Rodent Societies: An Ecological & Evolutionary Perspective

mainland source and the number of invasions are still de-

bated (Simpson 1952; Dubois et al. 1996; Jansa et al. 1999).

South American rodents can be subdivided into early and

late colonizers. Caviomorph rodents (13 families) represent

the oldest rodent radiation in South America, with the ear-

liest fossils dating to the Late Eocene or Early Oligocene

(Wyss et al. 1993). The murid subfamily Sigmodontinae

represents the most diverse rodent group in South America.

Timing of the sigmodontine invasion is a source of contro-

versy, with some advocating a recent origin subsequent to

the formation of the Panamanian land bridge 2 to 3 million

years ago (mya; Simpson 1950; Smith and Patton 1999)

and others suggesting an ancient invasion via waif dispersal

in the Early Miocene (Hershkovitz 1966; Reig 1986). There

are 59 species of rodents in Australia, making up 25% of

the terrestrial mammalian fauna. Fifty-seven percent of the

rodent species are endemic to Australia and are members of

the family Muridae. This island continent experienced two

invasions, one occurring approximately 10 to 15 mya (sub-

family Hydromyinae; Watts and Aslin 1981) and the other

2 mya (subfamily Murinae; Watts and Kemper 1989). Both

invasions were the result of waif dispersal from the Orien-

tal biogeographic region via Wallacea. The Nearctic, Pale-

arctic, and Oriental biogeographic regions show less en-

demism in terms of both rodent subfamilies and families.

Like most continents, the rodent faunal elements in these

regions are dominated by members of the families Sciuridae

and Muridae. Two families, Geomyidae and Heteromyidae,

are restricted to the New World, with their center of origin

Rodent Evolution, Phylogenetics, and Biogeography 9

Table 2.1 Species and genera of recent rodents

Family Genus Species

Muridae 281 1,326
Sciuridae 50 273
Echimyidae 20 78
Dipodidae 15 51
Myoxidae 8 26
Capromyidae 8 20
Heteromyidae 6 59
Octodontidae 6 9
Geomyidae 5 35
Caviidae 5 14
Bathyergidae 5 12
Erethizontidae 4 12
Ctenodactylidae 4 5
Heptaxodontidaea 45
Hystricidae 3 11
Anomaluridae 3 7
Chinchillidae 3 6
Dasyproctidae 2 13
Ctenomyidae 1 38
Abrocomidae 1 3
Castoridae 1 2
Thryonomyidae 1 2
Agoutidae 1 2
Aplodontidae 1 1
Pedetidae 1 1
Petromuridae 1 1
Dinomyidae 1 1
Hydrochaeridae 1 1
Myocastoridae 1 1

aRecently extinct.

Figure 2.1 Number of genera (open

bar) and species (black bar) per family

of rodent. Information was compiled

from Wilson and Reeder (1993). Aster-

isk (*) denotes monotypic families.