Undertrack fallout can occur when not all feet penetrate to the same depth in the sediment - if the trackway is exposed at a depth in the sediment lower than the original surface some of the tracks may be missing. Other, preservational factors will influence trackway morphology. For example a track produced by a myriapod as it walks over firm, dry sediment will appear different to one produced as it walks over soft, wet sediment, even though the gait parameters may be the same. Two sets of parallel track groups can be seen, individual track clusters are clear. This time the trace is made by the myriapod in a slightly wetter sediment.
Individual tracks can no longer be seen, they grade into each other producing parallel 'tramlines'.
Finally a myriapod trail produced in a very wet substrate. No evidence of tracks is preserved, instead a series of nested chevrons show where the myriapod's body has dragged over the surface, pulling the sediment with it. All these variations can cause confusion when trying to name a trackway or infer a producer. However they can also be valuable palaeoenvironmental or paleoecological indicators, for example a wet sediment trackway overprinted by a dry sediment trackway indicates a drying out sequence in the surrounding environment 5 .