WOODY PLANT GROWTH AS A PROXY FOR CLIMATE CHANGE AT THE DEVONIAN-CARBONIFEROUS BOUNDARY

Adaptive radiation of plants in the Middle and Late Devonian produced multiple clades of trees with woody tissues. Only lignophytes (progymnosperms, gymnosperms, and their descendents), however, produced successive layers of wood from a perennial vascular cambium that responded to seasonal variation of wet/dry or cold/warm climates. Periods of active growth were succeeded by dormancy that produced a permanent and distinctive cellular signature at the growth layer boundary. Suites of wood anatomical characters of basal lignophytes show that they grew the same as modern plants. Thus their growth layer boundaries can be interpreted to result from similar environmental cues. Woods from Middle and lower Late Devonian lignophytes (Aneurophyton germanicum, Triloboxylon arnoldii, T. ashlandicum, Tetraxylopteris schmidtii, and Callixylon zalesskyi), upper Late Devonian (Callixylon henkei), terminal Devonian (Laceya hibernica), and Late Devonian to possible Early Carboniferous (Araucarioxylon from Olentangy Shale) suggest that the growth layer boundaries of Middle to Late Devonian lignophytes were induced by wet/dry seasonal variation, which is consistent with their paleogeography at tropical and subtropical paleolatitudes. By contrast, growth layer boundaries of some terminal Devonian and earliest Carboniferous lignophytes from similar regions are more like those formed by cold-induced dormancy. These data are thus consistent with an equitable Devonian climate punctuated by a cold event near the D/C boundary.