Andrew K. Rindsberg
Geological Survey of Alabama
arindsberg@ogb.gsa.tuscaloosa.al.us
Emory University's Evolutionary Biology Study Group invites one or two prominent researchers to speak every year. On November 6 to 8, 1997, Dr. Anthony J. ("Tony") Martin hosted Prof. Adolf ("Dolf") Seilacher for two talks, a field trip, as well as a reception, visits with local scientists, and several excellent conversations over meals. Biologists, psychobiologists, anthropologists, and geologists participated. Seilacher's reputation drew paleontologists and geologists from as far away as 300 km. Surprisingly, he had never visited Georgia before.
Dolf spoke first to a small, informal noon seminar; Emory students, faculty members, and visitors attended as he spoke on undertracks. Dolf demonstrated, by reference to slabs especially from the Permian and Triassic of Germany, that detailed tracks can be produced within the sediment. In his view, most bedding planes that show footprints were interfacial, not surficial. In fact, this increased the probability of their being preserved. He pointed out that his actualistic experiments in the early 1950's with undertraces (Seilacher, 1953) were not followed up by other researchers for a long time, and that they have relevance for both vertebrate and invertebrate traces.
Psychobiologists in particular were intrigued to hear that the evolution of behavior could be analyzed in the rocks; their approach to the problem has historically taken a different path. In response to a question from the audience, Prof. Seilacher gave the opinion that the Laetoli hominid tracks are undertracks.
His second talk, a formal seminar given to a group of about seventy people, was on Macroevolution. Here he related Schindewolf's 1950 model of the evolution of types to contemporary concepts of mass extinction and macroevolution. Prof. Seilacher told us that mass extinctions seem not to come without being preannounced, even though evolution is blind to the future. In a pioneer phase, open niches are occupied by new bauplans, the "typogenesis" of Schindewolf (1950). This is followed by an established phase or "typostasis". Then the Golden Age can begin as niches increase in number due to narrowing specialization ("typolysis"). At this stage, any global change may bring on a mass extinction; asteroid falls are not the only possible calamity. We were treated to many examples of increasingly specialized (and downright bizarre) organisms, e.g., heteromorph ammonites, rudistid bivalves, and vendobionts, all illustrated by slides that easily qualify both as art and science. The end was thoughtful: We too live in a Golden Age, and the fate of the human race is dubious. "But," he concluded, "I think our species will make it through the transition from the Phanerozoic to the 'Anthropozoic'."
On Saturday, Tony Martin took a group of students and professionals to the huge cut on Interstate Highway 75 at Ringgold, Georgia, southeast of Chattanooga, Tennessee. Here, 800 m of Upper Ordovician and Lower Silurian strata are exposed continuously in one of the best trace-fossil sites in eastern North America (Frey and Chowns, 1973; Rindsberg and Chowns, 1986; Martin, 1993). Seilacher demonstrated his methods of observation and analysis to the group, fascinating students and faculty alike. His method emphasizes close observation of selected slabs, determining the orientation and order of events as recorded by sedimentary structures. There was no lack of material for discussion; as it happened, the topics ranged over the stylolites, way-up criteria, mudcracks, spreiten U-burrows, tidal-flat deposits (or not tidal-flat deposits), bryozoan morphology, phosphatic hardgrounds, restricted lagoonal faunas, the Ordovician-Silurian unconformity and Saharan glaciation, Chondrites, flute casts, and the maker of Trichophycus. Seilacher alternated teaching and humor, giving the mind a rest between lessons. By the end of each day, we all felt as if our short-term memories were full, but still wanted more. And we did get more, over beer.
Frey, R. W., and Chowns, T. M. 1972. Trace fossils from the Ringgold road cut (Ordovician and Silurian), Georgia. In Chowns, T. M. (ed.). Sedimentary environments in the Paleozoic rocks of northwest Georgia. Georgia Geological Society, Guidebook 11:25-55.
Martin, A. J. 1992 [1993]. Semiquantitative and statistical analysis of bioturbate textures, Sequatchie Formation (Upper Ordovician), Georgia and Tennessee, USA. Ichnos, 2(2):117-136.
Rindsberg, A. K., and Chowns, T. M. 1986. Ringgold Gap: progradational sequences in the Ordovician and Silurian of northwest Georgia. In Neathery, T. L. (ed.). Southeastern Section of the Geological Society of America, Centennial Field Guide, 6:159-162.
Schindewolf, O. H. 1950. Grundfragen der Paläontologie. E. Schweizerbart’sche Verlagsbuchhandlung, Erwin Nügele, Stuttgart. [Available in an English edition, 1993, as: Basic questions in paleontology: geologic time, organic evolution, and biological systematics (translated by Judith Schaefer). Chicago, University of Chicago Press, xviii + 467 p., 32 pl.]
Seilacher, Adolf. 1953. Studien zur Palichnologie, II. Die fossilen Ruhespuren (Cubichnia). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 98:87-124, 7 pl.
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