Paleontology 5The xerine ground squirrels presently occur mostly in
Africa (fi ve species) but are also found in southwest Asia
(Spermophilopsis). Fossil forms include Heteroxerus, known
from the early Oligocene to the late Miocene (26–5 MYA) in
Europe. The 8–10 recognized species are more common in
southwestern Europe than in central Europe. Another ge-
nus, Aragoxerus, has been described from the early Miocene
(23–16 MYA) in Spain. A third genus, Atlantoxerus, with more
robust teeth than Heteroxerus, includes fi ve species, although
the number may be reduced with further study. Atlantoxerus
is rare, but it is found from the early Miocene to the early
Pliocene (23–3 MYA) in Eurasia and from the middle Mio-
cene (16 MYA) onward in Africa, with one species still living
in northwest Africa.
Other African squirrels are also rare as fossils. Vulcanisci-
urus, of unknown affi nities within the Sciuridae, is known
from the early to late Miocene (23–5 MYA) in Africa. The
giant palm squirrel, Kubwaxerus, is known from the late
Miocene in Kenya, and the African sun squirrel, Heliosci-
urus, is known from the late Pleistocene (< 1 MYA) to the
Recent in Africa, with six living species.
The marmotine ground squirrels (including chipmunks,
marmots, and North American ground squirrels) are better
represented as fossils, particularly in North America. In Eu-
rope the reputed ground squirrel, Palaeosciurus, is attributed
to this group. It is a common fossil, comprising four species
found from the early Oligocene to the early Miocene (33–
MYA)—more frequent in central Europe than in southwest-
ern Europe—and in the early Miocene (23–16 MYA) in Asia.
Chipmunks occur early in the fossil record in North America.
Nototamias is reported in the late Oligocene to the middle
Miocene (24–12 MYA), and Tamia s from the early Miocene (
MYA) to the Recent. In Europe, three species of Tamia s are
recognized from the early Miocene to the early Pliocene (18–
MYA), mostly restricted to southeastern Mediterranean Eu-
rope, and the genus is known from the middle Miocene (
MYA) to the Recent in Asia. Sinotamias is known from the
middle to the late Miocene (16–5 MYA) in Asia, and the Chi-
nese rock squirrel, Sciurotamias, is known from the late Mio-
cene (12 MYA) and intermittently to the Recent in Asia.
Protospermophilus occurs in the late Oligocene to the
late Miocene (24–5 MYA) in North America. It retained the
tooth morphology of tree squirrels, although it is found in
situations that suggest it was a terrestrial squirrel. One
suppo sition is that it was still a seed feeder, like the tree
squirrels, and thus could not compete with the ground
squirrels, which were better adapted to grasslands. Mio-
spermophilus, which occurs from the late Oligocene to the
middle Miocene (24–12 MYA) in North America, has been
suggested to be ancestral to Spermophilus, which has be-
come the dominant ground squirrel of North America and
northern Eurasia and is now divided into eight distinct
genera (Noto citellus, Otospermophilus, Callospermophilus, Sper-
mophilus, Ictidomys, Poliocitellus, Xerospermophilus, and Uroc-
itellus). Another possibility is that modern ground squirrels
are derived from Spermophilinus, which is found from the
early Miocene to the early Pliocene (18–3 MYA) in central
and southwestern Europe, with four species being recog-
nized; possibly in the late Miocene in western Asia; and
more certainly in the early Pliocene (5–3 MYA) in eastern
Asia. Spermophilus itself occurs from the middle Miocene (
MYA) to the Recent in North America; in the late Miocene
(6 MYA) in Europe, where it is still extant; and in the early
Pleistocene (2 MYA), the middle Pleistocene, and the Recent
in Asia. In North America, antelope ground squirrels, Am-
mospermophilus, are known from the late Miocene (11 MYA)
to the Recent; and prairie dogs, Cynomys, are known from
the late Pliocene (2 MYA) to the Recent, with a dubious re-
cord in the middle Miocene.
Three genera—Paenemarmota, Palaearctomys, and Arcto-Douglassciurus jeffersoni skeleton at Smithsonian Institution’s
National Museum of Natural History. Photo courtesy James
Di Loreto, Smithsonian Institution.