Fossil of the month: Zoophycos
This month’s fossil of the month is Zoophycos. This fossil is not part of a distinct organism or plant (body fossil), but rather is a trace fossil. Trace fossils are the tracks, trails, burrows, or other markings left behind by organisms.
Zoophycos is a three-dimensional trace consisting of a central vertical shaft or tunnel (centimeters in length and usually 1 centimeter or less in width), and spiraling layers of lateral feeding traces (generally tens of centimeters in width). Feeding traces (technically called Fodichnia) are patterns preserved on or in a substrate by deposit-feeding organisms as they move through sediment in search of food. Zoophycos feeding traces consist of arcuate grooves and ridges (sometimes with a feathery or rope-like appearance), which are termed spreite. The spreite are arranged in broad, overlapping tongues and fans around a central shaft. The central shaft is the temporary home of the invertebrate organism, and the curving lines are the patterns made in the sediment as the organism burrowed and sifted for food around its central home.
Zoophycos represents the feeding traces of deposit-feeding (eating organic particles from sediment), worm-like invertebrate (lacking a backbone) organisms. As a trace fossil, Zoophycos is not necessarily the trace of a single genus or species of a worm-like organism, but rather is a preserved feeding pattern (a behavior) made under certain environmental conditions by an organism or different types of organisms with similar feeding structures and behaviors.
On some of the geologic quadrangle maps for Kentucky, the trace fossil Taonurus is listed. This trace genus name is no longer used, because it was found to be a synonym of Zoophycos. The arcuate traces of Taonurus were interpreted as the spiraling movement of clumps of sea grass in the sediment, but are now recognized as the feeding traces of invertebrate worm-like organisms.
Zoophycos has long been recognized as a common fossil in rock strata deposited in marine turbidite beds, which are generally deposited in relatively deep water, and modern Zoophycos feeding patterns made by worm-like organisms have been found in deep-sea sediments (Wetzel and Werner, 1980). Seilacher (1953a, b, 1967) named the Zoophycos ichnofacies for beds that displayed a low diversity of trace fossils, including Zoophycos, which were deposited in relatively deep water. Zoophycos, the individual trace fossil, also occurs in several other ichnofacies across a range of inferred water depths. Depth, however, is not the only control on ichnofacies distribution (Frey and Pemberton, 1984). Numerous reports have found Zoophycos and the Zoophycos ichnofacies in sediments deposited in shallower water, under stressful conditions, such as low oxygen levels (Ekdale and Mason, 1988), but not necessarily at great depths.
Zoophycos occurs in Cambrian through Recent strata and sediments (Ekdale and Lewis, 1991; Miller, 1991). In Kentucky, Zoophycos is widely distributed in marine siltstones and sandstones from the Ordovician through the Pennsylvanian Periods, but is perhaps most common in the Lower Mississippian Borden Formation, especially in the Farmers and Nancy Members (Chaplin, 1980).
- Chaplin, J.R., 1980, Stratigraphy, trace fossil associations, and depositional environments in the Borden Formation (Mississippian), northeastern Kentucky (Geological Society of Kentucky 1980 field conference): Kentucky Geological Survey, 114 p.
- Ekdale, A.A., and Lewis, D.W., 1991, The New Zealand Zoophycos revisited: Morphology, ethology, and paleoecology: Ichnos, v. 1(3), p .183–194.
- Ekdale, A.A., and Mason, T.R., 1988, Characteristic trace-fossil associations in oxygen-poor sedimentary environments: Geology, v. 16, no. 8, p. 720–723.
- Frey, R.W., and Pemberton, S.G., 1984, Trace fossil facies models, in Walker, R.G., ed., Facies models [2d ed.]: Geoscience Canada, p. 189–207.
- Miller, M.F., 1991, Morphology and paleoenvironmental distribution of Paleozoic Spirophyton and Zoophycos: Implications for the Zoophycos ichnofacies: Palaios, v. 6, no. 4, p. 410–425.
- Seilacher, A., 1953a, Studien zur Palichnologie I. Uber die methoden der Palichnologie: Neues Jahrbuch Geologie Palaontologie, Abh. 96, p. 421–452.
- Seilacher, A., 1953b, Studien zur Palichnologie II. Die fossilen Ruhespuren (Cubichnia): Neues Jahrbuch Geologie Palaontologie, Abh. 98, p. 87–124.
- Seilacher, D., 1967, Bathymetry of trace fossils: Marine Geology, v. 5, p. 413–428.
- Wetzel, A., and Werner, F., 1980, Morphology and ecological significance of Zoophycos in deep-sea sediments off NW Africa: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 32, p. 185–212.