Everything about The Ground Squirrel totally explained
The
ground squirrels are the members of the
Sciuridae most closely related to the
genus Marmota. They make up the
tribe Marmotini in the large and mainly
terrestrial squirrel
subfamily Xerinae, and containing six living genera. Well-known members of this largely
Holarctic group are the
marmots (
Marmota), the
susliks (
Spermophilus), and the
prairie dogs (
Cynomys). They are highly variable in size and
habitus, but most are remarkably able to rise up on their hind legs and stand fully erect comfortably for prolonged periods. They also tend to be far more gregarious than other squirrels and many live in colonies with complex social structure. Most Marmotini are rather short-tailed and large squirrels, and the
Alpine Marmot (
Marmota marmota) is the largest living member of the Sciuridae, at 53–73 cm in length and weighing 5–8 kg.
The
chipmunks of the genus
Tamias frequently spend time in trees. Also closer to typical squirrels in other aspects, they're occasionally considered a tribe of their own (Tamiini).
The ground squirrel is especially renowned for its tendency to rise up on its hind legs. It does this whenever it senses nearby danger, or when it must see over tall grasses. The squirrel then curls its paws flat against its chest and sends a screeching call to warn other family members about the presence of predators.
Evolution and systematics
Palaeosciurus from
Europe is the oldest known ground squirrel, and it doesn't seem to be particularly close to any of the two to three living lineages (subtribes) of Marmotini. The oldest fossils are from the
Early Oligocene, more than 30 mya (
million years ago), but the genus probably persisted at least until the mid-
Miocene, some 15 mya.
It isn't clear where the Marmotini originated. The subtribes probably diverged in the early to mid-
Oligocene, as primitive marmots and chipmunks are known from the
Late Oligocene of
North America. Unfortunately, the
fossil record of the "true" ground squirrels is less well known, beginning only in the mid-Miocene when modern susliks and prairie dogs are known to have inhabited their present-day range already.
Whether the Marmotini dispersed between North America and Eurasia via "island-hopping" across the
Bering Straits or the
Greenland region—which both at that time were temperate
habitat—and from which continent they dispersed to which, or if both continents brought forth distinct subtribes which then spread to the other, isn't known and would probably require more fossil material to be resolved. In any case, that the fairly comprehensive fossil record of Europe—at the relevant time separated from Asia by the
Turgai Sea—lacks ancient Marmotini except the indeterminate
Palaeosciurus might be taken to indicate that an East Asian or western North American origin with trans-Beringia dispersal is the slightly more satisfying hypothesis. This is also supported by the enigmatic Chinese genus
Sciurotamias, which may be the most ancient living lineage of this group, or—if the chipmunks are not included here—close to the common ancestor of the Tamiini and the Marmotini
sensu stricto.
In any case, expansion of the Marmotini to
Africa was probably prevented by
competitive exclusion by their close relatives the
Protoxerini and
Xerini—the native terrestrial and palm squirrels of that continent—which must have
evolved at the same time as the Marmotini did.
Subtribes and genera
Basal and
incertae sedis genera
Further Information
Get more info on 'Ground Squirrel'.
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