History Of Discovery

Our understanding of early vascular plants has an interesting history that, to a large degree, has greatly influenced many areas of paleobotany. In 1859, the Canadian geologist and paleobotanist Sir John William Dawson (FIG. 8.6t published a report on a Devonian vascular plant collected from the Gaspe region of Nova Scotia. His reconstruction showed a horizontal rhizome bearing upright, leafless, dichotomizing axes, to which were attached pairs of sporangia. Dawson named this interesting plant Psilophyton princeps (FIG. 8.7). Dawson's scientific colleagues virtually ignored this important discovery, however, perhaps because the plant he reconstructed looked so unusual and certainly because of its age. Several years later (Dawson, 1871) he described additional specimens, but, again, these were not seriously considered by the scientific community of the day. In the years that followed, other discoveries were made on plants with obvious vascular tissue, and gradually Dawson's initial report of Devonian vascular plants gained acceptance (Dawson, 1888).

One of the most spectacular discoveries in paleobotany finally proved beyond any doubt that vascular plants existed by the Early Devonian. Beginning in 1917, Robert Kidston (FIG. 8.8 t and William Lang published a series of papers detailing some exquisitely preserved vascular plants collected near the village of Rhynie, in Aberdeenshire, Scotland. This fossil-bearing rock (FIG. 8.9) consists of a fine-grained chert that is now regarded as coming from the upper part of the Lower Devonian, and dated at approximately 400 Ma (Rice et al., 1995). Recent palynological studies suggest a Pragian-?earliest Emsian age for the deposits (Wellman et al., 2006; and Wellman, 2007). Most of the fossils from the Rhynie locality showed that these plants did in fact consist of dichotomizing and, in general, leafless aerial stems (FIG. 8.10) arising from a horizontal aboveground or subterranean rhizomatous system. At the ends of some axes were terminal sporangia.

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