Systematics, Ontogeny, and Phylogenetic Implications of Exceptional Anatomically Preserved Cycadophyte Leaves from the Middle Jurassic of Bearreraig Bay, Skye, Northwest Scotland

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 (Cycadale...

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Bibliographic Details
Published in:	The Botanical review 2004-04, Vol.70 (2), p.105-120
Main Authors:	Dower, Beatrice L, Bateman, Richard M, Stevenson, Dennis Wm
Format:	Article
Language:	eng
Subjects:	Anatomy Bennettitales Calcite Company distribution practices Contents Cycadales Cycadopsida Cycads Distribution Environmental aspects Epidermis Flora Flowers & plants Fossils geographical distribution Jurassic Leaf characters Leaves Morphology New species Nilssonia tenuinervis Ontogeny Otozamites mortonii paleobotany Papillae Phylogenetics Phylogeny plant anatomy Plant cuticle plant morphology Plant tissues Plant veins Plants Preservation Ptilophyllum cutchense Stomata Systematics taxonomy Vascular tissue
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Summary:	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.
ISSN:	0006-8101 1874-9372