With over 1300 species, nearly globally distributed and tremendously diverse ecologically, the murids present a biologist with an almost unmanageably complex group. Systematists working with murids have divided the family into around 15 Recent subfamilies. In many instances these subfamilies are clearly cohesive and monophyletic entities, with members linked together by distribution, ecological attributes, and behavior as well as morphology, and (when available) fossils and molecular characteristics. In the past, some have been given the rank of family. In other instances the evidence for monophyly is less convincing. Nevertheless, dividing the Muridae into subfamilies makes it an easier group to comprehend, and current research on muroid systematics will, we hope, eventually clarify the makeup and relationships of its component subfamilies.
Sigmodontinae (423 species, 79 genera). New World rats and mice. Strictly New World in distribution, but found throughout the hemisphere. Very diverse and difficult to diagnose; includes forms that are strictly arboreal, others that are scansorial or terrestrial, some that are largely aquatic, and a few that are fossorial. Molar morphology is highly complex and variable. Food habits range from primarily herbivorous to primarily insectivorous; a few species are at least partly carnivorous; some consume large amounts of fungus. Includes such familiar genera as Peromyscus, Neotoma, Oryzomys. The number of species may be greatly underestimated.
Cricetinae (18 species, 7 genera). Hamsters. Southern Europe through Central Asia to the Pacific coast of China and Russia, where they are usually associated with drier habitats. Short tail, internal cheek pouches; also united by characteristics of dentition and ear ossicles. Primarily terrestrial; good diggers. Most species are granivores, storing seeds in their capacious cheek pouches.
Calomyscinae (6 species, 1 genus). Asian hamster-mouse. Central Asia. Small, like cricetids but lack cheek pouches and with a long tail. Peculiar species of very uncertain phylogenetic relationships. May be allied with the extinct subfamily Cricetodontinae.
Mystromyinae (1 genus, 1 species). White-tailed rat. Southern Africa. Hamster-like, no cheek pouches. Phylogenetic relationships unclear; some systematists suggest a close relationship with Nesomyinae.
Arvicolinae (143 species, 26 genera). Voles, lemmings, muskrats; also known as Microtinae. Broadly distributed across the Northern Hemisphere; does not enter Africa or SE Asia. Short nasals and stout, broadly bowed zygomatic arches; cheekteeth hypsodont and highly prismatic; numerous other apparent synapomorphies. Tail shorter than head and body. Most are terrestrial, but muskrats are aquatic and red tree mice are arboreal. Includes familiar field mice of North America and Europe. Most species are primarily herbivorous, seldom (but occasionally) including insects in their diets.
Gerbillinae (110 species, 14 genera). Gerbils, jirds, and sand rats. Another large group, restricted to Africa and the Middle East to Central Asia. Small to medium-sized mice and rats, with exceptionally broad zygomatic plates, causing the ventral portion of the infraorbital canal to appear as a deep slit; enlarged lacrimal that forms a ledge over the anterior margin of the orbit; bullae greatly inflated. Also united by numerous other cranial and dental features. Most species inhabit dry areas with sparse vegetation, including deserts. Granivorous and herbivorous, but some also consume large numbers of insects.
Cricetomyinae (6 species, 3 genera). Pouched rats and mice. Africa, south of the Sahara; most species are found in relatively arid habitats. Medium to large size (Cricetomys reaches 400 mm in head-body length), and possessing large internal cheek pouches. Cusp pattern of molars with similarities to both murines and cricetines. Ominivores, feeding largely on vegetable material but also eating some insects. Questionably monophyletic.
Petromyscinae (5 species, 2 genera). Rock mice and climbing swamp mouse. Southern Africa. Small mice, with tail either medium long (rock mice) or very long and semiprehensile (climbing swamp mouse); united by a number of cranial and dental features, but each genus showing strong specializations of its own. The relationship among petromyscines, dendromurines, and cricetomyines has been the subject of much debate.
Dendromurinae (23 species, 8 genera). African climbing mice, gerbil mice, fat mice, and forest mice. Africa south of the Sahara. Small to medium sized, tail moderately long to long. Much variation present in external and internal morphology, and also in habitat and other aspects of natural history; members of the group are linked primarily by dental characteristics.
Lophiomyinae (1 species, 1 genus). Maned or crested rat. East Africa, from Somalia to Tanzania. large rat with short limbs, broad feet, a bushy tail with a distinctive white-tipped tuft, and bold black and white pattern covering its body. Long hairs along the middle of its back can be erected, exposing glandular areas along the sides. Highly distinctive skull, with a roof of bone covering the temporal fossa. This roof is formed by extensions of the parietal, frontal, and jugal bones, and its surface is distinctively rough and granular. Also unusual in its complex, 5-chambered stomach. Arboreal, herbivorous.
Nesomyinae (14 species, 7 genera in 1991, but numbers of both species and genera are increasing rapidly). Malagasy rats and mice. Madagascar. Highly diverse group, including fossorial, scansorial, and arboreal forms; possibly a monophyletic radiation but that is under study. Primary characteristic uniting them is "occurs on Madagascar"!
Murinae (529 species, 122 genera; but additional species are being described every year). Old World rats and mice. The largest family of mammals. Originally found in Europe, Asia, Africa, Australia and some islands; now distributed worldwide due to introductions by humans. Upper molars usually with 3 extra lingual cusps, each forming part of a chevron-shaped loph in many species (third molar may lack these cusps). Size, shape, habits, and most cranial and dental characteristics hugely variable. Most species are terrestrial, but some are aquatic. Some are fossorial, others scansorial, others completely terrestrial. Some scamper, some hop, others swim. Diet varies from strict herbivory to specialization in earthworms or aquatic invertebrates. Some species are largely carnivorous.
Otomyinae (14 species, 2 genera). Vlei rats, karoo rats, and whistling rats. Southern and east central Africa. Upper molars are hypsodont and strongly lophodont or loxodont; individual teeth appear to be made up of transverse laminae; third molar larger than the first two. Unusually strongly developed zygomatic spine and notch, and zygomatic arch strong and bowed. A number of other unusual characteristics of cranium and mandible. Medium sized rats, primarily terrestrial, and mainly herbivorous. One species whistles when disturbed.
Platacanthomyinae (3 species, 2 genera). Malabar spiny mouse and blind tree mouse. India and Southeast Asia. Small mice with a moderately long to long tail with last 2/3 bushy; superficially resemble dormice (Myoxidae). Occlusal surface of molars flat, with distinctive parallel rows of ridges and valleys. Unusual palate and mesopterygoid region; coronoid process reduced. Probably arboreal, but not much is known; possibly herbivorous.
Myospalacinae (7 species, 1 genus). Zokors. Siberia, northern China. Medium to large size, short tail, body form like other fossorial rodents. Very large foreclaws. Defined by numerous characterics of the cranium and zygomatic region, which tend to be robust as is often true of fossorial rodents. Strongly fossorial; use forefeet for digging; feed on roots, bulbs, and other parts of plants.
Spalacinae (8 species, 2 genera). Blind mole rats. Southeastern Europe west to Middle East and south to northeastern Africa along the Mediterranean coast. Medium to large rats with bodies highly modified for fossorial life. Eyes vestigial and external ears rudimentary. Feet small and claws less developed than might be expected; most digging is done with the head and incisors. Distinctive row of stiffened hairs along the sides of the head, effectively increasing its breadth and probably helpful in digging. Skull strongly built and incisors unusually long. Strange murids very much adapted to digging. Herbivorous. Number of species and their relationships have proved very difficult to work out.
Rhizomyinae (15 species, 3 genera). Bamboo rats and African mole rats. Discontinuously distributed in east-central Africa and southeastern Asia. Medium to large size with bodies modified for digging. Body stocky, legs powerful, claws well deveoped, tail short. Skull is robust with short and broad rostrum, prominent crests, and strongly developed zygoma. The ventral portion of the infraorbital is reduced and the zygomatic plate is not well defined compared to most myomorphs. Vary from being strictly fossorial to primarily terrestrial. Use head and feet for digging. Herbivorous.
Phil Myers (author).
Carleton, M.D. and G.G. Musser. 1984. Muroid rodents. Pp. 289-388 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.