34-407: 1st row: Trirachodon berryi , Probainognathus jenseni ; 2nd row: Brasilitherium riograndensis , Castorocauda lutrasimilis ; 3rd row: Ornithorhynchus anatinus ( platypus ), Loxodonta africana ( African bush elephant ). Eucynodontia ("true dog teeth") is a clade of cynodont therapsids including mammals and most non-mammalian cynodonts. The oldest eucynodonts are known from
68-472: A common ancestor that they share with marsupials and placentals (from boreosphenidans ); this idea still has some critics. For example, the dentition of the Early Cretaceous monotreme Steropodon is similar to those of Peramus and dryolestoids , which suggests that monotremes are related to some pre-tribosphenic mammals, but, on the other hand, the status of neither of these two groups
102-442: A crown and a neck. The occlusal surface is rough and mostly flat, adapted for crushing and grinding plant material. The body is covered with cementum both above and below the gingival line, below which is a layer of enamel covering the entire length of the body. The cementum and the enamel invaginate into the thick layer of dentin. The opposite condition to hypsodont is called brachydont or brachyodont (from brachys 'short'). It
136-536: A fifth cusp. In many mammals, additional smaller cusps called conules appear between the larger cusps. They are named after their locations, e.g. a paraconule is located between a paracone and a metacone, a hypoconulid is located between a hypoconid and an entoconid. In bunodont molars, the cusps are low and rounded hills rather than sharp peaks. They are most common among omnivores such as pigs, bears, and humans. Bunodont molars are effective crushing devices and often basically quadrate in shape. Hypsodont dentition
170-439: A fourth cusp, the hypocone (hypoconid), subsequently evolved (see below). Quadrate (also called quadritubercular or euthemorphic) molars have a hypocone, an additional fourth cusp on the lingual (tongue) side of the upper molar, located posterior to the protocone. Quadrate molars appeared early in mammal evolution and are present in many species, including hedgehogs , raccoons , and many primates , including humans. There may be
204-596: A short, narrow snout with a wide orbital region. The zygomatic arches were relatively slender. Trirachodon was quite small for a cynodont, growing no larger than 50 cm in length. It had noticeably less molariform teeth than its closely related contemporary Diademodon . These teeth tended to be transversely broader than Diademodon as well. A bony secondary palate and precise postcanine tooth occlusion are seen as derived characteristics in Trirachodon that are similar to those of mammals . The type species
238-485: A simple, ring-like edge, as in mole rats , or a complex arrangement of series of ridges and cross-ridges, as those in odd-toed ungulates , such as equids . Lophodont molars have hard and elongated enamel ridges called lophs oriented either along or perpendicular to the dental row. Lophodont molars are common in herbivores that grind their food thoroughly. Examples include tapirs , manatees , and many rodents. When two lophs form transverse, often ring-shaped, ridges on
272-429: A tooth, the arrangement is called bilophodont . This pattern is common in primates, but can also be found in lagomorphs (hares, rabbits, and pikas) and some rodents. Extreme forms of lophodonty in elephants and some rodents (such as Otomys ) is known as loxodonty. The African elephant belongs to a genus called Loxodonta because of this feature. In selenodont molars (so-named after moon goddess Selene ),
306-442: Is T. berryi , named in 1895 on the basis of a single cranial skeleton. Three other specimens were later referred to T. kannemeyeri , which was distinguished from the type on the basis of snout length and number of postcanine teeth. These differences have since been considered too small to assign them to two different species, and thus the T. kannemeyeri has fallen out of use due to this possible synonymy. A new species, T. minor ,
340-725: Is a stub . You can help Misplaced Pages by expanding it . Trirachodon berryi Trirachodon (Greek: "three ridge tooth") is an extinct genus of cynodonts . Fossils have been found in the Cynognathus Assemblage Zone of the Beaufort Group in South Africa and the Omingonde Formation of Namibia , dating back to the Early and Middle Triassic . The skull of Trirachodon had
374-477: Is a type of dentition characterized by low-crowned teeth. Human teeth are brachydont. A brachydont tooth has a crown above the gingival line and a neck just below it, and at least one root. A cap of enamel covers the crown and extends down to the neck. Cementum is only found below the gingival line. The occlusal surfaces tend to be pointed, well-suited for holding prey and tearing and shredding. Zalambdodont upper molars have at least three main cusps, one larger on
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#1732790663340408-414: Is characterized by high-crowned teeth and enamel that extends far past the gum line, which provides extra material for wear and tear. Some examples of animals with hypsodont dentition are cattle and horses, all animals that feed on gritty, fibrous material. Hypsodont molars can continue to grow throughout life, for example in some species of Arvicolinae (herbivorous rodents). Hypsodont molars lack both
442-455: Is considered one of the most important characteristics of therian mammals is called a tribosphenic molar. Among living mammals, the tribosphenic tooth is found in most insectivorous mammals as well as young platypuses , even though adults platypuses are toothless. In tribosphenic teeth, the lower molar is divided into two regions: the three-cusped trigonid , or shearing end, and the talonid , or crushing heel. In modern tribosphenic molars,
476-541: Is on the lingual side of the tooth, while the anterior paracone and posterior metacone are on the buccal side. The protocone of the upper molar and talonid basin of the lower molar mesh together as a crushing system similar to a mortar and pestle . Tribosphenic molars were present in the direct ancestors of all three living mammal groups, but it was most likely not ancestral to mammals as a whole. Many paleontologists argue that it developed independently in monotremes (from australosphenidans ), rather than being inherited from
510-516: Is one of the earliest signs of cohabitation in a burrow complex by tetrapods (a partial burrow cast associated with Thrinaxodon liorhinus , also from the Beaufort Group, has recently been found that predates these burrows by several million years ). There have been many suggested reasons for this behavior in Trirachodon , including protection from predation, sites for reproduction and or rearing young, and thermoregulation. Recent studies in
544-426: Is well-established. Some Jurassic mammalia forms , such as docodonts and shuotheriids , have "reversed tribosphenic" molars, in which a talonid-like structure develops towards the front of the lower molar, rather than towards the rear. This variant is regarded as an example of convergent evolution . From the primitive tribosphenic tooth, molars have diversified into several unique morphologies. In many groups,
578-1200: The Early Triassic and possibly Late Permian . Eucynodontia includes two major subgroups, Cynognathia and Probainognathia . The clade was named in 1982 by Thomas Kemp , who defined it as all cynodonts more derived than Thrinaxodon . In 2001, Hopson and Kitching redefined the clade Eucynodontia as the least inclusive group containing Mammalia and Exaeretodon . Cladogram after Stefanello et al . (2023): Procynosuchus Galesaurus Thrinaxodon Platycraniellus Cynognathus Diademodon Langbergia Trirachodon Sinognathus Pascualgnathus Luangwa Scalenodon Mandagomphodon Massetognathus Exaeretodon Lumkuia Chiniquodon Probainognathus Bonacynodon Trucidocynodon Ectenion ( sic ) Diegocanis Protheriodon Prozostrodon Pseudotherium Therioherpeton Irajatherium Riograndia Diarthrognathus Pachygenelus Tritylodontidae Botucaraitherium Brasilodon Mammaliaformes [REDACTED] This cynodont -related article
612-499: The Omingonde Formation in Namibia have been attributed to the genus. At least 20 individuals have been found in one of the complexes. The entrance shafts slope down at shallow angles and have bilobate floors and vaulted roofs. The floors of the lower levels are less noticeably bilobate. The burrows typically terminate quite narrow. The tunnels tend to tightly curve as they progress deeper, with chambers branching off at right angles to
646-485: The mouth . They are more developed in mammals . They are used primarily to grind food during chewing . The name molar derives from Latin, molaris dens , meaning "millstone tooth", from mola , millstone and dens , tooth. Molars show a great deal of diversity in size and shape across the mammal groups. The third molar of humans is sometimes vestigial . In humans, the molar teeth have either four or five cusps . Adult humans have 12 molars, in four groups of three at
680-540: The back of the mouth. The third, rearmost molar in each group is called a wisdom tooth . It is the last tooth to appear, breaking through the front of the gum at about the age of 20, although this varies among individuals and populations, and in many cases the tooth is missing. The human mouth contains upper (maxillary) and lower (mandibular) molars. They are: maxillary first molar , maxillary second molar , maxillary third molar , mandibular first molar , mandibular second molar , and mandibular third molar . In mammals,
714-409: The base of the crown. Mammalian, multicusped cheek teeth probably evolved from single-cusped teeth in synapsids, although the diversity of therapsid molar patterns and the complexity in the molars of the earliest mammals make determining how this happened impossible. According to the widely accepted "differentiation theory", additional cusps have arisen by budding or outgrowth from the crown, while
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#1732790663340748-405: The bone histology of many specimens of Trirachodon have led to an increased understanding of the ontogeny and lifestyle of these animals. There is evidence in the growth rings of bones that growth rates in these animals was strongly influenced by the fluctuation in seasonal conditions in their environment. Molar (tooth) The molars or molar teeth are large, flat teeth at the back of
782-485: The crown of the molars and premolars is folded into a wide range of complex shapes. The basic elements of the crown are the more or less conical projections called cusps and the valleys that separate them. The cusps contain both dentine and enamel, whereas minor projections on the crown, called crenulations, are the result of different enamel thickness. Cusps are occasionally joined to form ridges and expanded to form crests. Cingula are often incomplete ridges that pass around
816-410: The lingual side and two smaller on the labial side. The large cusp is joined to the other two by crests, forming a narrow V- or λ (lambda)-shape. The term "zalambdodont" roughly translates to "very lambda-toothed". Zalambdodont molars are found in tenrecs , golden moles , solenodons , and marsupial moles among living mammals. In zalambdodont placentals, the larger inner cusp is homologous with
850-451: The lingual side, at the bottom of the W, are the metacone and paracone, and the stylar shelf is on the labial side. A protocone is present lingual to the ectoloph. Dilambdodont molars are present in shrews , moles , and some insectivorous bats . Lophodont teeth are easily identified by the differentiating patterns of ridges or lophs of enamel interconnecting the cusps on the crowns. Present in most herbivores, these patterns of lophs can be
884-414: The main tunnel. A semi-erect posture of the hindlimbs of Trirachodon is seen as an adaptation for sustained efficiency in locomotion in the tunnels. The relatively thick walls seen in these bones may also have provided extra rigidity to the limbs while digging. The burrows where the occupants were preserved inside are thought to have been filled with sediment in a flash flood; if it were a gradual filling,
918-607: The occupants would have had time to evacuate. Many features of the burrows suggest that they were used as colonial dwelling structures. The wide entrance would have been useful for a burrow inhabited by many individuals, and branching tunnels and terminating chambers would unlikely have been made by one animal. The worn, bilobate floors suggest that the tunnels were used rather frequently by numerous inhabitants as they passed one another while moving through them. A colonial lifestyle for Trirachodon suggests complex social behaviors previously thought to be unique to Cenozoic mammals, and
952-440: The paracone in a tribosphenic upper molar, while the metacone is absent, reduced or fused. Marsupial moles show the opposite condition, with the large cusp equivalent to the metacone, and the paracone absent instead. The protocone is either absent (as in some golden moles and tenrecs) or reduced to a small fourth cusp, positioned lingual to the large cusp at the tip of the V. The two labial cusps are located on an expanded shelf called
986-434: The rivalling "concrescence theory" instead proposes that complex teeth evolved by the clustering of originally separate conical teeth. Therian mammals (placentals and marsupials) are generally agreed to have evolved from an ancestor with tribosphenic cheek teeth, with three main cusps arranged in a triangle. Each major cusp on an upper molar is called a cone and is identified by a prefix dependent on its relative location on
1020-401: The stylar shelf. In the lower molars, the talonid region is reduced or absent, having lost its role as a crushing basin against the protocone. Zalambdodonty reduces tooth contact to a few simple shearing surfaces, though the evolutionary advantage of this tooth type is unclear. Like zalambdodont molars, dilambdodont molars have a distinct ectoloph, but are shaped like two lambdas or a W. On
1054-418: The tooth: proto-, para-, meta-, hypo-, and ento-. Suffixes are added to these names: -id is added to cusps on a lower molar (e.g., protoconid); -ule to a minor cusp (e.g., protoconulid). A shelf-like ridge left lower part of the crown (on an upper molar) is called a cingulum ; the same feature on the lower molar a cingulid, and a minor cusp on these, for example, a cingular cuspule or conulid. The design that
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1088-406: The trigonid is towards the front of the jaw and the talonid is towards the rear. The trigonid is defined by three large cusps: the protoconid is on the buccal/labial (cheek) side of the tooth, while the anterior paraconid and posterior metaconid are on the lingual (tongue) side. Upper molars look like three-pointed mountain ranges, with their features mirrored from the lower molars. The protocone cusp
1122-484: Was later proven to be from the traversodontid Scalenodon . All species of Trirachodon were suggested to by synonymous with the type species in 1972 except T. browni , which was synonymous with Diademodon tetragonus . Trirachodon is thought to have had a fossorial lifestyle. Scratch-marked burrow complexes found from the Driekoppen Formation in northeastern Free State , South Africa as well as
1156-488: Was named by Robert Broom in 1905 to describe a poorly preserved snout. Broom later named T. browni in 1915, in which he distinguished it from all other species on the basis of the length of the molars. In 1932, Broom proposed that T. berryi be reassigned to a new genus, Trirachodontoides . Another species of Trirachodon called T. angustifrons was named in 1946 from a narrow skull found in Tanzania , but this material
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