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Simian Shelf
The simian shelf is a bony thickening on the front of the ape mandible. Its function is to reinforce the jaw, though it also has the effect of considerably reducing the movement of the tongue by restricting the area available for muscles. Humans are the only primates to have protruding chins, though some fossils of early humans show evidence of a simian shelf. Evolution of the simian shelf In Maboko Island (1988), the lower jaw of a Kenyapithecus was found, and it provides signs of the simian shelf evolution in modern apes. Where the simian shelf is present, the bottom teeth will be leaning forward. This happened to be a unique feature of the Kenyapithecus leading there to be a link between the two. This sign of evolution was identified as shown through the lower incisors that lean forward and are known to be used to break hard objects. The lower incisors were concluded to be an adaptive feature as it was an adaptation for "hard object feeding including... large mandible... and u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movable bone of the skull (discounting the ossicles of the middle ear). It is connected to the temporal bones by the temporomandibular joints. The bone is formed prenatal development, in the fetus from a fusion of the left and right mandibular prominences, and the point where these sides join, the mandibular symphysis, is still visible as a faint ridge in the midline. Like other symphyses in the body, this is a midline articulation where the bones are joined by fibrocartilage, but this articulation fuses together in early childhood.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, p. 59 The word "mandible" derives from the Latin word ''mandibula'', "jawbone" (literally "one used for chewing"), from ''wikt:mandere ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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, and language. Humans are highly social and tend to live in complex social structures composed of many cooperating and competing groups, from families and kinship networks to political states. Social interactions between humans have established a wide variety of values, social norms, and rituals, which bolster human society. Its intelligence and its desire to understand and influence the environment and to explain and manipulate phenomena have motivated humanity's development of science, philosophy, mythology, religion, and other fields of study. Although some scientists equate the term ''humans'' with all members of the genus ''Homo'', in common usage, it generally refers to ''Homo sapiens'', the only extant member. Anatomically moder ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chin
The chin is the forward pointed part of the anterior mandible (List_of_human_anatomical_regions#Regions, mental region) below the lower lip. A fully developed human skull has a chin of between 0.7 cm and 1.1 cm. Evolution The presence of a well-developed chin is considered to be one of the morphological characteristics of ''Homo sapiens'' that differentiates them from other human ancestors such as the closely related Neanderthal, Neanderthals. Early human ancestors have varied Mandibular symphysis, symphysial morphology, but none of them have a well-developed chin. The origin of the chin is traditionally associated with the anterior–posterior breadth shortening of the dental arch or tooth row; however, its general mechanical or functional advantage during feeding, developmental origin, and link with human speech, physiology, and social influence are highly debated. Functional perspectives Robinson (1913) suggests that the demand to resist Mastication, masticatory stresses ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maboko Island
Maboko Island is a small island lying in the Winam Gulf of Lake Victoria, in Nyanza Province of western Kenya. It is about 1.8 km long by 1 km wide. It is an important Middle Miocene paleontological site with fossiliferous deposits that were discovered in the 1930s. The age of the deposits is estimated to be , and they are especially important for the abundance of primate fossils they contain. Excavations Miocene fossils in the fluvial deposits of Maboko was first discovered by Archdeacon W.E. Owen in 1933, who started an excavation later that year which yielded a lot of vertebrate fossils. Owen's excavations continued the following two years supervised by Donald Gordon MacInnes. Then few expeditions visited the island before MacInnes returned together with Louis Leakey in 1947. These excavations resulted in a large number of craniodental (crania and teeth) remains of a medium seized cercopithecoid monkey and cranial and postcranial remains of a large anthropoid ape ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kenyapithecus
''Kenyapithecus wickeri'' is a fossil ape discovered by Louis Leakey in 1961 at a site called Fort Ternan in Kenya. The upper jaw and teeth were dated to 14 million years ago. One theory states that ''Kenyapithecus'' may be the common ancestor of all the great apes. More recent investigations suggest ''Kenyapithecus'' is more primitive than that and is only slightly more modern than ''Proconsul'', which is considered to be an ape. Evidence suggests that ''Kenyapithecus wickeri'' was one of the species that started a radiation of apes out of Africa. Morphology Impressed by ''Kenyapithecus''s modern-looking teeth, Leakey declared ''Kenyapithecus'' to be "a very early ancestor of man himself." ''Kenyapithecus'' possessed craniodental adaptations for hard object feeding including thicker molar enamel, and a large mandible, large premolars and upper incisors that are similar to those seen in living pitheciine monkeys. ''Kenyapithecus'' also possessed macaque-like limbs adapted ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mandibular Symphysis
In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral halves of the mandible typically fuse at an early period of life (1-2 years). It is not a true symphysis as there is no cartilage between the two sides of the mandible. This ridge divides below and encloses a triangular eminence, the mental protuberance, the base of which is depressed in the center but raised on either side to form the mental tubercle. The lowest (most inferior) end of the mandibular symphysis — the point of the chin — is called the "menton". It serves as the origin for the geniohyoid and the genioglossus muscles. Other animals Solitary mammalian carnivores that rely on a powerful canine bite to subdue their prey have a strong mandibular symphysis, while pack hunters delivering shallow bites have a weaker one. When filter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primate Anatomy
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including humans). Primates arose 85–55 million years ago first from small terrestrial mammals, which adapted to living in the trees of tropical forests: many primate characteristics represent adaptations to life in this challenging environment, including large brains, visual acuity, color vision, a shoulder girdle allowing a large degree of movement in the shoulder joint, and dextrous hands. Primates range in size from Madame Berthe's mouse lemur, which weighs , to the eastern gorilla, weighing over . There are 376–524 species of living primates, depending on which classification is used. New primate species continue to be discovered: over 25 species were described in the 2000s, 36 in the 2010s, and three in the 2020s. Primates have large brai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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