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Systematics, Ontogeny, and Phylogenetic Implications of Exceptional Anatomically Preserved Cycadophyte Leaves from the Middle Jurassic of Bearreraig Bay, Skye, Northwest Scotland
Beatrice L. Dower, Richard M. Bateman and Dennis Wm. Stevenson
Vol. 70, No. 2 (Apr. - Jun., 2004), pp. 105-120
Stable URL: http://www.jstor.org/stable/4354471
Page Count: 16
You can always find the topics here!Topics: Leaves, Plant veins, Flora, Plants, Fossils, Phylogenetics, Stomata, Epidermis, Papillae, Anatomy
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The Middle Jurassic (Aalenian-Bajocian) shallow marine deposits of Bearreraig Bay, Skye, northwest Scotland, have yielded calcite-permineralized leaves of cycadophytes showing unusually well preserved anatomy. Morphological characters identify the leaves as Nilssonia cf. tenuinervis Seward (Cycadales), Otozamites mortonii sp. nov. (Bennettitales), a putative juvenile leaf showing imbricate, recurved pinnae, and Otozamites sp. Permineralized Jurassic cycadophytes occur in only four other localities worldwide; the better-known coeval adpression flora of Yorkshire lacks anatomical preservation. Past studies of fossil cycadophyte species have therefore emphasized morphology, whereas the Skye specimens reveal details of anatomy greatly exceeding published descriptions of similar species. The arrangement of vascular tissues in the rachis of Otozamites resembles that described for Ptilophyllum cutchense Morris (Bennettitales) from India. Stomata observed in the preserved cuticle of the Nilssonia leaf superficially resemble those of the extant cycad Macrozamia Miquel. Given the 180 million years separating these two genera, and the fragmentary preservation and equivocal phylogenetic position of Nilssonia, comparative interpretations remain tentative. Leaf characters have been little used in phylogenetic analyses, reflecting exaggerated fears of anatomical and morphological convergence; these characters therefore require particular attention when comparing fossil cycadophytes with their living relatives.
Botanical Review © 2004 New York Botanical Garden Press