior of the cranium.[7] Researchers conclude that both crania demonstrate a marked or almost reduced post-orbital constriction in both measurements of post-orbital constriction, compared to modern Homo sapiens.[7]

The Dali cranium was discovered in 1978 in Dali County, Shaanxi.[8] The cranium is described to be large with some robust features similar to early Western Homo sapiens and noticeable differentiation from the cranium of Homo erectus found in Zhoukoudian.[8] The Dali cranium was found to exhibit a pronounced or almost reduced post-orbital constriction with a post-orbital constriction index of 0.85,[8] much stronger than primates and early hominin and falling fairly close to the post-orbital constriction index of Homo sapiens. The Dali cranium is an example of the evolutionary development of post-orbital constriction as brain size enlarges and develops similar features found in modern Homo sapiens.

Temporalis Muscle

In species such as

temporalis muscle is used for chewing, there is no evidence that the supraorbital structure of primates is dependent upon their respective chewing habits or dietary preferences.[9]

See also

References

  1. ^
    OCLC 162571244
    .
  2. ISSN 1094-8074
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  3. PMID 6435455
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  4. ^ a b c Gamble, Clive (2014). Settling the Earth: The Archeology of Deep Human History. New York: Cambridge Univ. Press. pp. 148–151.
  5. ^ a b "Human evolution - Increasing brain size". Encyclopedia Britannica. Retrieved 2020-05-23.
  6. ^ "Archaic Homo sapiens | Learn Science at Scitable". www.nature.com. Retrieved 2020-05-23.
  7. ^
    ISSN 0918-7960
    .
  8. ^
    ISBN 9781315423135
    .
  9. JSTOR 25757416
    .
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