"We retain Brandt’s (1855) names for three of the five suborders (Sciuromorpha, Myomorpha, and Hystricomorpha), whereas some foremost rodent authorities have pointedly advised against continued employment of these Brantian epithets, especially at the subordinal rank (e.g., Landry, 1999:283; Wood, 1985). They have argued that the descriptive meaning of the terms does not strictly concord with the morphologies of included members, and that this contradiction will only continue to engender confusion. That the logical connotation of a taxon’s name should uniformly correspond to its taxonomic intention strikes us as puzzling. Not all members of the Superorder Afrotheria live in Africa, nor are all species of the Order Carnivora carnivorous. The species- to family-group ranks are rife with valid names whose logical meaning, as intended by the original descriptor, is partially inconsistent or actually misleading in terms of the currently accepted contents of the taxon, whether in strict morphological accuracy, indication of distribution, or implication of phylogenetic alliance. In reviewing 150 years of rodent classifications, we are impressed that few of our predecessors applied the features of infraorbital configuration and jaw shape in an overridingly typological touchstone of all rodent classification. Most made the distinction between, e.g., Myomorpha in its taxic sense and myomorphy as a morphological condition and routinely consulted additional traits. Thus, the hystricomorphous Dipodidae have been nearly always included within Myomorpha (in retrospect, correctly it would seem), and the sciuromorphous Geomyoidea have been considered by many to also fit within Myomorpha (in retrospect, perhaps incorrectly). And while Brandt’s taxonomic names qua morphological descriptors may not perfectly correspond to all members, they nonetheless do conform very well. The core family members of Sciuromorpha, Myomorpha, and Hystricomorpha have remained largely the same, and most, not all, do exhibit those fundamental zygomasseteric structures. More importantly, these core assemblages have survived recent scrutiny using ever more explicit principles for systematic classification and sophisticated methods for inferring phylogenetic relationship and assessing descent from a common ancestor."

Carleton & Musser, 2005, p. 751

Rodentia Sub-orders (Mammal Species of the World, 3rd ed., 2005)

Sub-order Masseteric condition Mandibular condition

Number of

families / species

Sciuromorpha

protogomorphous (Aplodontidae), sciuromorphous (Sciuridae),

“pseudo-myomorphous” (Gliridae)

sciurognathous 3 / 307

Castorimorpha sciuromorphous sciurognathous 3 / 102

Myomorphamyomorphous

(except Dipodidae, hystricomorphous)

sciurognathous 7 / 1569

Anomaluromorpha hystricomorphous sciurognathous 2 / 9

Hystricomorpha hystricomorphous

sciurognathous (only

Ctenodactylidae)hystricognathous

(rest)

18 / 290

Aplodontidae

• Monotypic (1 species)

• Restricted to NW US• “Primitive” rodent• Protrogomorphous-

Sciurognathous

Sciuridae

• 50 genera, 273 species

• Worldwide except Australia and southern South America

• Wide range of ecolomorphs

Ground Tree Flying

TamiasSpermophilusMarmota

SciurusTamiasciurus

Glaucomys

Squirrel body plans(N. American examples)

Tamias minimusLeast Chipmunk

Castoridae

• 1 genus, 2 species• Holarctic• Semi-aquatic• Specialize on

cambium

Muridae• >250 genera, >1300

species• Mice, rats, voles,

hamsters, gerbils

Muridae: Subfamilies

Murinae Old World mice & ratsCricetidae! volesSigmodontinae New World mice & ratsGerbillinae gerbilsSpalacinae blind mole-rats

+ 12 others!!!

Alaska

Anomaluridae

• Scaly-tailed squirrels

• 3 genera, 7 species• Western-central

Africa

Suborder: HystricomorphaAfrica

AKA “Phiomorpha”

Bathyergidae mole ratsHystricidae Old World porcupinesPetromuridae rock rats, dassie

ratsThryonomyidae cane rats

Suborder: HystricomorphaSouth America

AKA “Caviomorpha”

ErethizontidaeChinchillidaeDinomyidaeCaviidaeHydrochaeridaeDasyproctidae

AgoutidaeCtenomyidaeOctodontidaeAbrocomidaeEchimyidaeCapromyidaeMyocastoridae

Erethizontidae• New World porcupines• 4 genera, 12 species• Lowland tropics to

montane forests, deserts, coniferous forests

• Herbivores