nizers, and most biogeographic regions have rodent assem-
blages formed by continental exchanges followed by bursts
of speciation. This rapid diversification and the age of many
rodent lineages make the establishment of well-resolved
phylogenies challenging, especially in diverse groups like the
Muridae. Clearly, paleontological information and phylo-
genetic approaches using morphological comparisons are
essential for the establishment of a natural classification.
Nevertheless, to quote Hartenberger (1985; p. 25), “Pale-
ontology has many good questions to ask, but it is un-
able to provide answers by itself.” Obviously, questions re-
lated to the rodent radiations are probably some of the most
complex in vertebrate phylogenetics, and an accurate re-
construction of rodent evolutionary history requires the use
of multiple characters. Molecular data provide a wealth of
markers that can be used to construct detailed phyloge-
nies, and this is mandatory for portions of a phylogeny with
short internodes. Whole genome sequences of model mam-
malian species, some of which are rodents, offer a ready re-
source of molecular markers for future phylogenetic studies
on rodents. For instance, according to O’Brien et al. (1999),
there are approximately 3.2 billion nucleotide pairs in the
mammalian genome, and these data provide not only nu-
cleotide sequence information but higher order changes as-
sociated with gene rearrangements, duplications, indels,
amplification of sequence blocks, and so on. Many of these
markers may very well define the monophyly of groups that
would otherwise be intractable using only nucleotide se-
quences (e.g., Pascale et al. 1990).
Although our primary research is in the area of molecu-
lar phylogenetics, we are sensitive to the needs of behavioral
ecologists, who desire an accurate phylogenetic framework
for testing questions related to the evolutionary process.
Probably one of the best statements regarding this need was
made by Blumstein and Armitage (1998a; p. 10) who said,
“No published phylogenetic hypothesis includes all species
of interest. We eagerly anticipate the publication of in-
clusive and well-supported phylogenies.” Hopefully, our
summary of rodent phylogenetics and evolution provides a
starting point for future investigations pertaining to the evo-
lution of complex rodent societies.Rodent Evolution, Phylogenetics, and Biogeography 23