Relationships among subfamilies of Muroidea
The family Muridae has a worldwide distribution and rep-
resents the most diverse group of rodents, containing ap-
proximately 1,326 species subdivided into 17 subfamilies
(Musser and Carleton 1993). The two most diverse sub-
families are the Old World Murinae (500 species) and New
World Sigmodontinae (300 species). The myomorphous zy-
gomasseteric system, loss of the upper fourth premolar, and
characteristics of the first molar support monophyly of Mu-
ridae (Flynn et al. 1985). As indicated by Carleton and Mus-
ser (1984), lineages within the family show considerable
parallel changes in morphology, and although monophyly
of subfamilies is confirmed (Michaux and Catzeflis 2000),
relationships among most of the subfamilies and many gen-
era and species are poorly resolved. One primary explana-
tion for this lack of resolution within and between subfam-
ilies relates to the numerous adaptive radiations of murids
on most continents, and as indicated by Michaux and Catze-
flis (2000), these radiations are reflected in the “bush-like”
phylogenies often obtained with molecular data.
Two recent molecular phylogenetic studies based on nu-
clear gene sequences provide the most thorough investi-
gations of subfamilial relationships (Michaux and Catze-
flis 2000; Jansa and Weksler 2004). Both of these studies
suggest rather rapid radiations, resulting in a bush-like phy-
logeny for most subfamilies (fig. 2.6). Three subfamilies
containing subterranean species, Rhizomyinae, Spalacinae,
and Myospalacinae, represent the most basal clade, and
two recent studies suggest that this group be placed in a sep-
arate family, Spalacidae (Michaux et al. 2001; Norris et al.
2004). The larger clade consists of a polytomy containing
four lineages: (1) Calomyscinae; (2) a clade consisting of
Malagasy Nesomyinae (not monophyletic) and African Pet-
romyscinae, Mystromyinae, Cricetomyinae, and Dendro-
murinae; (3) a monophyletic Murinae sister to the subfam-
ilies Acomyinae and Gerbillinae; and (4) a clade containing
New World subfamilies Sigmodontinae, Tylomyinae, and
Neotomyinae, as well as the subfamilies Arvicolinae (Old
and New World) and Cricetinae (Old World).
The family Muridae is represented in the New World
by members of the subfamily Sigmodontinae, which can
be subdivided into North American and South American
groups (Hooper and Musser 1964; Carleton and Musser
1984; Musser and Carleton 1993). North American line-
ages are represented by 18 genera and 124 species, sub-
divided into two or more tribes. South American sigmo-
dontines presumably were derived from North American
stock, and today represent one of the most speciose groups
of rodents in South America, consisting of 61 genera and
299 species, subdivided into seven tribes (Musser and Car-
leton 1993; Weksler 2003). Comparisons of the phallus
by Hooper and Musser (1964) prompted these authors to
separate South American and North American sigmodon-
tines into reciprocally monophyletic groups, whereas Weks-
ler (2003) restricted the subfamily Sigmodontinae to only
South American forms. Two recent molecular studies (En-
gel et al. 1998; Weksler 2003) found support for the mono-
phyly of South American Sigmodontinae, with the genus
Sigmodon (a group occurring in North America, Cen-
tral America, and northern South America) occupying a
basal position in the phylogeny. These same studies found
little support for a sister-group relationship between North
American neotomine /peromyscine rodents and the South
American tribes of sigmodontines. However, based on the
analysis of cytochrome bsequences, Bradley et al. (2004)
did find strong support for the recognition of a monophy-
letic North American group, represented by four tribes, Pe-
romyscini, Neotomini, Baiomyini, and Tylomyini. Rela-
tionships among these tribes are more equivocal.18 Chapter Two
Figure 2.6 Phylogeny depicting relationships among subfamilies of muroid
rodents (Jansa and Weksler 2004).