Eolian Environments - Trace Fossils as Indicators of Sedimentary Environments - page 411

vines ( Ipomoea pes-caprae ) and bay geraniums ( Ambrosia hispida ) growing in
the same area today ( Curran, 2007 : fig. 14.7).
Animal trace fossils in the Bahamian eolianites are mainly attributed to the
work of burrowing insects ( Curran, 2007 ) and land-dwelling hermit crabs
( Walker et al., 2003 ). Although vertical tubes ( Skolithos linearis ) and irregular
tunnels made by solitary insects are common, the most striking trace fossils
are those attributed to the work of social insects. “Cluster burrows” are dense
aggregations of large, vertical shafts that are interpreted as the products of
brooding/hatching activities of sphecid (digger) wasps ( Curran, 2007 :fig.14-8A
and B). “Stellate burrows” are closely packed vertical shafts that radiate subhori-
zontally at the sediment surface, and they are interpreted as the products of the
organized nesting behavior of halictid (sweat) bees.
Quaternary eolianites along the eastern coast of the Yucatan Peninsula,
Mexico, resemble those in the Bahamas in being composed entirely of carbo-
nate grains. They too are often typified by dense aggregations of rhizomorphs
( McKee and Ward, 1983 : figs. 10, 12 and 33), but burrows of insects or other
animals are uncommon. Similar rhizomorph-dominated ichnofabrics in coastal
eolianites have been reported in other parts of the world ( Bird, 1972; Glennie
and Evamy, 1968; MacKenzie, 1964 ).
Quaternary eolianites along the northeastern coastline of the Gulf of
California in Sonora, Mexico, are composed of mixed carbonate/siliciclastic
sand ( Phelps, 2002 ). The climate was arid, and plant cover is sparse; so rhi-
zomorphs are rare in the eolianites. Burrows are common and diverse, but sur-
ficial tracks and trackways are almost totally absent from bed surfaces. Most
of the small burrows in the Pleistocene eolianites can be attributedwith confidence
to particular taxa of arthropods, including both insects (mostly cockroaches and
beetles) and arachnids (spiders and scorpions), which inhabit the modern dunes
in the same area today ( Fig. 2 A and B). Meniscate burrows ( Taenidium ) are the
most abundant trace fossils, and they were made mainly by desert roaches
( Arenivaga investigata , Family Polyphagidae, Order Blattaria). Non-meniscate
burrows ( Planolites and Skolithos ) are very common, and they were created
mostly by various taxa of beetles (Order Coleoptera), including scarabs
( Cyclocephala , Family Scarabaeidae), darkling beetles (Family Tenebrionidae),
and hister beetles ( Saprinus , Family Histeridae). Some of the Skolithos burrows
may have been made by crevice weaver spiders ( Kukulcania utahana ,Family
Filistatidae, Order Araneae), which construct short, web-lined, vertical shafts in
the modern dunes. Small spiral burrows ( Gyrolithes ) are abundant in the modern
dunes and fairly common in the Pleistocene eolianites. They clearly were pro-
duced by burrowing scorpions (Family Vaejovidae, Order Scorpiones), several
genera of which inhabit the dunes today.
Vertebrate trace fossils also occur in the Quaternary eolianites of Sonora,
Mexico. Trackways of lizards, rodents, and lagomorphs and sinuous trails of
snakes (rattlers, sidewinders, and gopher snakes) are commonly observed in
the sands of the modern dunes, but surficial tracks and trails are rarely