Teeth are common to most vertebrates, but mammalian teeth are distinctive in having a variety of shapes and functions. This feature first arose among the Therapsida during the Permian, and has continued to the present day, all Therapsid groups with the exception of the mammals are now extinct, but each of these groups possessed different tooth patterns, which aids with the classification of fossils. For example, the quoll is a dasyurid marsupial native to Australia. The quoll possesses four upper incisors and three lower incisors per left and right-hand side, along with two upper premolars and two lower premolars per side and four upper and four lower molars per side, giving the animal a complement of thirty-eight teeth. The Tiger quolls dental formula is as follows,4.1. 2-3.43.1. 2-3.4, rabbits and other lagomorphs usually shed their deciduous teeth before their birth, and are usually born with their permanent teeth. The teeth of rabbits complement their diet, which consist of a range of vegetation.
Since many of the foods are abrasive enough to cause attrition, rabbits have a total of 6 incisors, three upper premolars, three upper molars, two lower premolars, and two lower molars on each side. Three to four millimeters of tooth is worn away by every week. Anatomy of rabbit teeth The incisors and cheek teeth of rabbits are called aradicular hypsodont teeth and this is sometimes referred to as an elodent dentition. These teeth grow or erupt continuously, the growth or eruption is held in balance by dental abrasion from chewing a diet high in fiber. Rodents incisors grow continuously throughout their lives, a known as aradicular. Unlike humans whose ameloblasts die after tooth development, rodents continually produce enamel and these teeth are used for cutting wood, biting through the skin of fruit, or for defense. The teeth have enamel on the outside and exposed dentin on the inside, on the other hand, continually growing molars are found in some rodent species, such as the sibling vole and the guinea pig.
There is variation in the dentition of the rodents, but generally, rodents lack canines and premolars, an adult horse has between 36 and 44 teeth. All horses have twelve premolars, twelve molars, and twelve incisors, all male equines have four canine teeth between the molars and incisors. However, few horses have canines, and those that do usually have only one or two, which many times are only partially erupted. A few horses have one to four teeth, which are vestigial premolars. They are equally common in male and female horses and much more likely to be on the upper jaw, if present these can cause problems as they can interfere with the horses bit contact
The Jurassic is a geologic period and system that spans 56.3 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, known as the Age of Reptiles, the start of the period is marked by the major Triassic–Jurassic extinction event. The Jurassic is named after the Jura Mountains within the European Alps, by the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, on land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds appeared during the Jurassic, having evolved from a branch of theropod dinosaurs, other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals.
Crocodilians made the transition from a terrestrial to a mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, the chronostratigraphic term Jurassic is directly linked to the Jura Mountains. The name Jura is derived from the Celtic root jor, which was Latinised into juria, the Jurassic period is divided into the Early Jurassic and Late Jurassic epochs. The Jurassic System, in stratigraphy, is divided into the Lower Jurassic, the separation of the term Jurassic into three sections goes back to Leopold von Buch. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous period, the Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation, as in the Triassic, there was apparently no land over either pole, and no extensive ice caps existed. In contrast, the North American Jurassic record is the poorest of the Mesozoic, the Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate.
Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, the first of several massive batholiths were emplaced in the northern American cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are found in Russia, South America, Australasia. As the Jurassic proceeded and more groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are well represented nor well studied in Africa. Late Jurassic strata are poorly represented apart from the spectacular Tendaguru fauna in Tanzania, the Late Jurassic life of Tendaguru is very similar to that found in western North Americas Morrison Formation. During the Jurassic period, the primary living in the sea were fish
The cynodonts, in the clade Cynodontia, are therapsids that first appeared in the Late Permian. The group includes modern mammals as well as their extinct ancestors, nonmammalian cynodonts spread throughout southern Gondwana and are represented by fossils from South America, Africa and Antarctica. In the northern continents, fossils have found in eastern North America as well as in Belgium. Cynodontia is one of the most diverse groups of therapsids, richard Owen named Cynodontia in 1861, which he assigned to Anomodontia as a family. Robert Broom reranked Cynodonia as an infraorder, since retained by others, including Colbert and Kitching, Gauthier et al. and Rubidge, olson assigned Cynodontia to Theriodonta and Kitching to Theriodontia, and Rubridge and Sidor to Eutheriodontia. William King Gregory, Carroll, Gauthier et al, hopson and Kitching and Botha et al. all considered Cynodontia as belonging to Therapsida. Botha et al. seems to have followed Owen, but without specifying taxonomic rank, together with the extinct gorgonopsians and the therocephalians, the cynodonts themselves are part of a group of therapsids called theriodonts.
The oldest and the most basal cynodont yet found is Charassognathus, other basal cynodonts were the procynosuchids, a family that includes Procynosuchus and Dvinia. Cynodonts were among the few groups of synapsids that survived the Permian–Triassic extinction event and had a recovery after the extinction. The most derived cynodonts are found within the clade Eucynodontia, which contains the members of Mammalia. Representative genera of nonmammalian cynodonts include the large carnivorous cynognathids, the large herbivorous traversodonts. The presence of respiratory turbinates suggests a rapid metabolism and possibly endothermy, during their evolution, the number of cynodont jaw bones reduced. Cynodonts developed a secondary palate in the roof of the mouth and this caused air flow from the nostrils to travel to a position in the back of the mouth instead of directly through it, allowing cynodonts to chew and breathe at the same time. This characteristic is present in all mammals, early cynodonts have many of the skeletal characteristics of mammals.
The teeth were fully differentiated and the braincase bulged at the back of the head, outside of some crown-group mammals, all cynodonts probably laid eggs. The temporal fenestrae were larger than those of their ancestors. They have the secondary palate that other primitive therapsids lacked, except the therocephalians, the dentary was the largest bone in their lower jaw. The cynodonts probably had some form of warm-blooded metabolism and this has led to many reconstructions of cynodonts as having fur
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas, a distinctive characteristic common to these species is that most of the young are carried in a pouch. Well-known marsupials include kangaroos, koalas, opossums, Tasmanian devils, others include the numbat, the bandicoot, the bettong, the bilby, the quoll, and the quokka. Marsupials represent the clade originating from the last common ancestor of extant metatherians, like other mammals in the Metatheria, they give birth to relatively undeveloped young that often reside with the mother in a pouch, for a certain amount of time. Close to 70% of the 334 extant species occur on the Australian continent, the remaining 100 are found in the Americas — primarily in South America, but thirteen in Central America, and one in North America, north of Mexico. Taxonomically, the two divisions of Marsupialia are and Australian marsupials. The order Microbiotheria is found in South America, but is believed to be closely related to Australian marsupials.
There are many small species in each group. The term opossum is used to refer to American species, while similar Australian species are properly called possums, shrew opossums are more closely related to australidelphians than to true opossums. Order Notoryctemorphia. Marsupials have the characteristics of mammals—e. g. Mammary glands, three middle ear bones, and true hair, there are, striking differences as well as a number anatomical features that separate them from Eutherians. In addition to the front pouch, which contains multiple nipples for the protection and sustenance of their young, ossified patellae are absent in most modern marsupials and epipubic bones are present. Marsupials lack a gross communication between the right and left brain hemispheres, the skull has peculiarities in comparison to higher mammals. In general, the skull is small and tight. Holes are located in the front of the orbit, the cheekbone is enlarged and extends further to the rear. The angular extension of the jaw is bent toward the center.
Another feature is the palate which, in contrast to the higher mammals foramina. The teeth differ from that of mammals, so that all taxa except wombats have a different number of incisors in the upper and lower jaws
Symmetrodonta is a group of Mesozoic mammals and mammal-like synapsids characterized by the triangular aspect of the molars when viewed from above and the absence of a well-developed talonid. The traditional group of ranges in age from the latest Triassic to the Late Cretaceous. Most research during the 21st century has concluded that they do not represent a discrete phylogenetic category, the name is still used informally by some researchers for convenience, or restricted to the spalacotheriids and zhangheotheriids. At least symmetrodonts with acutely-triangulated molar cusps seem to form a monophyletic group. Although Zhangheotheriidae might be paraphyletic in relation to other forms, particular sub−groups of Symmetrodonta are better studied, e. g. Spalacotheriidae, which has acute−angled molariform teeth, strongly reduced talonids, and conspicuous anterior and posterior cingulids. Though some forms like Zhangheotherium retain a Meckelian groove, at least Spalacotheriidae lost it and their deciduous canines and premolars as well as long lower jaw indicate a carnivorous/insectivorous diet.
Zhangheotherium was specialised to a scansorial lifestyle and it shows evidence of tarsal spurs, indicating that, like most non-therian Mammaliaformes, at least some symmetrodonts were venomous like the modern platypus. One species, Spalacotheridium noblei, is notable for its small size and it is one of the smallest known mammals. Each individual molar is more than 0.25 mm across. Evolution of mammals Discovering a Missing Link
Monotremes are basal mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals. The only surviving examples of monotremes are all indigenous to Australia and New Guinea, the existing monotreme species are the platypus and four species of echidnas. There is currently debate regarding monotreme taxonomy. The word monotreme comes from the Greek μονός, monos and τρῆμα, trema, in common with reptiles and marsupials, monotremes lack the connective structure which in placental mammals is the primary communication route between the right and left brain hemispheres. Extant monotremes lack teeth as adults, fossil forms and modern platypus young have a tribosphenic form of molars, which is one of the hallmarks of extant mammals. Some recent work suggests that monotremes acquired this form of molar independently of placental mammals and marsupials, toothloss in modern monotremes might be related to their development of electrolocation. Monotreme jaws are constructed differently from those of other mammals.
Nonetheless, findings on the extinct species Teinolophos confirm that suspended ear bones evolved independently among monotremes, the external opening of the ear still lies at the base of the jaw. DNA suggests that while this trait is shared and is synapomorphic with birds, platypuses are still mammals, l-ascorbic acid is synthesized only in the kidneys. The monotremes have extra bones in the girdle, including an interclavicle and coracoid. Monotremes retain a reptile-like gait, with legs on the sides of, rather than underneath, the monotreme leg bears a spur in the ankle region, the spur is not functional in echidnas, but contains a powerful venom in the male platypus. This venom is derived from b-defensins, proteins that are present in mammals that create holes in viral and bacterial pathogens, some reptile venom is composed of different types of b-defensins, another trait shared with reptiles. It is thought to be an ancient mammalian characteristic, as many non-monotreme archaic mammal groups possess venomous spurs, the penis only carries semen, urine is excreted through the cloaca.
The monotreme penis is similar to a penis, and is covered by a preputial sac. However, the egg is retained for some time within the mother, which provides the egg with nutrients. Newborn monotremes are larval and fetus-like, much like those of marsupials, like all mammals, but have no defined nipples, excreting the milk from their mammary glands via openings in their skin. All species are long-lived, with low rates of reproduction and relatively prolonged parental care of infants, the zygotes of monotremes, undergo meroblastic division, which causes the ovum to split but not completely. Monotremes metabolic rate is low by mammalian standards
The raccoon, sometimes spelled racoon, known as the common raccoon, North American raccoon, northern raccoon and colloquially as coon, is a medium-sized mammal native to North America. The raccoon is the largest of the family, having a body length of 40 to 70 cm. Its grayish coat mostly consists of dense underfur which insulates it against cold weather, two of the raccoons most distinctive features are its extremely dexterous front paws and its facial mask, which are themes in the mythology of several Native American ethnic groups. Raccoons are noted for their intelligence, with studies showing that they are able to remember the solution to tasks for up to three years, the diet of the omnivorous raccoon, which is usually nocturnal, consists of about 40% invertebrates, 33% plant foods, and 27% vertebrates. As a result of escapes and deliberate introductions in the century, raccoons are now distributed across mainland Europe, Caucasia. Though previously thought to be solitary, there is now evidence that raccoons engage in social behavior.
Home range sizes vary anywhere from 3 hectares for females in cities to 5,000 hectares for males in prairies, after a gestation period of about 65 days, two to five young, known as kits, are born in spring. The kits are subsequently raised by their mother until dispersal in late fall, although captive raccoons have been known to live over 20 years, their life expectancy in the wild is only 1.8 to 3.1 years. In many areas and vehicular injury are the two most common causes of death, the word raccoon was adopted into English from the native Powhatan term, as used in the Virginia Colony. It was recorded on Captain John Smiths list of Powhatan words as aroughcun and it has been identified as a Proto-Algonquian root *ahrah-koon-em, meaning one who rubs and scratches with its hands. Similarly, Spanish colonists adopted the Spanish word mapache from the Nahuatl mapachitli of the Aztecs, in French and European Portuguese, the washing behavior is combined with these languages term for rat, respectively, raton laveur and ratão-lavadeiro.
The colloquial abbreviation coon is used in words like coonskin for fur clothing and in phrases like old coon as a self-designation of trappers. In the 1830s, the U. S. Whig Party used the raccoon as an emblem, causing them to be known as coons by their political opponents. Soon after that it became an ethnic slur, especially in use between 1880 and 1920, and the term is considered offensive. In 1780, Gottlieb Conrad Christian Storr placed the raccoon in its own genus Procyon and it is possible that Storr had its nocturnal lifestyle in mind and chose the star Procyon as eponym for the species. Based on fossil evidence from France and Germany, the first known members of the family Procyonidae lived in Europe in the late Oligocene about 25 million years ago. Similar tooth and skull structures suggest procyonids and weasels share a common ancestor, after the then-existing species crossed the Bering Strait at least six million years in the early Miocene, the center of its distribution was probably in Central America.
Coatis and raccoons have been considered to share common descent from a species in the genus Paranasua present between 5.2 and 6.0 million years ago
A cusp is a pointed, projecting, or elevated feature. In animals, it is used to refer to raised points on the crowns of teeth. A cusp is an occlusal or incisal eminence on a tooth, canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps, in certain populations the maxillary molars, especially first molars, will possess a fifth cusp situated on the mesiolingual cusp known as the Cusp of Carabelli. Buccal Cusp- One other variation of the upper first premolar is the Uto-Aztecan upper premolar and it is a bulge on the buccal cusp that is only found in Native American Indians, with highest frequencies of occurrence in Arizona. The name is not a term, it comes from a regional linguistic division of Native American Indian language groups. Buccal-The side of a tooth that is adjacent to the inside of the cheek, as opposed to lingual or palatal, although technically referring only to posterior teeth, this term may be employed to describe the facial surface of anterior teeth as well.
There are 4 main cusps found on the molars of the dentition of hominids. The hypocone is found on the lingual side of the tooth. It fits into the grooves of the dentition and is an adaptation for the overall grinding and tearing of foods using the occlusal of the tooth surface during occlusion or mastication. Its strength is due to the thickness of the enamel which differs among species of hominids, the hypocone appears to have evolved independently in more than twenty mammal species during the Cenozoic period. The metacone is a cusp on the molars of the dentition in hominids. It is found at the distal area of the tooth. The crests between the cusps are adaptations for slicing food during occlusion or mastication, the protocone is founding the molars of the upper dentition in Placental and Marsupial vertebrates. It is found at the area of the tooth. The crests between the cusps are adaptations for slicing food during occlusion or mastication, mamelon Cusp of Carabelli Talon cusp Ash, Major M. Nelson, Stanley.
WheelerS Dental Anatomy and Occlusion, 8th edition
A wisdom tooth or third molar is one of the three molars per quadrant of the human dentition. It is the most posterior of the three, Wisdom teeth generally erupt between the ages of 17 and 25. Most adults have four teeth, one in each of the four quadrants. Wisdom teeth commonly affect other teeth as they develop, becoming impacted and they are often extracted when or even before this occurs. Agenesis of wisdom teeth differs by population, ranging from zero in Tasmanian Aborigines to nearly 100% in indigenous Mexicans. The difference is related to the PAX9 gene, Wisdom teeth are vestigial third molars that helped human ancestors to grind plant tissue. After the advent of agriculture 10000 years ago, soft human diets became the norm, including carbohydrate, such diets typically result in jaws growing with less forwards growth than our paleolithic ancestors and not enough room for the wisdom teeth. This is not a change, but rather an environmental change. Wisdom teeth have long identified as a source of problems.
The oldest known impacted wisdom tooth belonged to a European woman of the Magdalenian period, a lack of room to allow the teeth to erupt results in a risk of periodontal disease and dental cavities that increases with age. Less than 2% of adults age 65 years or older maintain the teeth without cavities or periodontal disease, impacted wisdom teeth are classified by the direction and depth of impaction, the amount of available space for tooth eruption and the amount soft tissue or bone that covers them. The classification structure allows clinicians to estimate the probabilities of impaction, Wisdom teeth are classified by the presence of symptoms and disease. Treatment of a wisdom tooth is the same as any other tooth in the mouth. If impacted, treatment can be localized to the tissue overlying the impaction, extraction or coronectomy. The term probably came as a translation of the Latin dens sapientiae and this happens, when it does happen, in the case of people where the wisdom-teeth have not come up in early years.
National Institute of Clinical Health and Excellence Guideline to Wisdom teeth removal Wisdom tooth extraction WebMD article
Theria is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians and the metatherians, therian mammals give birth to live young without using a shelled egg. It is possible thanks to key proteins called syncytins, which allow exchanges between the mother and its offspring through a placenta even rudimental such as the marsupial ones, genetic studies have enlighted the viral origin of syncytins through endogenization process. Therian mammals no longer have the coracoid bone, contrary to their cousins monotremes, pinnae are a distinctive trait that is a therian exclusivity. The earliest known therian mammal fossil is Juramaia, from the Middle Jurassic of China, molecular data suggests that therians may have originated even earlier, during the Early Jurassic. The rank of Theria may vary depending on the system used. The textbook classification system by Vaughan et al. gives the following, marsupials Monotremes Placental mammals Theria — supercohort — Tree of Life