Cytochrome b divergence times.
The time-calibrate cytb tree (Fig. 3) showed that the genusReithrodontomys began to diverge ca. 6.83 mya (95% HPD = 5.46 –
8.36). The most common recent ancestor of the Aporodon clade was
at ca. 5.70 mya (95% HPD = 4.53 – 6.84), when the R. mexicanusclade I diverged from the rest of the species of this subgenus. Deep
divergences were mostly well supported (pP = 1), except for the split
between the R. mexicanus and R. tenuirostris species
groups ca. 5.35 mya (95% HPD = 4.31 – 6.48). The earliest divergence
in the R. mexicanus species group occurred ca. 4.45 mya (95% HPD
= 3.51 – 5.51) when R. spectabilis and R. gracilisseparated from the rest of the species while the most recent divergences
occurred between R. spectabilis and R. gracilis from
Yucatan (ca. 0.31 mya, 95% HPD = 0.18 – 0.48; see Discussion).