The Ichnofacies Paradigm - Trace Fossils as Indicators of Sedimentary Environments - page 112

Corophium volutator ). Moreover, both Rosselia and Skolithos can be used for
surface deposit-feeding at the sediment/water interface (e.g., Cirriformia
luxuriosa ; Gingras et al., 1999 ;cf. Nara, 1995, 2002 ). As with the Skolithos
Ichnofacies, it is evident that a range of behaviors and trophic styles can be
employed in order to survive in Cruziana Ichnofacies-associated settings, both
to exploit the available food resources and to contendwithother aspects of the local
environment (e.g., mixed grain-size substrates, high population densities, or lower
levels of dissolved oxygen).
One of the most common misinterpretations of ichnofacies is that any one
ichnofacies is characterized by a key behavior that fundamentally defines the
ethology expressed by each trace fossil within it (e.g., that all elements of the Sko-
lithos Ichnofacies equate to domiciles for the purpose of filter-feeding). As
alluded to above, the adaptive landscape in any depositional setting is complex,
and it is naive to ascribe a single behavior or trophic style as a panacea for survival
to a specific set of environmental conditions. As is evident from neoichnological
distributions, modern trace assemblages represent a community response to a
broad range of environmental parameters, rather than simply the nature of the
food resource. In the marine realm, other factors aside from food resources affect
burrow distributions, including the sedimentation rate, shifting of sediment,
grain sizes of sediment, and consistency of the substrate, oxygenation, and bio-
mass (see “Environmental Constraints” in Tables 1 and 2 ; Dashtgard, 2011a,b;
Dashtgard and Gingras, 2012; Dashtgard et al., 2008; Gingras et al., 2008b ). In
terrestrial settings, food distribution is commonly secondary to pore-water con-
centrations, climate, and precipitation (e.g., Buatois andM´ngano, 2011; Genise
et al., 2000; Hasiotis, 2002; Hasiotis et al., 2007; Hembree and Hasiotis, 2007 ).
Although in a trace-fossil assemblage it is the range of ethologies as well as
the dominant ethological response(s) that are important to identify, there are clear
associations between the dominant ethology expressed in a trace-fossil suite and
the environmental conditions towhich the tracemakers respond. Akey control on
animal behavior is the availability and delivery of food, wherein suspended food
tends to favor filter-feeding behaviors, and suspension settling of food favors
surface- and subsurface-deposit-feeding behaviors. As such, the fundamental
basis of themarine ichnofacies paradigm resides in the food-deliverymechanism
and food distribution (i.e., the food-resource paradigm) and its association with
substrate consistency. However, as ichnofacies evolve to address less-static
marine settings, other environmental factors will be seen to play an increasing
role in character of the allied ichnological suites.
A fundamental basis for the interpretation of ichnofacies is the worker's abil-
ity to recognize the range of behaviors that a trace fossil may represent (see
Table 3 ). For many trace fossils, this is broadly established in neoichnological
studies, and for others, careful analysis of their morphology has led to refined
interpretations of the behavior they represent. To this end, most of the ichnofacies
defining ethological groups (i.e., dwelling traces, deposit-feeding traces, grazing
traces, and farming systems) can be reliably identified (cf. Rindsberg, 2012 ).