By far the most abundant record of invertebrates in the Glen Canyon is trace fossils. Trace fossils are any record of an organism's existence that does not involve an actual body or body part. Burrows and tracks are two of the most common types of trace fossils, but there are many, many kinds.
In one area, a dark layer of rock about six inches thick runs through white sandstone. When pieces of it break free and weather, a complex system of tunnels is exposed (see left). These tunnels were made by invertebrates, probably some kind of arthropod, and their density shows how abundant life could be at times.
The only invertebrate body fossils found so far have been little freshwater snails. In the “