T
here arefour main components to this chapter.
First, we provide a detailed survey of rodent diver-
sity at the familial level, and in this survey we sum-
marize information on various attributes (e.g., morphology,
ecology, behavior) that both contribute to this diversity and
complicate the diagnosis of relationships between families
and genera. Second, we provide an introduction to the pa-
leontological and biogeographical history of rodents, and
elaborate on several hypotheses regarding rodent ancestry
and distribution. Third, we provide a detailed account of the
phylogenetic relationships of rodent families, and in some
cases genera. This account discusses phylogenetic hypothe-
ses based on more traditional studies of morphology and
paleontology, as well as recent studies employing molecular
phylogenetics. Finally, we provide some examples of how a
well-supported phylogeny for particular groups of rodents
can be used to test hypotheses related to the evolution of
complex social behavior and the evolution of life history
traits.
Rodent Diversity
In terms of abundance, diversity, and distribution, the order
Rodentia represents the most successful group in the class
Mammalia. There are 1,135 genera and 4,629 recognized
species of mammals, of which 443 genera (39%) and 2,015
species (43.5%) are rodents (Wilson and Reeder 1993). Of
the 29 extant families of rodents, approximately 89% of
rodent species diversity can be partitioned into five families
(table 2.1 and fig. 2.1): (1) Muridae (rats and mice), (2) Sci-
uridae (squirrels), (3) Echimyidae (spiny rats), (4) Hetero-
myidae (pocket mice and kangaroo rats) and (5) Dipodi-
dae (jerboas and jumping mice). The most speciose and
widely distributed family is the Muridae, representing 66%
of rodent taxa. Murid rodents are a significant component
of mammalian diversity on most continents, and ancestral
stocks of murids have experienced adaptive radiations on
several continents subsequent to invasion via either land
bridges or waif dispersal.Biogeographic distribution
Except for Antarctica, representatives of the order occur on
all continents and many oceanic islands. Most major bio-
geographic regions are characterized by unique rodent
fauna as well as rodent families shared among regions. Five
rodent families are endemic to sub-Saharan Africa, includ-
ing Bathyergidae, Thryonomyidae, Petromuridae, Anomal-
uridae, and Pedetidae (table 2.2). These families represent
older faunal elements dating to the Early Oligocene to
Lower Miocene (Lavocat 1978). More recent immigrants to
Africa include the Sciuridae (Lower Miocene), Muridae (Up-
per Miocene to Plio-Pleistocene), Myoxidae (Upper Mio-
cene to Pliocene), and Hystricidae (Plio-Pleistocene). North-
ern Africa contains two additional families: Dipodidae
(Oligocene) and currently endemic Ctenodactylidae (Mio-
cene). Although Madagascar has been isolated from Africa
since the Late Cretaceous, this island contains the endemic
murid subfamily Nesomyinae, represented by nine genera
and 21 species (Jansa et al. 1999). Apparently, nesomyines
colonized Madagascar via over-water dispersal, but the