Rock Art

The Crafoord Prize, the Nobel equivalent for the geosciences and three other fields, has been awarded to only one paleontologist. Adolf Seilacher, the 80-something-year-old recipient, asserts that his career has been spent as a paleodetective, a sleuth in deep time. Sherlockian reconstruction of ancient events requires both scientific and artistic insight; Seilacher’s work in structural morphology and ichnology involves a surprising amount of the latter.

Ichnology is the study of trace fossils, or biogenic structures that provide evidence of the maker’s activity. Dinosaur footprints are one example. Worm burrows are another. Animal traces litter the landscape; while conducting research this summer, I began to notice the residue of animal life everywhere, in and outside the fossil record. For example, tadpoles nest in polygonal pits on the bottoms of ponds and puddles. Shallow pools in the quarries of Wisconsin house tessellations of these structures. On certain slabs in Amherst College's natural history collection, facsimiles of tadpole nests are found alongside dinosaur tracks. In fact, Amherst’s first science professor and third president (as well as my distant relative), Edward Hitchcock, correlated modern tadpole nests with those sedimentary features, although they have since been recognized as polygonal mud cracks.

Seilacher’s diagrammatic illustrations of trace fossil production are famous in the paleontological community. He identified the asymmetrical and elongate marks of Dimorphichnus as scratches left by trilobites traveling obliquely to the water current. Accompanying a description of his interpretation, Seilacher drew an exquisite overlay depicting the leg and body motions of the trace maker. To explain fractional worm burrows that cross through different depositional layers of sedimentary rock, he invoked spiraling worm networks in three-dimensional space and intricately illustrated hypothetical full burrow systems.

Trace fossils are important as both environmental and behavioral indicators. Seilacher proposed the idea of ichnofacies, or assemblages of certain types of trace fossils found in different environmental conditions. Water depth and oxygen levels are two variables that can determine ichnofacies. The pioneering ichnologist also expanded the application of trace fossils as behavioral indicators, including the proposal of a scheme for trace fossil subdivision based on function (e.g., dwelling vs. farming structures).

The reason I write about ichnology and concentrate on the field’s catalyzing scientist is that in an upcoming post, I hope to explain my summer research involving trace fossils in more depth. To appreciate the curiously arranged divots and tubes dotting rocks and speckling modern soil, one must imagine history as it transpired, the animals as they breathed. When used in conjunction, art and science provide indispensable tools with which to tackle the task.