Rodent Societies: An Ecological & Evolutionary Perspective

the basal lineages in the Bathyergidae, Heterocephalus(40 –
48 myr), and Heliophobius(32 – 40 myr), may have been
constrained northward by the Ethiopian highlands but was
relatively unimpeded south and west (fig. 36.2, nodes 1 and
2; fig. 36.3a to 36.3c; Faulkes et al. 2004). Estimates of the
divergence of Georychus/Bathyergusfrom their common

ancestor with Cryptomys(20 –26 myr; fig. 36.2, node 3;

fig. 36.3c) coincide with the beginning of volcanism in the

Kenya rift, and possibly favored the expansion into south-

ern Africa rather than to the north and west. Aridification

of the Saharo-Arabian belt was also beginning at this time

and would have further restricted the Bathyergidae to sub-

African Mole-Rats: Social and Ecological Diversity 429

Figure 36-2 Phylogram based on maximum parsimony analysis of 18 bathyergid mtDNA haplotypes (combined 12S rRNA and cytochrome b

gene sequences) and outgroup species Thryonomys swinderianus(cane rat). Numbers above each branch refer to the percent bootstrap values

following 100 replications, after weighting sites with the rescaled consistency index. Divergence times of selected internal nodes (numbered

1–5 for reference in text) are in million years before present (myr; data adapted from Faulkes et al. 1997a, 2004).