A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

(at the

sagittal suture The sagittal suture, also known as the interparietal suture and the ''sutura interparietalis'', is a dense, fibrous connective tissue joint between the two parietal bones of the skull. The term is derived from the Latin word ''sagitta'', meaning ...

) of many

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

ian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exceptionally strong

jaw The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serv ...

muscles. The sagittal crest serves primarily for attachment of the

temporalis muscle In anatomy, the temporalis muscle, also known as the temporal muscle, is one of the muscles of mastication (chewing). It is a broad, fan-shaped convergent muscle on each side of the head that fills the temporal fossa, superior to the zygomati ...

, 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 line The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named ...

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 Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent be ...

, 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

ape Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its siste ...

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 east ...

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 herbivorous, predominantly ground-dwelling 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 fi ...

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 known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...

s such as

Bili ape The Bili apes or Bondo mystery apes were names given in 2003 in sensational reports in the popular media to a purportedly new species of highly aggressive, giant ape supposedly inhabiting the wetlands and savannah around of the village of Bili in ...

s. The largest sagittal crest ever discovered in the

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

lineage belongs to the "Black Skull", ''

Paranthropus aethiopicus ''Paranthropus aethiopicus'' is an extinct species of robust australopithecine from the Late Pliocene to Early Pleistocene of East Africa about 2.7–2.3 million years ago. However, it is much debated whether or not ''Paranthropus'' is an invali ...

'' field number

KNM WT 17000 KNM-WT 17000 (also known as "The Black Skull") is a fossilized adult skull of the species ''Paranthropus aethiopicus''. It was discovered in West Turkana, Kenya by Alan Walker in 1985. Estimated to be 2.5 million years old, it is an adult with ...

, 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

{{Reflist

External links

"Black Skull" (Australopithecus aethiopicus, specimen KNM-WT 17000)
��ArcheologyInfo.com Skull

Function

Apes and hominins

See also

References

External links