Taylor, Wilson A. .
Lamellae in fossil and modern spore walls: variability, homology and usefulness in taxonomic assessment.
There is a limited number of ultrastructural features upon which to base conclusions about taxonomic affinity in dispersed fossil spores. This problem is especially acute prior to the appearance of macrofossil remains that serve to offer candidate groups for consideration (e.g., pre-Middle Silurian). One of the few recurrent and useful features is the lamella. Lamellae are widely considered to be the plesiomorphic building block of land plant spores. This conclusion is based in part on the nearly universal appearance of lamella in early developmental stages in modern spores/pollen, and their appearance in (presumably) mature dispersed spores as early as the Middle Cambrian. However, the range of lamellar morphotypes is broad and no one has considered the full array of structures that can be considered lamellae. In the modern liverwort Sphaerocarpos. drewi, lamella thickness ranges from 260-400nm. In the Lower Silurian dispersed dyad Dyadospora murusdensa, the range is 10-30nm. Does such a disparity call into question the purported homology between these lamellae? Perhaps not, considering that other modern liverworts have at least some lamellae that are as thin as 10nm. And why do lamellae in many modern and a few fossil spores appear tripartite, while others do not? Post burial changes are certainly a factor, but may not explain all the disparity. A thorough consideration of lamellar structure, development, taxonomic occurrence and fossil range will help determine the usefulness of this common ultrastructural feature in understanding primitive land plant spores; this presentation will describe the results of such a study.
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1 - University of Wisconsin-Eau Claire, Department of Biology, 105 Garfield Ave., P.O. Box 4004, Eau Claire, Wisconsin, 54702, USA
Presentation Type: Oral Paper
Date: Monday, August 15th, 2005
Time: 11:45 AM