Significance of the Cairo fossil forest site

William Stein
Department of Biology
Binghamton University

The quarry surface our team has surveyed represents an ancient paleosol (ancient forest soil horizon) that preserves dramatic evidence of one of the oldest forests known on Earth. Age of this horizon is approximately 387 million years b.p. and represents the latest part of the Middle Devonian Epoch. At about this time, trees make their first appearance in the fossil record producing forests (a process termed “aforestation”) covering the land surface for the first time in geologic history. This event likely changed the Earth’s ecosystem profoundly in several ways. Possibly among the most important was a decrease in atmospheric carbon dioxide (actually measured by isotope data) likely resulting in cooling of the climate, changes in nutrient cycling, modified weathering patterns, and a major mass extinction near the end of the Devonian. All of these interrelated changes are of interest as we try to understand the potential effects of the more‐or‐less opposite process of “deforestation” observed in many parts of the world today.

As of this date, only two forests of this age are known worldwide and none older. Both are from the Catskills of New York State. By far the best known is the ancient forest of Gilboa made famous by discoveries at Riverside Quarry Gilboa in the 1920’s, and with the iconic museum display designed by Winifred Goldring, State Paleontologist, at the old New York State Museum, Albany. Excavation at the Riverside Quarry associated with construction of the Schoharie Dam revealed a dense stand of Eospermatopteris tree bases in life position, preserved as sandstone casts, but with main trunks invariably broken. This circumstance resulted in long‐term uncertainty about the nature of the trees. In 2007 (Nature 446, 904‐907), our group showed attachment of Eospermatopteris bases to Wattieza foliage (class Cladoxylopsida) and a palm‐like reconstruction for the whole tree based on well‐preserved crown and trunk material from a nearby locality. Subsequently, we have recovered stem and root anatomy from Eospermatopteris casts directly, and have identified a very young individual with wellpreserved anatomy in the important stem‐to‐base transition region.

Although causing a stir at the time, and found in nearly all textbooks written since, the Riverside Quarry site has long been covered by debris and therefore inaccessible. Our recent paper (Nature 483, 78‐81) represented a once‐in‐a‐lifetime, but very brief, opportunity to observe this occurrence first‐hand. Much to our surprise, we found the paleosol intact showing what amounts to “footprint” evidence of this forest. We were able to walk among spots representing rooted trees, notice their different positions, sizes, and types. The result was our published map and a substantially clearer view of what this ancient forest was really like. Instead of one, we ultimately observed three distinct kinds of trees at this site – a startling observation new to science.

We now turn much of our attention and energy to the paleosol at Cairo Quarry. The forest footprint evidence at this site is equally important and very exciting. As you have seen, we already have quite a map, more extensive than at Giboa, and will likely add more real estate to it this summer. In addition, it is clear that the forest represented at Cairo is different from that at Gilboa in several important respects and, as a result, enriches and clarifies complexity of the Catskill’s ancient landscape. At Cairo we see several large, tapered, and radiating root systems that probably belonged to a plant otherwise known from stem and leaf fragments as Archaeopteris. This plant was completely missing at Gilboa, but from evidence collected in the Catskills and worldwide, we know it to be an important member the forest ‐ somewhere. Now we know at least one place! The setting at Cairo suggests that Archaeopteris anchored another part of the ancient Catskill landscape, perhaps in bays some distance from any river, but close to the shore of North America’s shallow continental ocean to the west. At some point, there was a flood bringing a distinctive color of sand into the forest, perhaps killing the trees, and several kinds of marine fish. Some fish were whole, whereas others were broken into many fragments. The whole fish were trapped, and presumably died among Archaeopteris’s roots. Thus, we see preserved not only the footprint of this part of the forest, but a geological event lasting for perhaps only a few hours to days and preserved as an “instant in time” so long ago. Views such as this are very rare, and very important because the can potentially tell us so much. Catastrophes such as the volcanic eruption of Vesuvius preserving Pompeii, or this ancient Catskill flood, seal into the rocks evidence that otherwise would have been scattered and lost.

We hope to continue our work at Cairo for some time yet, as there’s a lot left that we might be able to accomplish. So far, we have mapped and taken some samples of paleosol, plants, and fish. This summer, we hope to drill approximately 6 shallow core holes to allow three‐dimensional reconstruction of the sediments at the site and to allow our British colleagues to analyze the sediments chemically. Our team will be more than happy to assist in preservation and display of the site if that’s what the Town of Cairo desires. As it stands, the whole occurrence of fossil footprints and fish are ephemeral. In time, weathering will take its toll unless the surface is somehow stabilized. However, preventing traffic on that surface will significantly slow down the weathering process. We are very thankful that this form of protection is already being put in place.