Eolian Environments - Trace Fossils as Indicators of Sedimentary Environments - page 416

dune foresets on which the dinosaurs were walking. Many of the tracks are very
well preserved and show distinct anatomical details of the foot, such as pads on
the individual digits and claw impressions, and several examples contain the
original sediment infill remaining inside the tracks. In some other examples,
the sediment infill was eroded away, partly exposing the base of the track along
with a set of concentric circles extending up to 20 cm outward from the track,
reflecting the outward deformation of the sand when the heavy animal stepped
in it. In still other examples, the track was eroded away completely, leaving just
the set of concentric circles in the sand, and the authors point out that such a
preservation mode might be easily mistaken for non-biogenic deformation of
the sediment rather than the dinosaur trace fossils that it actually represents.
3.3 Uniformitarian Approach to Eeolian Ichnofacies
Because of the general lack of body fossils in eolianites, a uniformitarian approach
of seeking modern analogs to link a trace fossil with the tracemaker is obligatory.
Virtually all the tracemaking animals inmodern dune fields are arthropods (mostly
insects and arachnids) and vertebrates (mostly reptiles and mammals), so attri-
bution of traces to the tracemakers is a fairly straightforward accomplishment in
geologically young eolianites, but a uniformitarian interpretation becomes more
and more tenuous as older and older eolianites are examined.
Although there have been many studies of the ecology of organisms that
inhabit sandy deserts today, there have been relatively few studies that focus spe-
cifically on the preservable traces that theymake inmodern sand dunes ( Eiseman
andCharney, 2010 ). Ahlbrandt et al. (1978) described the common traces created
by present-day dune dwellers, mostly from examples in the Great Sand Dunes of
southern Colorado, and their observations have beenwidely cited in the literature
as modern analogs for many trace fossils in ancient eolianites.
Ichnology in most Late Cenozoic eolianites can be linked directly with ich-
nology inmodern dunes. Curran (2007) easily found the link betweenmodern and
Pleistocene rhizomorphs (at the genus and species level) in the Bahamas, and
Phelps (2002) confidently linked modern and Pleistocene arthropod burrows with
their burrowers (at the genus and species level in many cases) in Mexico. Forn ´ s
et al. (2002) correctly identified the genus and species of extinct goats that pro-
duced fossilized footprints in Pleistocene eolianites on the island of Mallorca, and
Mil ` n et al. (2007) reasonably assigned fossilized footprints in Pleistocene eolia-
nites on the island of Rhodes to the work of elephants and camels. Roberts et al.
(2008) were easily able to attribute abundant fossil trackways in Pleistocene
eolianites in South Africa to extant African elephants, and Roberts (2008) found
footprints that obviously were made by prehistoric humans in Pleistocene eolian
deposits at two sites in South Africa that have been dated as 120,000 years old.
Trace fossils in Mesozoic eolianites sometimes can benefit from analogs with
modern arthropod tracks and burrows ( Albers, 1975; Ekdale and Picard, 1985;
Ekdale et al., 2007 ). However, this is not the casewithmany vertebrate trace fossils,