This fundamental classification is founded on the supposed or inferred behavioral characteristics represented by the trace fossils (Table 14.1). The most important categories relate to feeding, dwelling, and locomotion. As the units are divided on the basis of activity there maybe some overlap between them if the organism performed more than one behavior (for example, feeding and crawling) at the same time. Also, different parts of the trace fossil structure may fall into different categories.
Table 14.1 Ethological classification of trace fossils; 11 categories comprise the scheme. The characteristics of the eight main groups are shown. Those omitted are: praedichnia (predation traces), aedificichnia (structures built above the substrate), and calichnia (breeding nests).
Description of behavior
Preservation and structure
Example ichnogera (and their possible producers)
Cubichnia Resting or hiding traces formed during a temporary pause in locomotion. Rather than resting, the traces usually represent feeding by stationary feeders or refuge
Domichnia Dwelling traces formed by burrowing or boring into the substrate. Traces represent the long-term home of an animal that is stationary in the burrow
Usually as casts on the bottom of beds. Morphology reflects the nature of the undersurface of the resting organism
Deep excavations of varying shape found within beds. Usually form an anastomosing tubular structure, or a straight or a U-shaped burrow
Skolithos (tube worm)
Fugichnia Escape structures formed when animal moves rapidly upward to prevent burial by a sudden influx of sediment or, more rarely, laterally to avoid predators
Equilibrichnia Adjustment traces formed by infaunal animals maintaining the position of their burrow with respect to a gradually agrading or degrading sea floor
Usually within beds in association with domichnia. Sediment at the proximal end of the burrow is reworked and lamination is disturbed
Occurs within beds in association with domichnia. Distinct laminations formed parallel with the main burrow
Escape structure made by bivalve
Escape structures made by polychaete
Repichnia Locomotion traces that represent directed movement (from A to B). Includes walking, crawling, tunneling, and running
Found as casts on the bottom of beds or as epireliefs. Characteristically continuous, elongate trails, sometimes revealing the motion of limbs
Upward movement Cruziana (trilobite)
Downward movement Diplichnites (arthropod)
Pascichnia Grazing traces formed by the systematic exploitation of a particular area of the sediment for food
Agrichnia Traps and farming traces formed by animals that trap food particles or grow algae. Structures represent feeding and dwelling in a fixed area
Fodinichnia Traces that represent two functions:
deposit feeding and dwelling. Excavations are made as the organism eats the sediment and digests the food within it
Horizontal traces found on or beneath the bedding plane. Distinctive furrowed trails with sinuous, meandering form but paths rarely cross
Complicated horizontal network of burrows with multiple openings to the surface. Usually preserved as hyporeliefs on bottom bed surface
Three-dimensional form usually found within bed. Generally horizontal but more complex forms can have branched networks of burrows
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