 |
Changes to the dental morphology and jaw are major elements of hominid evolution. 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 uniquely human chin.
Today, humans possess 32 permanent teeth with a dental formula of 2.1.2.32.1.2.3. [1] This breaks down to two pairs of incisors, one pair of canines, two pairs of premolars, and three pairs of molars on each jaw. [1] In modern day humans, incisors are generally spatulate with a single root while canines are also single rooted but are single cusped and conical. [1] Premolars are bicuspid while molars are multi-cuspid. [1] The upper molars have three roots while the lower molars have two roots. [1]
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 enamel in the areas that are exposed. [2] Enamel, itself, is composed of hydroxyapatite, a calcium phosphate crystal. [2] 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. [1]
According to the theory of evolution, humans evolved from a common ancestor of chimpanzees. Researchers hypothesize 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 troglodytes dental morphology include the presence of peripherally located cusps, thin enamel, and strong facial prognathism. [3]
Sahelanthropus tchadensis is thought to be one of the earliest species belonging to the human lineage. Fossils date back to 7 million years ago. [4] 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. [4]
The species was thought 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. [5] The upper canines contain a mesial groove which differs from both Australopithecus and Ardipithecus. [5] The canines, in general, were very ape-like but were much smaller. [5] Like modern humans, Orrorin had post-canines that were smaller and were microdont. [5]
Dated to live around 5.6 to 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. [6] 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. [6] The canines in chimpanzees can be particularly sharp as they are often shaped through use and wear against the lower teeth. [6] 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. [6]
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. [6]
Hominid species that lived 3.9 to 2.9 million years ago. Compared to modern apes, A. afarensis and A. africanus have much smaller molars and canines, but they are still larger than those of humans’. [7] The smaller molars have been attributed to consuming seeds. [8] The jaws of both A. afarensis and A. africanus are very much prognathic. [9] 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. [8]
Studies of Australopithecine diets through dental microwear showed that they were largely frugivorous but there is some archaeological evidence for meat consumption. [10] The shift in dietary capacities gave Australopithecines the advantage survive in several different habitats. [8]
Megadont hominids, in normal, show the greatest reduction in canines, but the premolars were abnormally large. [8]
Determined to have lived 2 to 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 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’. [11] 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. [12] This has been interpreted as researchers as evidence for the hominids chewing predominantly with their back teeth. [13] In addition, P. boisei possesses the thickest enamel of any hominid specimens found. [11] Despite such large back teeth, the incisors and canines were smaller than other species from the time. [12]
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.
Hominid species for evidence of remains date from 1.9 million years ago to 70000 years ago. The dental arcade is smaller than that of australopithecine 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. [14] The incisors also begin to show the shovel-shaped appearance, which can be attributed to a change towards a hunter-gatherer diet. [14] The reduction in molar size has been linked to the eating of softer foods, including cooked foods as well as more meat. [15]
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.
Hominid species dating from 600000 to 300000 years ago. Analysis of H. 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. [16] In general, when compared to humans, H. heidelbergensis shows a larger jaw and smaller teeth. [17]
Although not a direct ancestor of Homo sapiens, Neanderthals are considered to be close relatives. Living 500000 to 30000 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. [3] Neanderthals also possessed larger molars and canine teeth with no grooves. [3]
The general characterizing feature of the dental morphology of humans are the lack of facial prognathism, a parabola-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. [8] The reduction in the dental arcade was accompanied by molars moving posteriorly and axial inclination of the molar roots. [8]
Evolution of the mandible has also been hypothesized to provide the necessary physiology required for speech. [8] However, these changes are also linked to the development of obstructive sleep apnea. [8] Furthermore, the evolution of the maxillomandibular 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. [8] 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 Neanderthals. 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. [8]
| Pan troglodytes | 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 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 | 2.1.2.32.1.2.3 |
| Y-5 cusp pattern | Present | Present | Present | Present | Present | Present | Present | Present | Present | Present | Present | Present | Present |
| Cusp location | Peripheral | Central | Central | Central | Central | Central | Central | Central | Central | Central | Central | Central | Central |
| 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 | Mild | Mild |
| Shape of palate in mandible 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 |
Ardipithecus is a genus of an extinct hominine that lived during the Late Miocene and Early Pliocene epochs in the Afar Depression, Ethiopia. Originally described as one of the earliest ancestors of humans after they diverged from the chimpanzees, the relation of this genus to human ancestors and whether it is a hominin is now a matter of debate. Two fossil species are described in the literature: A. ramidus, which lived about 4.4 million years ago during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago. Initial behavioral analysis indicated that Ardipithecus could be very similar to chimpanzees, however more recent analysis based on canine size and lack of canine sexual dimorphism indicates that Ardipithecus was characterised by reduced aggression, and that they more closely resemble bonobos.
Kenyanthropus is a genus of extinct hominin identified from the Lomekwi site by Lake Turkana, Kenya, dated to 3.3 to 3.2 million years ago during the Middle Pliocene. It contains one species, K. platyops, but may also include the 2 million year old Homo rudolfensis, or K. rudolfensis. Before its naming in 2001, Australopithecus afarensis was widely regarded as the only australopithecine to exist during the Middle Pliocene, but Kenyanthropus evinces a greater diversity than once acknowledged. Kenyanthropus is most recognisable by an unusually flat face and small teeth for such an early hominin, with values on the extremes or beyond the range of variation for australopithecines in regard to these features. Multiple australopithecine species may have coexisted by foraging for different food items, which may be reason why these apes anatomically differ in features related to chewing.
Paranthropus is a genus of extinct hominin which contains two widely accepted species: P. robustus and P. boisei. However, the validity of Paranthropus is contested, and it is sometimes considered to be synonymous with Australopithecus. They are also referred to as the robust australopithecines. They lived between approximately 2.9 and 1.2 million years ago (mya) from the end of the Pliocene to the Middle Pleistocene.
Australopithecus is a genus of early hominins that existed in Africa during the Pliocene and Early Pleistocene. The genera Homo, Paranthropus, and Kenyanthropus evolved from some Australopithecus species. Australopithecus is a member of the subtribe Australopithecina, which sometimes also includes Ardipithecus, though the term "australopithecine" is sometimes used to refer only to members of Australopithecus. Species include A. garhi, A. africanus, A. sediba, A. afarensis, A. anamensis, A. bahrelghazali and A. deyiremeda. Debate exists as to whether some Australopithecus species should be reclassified into new genera, or if Paranthropus and Kenyanthropus are synonymous with Australopithecus, in part because of the taxonomic inconsistency.
Sahelanthropus tchadensis is an extinct species of the hominid dated to about 7 million years ago, during the Miocene epoch. The species, and its genus Sahelanthropus, was announced in 2002, based mainly on a partial cranium, nicknamed Toumaï, discovered in northern Chad.
Gigantopithecus is an extinct genus of ape that lived in southern China from 2 million to approximately 300-200,000 years ago during the Early to Middle Pleistocene, represented by one species, Gigantopithecus blacki. Potential identifications have also been made in Thailand, Vietnam, and Indonesia. The first remains of Gigantopithecus, two third molar teeth, were identified in a drugstore by anthropologist Ralph von Koenigswald in 1935, who subsequently described the ape. In 1956, the first mandible and more than 1,000 teeth were found in Liucheng, and numerous more remains have since been found in at least 16 sites. Only teeth and four mandibles are known currently, and other skeletal elements were likely consumed by porcupines before they could fossilise. Gigantopithecus was once argued to be a hominin, a member of the human line, but it is now thought to be closely allied with orangutans, classified in the subfamily Ponginae.
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 invalid grouping and is synonymous with Australopithecus, so the species is also often classified as Australopithecus aethiopicus. Whatever the case, it is considered to have been the ancestor of the much more robust P. boisei. It is debated if P. aethiopicus should be subsumed under P. boisei, and the terms P. boisei sensu lato and P. boisei sensu stricto can be used to respectively include and exclude P. aethiopicus from P. boisei.
Australopithecus garhi is a species of australopithecine from the Bouri Formation in the Afar Region of Ethiopia 2.6–2.5 million years ago (mya) during the Early Pleistocene. The first remains were described in 1999 based on several skeletal elements uncovered in the three years preceding. A. garhi was originally considered to have been a direct ancestor to Homo and the human line, but is now thought to have been an offshoot. Like other australopithecines, A. garhi had a brain volume of 450 cc (27 cu in); a jaw which jutted out (prognathism); relatively large molars and premolars; adaptations for both walking on two legs (bipedalism) and grasping while climbing (arboreality); and it is possible that, though unclear if, males were larger than females. One individual, presumed female based on size, may have been 140 cm tall.
Paranthropus robustus is a species of robust australopithecine from the Early and possibly Middle Pleistocene of the Cradle of Humankind, South Africa, about 2.27 to 0.87 million years ago. It has been identified in Kromdraai, Swartkrans, Sterkfontein, Gondolin, Cooper's, and Drimolen Caves. Discovered in 1938, it was among the first early hominins described, and became the type species for the genus Paranthropus. However, it has been argued by some that Paranthropus is an invalid grouping and synonymous with Australopithecus, so the species is also often classified as Australopithecus robustus.
Paranthropus boisei is a species of australopithecine from the Early Pleistocene of East Africa about 2.5 to 1.15 million years ago. The holotype specimen, OH 5, was discovered by palaeoanthropologist Mary Leakey in 1959 at Olduvai Gorge, Tanzania and described by her husband Louis a month later. It was originally placed into its own genus as "Zinjanthropus boisei", but is now relegated to Paranthropus along with other robust australopithecines. However, it is also argued that Paranthropus is an invalid grouping and synonymous with Australopithecus, so the species is also often classified as Australopithecus boisei.
The Hominini form a taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera Homo (humans) and Pan and in standard usage excludes the genus Gorilla (gorillas).
Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally Australopithecus, and it typically includes the earlier Ardipithecus, Orrorin, Sahelanthropus, and (sometimes) Graecopithecus. All these closely related species are now sometimes collectively termed australopiths or homininians. They are the extinct, close relatives of modern humans and, together with the extant genus Homo, comprise the human clade. Members of the human clade, i.e. the Hominini after the split from the chimpanzees, are now called Hominina.
Australopithecus bahrelghazali is an extinct species of australopithecine discovered in 1995 at Koro Toro, Bahr el Gazel, Chad, existing around 3.5 million years ago in the Pliocene. It is the first and only australopithecine known from Central Africa, and demonstrates that this group was widely distributed across Africa as opposed to being restricted to East and southern Africa as previously thought. The validity of A. bahrelghazali has not been widely accepted, in favour of classifying the specimens as A. afarensis, a better known Pliocene australopithecine from East Africa, because of the anatomical similarity and the fact that A. bahrelghazali is known only from 3 partial jawbones and an isolated premolar. The specimens inhabited a lakeside grassland environment with sparse tree cover, possibly similar to the modern Okavango Delta, and similarly predominantly ate C4 savanna foods—such as grasses, sedges, storage organs, or rhizomes—and to a lesser degree also C3 forest foods—such as fruits, flowers, pods, or insects. However, the teeth seem ill-equipped to process C4 plants, so its true diet is unclear.
Dental anatomy is a field of anatomy dedicated to the study of human tooth structures. The development, appearance, and classification of teeth fall within its purview. Tooth formation begins before birth, and the teeth's eventual morphology is dictated during this time. Dental anatomy is also a taxonomical science: it is concerned with the naming of teeth and the structures of which they are made, this information serving a practical purpose in dental treatment.
Post-canine megadontia is a relative enlargement of the molars and premolars compared to the size of the incisors and canines. This phenomenon is seen in some early hominid ancestors such as Paranthropus aethiopicus.
Lufengpithecus is an extinct genus of ape, known from the Late Miocene of East Asia. It is known from thousands of dental remains and a few skulls and probably weighed about 50 kg (110 lb). It contains three species: L. lufengensis, L. hudienensis and L. keiyuanensis. Lufengpithecus lufengensis is from the Late Miocene found in China, named after the Lufeng site and dated around 6.2 Ma. Lufengpithecus is either thought to be the sister group to Ponginae, or the sister to the clade containing Ponginae and Homininae.
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 ; Gorilla ; Pan ; and Homo, of which only modern humans remain.
Odontometrics is the measurement and study of tooth size. It is used in biological anthropology and bioarchaeology to study human phenotypic variation. The rationale for use is similar to that of the study of dentition, the structure and arrangement of teeth. There are a number of features that can be observed in human teeth through the use of odontometrics.
Australopithecus deyiremeda is an extinct species of australopithecine from Woranso–Mille, Afar Region, Ethiopia, about 3.5 to 3.3 million years ago during the Pliocene. Because it is known only from three partial jawbones, it is unclear if these specimens indeed represent a unique species or belong to the much better-known A. afarensis. A. deyiremeda is distinguished by its forward-facing cheek bones and small cheek teeth compared to those of other early hominins. It is unclear if a partial foot specimen exhibiting a dextrous big toe can be assigned to A. deyiremeda. A. deyiremeda lived in a mosaic environment featuring both open grasslands and lake- or riverside forests, and anthropologist Fred Spoor suggests it may have been involved in the Kenyan Lomekwi stone-tool industry typically assigned to Kenyanthropus. A. deyiremeda coexisted with A. afarensis, and they may have exhibited niche partitioning to avoid competing with each other for the same resources, such as by relying on different fallback foods during leaner times.
Homo naledi is an extinct species of archaic human discovered in 2013 in the Rising Star Cave system, Gauteng province, South Africa, dating to the Middle Pleistocene 335,000–236,000 years ago. The initial discovery comprises 1,550 specimens of bone, representing 737 different skeletal elements, and at least 15 different individuals. Despite this exceptionally high number of specimens, their classification with other Homo species remains unclear.