MIDDLE DEVONIAN TERRESTRIAL ECOSYSTEM IN THE CATSKILL REGION: EVIDENCE FROM TREE-SIZE ROOTING TRACE FOSSILS

Plants of Middle to Upper Devonian age from the Catskill region have long fascinated paleobotanists due to their primitive form and tenuous relationships with later floras. There is keen interest in placing these plants in an ecological context since fossils of this age record the origin of trees and therefore forests - an “event” of first order significance in Earth history.

Inferring the ecology of reconstructed earliest trees is difficult. However in situ rooting structures in paleosols provide useful evidence. To date, two sites with extensive exposure in plan view have been extensively studied. The first, a fine-grain blue paleosol at Riverside Quarry Gilboa NY, consists of a dense stand of pseudosporochnaleans with minor representation of aneurophytaleans, and a single arborescent lycopsid. Although pseudosporochnaleans of different sizes are observed, the stand appears mostly to be an ephemeral cohort associated with periodic disturbance at the site. Aneurophytaleans although woody, were clearly subdominant and potentially vine-like in life form. The lycopsid was likely of the cormose type, but interestingly, not associated a coal-forming environment.

The second site near Cairo NY consisting of mottled mudstone, records an event of flooding bringing in extraneous sediment onto a comparatively stable paleosol surface, possibly killing trees in place. Although not abundant, pseudosporochnaleans are also present at this site suggesting their high ecological latitude. By far the most conspicuous are extensive, complex and strikingly modern root systems likely belonging to Archaeopteris. A third type of rooting system is also present at the site indicating a very different tree that has not yet been linked to contemporaneous body fossils.

The paleosol rooting evidence of earliest forests collected so far strongly indicates heterogeneity in this ecosystem that must be taken into account when considering causal relationships between the earliest trees and global environment or long-term environmental or evolutionary trends. Thus, the problem is very much like a modern one in ecological scope and importance.