Sciuromorpha ( 'squirrel-like') is a

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 ...

suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

that includes several rodent

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

. It includes all members of the

Sciuridae 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 ...

(the squirrel family) as well as the

mountain beaver The mountain beaver (''Aplodontia rufa'')Other names include boomer, mountain boomer, ground bear, giant mole, gehalis, sewellel, suwellel, showhurll, showtl, and showte, as well as a number of other Native American terms. "Mountain beaver" is a ...

species. Traditionally, the term has been defined on the basis of the shape of the

infraorbital canal The infraorbital canal is a canal found at the base of the orbit that opens on to the maxilla. It is continuous with the infraorbital groove and opens onto the maxilla at the infraorbital foramen. The infraorbital nerve and infraorbital artery t ...

. A

sciuromorphous The zygomasseteric system (or zygomasseteric structure) refers to the anatomical arrangement of the masseter muscle and the zygomatic arch (cheek bone) in the skulls of rodents. This system plays a crucial role in the diverse chewing mechanics ...

zygomasseteric system The zygomasseteric system (or zygomasseteric structure) refers to the anatomical arrangement of the masseter muscle and the zygomatic arch (cheek bone) in the skulls of Rodent, rodents. This system plays a crucial role in the diverse chewing mechan ...

is characterized by attachment of the lateral

masseter muscle In anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it is the ...

along the side of the

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

. Unlike

hystricomorphous The zygomasseteric system (or zygomasseteric structure) refers to the anatomical arrangement of the masseter muscle and the zygomatic arch (cheek bone) in the skulls of rodents. This system plays a crucial role in the diverse chewing mechanics ...

and

myomorphous The zygomasseteric system (or zygomasseteric structure) refers to the anatomical arrangement of the masseter muscle and the zygomatic arch (cheek bone) in the skulls of rodents. This system plays a crucial role in the diverse chewing mechanics ...

rodents, the medial masseter muscle does not pass through the infraorbital canal. Among extant rodents, only the families Sciuridae,

Castoridae Castoridae is a family of rodents that contains the two living species of beavers and their fossil relatives. A formerly diverse group, only a single genus is extant today, ''beaver, Castor.'' Two other genera of "giant beavers", ''Castoroides'' ...

Heteromyidae Heteromyidae is a family of rodents consisting of kangaroo rats, kangaroo mice, pocket mice and spiny pocket mice. Most heteromyids live in complex burrows within the deserts and grasslands of western North America, though species within the ...

, and Geomyidae are truly sciuromorphous. Some authorities would exclude the Geomyidae and Heteromyidae from that list due to the attachment of the medial masseter directly behind the

zygomatic arch In anatomy, the zygomatic arch (colloquially known as the cheek bone), is a part of the skull formed by the zygomatic process of temporal bone, zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the ...

. Carleton and Musser (2005) redefined the rodent suborders on morphological and

molecular A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, ...

grounds. They defined the Sciuromorpha as including three families, Sciuridae,

Aplodontiidae The family Aplodontiidae also known as Aplodontidae, Haplodontiidae or Haploodontini is traditionally classified as the sole extant family of the suborder Protrogomorpha. It may be the sister family of the Sciuridae. There are fossils from the O ...

, and Gliridae. Of these, only the Sciuridae are truly sciuromorphous. The Aplodontiidae are protrogomorphous and the Gliridae are myomorphous. The connection between Aplodontiidae and Sciuridae has been proposed numerous times in the past. The two families have been united into a common

infraorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between Family_(biology), family and Class_(biology), class. In biological classification, the order is a taxonomic rank used in the classific ...

(Sciurida) or superfamily (Sciuroidea). It has long been suggested that

dormice A dormouse is a rodent of the family (biology), family Gliridae (this family is also variously called Myoxidae or Muscardinidae by different taxonomists). Dormice are nocturnal animals found in Africa, Asia, and Europe. They are named for their ...

(Gliridae) are not particularly related to the

Myomorpha The suborder Myomorpha contains 1,524 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 t ...

, and their zygomasseteric structure has been termed "pseudomyomorphy". The connection between squirrels and dormice has been almost exclusively suggested through genetic studies, and to a lesser degree via the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

rodent Reithroparamys.

Current families

The suborder Sciuromorpha contains 307 living species in 61 genera and three families. At least three extinct families are also recognised. * † Allomyidae *

– mountain beaver * †

Mylagaulidae The Mylagaulidae or mylagaulids are an extinct clade of sciuromorph rodents nested within the family Aplodontiidae. They are known from the Neogene of North America and China. The oldest member is the Late Oligocene '' Trilaccogaulus montanensi ...

– squirrels, chipmunks, marmots, flying squirrels, etc. * † Reithroparamyidae * Gliridae – dormice

Historical families

– beavers * Geomyidae – pocket gophers *

– pocket mice, kangaroo rats, and kangaroo mice *

Pedetidae The Pedetidae are a family (biology), family of rodents. The two living species, the springhares, are distributed throughout much of Southern Africa and also around Kenya, Tanzania, and Uganda. Fossils have been found as far north as Turkey.McKen ...

– springhares * Anomaluridae – anomalures

References

Other Sources

* Carleton, M. D. and G. G. Musser (2005). "Order Rodentia". pp. 745–752 in ''Mammal Species of the World A Taxonomic and Geographic Reference'' (D. E. Wilson and D. M. Reeder eds.). Baltimore: Johns Hopkins University Press.

External links

* {{Taxonbar, from=Q724477 Rodent taxonomy Mammal suborders Extant Eocene first appearances Taxa named by Johann Friedrich von Brandt