Stuart, Stephanie A. , Erwin, Diane M. .
Fertile sporophytes of Azolla from the early Eocene Wind River flora, Wind River Basin, Wyoming, U.S.A.
THE fossil record of Azolla is known primarily from macerated megaspore complexes, megaspores, and the microspore-containing massulae, with over 50 species currently recognized. By contrast, remnants of whole sporophytes, especially those bearing intact sporocarps, are rare, with vegetative remains known for just seven species. Here we reconstruct an early Eocene Azolla from the Wind River flora of Wyoming. Reconstruction is based on several large fertile plants collected from two localities within the Wind River Formation: the Fish Lake and Wind River sites. Sporophytes are well-preserved adpressions showing attached leaves, roots, mega- and microsporocarps. Plants are at least 6.0 cm long, prostrate, triangular in outline, with one to two orders of alternate, pinnate branching, and one leaf between each branch. Roots occur singly, one per node, at some or possibly all nodes on a branch. Leaves are alternate, with sporocarps associated with each sporophyll. On fertile branches, sporocarps are numerous, appear paired, and in some specimens, produced at every node. Megaspore complexes appear multifloated and on average measure 630 x 480 μm (major axis x minor axis) with megaspores that are 400 x 350 μm. Both the megaspore and float region are enclosed by a filosum that varies from scattered filaments to a thick, matted covering. Microsporocarps, 0.63 to 1.1 mm in diameter, have at least 16 massulae per sporocarp. Massulae are 150 to 300 μm wide with numerous anchor-shaped glochidia clearly visible on their surface; the microspores measure 16 to 17 μm in diameter. The Wind River fern predates A. berryi in middle Eocene rocks in the neighboring Green River basin to the south. Its exquisite preservation and presence in older Wind River basin strata allows not only comparison to fossil and extant species, but also discussion of its phytogeographic history, ecology, and phylogenetic position.
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1 - University of California, Berkeley, Department of Integrative Biology, 3060 Valley Life Sciences Bldg #3140, Berkeley, California, 94720, USA
2 - University of California Berkeley, Museum of Palenontology, 1101 Valley Life Sciences Building, Berkeley, California, 94720-4780, USA
Wind River Formation
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 4:00 PM