Evolutionary significance of the Late Devonian lycopsids of the northcentral America
Keywords:Lycopsids, evolution, Late Devonian, Northcentral America
The paper focusses on the evolutionary characters revealed by the lycopsid axes and cones of North America. Highlighted especially are the specimens collected from the Late Devonian greyish-black shale of Greater Cleveland, Ohio and from the Late Devonian silty shale of Venango Formation in Erie County and Pennsylvania. Axes and cones are very large in dimensions comparable to those of Carboniferous. Dominance of many different kinds of lycopsids in the collection suggests that the coastal marshes of Late Devonian sea had forests of respectable size lycopsid trees. Clevelandodendron ohioensis, a slender, unbranched plant with an apical heterosporous cone and short, basal appendages, shows isotalean growth habit similar to a few Carboniferous genera and Triassic Pleuromeia-like forms. This, coupled with presence of Skilliostrobus-like cones from the Triassic of Australia and Tasmania, suggest lineage of Triassic lycopsids from the Late Devonian forms of the Cleveland Shale.