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We have come to Lander in west central Wyoming to search for fossils in the Nugget sandstone. Remains or evidence of ancient organisms are rarer in the Nugget than rutabagas in Washakie County, Wyoming. Several organic trails have been reported, but just where they were seen and what they are no one knows.
The light is critical. The remains, if remains they are, may stand in relief for only an hour shadowed at the crucial angle. We might not see them at all on cloudy days.
Small recent dunes made of old-gold-colored sand sit on the large ancient dunes. The small dunes may cover the ancient traces we thought we saw. I scuff the sand away above a Nugget dune. No trails, but my boot is full of sand.
The sun is too high, I think. There is too much light. It is hot and dry. We may even be in the wrong place. … I crawl on all fours, head moving left and right, neck protesting the quick movements. Loose sand sticks to my hand. My right knee aches. Crawling up the gentle slope of an ancient dune I raise up to see where I'm going and catch sight of a trail on a bedding plane.
M. Dane Picard (One Geologist's Earth, 1983)


Trace fossils are very peculiar things. More often than not, the greatest difficulty in dealing with them is simply recognizing that they are trace fossils in the first place! Many a spirited argument has arisen on the outcrop between geologists who take opposing views on the biogenic vs. non-biogenic origin of a particular structure in the rock, and a good share of these arguments go unresolved because of either poor preservation of the structure or lack of clear criteria for distinction between alternative solutions.

We cannot do much about the preservation state, although there are some ways by which we can enhance the visibility of a structure or its component features (see Chapter 4, this volume). We also can seek to develop objective criteria to help us distinguish between biogenic structures and primary (mainly physical) or secondary (mainly chemical) non-biogenic structures. The pitfalls of recognition and identification are many, however, so workers always must proceed with caution and keep their minds open.

If presented with a problematic structure, some criteria which may lead one to consider a biogenic origin include the following items (Table III-1). Be sure to note that the occurrence of one or more of these features may not assure a stamp of certainty on the identification, but at least its (their) occurrence may assist in offering an intelligent guess.

(1) Obvious resemblance of the structure in question to the body form or a body part of an organism. Footprints are a good example of this, because the

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