إدارة الموسوعة 1: مراجعة واحدة

2016-11-14T04:32:55Z

مراجعة واحدة

صفحة جديدة

{{Orphan|date=April 2015}}

One of the major changes throughout [[hominid]] evolution, are the changes to the dental morphology and jaw. These changes were driven by the types and processing of food eaten. The evolution of the jaw is thought to have facilitated [[encephalization]], speech, and the formation of the chin, a uniquely human feature.

== Background ==

Today, humans possess 32 permanent teeth with a [[dental formula]] of 2123.<ref>Scott, G. R., & Turner, C. G. (1997). The anthropology of modern human teeth: Dental morphology and its variation in recent human populations. Cambridge ; New York: Cambridge University Press.</ref> This breaks down to four incisors, two canines, four premolars, and six molars on the upper and lower sets of teeth.<ref>Scott, G. R., & Turner, C. G. (1997). The anthropology of modern human teeth: Dental morphology and its variation in recent human populations. Cambridge ; New York: Cambridge University Press.</ref> In modern day humans, incisors are generally spatulate with a single root while canines are also single rooted but are single cusped and conical.<ref>Scott, G. R., & Turner, C. G. (1997). The anthropology of modern human teeth: Dental morphology and its variation in recent human populations. Cambridge ; New York: Cambridge University Press.</ref> Premolars are bicuspid while molars are multi-cuspid.<ref>Scott, G. R., & Turner, C. G. (1997). The anthropology of modern human teeth: Dental morphology and its variation in recent human populations. Cambridge ; New York: Cambridge University Press.</ref> The upper molars have three roots while the lower molars have two roots.<ref>Scott, G. R., & Turner, C. G. (1997). The anthropology of modern human teeth: Dental morphology and its variation in recent human populations. Cambridge ; New York: Cambridge University Press.</ref>

General patterns of dental morphological evolution throughout human evolution include a reduction in facial [[prognathism]], the presence of a Y5 cusp pattern, the formation of a parabolic palate and the loss of the [[diastema]].

Human teeth are made of dentin and are covered by [[Tooth enamel|enamel]] in the areas that are exposed.<ref>{{cite journal | last1 = Staines | first1 = M. | last2 = Robinson | first2 = W. H. | last3 = Hood | first3 = J. A. A. | year = 1981 | title = Spherical indentation of tooth enamel | url = | journal = Journal of Materials Science | volume = 16 | issue = 9| pages = 2551–2556 | doi = 10.1007/bf01113595 }}</ref> Enamel, itself, is composed of hydroxyapatite, a calcium phosphate crystal.<ref>{{cite journal | last1 = Staines | first1 = M. | last2 = Robinson | first2 = W. H. | last3 = Hood | first3 = J. A. A. | year = 1981 | title = Spherical indentation of tooth enamel | url = | journal = Journal of Materials Science | volume = 16 | issue = 9| pages = 2551–2556 | doi = 10.1007/bf01113595 }}</ref> The various types of human teeth perform different functions. Incisors are used to cut food, canines are used to tear food, and the premolars and molars are used to crush and grind food.<ref>Scott, G. R., & Turner, C. G. (1997). The anthropology of modern human teeth: Dental morphology and its variation in recent human populations. Cambridge ; New York: Cambridge University Press.</ref>

== History ==

=== Hominidae ===

==== Chimpanzees ====

Humans have evolved from a most recent common ancestor with [[chimpanzees]] and researchers agree that the earliest hominid ancestor would have similar dental morphology to chimpanzees today. Thus, comparisons between chimpanzees and ''[[Homo sapiens]]'' could be used to identify major differences. Major characterizing features of ''Pan troglodyte'' dental morphology include the presence of peripherally located cusps, thin enamel, and strong facial prognathism.<ref>Scott, G. R., & Irish, J. D. (2013). Anthropological perspectives on tooth morphology: Genetics, evolution, variation. Cambridge: Cambridge University Press.</ref>

=== Earliest Hominids ===

==== ''Sahelanthropus tchadensis'' ====

''[[Sahelanthropus tchadensis]]'' is thought to be one of the earliest species belonging to the human lineage. Fossils date back to 7 mya.<ref>{{cite journal | last1 = Brunet | first1 = | display-authors = 1 | last2 = et al | year = 2002 | title = A new hominid from the Upper Miocene of Chad, Central Africa | doi = 10.1038/nature00879 | journal = Nature | volume = 418 | issue = | pages = 145–151 }}</ref> The only fossils that remain are five pieces of the jaw, teeth, and a small cranium. These skeletal pieces show dental features that include a U-shaped palate and canines smaller than those of a chimpanzee’s.<ref>{{cite journal | last1 = Brunet | first1 = | display-authors = 1 | last2 = et al | year = 2002 | title = A new hominid from the Upper Miocene of Chad, Central Africa | doi = 10.1038/nature00879 | journal = Nature | volume = 418 | issue = | pages = 145–151 }}</ref>

==== ''Orrorin tugenensis'' ====

The species was though to have lived 6.1 to 5.7 million years ago. Fossil remains have provided very important information regarding dental morphology. ''[[Orrorin]]'' had smaller teeth relative to body size and the enamel was thicker.<ref>Henke, Winfried (2007). Henke, Winfried; Hardt, Thorolf; Tattersall, Ian, eds. Handbook of paleoanthropology: Phylogeny of hominids. Springer. pp. 1527–9. ISBN 978-3-540-32474-4</ref> The upper canines contain a mesial groove which differs from both Australopithecus and ''Ardipithecus''.<ref>Henke, Winfried (2007). Henke, Winfried; Hardt, Thorolf; Tattersall, Ian, eds. Handbook of paleoanthropology: Phylogeny of hominids. Springer. pp. 1527–9. ISBN 978-3-540-32474-4</ref> The canines, in general, were very ape-like but were much smaller.<ref>Henke, Winfried (2007). Henke, Winfried; Hardt, Thorolf; Tattersall, Ian, eds. Handbook of paleoanthropology: Phylogeny of hominids. Springer. pp. 1527–9. ISBN 978-3-540-32474-4</ref> Like modern humans, ''Orrorin'' had post-canines that were smaller and were microdont.<ref>Henke, Winfried (2007). Henke, Winfried; Hardt, Thorolf; Tattersall, Ian, eds. Handbook of paleoanthropology: Phylogeny of hominids. Springer. pp. 1527–9. ISBN 978-3-540-32474-4</ref>

==== ''Ardipithecus'' ====

Dated to live around 5.6 – 4.4 million years ago. Fossils show ''[[Ardipithecus]]'' to have canine teeth that were reduced, much like later hominids. The jaw of ''Ardipithecus'' was very much prognathic.<ref>{{cite journal | last1 = Suwa | first1 = G | last2 = Asfaw | first2 = B. | last3 = Kono | first3 = R. T. | last4 = Kubo | first4 = D. | last5 = Lovejoy | first5 = C. O. | last6 = White | first6 = T. D. | display-authors = 6 | last7 = et al | year = 2009 | title = The Ardipithecus ramidus skull and its implications for hominid origins | url = | journal = Science | volume = 326 | issue = 5949| pages = 68–68, 68e1-68e7 | doi = 10.1126/science.1175825 }}</ref> The teeth of ''Ardipithecus ramidus'' in particular showed that the species was probably an omnivore. The upper canines are less sharp than a chimpanzee’s, possibly due to them being smaller in general.<ref>{{cite journal | last1 = Suwa | first1 = G | last2 = Asfaw | first2 = B. | last3 = Kono | first3 = R. T. | last4 = Kubo | first4 = D. | last5 = Lovejoy | first5 = C. O. | last6 = White | first6 = T. D. | display-authors = 6 | last7 = et al | year = 2009 | title = The Ardipithecus ramidus skull and its implications for hominid origins | url = | journal = Science | volume = 326 | issue = 5949| pages = 68–68, 68e1-68e7 | doi = 10.1126/science.1175825 }}</ref> The canines in chimpanzees can be particularly sharp as they are often shaped through use and wear against the lower teeth.<ref>{{cite journal | last1 = Suwa | first1 = G | last2 = Kono | first2 = R. T. | last3 = Simpson | first3 = S. W. | last4 = Asfaw | first4 = B. | last5 = Lovejoy | first5 = C. O. | last6 = White | first6 = T. D. | display-authors = 6 | last7 = et al | year = 2009 | title = Paleobiological implications of the Ardipithecus ramidus dentition | url = | journal = Science | volume = 326 | issue = 5949| pages = 69–69, 94-99 | doi = 10.1126/science.1175824 }}</ref> In addition, there is less sexual dimorphism in the size of the canines, a feature that is seen in humans and is heavily contrasted to chimpanzees.<ref>{{cite journal | last1 = Suwa | first1 = G | last2 = Kono | first2 = R. T. | last3 = Simpson | first3 = S. W. | last4 = Asfaw | first4 = B. | last5 = Lovejoy | first5 = C. O. | last6 = White | first6 = T. D. | display-authors = 6 | last7 = et al | year = 2009 | title = Paleobiological implications of the Ardipithecus ramidusdentition | url = | journal = Science | volume = 326 | issue = 5949| pages = 69–69, 94-99 | doi = 10.1126/science.1175824 }}</ref>

The size of these canines have been used to infer the behaviours of ''[[Ardipithecus ramidus]]''. In great contrast to the social patterns of chimpanzees, the smaller upper canine teeth suggest that the species was not very aggressive, especially in terms of the relationship between males and other groups.<ref>{{cite journal | last1 = Suwa | first1 = G | last2 = Kono | first2 = R. T. | last3 = Simpson | first3 = S. W. | last4 = Asfaw | first4 = B. | last5 = Lovejoy | first5 = C. O. | last6 = White | first6 = T. D. | display-authors = 6 | last7 = et al | year = 2009 | title = Paleobiological implications of the Ardipithecus ramidusdentition | url = | journal = Science | volume = 326 | issue = 5949| pages = 69–69, 94-99 | doi = 10.1126/science.1175824 }}</ref>

=== Archaic Hominids ===

==== ''Australopithecus afarensis'' ====

Hominid species that lived 3.9 – 2.9 million years ago. Compared to modern apes, ''afarensis'' as ''africanus'' have much smaller molars and canines, but they are still larger than those of humans’.<ref>{{cite journal | last1 = Kustaloglu | first1 = O.A. | year = 1961 | title = Australopithecus and Paranthropus dentitions | url = | journal = Southwestern Journal of Anthropology | volume = 17 | issue = | pages = 226–238 | doi=10.1086/soutjanth.17.3.3629043}}</ref> The smaller molars have been attributed to consuming seeds.<ref>{{cite journal | last1 = Emes | first1 = Y. | last2 = Aybar | first2 = B. | last3 = Yalcin | first3 = S. | year = 2011 | title = On the Evolution of Human Jaws and Teeth: A Review | url = | journal = Bull Int Assoc Paleodont | volume = 5 | issue = 1| pages = 37–47 }}</ref> The jaws of both ''afarensis'' and ''africanus'' are very much prognathic.<ref>Rak, Y. 1983. The australopithecine face. New York, Academic Press.</ref> The lack of shearing crests in the blunt teeth have also been cited as evidence of a species that could chew buds or flowers but they were still able to consume meat.<ref>{{cite journal | last1 = Emes | first1 = Y. | last2 = Aybar | first2 = B. | last3 = Yalcin | first3 = S. | year = 2011 | title = On the Evolution of Human Jaws and Teeth: A Review | url = | journal = Bull Int Assoc Paleodont | volume = 5 | issue = 1| pages = 37–47 }}</ref>

Studies of [[Australopithecine]] diets through dental microwear showed that they were largely frugivorous but there is some archaeological evidence for meat consumption.<ref>{{cite journal | last1 = Sponheimer | first1 = M. | last2 = Lee-Thorp | first2 = J. | last3 = Codron | first3 = D. | last4 = Codron | first4 = J. | last5 = Baugh | first5 = A.T. | last6 = Thackeray | first6 = F. | year = 2005 | title = Hominins, sedges, and termites: new carbon isotope data from the Sterkfontein valley and Kruger National Park | url = | journal = Journal of Human Evolution | volume = 48 | issue = | pages = 301–312 | doi=10.1016/j.jhevol.2004.11.008}}</ref> The shift in dietary capacities gave Austrolopithecines the advantage survive in several different habitats.<ref>Emes, Y., Aybar, B., Yalcin, S. (2011). On the Evolution of Human Jaws and Teeth: A Review. Bull Int Assoc Paleodont. 5(1): 37-47.</ref>

=== Archaic Megadont Hominids ===

Megadont hominids, in normal, show the greatest reduction in canines, but the premolars were abnormally large.<ref>Emes, Y., Aybar, B., Yalcin, S. (2011). On the Evolution of Human Jaws and Teeth: A Review. Bull Int Assoc Paleodont. 5(1): 37-47.</ref>

==== ''Paranthropus robustus'' ====

Determined to have lived 2-1.2 million years ago. True to its name, ''[[Paranthropus robustus]]'' had a more massive jaw and teeth than Homo species. In addition, the species had thicker enamel than any hominid species from the time. There is also evidence from muscle markings on jaws that robustus would have had a diet that was based on hard, tough to chew foods in times of nutritional stress. Research does show, that in general, their diet was very broad.

==== ''Paranthropus boisei'' ====

''[[Paranthropus boisei]]'' was a hominid species dated to have lived from 2.3 to 1.2 million years ago. The evidence from fossils shows morphological traits designed for chewing hard, tough foods and is commonly referred to as the ‘Nutcracker Man’.<ref>Findings Challenge Conventional Ideas on Evolution of Human Diet, Natural Selection Newswise, Retrieved on March 30, 2015.</ref> Not only do the back molars have double the area that the molars of modern humans possess, but the premolars and the first and second molars were found to be four times larger than the teeth found in humans.<ref>{{cite journal | last1 = Wood | first1 = Bernard | last2 = Lieberman | first2 = Daniel E | year = 2001 | title = Craniodental variation in Paranthropus boisei: A developmental and functional perspective | url = | journal = American Journal of Physical Anthropology | volume = 116 | issue = 1| pages = 13–25 | doi = 10.1002/ajpa.1097 }}</ref> This has been interpreted as researchers as evidence for the hominids chewing predominantly with their back teeth.<ref>Smithsonian Institution. (2015). Paranthropus robustus. Retrieved from < http://humanorigins.si.edu/evidence/human-fossils/species/paranthropus-robustus></ref> In addition, ''P. boisei'' possesses the thickest enamel of any hominid specimens found.<ref>Findings Challenge Conventional Ideas on Evolution of Human Diet, Natural Selection Newswise, Retrieved on March 30, 2015.</ref> Despite such large back teeth, the incisors and canines were smaller than other species from the time.<ref>{{cite journal | last1 = Wood | first1 = Bernard | last2 = Lieberman | first2 = Daniel E | year = 2001 | title = Craniodental variation in Paranthropus boisei: A developmental and functional perspective | url = | journal = American Journal of Physical Anthropology | volume = 116 | issue = 1| pages = 13–25 | doi = 10.1002/ajpa.1097 }}</ref>

=== Pre-Modern Homo ===

==== ''Homo habilis'' ====

The species is dated to have lived 2.1 to 1.5 million years ago. Very little is known about the dental morphology. However, in conjunction with dental evolution, it is expected that ''[[Homo habilis]]'' would display smaller teeth than those of the hominids before them. Furthermore, there would be a reduction in facial prognathism.

==== ''Homo erectus'' ====

Hominid species for evidence of remains date from 1.9 million years ago to 70 000 years ago. The dental arcade is smaller than that of Austrolopithicene species and following the trend, prognathism was reduced within the species.

Earlier ''Homo erectus'' species exhibited larger teeth than Homo sapiens do today, but the teeth are smaller than early Homo species.<ref>Relethford, J. The Human Species: 2nd edition. Toronto: Mayfield Publishing Company, 1994.</ref> The incisors also begin to show the ‘shovel-shape’ appearance, which can be attributed to a change towards a hunter-gatherer diet.<ref>Relethford, J. The Human Species: 2nd edition. Toronto: Mayfield Publishing Company, 1994.</ref> The reduction in molar size has been linked to the eating of softer foods, including cooked foods as well as more meat.<ref>O’Neill, D. (2013). Homo erectus. Early Human Evolution – A Survey of the Biological and Cultural Evolution of Homo habilis and Homo erectus. Retrieved from < http://anthro.palomar.edu/homo/homo_2.htm>.</ref>

==== ''Homo ergaster'' ====

Hominid species that lived 1.8 to 1.3 million years ago. Continuing the pattern of hominid dental morphological evolution, ergaster had a less prognathic face, smaller dental arcade. The mandibular symphysis is also shown to have grown. In general the dentition, is very similar to that of Homo erectus.

==== ''Homo heidelbergensis'' ====

Hominid species dating from 600 000 to 300 000 years ago. Analysis of ''heidelbergensis'' skeletons have led researchers to find that the jaw of the species featured new traits in the form of taurodont molars, a reduced M3 molar, and a large buccal cusp in the P3 premolar.<ref>Schoetensack, O. 1908. Der Unterkiefer des Homo heidelbergensis aus den Sanden von Mauer bei Heidelberg. Leipzig: Wilhelm Engelmann</ref> In general, when compared to humans, ''heidelbergensis'' shows a larger jaw and smaller teeth.<ref>Smithsonian Institution (2015). Homo heidelbergensis. Retrieved from < http://humanorigins.si.edu/evidence/human-fossils/species/homo-heidelbergensis>.</ref>

==== ''Homo neanderthalensis'' ====

Although not a direct ancestor of Homo sapiens, [[Neanderthals]] are considered to be close relatives. Living 250 000 to 30 000 years ago, Neanderthals were named after the valley they were discovered in. Aside from just dentition, Neanderthals were more robust in general. Through analysis of specimens, the face of Neanderthals showed more prognathism, resulting in a [[retromolar space]] posterior to the third molar.<ref>Scott, G. R., & Irish, J. D. (2013). Anthropological perspectives on tooth morphology: Genetics, evolution, variation. Cambridge: Cambridge University Press.</ref> Neanderthals also possessed larger molars and canine teeth with no grooves.<ref>Scott, G. R., & Irish, J. D. (2013). Anthropological perspectives on tooth morphology: Genetics, evolution, variation. Cambridge: Cambridge University Press.</ref>

=== Modern Day Humans ===

==== ''Homo sapiens'' ====

General characterizing feature of the dental morphology of humans are the lack of facial prognathism, a parabolic shaped mandible and maxilla, and molars that are the same size as the front teeth. Humans also have small crowns in relation to body mass and tend to show a reduction in cusp and root number.<ref>Emes, Y., Aybar, B., Yalcin, S. (2011). On the Evolution of Human Jaws and Teeth: A Review. Bull Int Assoc Paleodont. 5(1): 37-47.</ref> The reduction in the dental arcade was accompanied by molars moving posteriorly and axial inclination of the molar roots.<ref>Emes, Y., Aybar, B., Yalcin, S. (2011). On the Evolution of Human Jaws and Teeth: A Review. Bull Int Assoc Paleodont. 5(1): 37-47.</ref>

Evolution of the mandible has also been hypothesized to provide the necessary physiology required for speech.<ref>Emes, Y., Aybar, B., Yalcin, S. (2011). On the Evolution of Human Jaws and Teeth: A Review. Bull Int Assoc Paleodont. 5(1): 37-47.</ref> However, these changes are also linked to the development of obstructive sleep apnea.<ref>Emes, Y., Aybar, B., Yalcin, S. (2011). On the Evolution of Human Jaws and Teeth: A Review. Bull Int Assoc Paleodont. 5(1): 37-47.</ref> Furthermore, the evolution of the maxilo-mandibular system has been linked to encephalization. As the jaw changed and the muscles become weaker, the pressure on the cranial sutures lowered, and encephalization occurred.<ref>Emes, Y., Aybar, B., Yalcin, S. (2011). On the Evolution of Human Jaws and Teeth: A Review. Bull Int Assoc Paleodont. 5(1): 37-47.</ref> In addition, the overall changes in the mandible and the maxilla have led to the ability for humans to speak.

Additionally, the evolution and reduction in the jaw has left little room for the third molar, or wisdom tooth, to form. As a result, many individuals choose to remove them through surgery.

One of the defining features among ''[[Homo sapiens]]'' is the presence of a chin. A protruding chin was absent in archaic hominids, as well as [[Neandertals]]. Research has shown conflicting views on the function of the chin. Many claim that it provides resistance to forces that cause bending of the mandible while others claim there is no outright purpose to the formation and merely emerged as a point after the shortening of the mandible.<ref>Emes, Y., Aybar, B., Yalcin, S. (2011). On the Evolution of Human Jaws and Teeth: A Review. Bull Int Assoc Paleodont. 5(1): 37-47.</ref>

== Summary of Dental Morphology Evolution ==

{| class="wikitable"
|-
! !! ''[[Pan troglodyte]]'' !! ''[[Sahelanthropus tchadensis]]'' !! ''[[Orrorin tugenensis]]'' !! ''[[Ardipithecus]]'' !! ''[[Australopithecus afarensis]]'' !! ''[[Paranthropus robustus]]'' !! ''[[Paranthropus boisei]]'' !! ''[[Homo habilis]]'' !! ''[[Homo erectus]]'' !! ''[[Homo ergaster]]'' !! ''[[Homo heidelbergensis]]'' !! ''[[Homo neanderthalensis]]'' !! ''[[Homo sapiens]]''
|-
| [[Dental Formula]] || 2123 || 2123 || 2123 || 2123 || 2123 || 2123 || 2123 || 2123 || 2123 || 2123 || 2123 || 2123 || 2123
|-
| Y-5 Cusp Pattern || Present || Present || Present || Present || Present || Present || Present || Present || Present || Present || Present || Present || Present
|-
| Cusp Location || Periphery || Centrally || Centrally || Centrally || Centrally || Centrally || Centrally || Centrally || Centrally || Centrally || Centrally || Centrally || Centrally
|-
| Enamel Thickness || Thin || Intermediate || Thick || Intermediate || Thick || Very Thick || Very Thick || Very Thick || Very Thick || Very Thick || Very Thick || Very Thick || Very Thick
|-
| Facial Prognathism || Very Strong || Very Strong || Strong || Strong || Strong || Moderate || Moderate || Moderate || Mild || Mild || Mild || Strong || Mild
|-
| Shape of palate in manible and maxilla || U-Shaped || U-Shaped || U-Shaped || U-Shaped || U-Shaped || U-Shaped || U-Shaped || U-Shaped || U-Shaped || U-Shaped || U-Shaped || U-Shaped || Parabolic
|-
| Chin || Absent || Absent || Absent || Absent || Absent || Absent || Absent || Absent || Absent || Absent || Absent || Absent || Present
|-
| Size of Canines || Very Large || Large || Moderate || Mild || Mild || Mild || Mild || Mild || Mild || Mild || Mild || Mild || Mild
|}

== References ==
{{Reflist}}

[[Category:Teeth]]
[[Category:Homininae]]
[[Category:Biological anthropology]]

Hominid dental morphology evolution - تاريخ المراجعة

إدارة الموسوعة 1: مراجعة واحدة