Abstract
Studies carried out since 1959 and recently summarized by us have demonstrated higher land plant-type microfossils (trilete spores, spore tetrads, tracheid-like tubes, cuticle-like tissues) from rocks of latest Ordovician to latest Silurian age. Vascular plant body fossils are unknown until mid-Late Silurian (Ludlovian) time. Pre-Late Ordovician land plant-type fossils, either body fossils or microfossils, are not recognized with any assurance. The latest Ordovician may mark the first appearance of such materials and may coincide with the initial evolution of continental vegetation of higher photosynthetic land plants, although these may have been preceded by plant life lower on the evolutionary scale, such as algae, fungi, lichens, and plants of similar morphologic levels of organization.
Because previously studied plant fossils occur in shallow water or nearshore marine depositional sites, unequivocal proof for their nonmarine origin is lacking, although their apparent functional morphology repudiates the possibility of wholly submerged plants. A recent report by Pratt, Phillips, and Dennison now removes lingering doubts about the minimum date when higher land plants occupied the continental environment; they reported definite nonmarine (freshwater or terrestrial), nonvascular higher land plant material of early Llandoverian (earliest Silurian) age near the north end of Massanutten Mountain, Virginia. Their discovery provides hitherto lacking unequivocal proof for nonmarine, pre-latest Silurian (Pridolian-early Downtonian) higher land plants. Coeval fossils that we have been studying are morphologically identical to theirs. It is now clear that there was a significant lag, at least the entire Silurian Period, before undoubted nonmarine animals evolved and were preserved in the fossil record.
