Trace fossils are great sedimentological tools; they can tell us a lot about the local energy conditions, instantaneous sedimentation styles, and substrate conditions, and tend to be controlled by traditionally hard-to-figure-out paleoenvironmental proxies like salinity, light, and nutrient availability. So, seds-oriented folks trying to get some really detailed info about depositional environments tend to go crazy over these arcane little scratches, tubes, and trails found in the rock record.
However, if you're one of the paleontologically oriented sorts, then I reckon trace fossils must be really aggravating, form a biological perspective at least. Oh, sure, you can get some morphological detail out of them, and narrow down the sort of critter that made them, but don't you just hate how damn COY those little fossils are about the trace-maker's REAL identity?
In a few lucky cases, though, the sedimentary record has conspired to give us little glimpses of the tracemakers identity. But man! It's just so sad, isn't it:
The picture above is of the Jurassic Horseshoe crab Mesolimulus walchi, from Germany, along with its very own preserved trail (probably of the ichnogenus Kouphichnium, but I might be wrong). I took these pictures at the AMNH a couple of years ago...and it was under weird museum mood-lighting, so it was a little darker than optimal for picture taking.
Anyway, this poor little fellow was just tooling along the anoxic bottom, trying to find some oxygen, I reckon, when he just gave up the ghost. I mean, look at him there, and the end of his trail, forever entombed in sediment!