rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

s, sphenopalatine vacuities are perforations of the roof of the mesopterygoid fossa, the open space behind the

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sep ...

, in between the parapterygoid fossae. They may perforate the presphenoid or basisphenoid bone. Their development and form are variable between and within species, and features of the sphenopalatine vacuities have been used as characters in

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

analyses.Weksler, 2006, p. 37; Steppan, 1995, pp. 37–38; Carleton, 1980, p. 44 Among

Oryzomyini Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 distributed from the eastern United States to the southernmost parts of S ...

, a mainly South American group, a 2006 study distinguished three character states—large, wide vacuities, as among others in ''

Oligoryzomys ''Oligoryzomys'' is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos.Musser and Carleton, 2005 The genus is found from Mexico to Tierra del Fuego and includes approximately 1 ...

'' and ''

Holochilus ''Holochilus'' is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae,* sometimes called marsh rats. It contains five living species, '' H. brasiliensis'', '' H. chacarius'', '' H. nanus'', '' H. oxe'', and '' H. sciureus ...

''; small, narrow vacuities, as among others in ''

Lundomys ''Lundomys molitor'', also known as Lund's amphibious ratMusser and Carleton, 2005, p. 1124 or the greater marsh rat, is a semiaquatic rat species from southeastern South America. Its distribution is now restricted to Uruguay and nearby Ri ...

'' and '' Nephelomys''; and no or vestigial vacuities, as among others in '' Mindomys'' and ''

Oryzomys ''Oryzomys'' is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat (''O. palustris'') of the United States and ...

''.Weksler, 2006, p. 37

Phyllotini The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species c ...

all have very large sphenopalatine vacuities, as does ''Sigmodon''. The vacuities in ''

Reithrodon ''Reithrodon'' is a genus of rodent in the family Cricetidae. It contains the following living species: * Bunny rat (''Reithrodon auritus'') * Naked-soled conyrat (''Reithrodon typicus'') The scientific name translates as "channel tooth" and ...

'', formerly considered a phyllotine, are especially large.Steppan, 1995, p. 38 ''

Nyctomys Sumichrast's vesper rat (''Nyctomys sumichrasti'') is a rodent of the family Cricetidae found from southern Mexico to Panama. It is named for François Sumichrast, the collector of the first specimen, and its closest relative is probably Hatt's ...

'' is special in having sphenopalatine vacuities restricted to the basisphenoid bone. Character polarity for the development of the vacuities in

Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At over 870 species, it is either the largest or second-largest family ...

is difficult to determine, but their absence may be primitive in the

Neotominae The Neotominae are a subfamily of the family Cricetidae. They consist of four tribes, 16 genera, and many species of New World rats and mice, predominantly found in North America. Among them are the well-known deer mice, packrats, and grasshopp ...

. The development of sphenopalatine vacuities has also been used to distinguish among members of the

Sciurini Sciurini () is a tribe that includes about forty species of squirrels,Thorington and Hoffmann, 2005, p. 754 mostly from the Americas. It includes five living genera—the American dwarf squirrels, '' Microsciurus''; the Bornean '' Rheithrosc ...

group of

squirrel Squirrels are members of the family Sciuridae (), a family that includes small or medium-sized rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrel ...

s.Moore, 1959, p. 179

References

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Literature cited

*Carleton, M.D. 1980. Phylogenetic relationships in neotomine-peromyscine rodents (Muroidea) and a reappraisal of the dichotomy within New World Cricetinae. Miscellaneous Publications, Museum of Zoology, University of Michigan 157:i–vii+1–146. *Moore, J.C. 1959
Relationships among the living squirrels of the Sciurinae
Bulletin of the American Museum of Natural History 118:157–206. *Steppan, S.J. 1995. Revision of the tribe Phyllotini (Rodentia: Sigmodontinae), with a phylogenetic hypothesis for the Sigmodontinae. Fieldiana Zoology 80:1–112. *Weksler, M. 2006
Phylogenetic relationships of oryzomyine rodents (Muroidea: Sigmodontinae): separate and combined analyses of morphological and molecular data
Bulletin of the American Museum of Natural History 296:1–149. Rodent anatomy