Format: ORAL

Peter R. Crane1,2, Kaj Raunsgaard Pedersen4, Else Marie Friis3,4

1 Oak Spring Garden Foundation, 1776 Loughborough Lane, Upperville, VA 20184, USA 2 Yale School of the Environment, New Haven, CT 06511, USA 3 Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden 4 Department of Geoscience, University of Aarhus, Aarhus, Denmark

Understanding the structure of bennettitalean seeds is important so they can be compared with those of other seed plants, but their interpretation has been controversial for more than a century. A key question is whether or not the integument is surrounded by an envelope, as in seeds of Gnetales and Erdtmanithecales, and hence whether the seeds are, or are not, chlamydospermous. Resolving this question, even in well preserved material, is difficult because the seeds are small and tightly packed in a mass of interseminal scales causing different tissue layers to adhere closely together. Non-destructive reinvestigation of exceptionally well-preserved permineralized seeds of Bennettites morieri using three dimensional visualization by synchrotron radiation X-ray tomographic microscopy (SRXTM) indicates the presence of an envelope, as well as two distinctive features seen in several dispersed fossil chlamydospermous seeds; i) closure of the micropyle by radial expansion of the cells of the inner epidermis of the micropylar tube (as also occurs in extant Gnetum gnemon, extinct Protoephedrites and extinct Williamsonia); and, ii) the presence of distinctively angled and radially aligned cells in the apical portion of the envelope (not easily seen in some other permineralized bennettitalean ovules). These results support the hypothesis that Bennettitales, Erdtmanithecales and Gnetales are closely related, and suggest that the ovulate ‘flowers’ of Bennettitales are multiaxial compound heads.