Eolian Environments - Trace Fossils as Indicators of Sedimentary Environments - page 420

Sand swimming is not a commonly observed habit of mammals in desert
dunes. However, one species that does employ such behavior is the Grant's golden
mole ( Eremitalpa granti ), an insectivore which inhabits the driest parts of the
NamibDesertinsouthernAfrica( Fielden et al., 1990; Perrin and Fielden,
1999; Seymour et al., 1998 ). Not to be confused with a true mole (Family
Talpidae), the golden mole (Family Chrysochloridae) is thought to be more
closely related to tenrecs. The golden mole is essentially blind, and although it
forages for termites on the sand surface at night, it is known to swim quite effec-
tively beneath the surface of the dry sand during the day in search of termites to
eat. Unlike sandfish lizards and sand boas, the Grant's goldenmole swims through
the substrate by using its clawed feet, and undulatory body motions apparently do
not play a big role in propelling it forward. Sand collapses behind the animal as it
moves, leaving no open or walled burrow in its wake, and so primary stratification
of sand is disrupted in a major way. However, little or nothing is known of the
ichnofabric details created by the animal's movements inside the sand dunes.
The ichnofabric implications of sand-swimming behavior in dry dunes in the
geological record are intriguing, but they have not been investigated thoroughly.
Although vertebrate burrows have been described in some Mesozoic eolianites
( Loope, 2006a, 2008 ), they exhibit features such as distinct walls and/or menis-
cate backfill that are inconsistent with those resulting from sand swimming. Ver-
tebrate burrows are essentially unknown in pre-Mesozoic eolianites.
Because the effect of sand swimmers on the unconsolidated substrate is
manifested primarily in the form of disturbed laminae and irregular collapse
structures, it is quite possible that a sand-swimming ichnofabric would be mis-
identified as a non-biogenic, soft-sediment deformation fabric. If sand-
swimming ichnofabrics can be recognized with confidence in ancient eolianites,
there will be important paleobiologic, sedimentologic, and paleoclimatic impli-
cations. Sand swimmers today bury themselves to escape the intense daytime
heat (often up to 50 C) on dry dune surfaces where there is no benefit of shade
from leafy plants, but these animals are not inactive inside the dunes. In fact,
they are known to move rapidly and efficiently through the sand, presumably
in search of infaunal insects for a meal.
Evidence of sand swimming probably occurs unrecognized in many eolia-
nite units, especially geologically young ones, and it simply remains for geolo-
gists to try to understand what they see in the rocks. Recognition and description
of sand-swimming ichnofabrics in the geological record have the potential of
revealing new knowledge and insights regarding life in ancient deserts.
5. CONCLUSIONS
One of the great challenges to ichnologists is that we often are forced to study
the product in the absence of the producer. This is especially true with eolia-
nites. Trace fossils occur but are scarce in dune deposits. Body fossils are as