HEERMANNI GROUP HEERMANNI GROUP
_Dipodomys heermanni_ _Dipodomys heermanni_
_Dipodomys morroensis_ _Dipodomys agilis_
_Dipodomys mohavensis_ _Dipodomys ingens_
_Dipodomys leucogenys_ _Dipodomys venustus_
_Dipodomys panamintinus_ _Dipodomys elephantinus_
_Dipodomys stephensi_
_Dipodomys ingens_
SPECTABILIS GROUP SPECTABILIS GROUP
_Dipodomys spectabilis_ _Dipodomys spectabilis_
_Dipodomys nelsoni_ _Dipodomys nelsoni_
PHILLIPSII GROUP NOW IN MERRIAMI GROUP BELOW
_Dipodomys phillipsii_
_Dipodomys perotensis_
_Dipodomys ornatus_
_Dipodomys elator_
MERRIAMI GROUP MERRIAMI GROUP
_Dipodomys merriami_ _Dipodomys merriami_
_Dipodomys nitratoides_ _Dipodomys nitratoides_
_Dipodomys platycephalus_ _Dipodomys platycephalus_
_Dipodomys margaritae_ _Dipodomys margaritae_
_Dipodomys insularis_ _Dipodomys insularis_
_Dipodomys mitchelli_ _Dipodomys mitchelli_
_Dipodomys phillipsii_
_Dipodomys ornatus_
_Dipodomys elator_
ORDII GROUP ORDII GROUP
_Dipodomys ordii_ _Dipodomys ordii_
_Dipodomys microps_
COMPACTUS GROUP NOW IN ORDII GROUP ABOVE
_Dipodomys compactus_
_Dipodomys sennetti_
AGILIS GROUP NOW IN HEERMANNI GROUP ABOVE
_Dipodomys agilis_
_Dipodomys venustus_
_Dipodomys elephantinus_
MICROPS GROUP NOW IN ORDII GROUP ABOVE
_Dipodomys microps_
_Dipodomys levipes_
DESERTI GROUP DESERTI GROUP
_Dipodomys deserti_ _Dipodomys deserti_
WERE IN HEERMANI GROUP ABOVE PANAMINTINUS GROUP
_Dipodomys panamintinus_
_Dipodomys stephensi_
Names of the subspecies are omitted from the groups named above and only
the names of full species, as understood by Grinnell and as understood
now, have been used. It will be noted that the phylogenetic order
follows that of Grinnell rather than the one proposed herein.
The fossil record of the kangaroo rats is so scanty that one can but
speculate on the evolutionary sequence. Wood (1935) presented a
diagnosis of the early phyletic history up to and through _Cupidinimus_;
this is probably as correct as can be made. I cannot, however, share his
view that the recent species of _Dipodomys_ have originated from a
descendant of _Cupidinimus nebraskensis_; instead, I think that the
Recent species originated from some unknown ancestor in the southwest.
[Illustration: FIG. 21. Diagrammatic representation of the relationships
and history of the Recent species _Dipodomys_.]
In view of the foregoing evidence it seems best to estimate the
relationships and history of the various species and groups of species
only as far back as the early Pleistocene (see Figure 21). Inasmuch as
faunas of fossil mammals from the mid-Pleistocene contain few, if any,
Recent species (see Hibbard, 1937:193), the living species of
_Dipodomys_ have probably had a geologic history no longer than the
period of time which has elapsed since the middle Pleistocene, or at the
earliest the early Pleistocene. Of the Recent species, only _Dipodomys
agilis_ is known as a fossil; it was found in the late Pleistocene tar
pits of California. Under the heading "_Dipodomys near ingens_,"
however, Schultz (1938:206) recorded remains of kangaroo rats from the
tar seeps of McKittrick in the San Joaquin Valley of California.