A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

ian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exceptionally strong jaw muscles. The sagittal crest serves primarily for attachment of the temporalis muscle, which is one of the main chewing muscles. Development of the sagittal crest is thought to be connected to the development of this muscle. A sagittal crest usually develops during the juvenile stage of an animal in conjunction with the growth of the temporalis muscle, as a result of convergence and gradual heightening of the temporal lines.

Function

A sagittal crest tends to be present on the skulls of adult animals that rely on powerful biting and clenching of their teeth, usually as a part of their hunting strategy. Skulls of some dinosaur species, including tyrannosaurs, possessed well developed sagittal crests. Among mammals, dogs, cats, lions, and many other carnivores have sagittal crests, as do some leaf eaters, including tapirs and some apes.

Apes and hominins

Sagittal crests are found in robust

great ape The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); '' Gorilla'' (the ...

s, and some early hominins (''

Paranthropus ''Paranthropus'' is a genus of extinct hominin which contains two widely accepted species: ''Paranthropus robustus, P. robustus'' and ''P. boisei''. However, the validity of ''Paranthropus'' is contested, and it is sometimes considered to be sy ...

''). Prominent sagittal crests are found among male

gorilla Gorillas are primarily herbivorous, terrestrial great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or five su ...

s and

orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...

s, but only rarely occur in male

chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of Hominidae, great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close rel ...

s such as Bili apes. The largest sagittal crest ever discovered in the

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

lineage belongs to the "Black Skull", '' Paranthropus aethiopicus'' field number KNM WT 17000, the earliest known robust hominid ancestor and the oldest robust australopithecine discovered to date. The prominence of the crest appears to have been an adaptation for the ''P. aethiopicus heavy chewing, and the Black Skull's cheek teeth are correspondingly large. Smaller sagittal crests are also present on the skulls of other Paranthropines, including ''Paranthropus boisei'' and ''Paranthropus robustus''. The shrinking of the sagittal crest in human ancestors was widely attributed to a growing brain and shrinking teeth. However, it was discovered in 2004 by a group of researchers led by Dr. Hansell Stedman, that a frameshift mutation shrank the individual muscle fibers of the temporalis muscle, which attached to the sagittal crest. This was believed to have allowed brain size to increase, since the crest was no longer strictly necessary, but a later paper from 2017, led by researchers from George Washington University, found that the increase in brain size and reduction of tooth size were not linked, as originally hypothesized.

References

External links

"Black Skull" (Australopithecus aethiopicus, specimen KNM-WT 17000)
{{Webarchive, url=https://web.archive.org/web/20081228130004/http://www.archaeologyinfo.com/17000.htm , date=2008-12-28 —ArcheologyInfo.com Skull

Function

Apes and hominins

See also

References

External links