Hernandez-Castillo, Genaro R. , Stockey, Ruth A. , Rothwell, Gar W. , Mapes, Gene .
Diversity among Pennsylvanian age walchian conifer plants: a third species of the genus Emporia.
A third species of the walchian conifer Emporia (Voltziales) is described as a whole plant based on specimens from the rich fossil biota at the Late Pennsylvanian age Hamilton Quarry, Kansas. This conifer has plagiotropic branches with simple and forked leaves, heterophylly, simple pollen cones, and compound ovulate cones. Stems have an endarch eustele, dense wood and secretory cells in the pith. Leaves are amphistomatic with two adaxial stomatal bands, and two longitudinal abaxial rows with numerous trichome bases. Pollen cones are simple with helically arranged microsporophylls and adaxial pollen sacs. Prepollen is monolete and monosaccate (Potonieisporites). Ovulate cones are compound with bilaterally symmetrical dwarf shoots in the axils of helically arranged bracts with forked tips. Dwarf shoots bear up 45 sterile scales and 1-2 sporophylls. Ovules are inverted, winged and resemble those of E. lockardii. This is the fifth and last conifer to be reconstructed from the Hamilton Quarry. Three species of a walchian conifer genus is highly unusual, as most Paleozoic conifers are monotypic. The uncommon species richness of Emporia suggests rapid evolution in the Late Pennsylvanian of Kansas. Documentation of three Emporia species is probably possible only because there are thousands of specimens available to reconstruct whole-plants. These reconstructed conifers support a previous hypothesis of vegetational transition near the Pennsylvanian-Permian boundary, where low non-conifer species diversity is associated with conifer trees of small stature bearing large numbers of pollen and ovulate cones, and leaves with thick cuticles and many trichomes. These associations suggest that some early conifers were colonizers of unstable, water stressed environments. This conclusion is consistent with the hypothesis that rapid phenotypic evolution is correlated with environmental instability, and it accounts for the dramatically different patterns of species distribution between the wetlands and the extra-basinal environments of the late Paleozoic equatorial tropics.
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1 - Universidad Nacional Autonoma de Mexico, Departamento de Paleontología, Instituto de Geología, México City, 04510, México
2 - University of Alberta, Department of Biological Sciences, Biological Sciences Centre, Cw 405, Edmonton, Alberta, T6G 2E9, Canada
3 - Ohio University, Department of Environmental & Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Williford A/Hilton
Date: Monday, July 9th, 2007
Time: 2:45 PM