Tribe Gerbillini, Subtribe Gerbillina. Gerbillus has never been adequately revised. Lay (1983) summarized taxonomic difficulties attendant with determining if the genus was monophyletic, discussed significant character complexes that would bear on any scheme to separate species into subgenera (nature of plantar surfaces, size of auditory bulla, relative tail length, dental traits, accessory tympanum, and karyotype), provided an annotated checklist of the species he considered valid, and a list of named forms with literature citations and type localities (including geographic coordinates). Lack of concordance among the suites of characters discouraged Lay from allocating species to higher categories conventionally recognized as either subgenera or genera (see Pavlinov et al., 1990, for example), and he felt compelled to recognize a single genus without subgenera until the group was systematically re-evaluated. Several taxonomic revisions, pertinent faunal stuides (referred to in the accounts of species), reviews, and the important monograph by Pavlinov et al. (1990) have emerged since 1983; these in combination with our study of specimens and Lay's taxonomic overview form the basis for our summary, which can be viewed as a working hypothesis of specific diversity in Gerbillus. In extracting the species usually associated with Dipodillus, we follow Pavlinov et al. (1990) and Pavlinov (2001) in recognizing those species as a separate cluster (Dipodillus) related to species of Gerbillus and depart from Lay’s arrangement. Pavlinov (in litt., 2002), however, stressed that "Dipodillus and Gerbillus could be both paraphyletic and the subgenera in each of them are certainly grades and not clades." Within Gerbillus, our listing of species under subgenera Gerbillus or Hendecapleura generally echos the treatments by Pavlinov et al. (1990) and F. Petter (1975b).
An excellent account of species occurring east of the Euphrates River was provided by Lay and Nadler (1975). The distribution of six species endemic to North Africa was mapped and discussed by Cheylan (1990) in the context of assessing endemism and speciation of Mediterranean mammals. Tranier and Julien-Laferriere (1990) commented on suggested identities of several species from North Africa. Qumsiyeh and Schlitter (1991) summarized chromosomal data; subsequent documentation of chromosomal complements and their significance to reconstructing phylogenetic relationships among species of Gerbillus will be found in some of the references cited in various accounts of species. A contribution to allozymic variation within and between species was offered by Nevo (1982). Evolutionary tendencies within Gerbillus, as reflected in dental traits, were discussed by F. Petter (1973c), and significance of variation in incisor microstructure within the genus was reported by Flynn (1982c). Species of Gerbillus were included by Bonhomme et al. (1985) and Pascale et al. (1990) in their assessment of phylogenetic relationships among muroid rodents with electrophoretic and DNA-sequence data. Volobouev et al. (1995b:258) characterized and isolated two repeated DNA sequences in G. nigeriae, G. aureus, and G. nanus and pointed out that ". . . in Gerbillus species, chromosomal evolution involves rearrangements of both repeated sequences and other chromosomal structures." Osborn and Helmy (1980) provided clear morphological comparisons among species of Gerbillus occurring in Egypt. Granjon et al. (2002a) pointed out that seven species of Gerbillus (G. cf nancillus, G. henleyi, G. nanus, G. gerbillus, G. nigeriae, G. tarabuli, and G. cf pyramidum) and two of Dipodillus (D. campestris and D. rupicola) can be unambiguously identified in the West African Subsaharan sahelian region between southeastern Mauritania, northern Mali, and western Niger.
Evolutionary history as documented by fossils dates to early Pleistocene of China (Lucas, 2001), late Pleistocene of C India (Patnaik, 1995) and middle Pliocene to early Pleistocene of Africa (Denys, 1989b, 1999; Tong, 1989; Wesselman, 1984; Wessels, 1998). The earliest member of Gerbillini and relative of Gerbillus is Debruijnimys from early Pliocene of Spain and late Pliocene of North Africa (Castillo and Agustí, 1996; Wessels, 1998).