Aneurophyte progymnosperms are common shrubs of an early Late Devonian (basal Frasnian Oneonta Fm.) flora from a quarry near Ashland, New York. Floristic census of the marine bay-fill/prodelta deposits at the lowest quarry bench shows that the regional flora was dominated by aneurophytes (80-85%) with Tetraxylopteris the commonest of these (plus Triloboxylon & Proteokalon). Lesser components include cladoxylalean trees and vines (Pseudosporochnus & Rhymokalon), the progymnosperm tree Archaeopteris (Callixylon zalesskyi and A. macilenta) and a few scarce lycopsids (Archaeosigillaria). Delta progradation established vegetated floodplains with sandy paleosols on this site within 4 m upsection. Farther upsection, paleosols are commoner, thicker, and mud-dominated. The floor of the uppermost quarry bench exposes about 1 ha of horizontal paleosol from which we uncovered six small test plots that show stump bottom casts, root penetration zones, and other depositional features of this floodplain soil. Shrink/swell slickensides, many with root penetrations, characterize this vertisol. XRD and SEM analyses show a combined kaolinite/smectite signature, illite (derived from smectite?), and an absence of caliche carbonate, which suggest a savanna-like paleoclimate. Larger stumps are more widely spaced while smaller root zones are closer and clustered farther away from the larger stumps. The ratio of large to small stumps/root masses corresponds to our gross floristic census and suggests that this floodplain paleosol exposure is representative of the regional vegetation of this time on the Catskill Delta. Except for Archaeopteris, these were short-lived taxa, which implies considerable successional turnover. This mixed community, was rapidly re-organized, however, by the world-wide spread of Archaeopteris, a large tree with a much branched, leafy, and shade producing crown, and decline then extinction of aneurophytes, small xeromorphic shrubs with high light tolerance. Nearby quarries of slightly younger strata show greater domination by Archaeopteris, which reaches nearly 95% of biomass by mid Frasnian time.

Key words: Archaeopteris, Devonian, progymnosperm