540 Chapter j PALEOCONTINENTS The Present is the Key to the Past: HUGH RANCE j8 Late Devonian Gilboa forest < the first forest > And Gustave [de] Beaumont [1802-1866], who had accompanied [Alexis de] Tocqueville [1805-1859] declared after they had visited a wilderness under assault by pioneers, ‘There is ... in America a general feeling of hatred against trees.’ —David Traxel.2

Primitive (simple) vascular plants exist today, and from a study of these living fossils and the fossil record, the story of plant evolution can be pieced together. Spore-shedding plants, living and fossil, are found in what are or were swamps and in wet environments (shaded damp glades, in the spray of waterfalls). This being so, spore-shedding plants cannot be said to be fully terrestrial. The familiar ferns can be used to illustrate this (see Topic j10) and to explain why these plants would have forever left bare the hillslopes of the landscape. Living horsetail rushes and groundpines (living representatives of extinct sphenopsids and lycopsids respectively) have had little variety and abundance, and all have been small plants since the decline of these flora during the Permian. Their heyday (time of maximum diversity and abundance) was during the Carboniferous when many tree species of sphenopsids and lycopsids reached heights of 30 meters. The spore-shedding sphenopsids and lycopsids first appear in the fossil record in the Devonian Period. The lycopsid Gilboa forest Excavations for a pumped-water storage project near the villages of Blenheim and Gilboa, New York, disclosed in the Catskill formation the oldest known forest. Found in the 1920's were the upright stumps of more than fifty trees, and found in 2007 by Christopher M. Berry are two, 26 feet in height, fallen sideways, each intact with trunk, branches, twigs and crown, and of the genus Wattieza.2 The fossils of these fernlike trees are sandstone casts in black shale; the once mucky soil in which they grew. In this same paleosoil are thin, carbonized, roots that radiated from the bulbous base of these trees. Correlatable with the Middle Devonian Gilboa-forest shale are other lens-shaped layers of black shale that contain beautifully preserved plants of several other plant species.3 The environment is seen as wet-tropical riparian, replete with shrublike plants and, locally, trees shading a tufted mat of tall, but mossy, herbs.4 Ferns, sphenopsids, and lycopsids, likely evolved in the Early Devonian from psilophytes, which were the first higher plants and include the Silurian Rhynie flora (see Topic j11). “Higher” here refers to vascular tissue as this can gives a plant the stiffness not to sprawl as do “lower” pants, which are those with no vascular tissue.

Figure j9.1 5 The evolution and diversity of plants The widespread appearance of megaphyll leaves, with their branched veins and planate form, coincided with a 90% drop in atmospheric pCO2 near the close of the Devonian Period. This was 40 million years after simple leafless vascular plants first colonized freshwater swamps in the Late Silurian.6