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16. CONTINENTAL ICHNOLOGYi FUNDAMBNTAL PROCESSES AND CONTROLS ON TRACĘ FOSSIL DISTRIBUTION

Stroma tol i tes and biolaminales are media that can have other organisms living on their surfaces or be bored (Ekdale et al., 1984; Hasiotis, 2002, 2004). Some organisms, termed endobionts even have the ability lo prevent the microbial community from growing over the top of them, producing a cylindrical pit where the endosymbionts lives.

Such lithified media as sandstone, mud rock, and limestone can also be bored by organisms living in terrestrial and aquatic environments (e.g., Mikulaś and Cflek, 1998; Hasiotis, 2004). These types of substrata are considered hardgrounds because lithifi-cation of the matrix does not allow an organism to push aside grains to construct a burrow, but rather forces an organism to produce a boring (e.g., Ekdale et al./1984). The bones of organisms can also serve as substrata in which organisms can leav«? their mi ero- or macroscopic traces. These traces inelude bite marka, insect borings, fungal borings, £? v.^re& produced by injuries

TERRESTRIAI

TRACEMAKER Ci■■. '■-/ •

The Continental realm contains the greates; diver-sity of life on Earth today, composed mostly of insects, other arthropods, higher plants, and a lesser diversity of vertebrates, non-arthropod invertebrates, fungi, and protists (Wilson, 1992). The vast majority of these and other Continental organisms are terrestrial in habitat and, in one way or the other, play a role in soil formation (Thorpe, 1949; Hole, 1981; Wilson, 1992). There is a strong likelihood that a similar relationship in biodiversity existed as far back as the Mesozoic (e.g., Retallack, 2001; Hasiotis, 2004). The traces produced by Continental biota serve as proxies that record body size, presence in the media, type of activity, effeets on the media, and habitat preference (Wallwork, 1970; Hasiotis, 2000, 2004). The original classifications were developed for organisms living in soils, but they can be extended to aquatic organisms and to tracę fossils.

Organism Size

Organisms are classified as microfauna (20-200 pm), mesofauna (200 pm-1 cm), and macrofauna (>1 cm) according to size (Fig. 16.5A; Wallwork, 1970). Although there is a considerable rangę of body sizes of trace-making organisms, many taxonomic groups occupy fairly distinct size ranges. Most organisms

living in the soil are easily overlooked because the bulk of biodiversity and biomass are micro- and mesofauna (Wallwork, 1976; Wilson, 1992).

Presence in the Media

The presence of organisms in different media varies widely and is classified according to their degree of time spent in it (Fig. 16.5B). The amount of time spent in a medium by organisms and their developmen(^H stages varies greatly for many different reasons ’ (Wallwork, 1970; Hole, 1981; Eisenbeis and Wichard, \ 1987). Organisms that live above the surface of a medium and have minimal impact on it are referred to as epigeon. Organisms that have a transient to periodk interaction with a medium are referred to as geophiles, ; those with permanent interaction are referred U 1 ńonts. Transient fauna are adult forms of | rns that use a medium for temporary shelter r)V«ge during periods of inactivity. Temporary fauna ented by the distinct stage or stages )pment (egg->nymph or juvenile->adult;

. i va->pupa->adult) a medium as one active Irom which an adult emerges and joins the is another active life stage. Periodic fauna >end a greater amount of time within a medium and, is, ha ve a much closer relationship to it. Here all life stages are completed within a medium where the organisms spend most of their lives, however, the adults will emerge to join the epigeon, matę, and begin the cyde again. Permanent faunas complete all life stages belowground and rarely appear at the surface. Accidental faunas are animals that live above* ground but fali, blow, or wash into a medium, and contribute the least to soil formation and soil ecosystems (Hole, 1981).

Type of Activłty

Organism behavior, particularly for those that burrow, can be divided into two main types of activities: locomotion and feeding (Fig. 16.50. Others consider locomotion, feeding, and reproduc-tion as the main behaviors (e.g., Odum, 1971; Aber and Melillo, 1991), however, it is rare that direct evidence of the act of reproduction is preserved but indirect evidence in the form of excavated and constructed structures (Le., burrows) are often pre* served (Genise et al., 2000; Hasiotis, 2000, 2002,2003, and references therein). All behaviors are linked because animals use locomotion while feeding or to avoid being eaten, and to look for mates and construct nests. Locomotion is the process by which meso- and