Muroid molar

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Megalomys desmarestii sin i 26124 m.png
Upper (left) and lower (right) molar row of Megalomys desmarestii , showing commonly used nomenclature for the molars.

Rodents of the superfamily Muroidea, which includes mice, rats, voles, hamsters, bamboo rats, and many other species, generally have three molars in each quadrant of the jaws. A few of the oldest species retain the fourth upper premolar, and some living species have lost the third and even the second molars. Features of the molar crown are often used in muroid taxonomy, and many different systems have been proposed to name these features.

Rodent Diverse order of mammals

Rodents are mammals of the order Rodentia, which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents ; they are found in vast numbers on all continents except Antarctica. They are the most diversified mammalian order and live in a variety of terrestrial habitats, including human-made environments.

Muroidea superfamily of mammals

The Muroidea are a large superfamily of rodents, including mice, rats, voles, hamsters, gerbils, and many other relatives. They occupy a vast variety of habitats on every continent except Antarctica. Some authorities have placed all members of this group into a single family, Muridae, due to difficulties in determining how the subfamilies are related to one another. The following taxonomy is based on recent well-supported molecular phylogenies.

Molar (tooth) large tooth at the back of the mouth

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 mammal groups.

Contents

Description

Muroids are most closely related to the Dipodidae, a smaller group of rodents that includes the jerboas, birch mice, and jumping mice. [1] Jerboas have a dental formula of 1.0.0–1.31.0.000.3 × 2 = 16–18, including incisors in the upper and lower jaws, three molars in the upper and lower jaw, and in most species a small premolar (the fourth upper premolar, P4) in the upper jaw only. [2] In contrast, all muroids lack the P4, [3] but some species of Pappocricetodon from the Eocene of Asia, one of the earliest known muroids, do have a P4. [4] Some have suggested that the first molar in muroids is in fact a retained deciduous premolar, but this hypothesis has been discredited. [5] Several species have lost the M3 and/or m3, [3] and four species of the New Guinea murine genus Pseudohydromys have also lost the M2 and m2, so that they only have four minute molars. [6]

Dipodidae family of mammals

The Dipodidae, or dipodids, are a family of rodents found across the Northern Hemisphere, the sole family in the superfamily Dipodoidea. This family includes over 50 species among the 16 genera. They include the jerboas, jumping mice, and birch mice. Different species are found in grassland, deserts, and forests. They are all capable of saltation, a feature that is most highly evolved in the desert-dwelling jerboas.

Jerboa hopping desert rodents

Jerboas form the bulk of the membership of the family Dipodidae. Jerboas are hopping desert rodents found throughout Arabia, Northern Africa and Asia. They tend to live in hot deserts.

Birch mouse genus of mammals

Birch mice are small jumping desert rodents that resemble mice with a long tufted tail and very long hind legs, allowing for remarkable leaps. All variants possess a long tail of 65 to 110 mm of length and weigh about 6 to 14 g. Head and body length of 50 to 90 mm and hind foot length of 14 to 18 mm. The skin color is light brown or dark-brown to brownish yellow on the upper side and paler on the underside, but generally brownish.

Nomenclature

In 1977, Reig noted that eleven distinct nomenclatures had been proposed for the features of "cricetid" (generalized muroid) molars, by Schaub, Viret, Winge, Wood and Wilson, Hershkovitz, James, Vandebroek, Fahlbusch, Alker, Vorontzov, and Mein and Freudenthal. [7] He concluded that none of these were satisfactory and proceeded to propose another, "unifying" nomenclature. [8] Additional nomenclatures have been proposed for the Murinae [9] and for other, smaller groups.

Murinae subfamily of rodents

The Old World rats and mice, part of the subfamily Murinae in the family Muridae, comprise at least 519 species. Members of this subfamily are called murines. This subfamily is larger than all mammal families except the Cricetidae and Muridae, and is larger than all mammal orders except the bats and the remainder of the rodents.

Ontogeny

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Megalomys desmarestii sin s 26124.png
Megalomys desmarestii dex s 26124.png
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Ontogeny of the molars in Megalomys desmarestii . From left to right: Left upper molar row of an older animal, left upper molar row of a younger animal, right upper molar row of the same young animal with the M3 not yet erupted, left lower molar row of the older animal, left lower molar row of the younger animal.

Muroids are often considered adult when the third molar has erupted. [10] After the molars erupt, wear progressively obliterates the distinct features of the molar crown. [11]

Related Research Articles

Pouched rat subfamily of mammals

Pouched rats are a group of African rodents in the subfamily Cricetomyinae. They are members of the family Nesomyidae, which contains other African muroids such as climbing mice, Malagasy mice, and the white-tailed rat. All nesomyids are in the superfamily Muroidea, a large and complex clade containing 1/4 of all mammal species. Sometimes the pouched rats are placed in the family Muridae along with all other members of the superfamily Muroidea.

<i>Papagomys</i> genus of mammals

Papagomys is a genus of very large rats in the tribe Rattini of the subfamily Murinae. It contains two species, which are known only from the Indonesian island of Flores:

Myomorpha suborder of mammals

The suborder Myomorpha contains 1,137 species of mouse-like rodents, nearly a quarter of all mammal species. Included are mice, rats, gerbils, hamsters, lemmings, and voles. They are grouped according to the structure of their jaws and molar teeth. They are characterized by their myomorphous zygomasseteric system, which means that both their medial and lateral masseter muscles are displaced forward, making them adept at gnawing. As in the hystricognathous rodents, the medial masseter muscle goes through the eye socket, a feature unique among mammals. Myomorphs are found worldwide in almost all land habitats. They are usually nocturnal seed-eaters.

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<i>Leptomys</i> genus of mammals

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Ernst Mayrs water rat species of mammal

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Zygomatic plate

In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch (cheekbone). At the back, it connects to the front (maxillary) root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary bone, or upper jaw, which also contains the upper cheekteeth. Primitively, rodents have a nearly horizontal zygomatic plate. In association with specializations in zygomasseteric system, several distinct morphologies have developed across the order.

Guy Graham Musser is an American zoologist. His main research is in the field of the rodent subfamily Murinae, in which he has described many new species.

The southern small-toothed moss mouse is a species of rodent in the family Muridae found on the slopes of Mount Bosavi, Papua New Guinea.

<i>Baiyankamys</i> genus of mammals

Baiyankamys is a genus of amphibious murid rodents. It was originally described, along with the species Baiyankamys shawmayeri by Hinton in 1943 after he found the remains of a single individual in south east of the Bismarck Mountain Range, north east New Guinea. Tate, in 1951 and, Laurie and Hill in 1954, confirmed the existence of both the species and genus.

Mirza's eastern moss rat is a species of rodent endemic to New Guinea.

Mirza's western moss rat is a species of rodent endemic to Papua New Guinea.

Laurie’s moss mouse is a species of mouse belonging to the family Muridae that is endemic to Papua New Guinea. It was first described in 2009.

Woolley's moss mouse,, is a species of mouse endemic to Papua New Guinea. It was first described in 2009.

References

  1. ↑ Carleton and Musser, 2005, p. 749
  2. ↑ Ellerman, 1940, p. 561
  3. 1 2 Carleton and Musser, 1984, p. 292
  4. ↑ Emry, 2007, p. 147
  5. ↑ Reig, 1977, p. 228
  6. ↑ Helgen and Helgen, 2009, p. 240
  7. ↑ Reig, 1977, p. 232
  8. ↑ Reig, 1977, p. 235
  9. ↑ Musser and Newcomb, 1983, p. 332
  10. ↑ Voss, 1991, p. 16; Musser et al., 1998, p. 17
  11. ↑ Voss, 1991, p. 16; Zijlstra et al., 2008, p. 29

Literature cited

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