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

Abstract

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 asNilssonia cf.tenuinervis Seward (Cycadales),Otozamites mortonii sp. nov. (Bennettitales), a putative juvenile leaf showing imbricate, recurved pinnae, andOtozamites 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 ofOtozamites resembles that described forPtilophyllum cutchense Morris (Bennettitales) from India. Stomata observed in the preserved cuticle of theNilssonia leaf superficially resemble those of the extant cycadMacrozamia Miquel. Given the 180 million years separating these two genera, and the fragmentary preservation and equivocal phylogenetic position ofNilssonia, 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.