Many different terms have been proposed for features of the tooth crown in mammals.
The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn in 1907 and is, although with many variations, the one that continues today. [1] [2] [3]
Tooth structures bear suffixes in order to note the type of structure they are and whether they are present in the upper or lower molars.
The positions of tooth features are described along four directions: mesial (forwards, towards the chin), distal (backwards, towards the jaw joint), lingual (inwards, towards the tongue), and buccal or labial (outwards, towards the cheek).
Therians (marsupials and placentals) ancestrally have roughly triangular upper molars, with the apex pointing lingually (inwards) and the flat edge positioned labially (outwards). This fundamental three-pointed structure is sometimes called the trigon. Three major cusps are almost always present:
Other common features include:
Therians ancestrally have lower molars which are longer from front-to-back than from side-to-side. Five to six cusps are most common. The trigonid region at the front part of the molar is triangular, with three large cusps:
The talonid region at the rear part of the molar has two to three relatively small cusps which define the rear rim of a low basin:
Other common features include:
These are a list of tooth features identified in the rodent family Cricetidae (hamsters, voles, New World mice and rats, etc.). Source: [5]
Name | Nomenclature term is used in | Definition | Comments | Image |
---|---|---|---|---|
Anterolingual conule | Reig (1977) [5] | A conule on the lingual side of an anterocone divided by an anteromedian flexus or fossette | ||
Anteromedian flexus | Reig (1977) [5] | A longitudinal flexus dividing the anterocone into anterolabial and anterolingual conules | ||
Anterolabial conule | Reig (1977) [5] | A conule on the labial side of an anterocone divided by an anteromedian flexus or fossette | ||
Anterocone | Reig (1977) [5] | A cusp at the front of the tooth that may be divided into anterolabial and anterolingual conules | ||
Protostyle | Reig (1977) [5] | A style in front of the protocone, in the protoflexus | ||
Protoflexus | Reig (1977) [5] | A flexus between the protocone and the anterolingual conule | ||
Anterior mure | Reig (1977) [5] | A crest connecting the anterocone to the protocone | ||
Protocone | Reig (1977) [5] | One of the main cusps, at the anterolingual side | ||
Enterostyle | Reig (1977) [5] | A style between the protocone and the hypocone, in the hypoflexus | ||
Enteroloph | Reig (1977) [5] | A crest connecting the enterostyle to the mesocone | ||
Hypoflexus | Reig (1977) [5] | A flexus between the protocone and the hypocone | ||
Mesocone | Reig (1977) [5] | A conule in the median mure where the mesoloph is attached to it | ||
Median mure | Reig (1977) [5] | A crest connecting the protocone/paracone to the hypocone/metacone | ||
Hypocone | Reig (1977) [5] | One of the main cusps, at the posterolingual side | ||
Procingulum | Reig (1977) [5] | The front part of the tooth, before the anterior mure | ||
Anteroflexus | Reig (1977) [5] | A flexus between the anteroloph and the anterolabial conule | ||
Anteroloph | Reig (1977) [5] | A crest between the paracone and the anterolabial conule that may be connecting to a parastyle | ||
Parastyle | Reig (1977) [5] | A style in front of the paracone | ||
Paraflexus | Reig (1977) [5] | A flexus in front of the paracone | ||
Protolophule | Reig (1977) [5] | A small crest in the paraflexus, connected to the protocone | ||
Paraloph | Reig (1977) [5] | A crest attaching the paracone to the protocone or the median mure | ||
Paracone | Reig (1977) [5] | One of the main cusps, at the anterolabial side | ||
Paralophule | Reig (1977) [5] | A small crest attached to the back side of the paracone | ||
Mesoflexus | Reig (1977) [5] | A flexus between the mesoloph and the paracone | ||
Mesostyle | Reig (1977) [5] | A style at the labial margin between the paracone and metacone | ||
Mesoloph | Reig (1977) [5] | A crest in front of the metaflexus, connected to the median mure | ||
Metaflexus | Reig (1977) [5] | A flexus in front of the metacone | ||
Metalophule | Reig (1977) [5] | A small crest attached to the front side of the metacone | ||
Metacone | Reig (1977) [5] | One of the main cusps, at the posterolabial side | ||
Metaloph | Reig (1977) [5] | A crest attaching the paracone to the hypocone | ||
Posteroflexus | Reig (1977) [5] | A flexus between the posteroloph and the metacone | ||
Posterostyle | Reig (1977) [5] | A crest on the posterolabial corner of the molar | ||
Posteroloph | Reig (1977) [5] | A crest at the back of the molar, connected to the hypocone |
Name | Nomenclature term is used in | Definition | Comments | Image |
---|---|---|---|---|
Anterolingual conulid | Reig (1977) [5] | A conulid on the lingual side of an anteroconid divided by an anteromedian flexid or fossettid | ||
Anteromedian flexid | Reig (1977) [5] | A longitudinal flexid dividing the anteroconid into anterolabial and anterolingual conules | ||
Anterolabial conulid | Reig (1977) [5] | A conulid on the labial side of an anteroconid divided by an anteromedian flexid or fossettid | ||
Anteroconid | Reig (1977) [5] | A cusp at the front of the tooth that may be divided into anterolabial and anterolingual conulids | ||
Anterolabial cingulum | Reig (1977) [5] | A crest before the protoconid and protoflexid | ||
Protostylid | Reig (1977) [5] | A stylid in front of the protoconid, in the protoflexid | ||
Protoflexid | Reig (1977) [5] | A flexid between the protoconid and the anterolabial conulid | ||
Anterior murid | Reig (1977) [5] | A crest connecting the anteroconid to the protoconid | ||
Protoconid | Reig (1977) [5] | One of the main cusps, at the anterolabial side | ||
Ectostylid | Reig (1977) [5] | A stylid between the protoconid and the hypoconid, in the hypoflexid | ||
Ectolophid | Reig (1977) [5] | A crest connecting the ectostylid to the mesoconid | ||
Hypoflexid | Reig (1977) [5] | A flexid between the protoconid and the hypoconid | ||
Mesoconid | Reig (1977) [5] | A conulid in the median murid where the mesolophid is attached to it | ||
Median murid | Reig (1977) [5] | A crest connecting the protoconid/metaconid to the hypoconid/entoconid | ||
Hypoconid | Reig (1977) [5] | One of the main cusps, at the posterolabial side | ||
Procingulum | Reig (1977) [5] | The front part of the tooth, before the anterior murid | ||
Anteroflexid | Reig (1977) [5] | A flexid between the anterolophid and the anterolingual conulid | ||
Anterolophid | Reig (1977) [5] | A crest between the metaconid and the anterolabial conulid that may be connecting to a metastylid | ||
Metastylid | Reig (1977) [5] | A stylid in front of the metaconid | ||
Metaflexid | Reig (1977) [5] | A flexid in front of the metaconid | ||
Protolophulid | Reig (1977) [5] | A small crest in the mesoflexid, connected to the protoconid | ||
Metalophid | Reig (1977) [5] | A crest attaching the metaconid to the protoconid or the anterior murid | ||
Metaconid | Reig (1977) [5] | One of the main cusps, at the anterolingual side | ||
Metalophulid | Reig (1977) [5] | A small crest attached to the back side of the metaconid | ||
Mesoflexid | Reig (1977) [5] | A flexid between the mesolophid and the paraconid | ||
Mesostylid | Reig (1977) [5] | A stylid at the labial margin between the metaconid and entoconid | ||
Mesolophid | Reig (1977) [5] | A crest in front of the entoflexid, connected to the median murid | ||
Entoflexid | Reig (1977) [5] | A flexid in front of the entoconid | ||
Entolophulid | Reig (1977) [5] | A small crest attached to the front side of the entoconid | ||
Entoconid | Reig (1977) [5] | One of the main cusps, at the posterolingual side | ||
Entolophid | Reig (1977) [5] | A crest attaching the entoconid to the hypoconid or median murid | ||
Posteroflexid | Reig (1977) [5] | A flexid between the posterolophid and the metaconid | ||
Hypolophulid | Reig (1977) [5] | A small crest in the posteroflexid attached to the posterolophid | ||
Posterostylid | Reig (1977) [5] | A crest on the posterolingual corner of the molar | ||
Posterolophid | Reig (1977) [5] | A crest at the back of the molar, connected to the hypoconid |
The molars or molar teeth are large, flat teeth at the back of 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.
Ambondro mahabo is a mammal from the Middle Jurassic (Bathonian) Isalo III Formation of Madagascar. The only described species of the genus Ambondro, it is known from a fragmentary lower jaw with three teeth, interpreted as the last premolar and the first two molars. The premolar consists of a central cusp with one or two smaller cusps and a cingulum (shelf) on the inner, or lingual, side of the tooth. The molars also have such a lingual cingulum. They consist of two groups of cusps: a trigonid of three cusps at the front and a talonid with a main cusp, a smaller cusp, and a crest at the back. Features of the talonid suggest that Ambondro had tribosphenic molars, the basic arrangement of molar features also present in marsupial and placental mammals. It is the oldest known mammal with putatively tribosphenic teeth; at the time of its discovery it antedated the second oldest example by about 25 million years.
Brachytarsomys mahajambaensis is an extinct rodent from northwestern Madagascar. It is known from nine isolated molars found in several sites during fieldwork that started in 2001. First described in 2010, it is placed in the genus Brachytarsomys together with two larger living species, which may differ in some details of molar morphology. The presence of B. mahajambaensis, a rare element in the local rodent fauna, suggests that the region was previously more humid.
Nesomys narindaensis is an extinct rodent that lived in northwestern Madagascar. It is known from subfossil skull bones and isolated molars found in several sites during field work that started in 2001. First described in 2010, it is placed in the genus Nesomys together with three smaller living species, which may differ in some details of molar morphology. The presence of N. narindaensis, a rare element in the local rodent fauna, suggests that the region was previously more humid.
Hipposideros besaoka is an extinct bat from Madagascar in the genus Hipposideros. It is known from numerous jaws and teeth, which were collected in a cave at Anjohibe in 1996 and described as a new species in 2007. The site where H. besaoka was found is at most 10,000 years old; other parts of the cave have yielded H. commersoni, a living species of Hipposideros from Madagascar, and some material that is distinct from both species. H. besaoka was larger than H. commersoni, making it the largest insectivorous bat of Madagascar, and had broader molars and a more robust lower jaw. As usual in Hipposideros, the second upper premolar is small and displaced from the toothrow, and the second lower premolar is large.
Triaenops goodmani is an extinct bat from Madagascar in the genus Triaenops. It is known from three lower jaws collected in a cave at Anjohibe in 1996, and described as a new species in 2007. The material is at most 10,000 years old. A bat humerus from the same site could not be identified as either T. goodmani or the living T. menamena. T. goodmani is identifiable as a member of Triaenops or the related genus Paratriaenops by a number of features of the teeth, such as the single-cusped, canine-like fourth premolar and the presence of a gap between the entoconid and hypoconulid cusps on the first two molars. T. goodmani is larger than the living species of Triaenops and Paratriaenops on Madagascar, and on the first molar the protoconid cusp is only slightly higher than the hypoconid, not much higher as in the other species.
Agathaeromys is an extinct genus of oryzomyine rodents from the Pleistocene of Bonaire, Netherlands Antilles. Two species are known, which differ in size and some details of tooth morphology. The larger A. donovani, the type species, is known from hundreds of teeth that are probably 900,000 to 540,000 years old, found in four localities. A. praeuniversitatis, the smaller species, is known from 35 teeth found in a single fossil site, which is probably 540,000 to 230,000 years old.
Donodontidae is an extinct family of cladotherian mammals known from the Late Jurassic and Early Cretaceous of North Africa. When originally named in 1991, Donodontidae was a monotypic family containing a single species: Donodon perscriptoris. In 2022, four more species were designated and placed within the family: Donodon minor, Stylodens amerrukensis, Anoualestes incidens, and Amazighodon orbis. All five species are endemic to the Ksar Metlili Formation of Morocco, which is dated to the Tithonian and Berriasian. Donodontid fossils are restricted to postcanine teeth and associated jaw fragments.
Dermotherium is a genus of fossil mammals closely related to the living colugos, a small group of gliding mammals from Southeast Asia. Two species are recognized: D. major from the Late Eocene of Thailand, based on a single fragment of the lower jaw, and D. chimaera from the Late Oligocene of Thailand, known from three fragments of the lower jaw and two isolated upper molars. In addition, a single isolated upper molar from the Early Oligocene of Pakistan has been tentatively assigned to D. chimaera. All sites where fossils of Dermotherium have been found were probably forested environments and the fossil species were probably forest dwellers like living colugos, but whether they had the gliding adaptations of the living species is unknown.
Afrasia djijidae is a fossil primate that lived in Myanmar approximately 37 million years ago, during the late middle Eocene. The only species in the genus Afrasia, it was a small primate, estimated to weigh around 100 grams (3.5 oz). Despite the significant geographic distance between them, Afrasia is thought to be closely related to Afrotarsius, an enigmatic fossil found in Libya and Egypt that dates to 38–39 million years ago. If this relationship is correct, it suggests that early simians dispersed from Asia to Africa during the middle Eocene and would add further support to the hypothesis that the first simians evolved in Asia, not Africa. Neither Afrasia nor Afrotarsius, which together form the family Afrotarsiidae, is considered ancestral to living simians, but they are part of a side branch or stem group known as eosimiiforms. Because they did not give rise to the stem simians that are known from the same deposits in Africa, early Asian simians are thought to have dispersed from Asia to Africa more than once prior to the late middle Eocene. Such dispersals from Asia to Africa also were seen around the same time in other mammalian groups, including hystricognathous rodents and anthracotheres.
Indraloris is a fossil primate from the Miocene of India and Pakistan in the family Sivaladapidae. Two species are now recognized: I. himalayensis from Haritalyangar, India and I. kamlialensis from the Pothohar Plateau, Pakistan. Other material from the Potwar Plateau may represent an additional, unnamed species. Body mass estimates range from about 2 kg (4.4 lb) for the smaller I. kamlialensis to over 4 kg (8.8 lb) for the larger I. himalayensis.
Sivaladapis is a genus of adapiform primate that lived in Asia during the middle Miocene.
Exiguodon is an extinct genus of hyainailourid hyaenodont mammal of the subfamily Hyainailourinae. Remains are known from early Miocene deposits in Kenya and Uganda, in East Africa.
Sectisodon is an extinct genus of hyainailourid hyaenodont mammal of the subfamily Hyainailourinae from early Oligocene to early Miocene deposits in Egypt and Uganda.
Notoetayoa is an extinct genus of mammal, from the order Xenungulata. It contains a single species, Notoetayoa gargantuai, which lived during the Middle Paleocene. Its fossilized remains were discovered in South America.
Archaeogaia is an extinct genus of notoungulates that lived during the Early and Middle Paleocene of what is now Argentina. It is one of the oldest known unequivocal notoungulates.
Holoclemensia is an extinct genus of mammal of uncertain phylogenetic placement. It lived during the Early Cretaceous and its fossil remains were discovered in Texas.
Cokotherium is an extinct genus of eutherian mammal from the Early Cretaceous of China. It includes a single species, Cokotherium jiufotangensis, known from a single partial skeleton, missing a portion of the hindlimbs and tail. It was recovered from the Jiufotang Formation, the upper part of the fossiliferous Jehol biota. The generic name of Cokotherium honors the nickname of the late paleontologist Chuan-Kui Li, a specialist on the Jiufotang Formation. The specific name refers to the formation in question. Cokotherium is one of the youngest and most well-preserved Early Cretaceous eutherians, illustrating an array of transitional conditions between Early Cretaceous and Late Cretaceous members of Eutheria.
Lonchocyon is an extinct genus of arctoid carnivorans, with possible affinities to amphicyonids or hemicyonine bears. It contains a single species, Lonchocyon qiui, known from a single left mandible discovered at the fossil-bearing locality Haerhada at the base of the Baron Sog Formation, which is located in Inner Mongolia, China, and dates to the late Eocene. This taxon is notable for its large size in comparison to other arctoid carnivorans of the Eocene epoch, and for its hypercarnivorous adaptions, most notably its large canine and strongly reduced premolars. The genus name is a combination of Greek lonch, meaning spear and referencing the spear-like paraconid on its lower carnassial, and cyon, meaning dog. The specific name honours Professor Zhan-Xiang Qiu.
Alagtsavbaatar is an extinct species of carnivorous cat-like carnivoran belonging to the infraorder Aeluroidea. It was endemic to Asia, with all known specimens being found in Mongolia, and lived during the late Eocene epoch. It is a monotypic genus, with the type and only known species being A. indigenus, and is named after the Alag Tsav locality where its remains were first discovered.
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