Jud, Nathan A. , Rothwell, Gar W. , Stockey, Ruth A. .
Anatomy of an Upper Cretaceous bennettitalean stem.
A fossil bennettitalean (cycadeoidalean) stem base has been recovered from the Upper Cretaceous (Coniacian) Eden Main locality on Vancouver Island, British Columbia, Canada. This fossil consists of a stem with diverging leaf traces and adventitious roots. It displays the dense wood anatomy and non-girdling leaf traces that differentiate bennettitalean stems from cycadalean stems, and also shows a novel combination of anatomical features within Bennettitales. No leaf bases or ramentum are preserved. The woody eustele surrounds a large parenchymatous pith that lacks mucilage sacs. Cortex contains forking mucilage ducts and leaf traces that are made up of 1-8 vascular bundles arranged in a row. Each bundle consists of crescent shaped xylem opening abaxially, and exterior phloem. There is evidence for two forms of herbivory within the stem tissues. These include a large gallery with reaction tissue, and small galleries that contain coprolites. An entrance hole 3 mm in diameter is located on the surface of the stem, leading to the large sediment-filled gallery in the pith. The large gallery measures up to 7 mm across and 15 mm deep. Wound response tissue in the form of traumatic cellular proliferations occurs in rings and plates throughout the plant body. Such tissue is most highly developed lining the periphery of the large gallery, where it resembles "nutritive tissue" as described in the gall and ant-plant literature. Smaller galleries containing coprolites of oribatid mites are present in the cortex, but there is no associated wound response tissue. This fossil represents a new genus of Bennettitales documenting greater structural diversity among the Cretaceous cycadeoids than previously known, and revealing that at least two types of animals fed on this plant.
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1 - Ohio University, Department of Environmental and Plant Biology, Porter Hall, Athens, OH, 45701, USA
2 - Ohio University, Department of Environmental & Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
3 - University of Alberta, Department of Biological Sciences, Biological Sciences Centre, Cw 405, Edmonton, Alberta, T6G 2E9, Canada
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 28th, 2008
Time: 10:15 AM