Footprints in the Sands of Time
By Jack Kallmeyer

Trace Fossil Analysis Adolf Seilacher. Springer, New York, 2007. $69.95., hard-cover; 226 pp. The book is well illustrated with black & white drawings and photographs. Also included are a 10 pp. Index, 2 pp. Glossary, 2 pp. General References and more extensive references associated with each chapter.

Seilacher has produced a comprehensive source book for those of us interested in trace fossils, their origins and their makers. This is a book, as the title indicates, concerning analysis and study of trace fossils - ichnology . It is not intended as an identification guide of all known traces and their makers. Traces discussed are worldwide in occurrence and Cincinnatian examples are included.

A word on organization is needed before I proceed into the rest of the review. Trace Fossil Analysis is organized into fifteen chapters. The chapter subjects can be specific to a particular type of trace maker or to a more generic type of trace based upon form. Because of this there can be some back and forth referencing between chapters. Each chapter contains five Plates, each of which contain multiple line drawings of traces. All chapters begin with a page or so of introductory text followed by lists of references, one for the introductory text and a list for each of the five Plates. The reference lists are two to four pages in length. The remainder of the chapter presents the Plates and about a page of explanatory text for each one in turn. Various photographs of actual trace fossils are interspersed throughout.

Trace Fossil Analysis begins with a single chapter on vertebrate trace fossils. Important in this chapter are the descriptions of the morphologically different tracks made by a single vertebrate animal. Seilacher illustrates and explains how one animal can make tracks of dramatically different appearance based on the condition of the substrate being walked on, by the behavior the animal is exhibiting at the time and the circumstances of preservation. This type of analysis has been used to debunk the “man tracks” next to dinosaur footprints along the Paluxy River near Glenn Rose, Texas. Young earth creationists have typically claimed that the huge human footprint shaped tracks disprove evolution and the geologic timescale. Even intentionally faked tracks are mentioned here, although not in reference to the Paluxy River fakes but to some from a Triassic sandstone in Europe.

Trilobite traces are first covered in the chapter on Arthropod Trackways and then later in chapters on Trilobite Burrows, Resting Traces and Cruziana Stratigraphy. If you haven’t seen or collected trilobite tracks you may be surprised at how many variations appear, again, just like the vertebrate trackways, depending on what the animal was doing when the tracks were made. Some trilobite trackways can be extremely complex as Seilacher illustrates with a lower Cambrian trace from Pakistan (27). The trace, resembling the sideways strokes of a stiff brush, was made by a trilobite moving sideways back and forth on the sea floor in an apparent hunt for food.

The chapter on Trilobite Burrows includes both what we know locally as Rusophycus and Cruziana. Seilacher refers all of these to Cruziana including reference to our local Flexicalymene burrow Rusophycus pudicum as Cruziana pudica. The multitude of drawings show actual traces and the modes in which they were made. In describing trilobite biology, Seilacher is able to infer purpose for burrowing. The most probable reasons for burrowing are for feeding and as an aid in molting or protection after molting. To my sensibilities it was refreshing to see that the term “nest” is never referred to in describing these burrows. Nest implies a breeding function and so far there is no evidence to support this description.

Rusophycus-type traces can also help resolve some trilobite anatomy. Seilacher has examples that clearly show how many claws a trilobite had on each leg which varies with the trilobite species.

One of the more interesting Plates in this section pertains to the burrowing behavior of some Silurian trilobites. The trace Cruziana ancora is surprising. This is a shallow “U” shaped trilobite burrow like a tunnel with both ends open. Well preserved examples from Argentina have shown that the burrows are oriented with the current direction. Without detailed study and interpretation, this burrow would have been classified as a worm burrow.

If you are not familiar with Cruziana trace fossils in general, picture first a typical Rusophycus style burrow and then imagine the dug-in trilobite moving forward for some distance. This makes a pathway, if you will, rather than a trackway of footprints. Cruziana are interpreted as feeding traces with many found in the Kope here in Cincinnati.

Seilacher discounts the interpretation of trilobite hunting behavior as based upon local specimens of Rusophycus carleyi aligned with the termination of worm burrows. These burrows were recently interpreted by Brandt et. al. in the Journal of Paleontology as evidence for hunting behavior by Isotelus. Seilacher offers that “ the published specimens may not be representative, but result perhaps from accidental superposition and biased sampling” and, “...burrowing trilobites were probably sediment processors rather than predators, as shown by the lack of differentiated mouth parts (210). He further cautions that “trace fossils are strictly autochthonous [found in the place where they were made - not transported], but that they do not necessarily represent isochronous [made at the same time] snapshots” (210). In making these statements Seilacher may not be aware that quite a few of these specimens are known and that the worm burrow is sized in proportion to the size of the Rusophycus implying that the Isotelus was smart enough not to bite off more than he could chew. Surprising in this rejection of the Brandt paper, Seilacher does not provide a citation for it in his reference lists which seems to me to be a serious omission so I will provide it here: Brandt, D.S., Meyer, D. L., Lask, P. B.. Isotelus (Trilobita) “Hunting Burrow” From Upper Ordovician Strata, Ohio. Journal of Paleontology, 69:1079-1083.

The chapter on Arthropod tunnels does include some traces interpreted as nests. These though are from insects of the Oligocene and not trilobites. Some of the traces shown here cannot be pointed to any specific animal or in some cases even to a specific class of animals. Falling into this category is a broad group of traces classed with the rhizocoralliids. Seilacher points out that despite this common classification, modern equivalents of these are made by groups as diverse as worms, crustaceans and insect larva (56). Within these rhizocoralliids is the Cincinnatian form Diplocraterion - the ever present U-tube burrows - interpreted as a dwelling burrow of a suspension feeder suspected of also using chemosymbiosis (58). 

Chapter 9 of Trace Fossil Analysis discusses forms classed as arthrophycids and again these are traces similar in structure but not necessarily made by the same kind of animal. These traces show specific forms of ridging along their length. Among others, Seilacher illustrates the Cincinnatian form of Phycodes flabellum.

Chapter 10 includes many forms of subsurface miners including chondritids, another common form found in the Cincinnatian. Although no specific Cincinnatian examples are illustrated, the descriptions and diagrams of other species and ages will be familiar to local collectors. Chondritids form branching tunnels not unlike what you would expect from plant roots. Among some of the behaviors of this trace maker is the backfilling of burrows with fecal material and burrows that do not cross or intersect. These too are presumed to use chemosymbiosis like Diplocraterion and are commonly associated with them (58).

One of the more difficult traces to interpret is Paleodictyon. This trace, exhibiting a honeycomb pattern, is also found in the Cincinnatian - Seilacher implies that this local example is actually a pseudo-trace fossil formed by a rolling coral head (165). According to Trace Fossil Analysis Paleodictyon is a deep water form from the Ordovician through the present (156). The biggest problem is in determining how this pattern was made and by what kind of animal. Seilacher discusses viewing modern Paleodictyon structures near deep ocean vents. He was unable to spend enough time at depth to completely analyze what he saw or identify the maker(156).

A valuable inclusion in Trace Fossil Analysis is chapter 12 on Pseudo-Traces. This covers not only sedimentary structures that look like trace fossils but also real body fossils that look like traces as well. The latter group includes some of the Ediacaran fossils. I liked this presentation because it includes many types we see in the local rocks. Pseudo tracks and trails can be produced by trilobites, gastropods or crinoid stems rolling around or across the sea floor. Even water currents across a stationary object can produce a leeward erosional pattern in the sediment that appears to be a legitimate trace fossil. Others include concretions and dessication cracks.

One of Seilacher’s areas of specialization is the Ediacaran Pre-Cambrian fossils so he includes an entire chapter devoted to just these earliest traces of multicellular life.

In the final chapter Seilacher discusses how trace fossils can assist in the interpretation of geological processes and the time sequence of events. Trace fossil analysis is used to infer water depth and near-shore or off-shore environments. Trace fossils are used to interpret the time sequence of events in hardground formation. Also included in this final chapter are the unusual Solnhofen Limestone mortichnia - the death marches of animals leading to their preserved body fossils. 

Much more is covered in this book than I have room to discuss including some very bizarre forms. In conclusion, Trace Fossil Analysis will be very helpful to anyone whose preferred collecting area includes preserved trace fossils. 

Readability - College level text with undefined technical terms used.

On the Upside - Valuable to worldwide collectors. An invaluable resource for promoting the understanding of traces and trace makers.

On the Downside - Trace Fossil Analysis is somewhat expensive, possibly limiting its exposure to casual collectors. Trace fossils are difficult to classify since only some can be tied to specific trace makers while others can only be classified by form. This makes the organization of a book on them difficult. The organization of Trace Fossil Analysis is set up for students of ichnofossils and not so much for collectors.

Overall Rating - I can highly recommend Trace Fossil Analysis to anyone who would like to know more about enigmatic traces and has the desire to better understand life through the ages. 

Overall Rating - Highly recommended, especially to those with questions about the fact of evolution.

Click here to read the previous issue. Click here to read the next issue.