A REAPPRAISAL OF THE DINANTIAN FLORAS AT OXROAD BAY, EAST-LOTHIAN, SCOTLAND .1. FLORISTICS AND THE DEVELOPMENT OF WHOLE-PLANT CONCEPTS

Re-investigation of species-rich late Tournaisian floras at Oxroad Bay reveals eight plant-bearing exposures that represent four distinct stratigraphic levels. The allochthonous megafossil assemblages vary in degrees of disarticulation, modes of preservation and taxonomic composition. Within-site stratigraphic distributions are presented for 43 anatomically-preserved organ-species; of these, 12 are new to science, 18 have not previously been recorded at the locality, 21 are illustrated from the locality for the first time and 19 are currently considered endemic. Another six have been recorded in error from unprovenanced water-worn blocks. Nineteen adpressed organ-species are also described. Methods and concepts of whole-plant reconstruction are reviewed. At least 11 whole-plant species occur at Oxroad Bay. The lycopsids comprise an enigmatic plant with an Asteroxylon-like stele and two morphologically- and ecologically-distinct species of Oxroadia. A new species of Protocalamites demonstrates the earliest evidence of heterospory and tuberoid stem-bases in the sphenopsid clade. Cladoxylon and Stauropteris represent the pteropsids. At least five lyginopterid pteridosperm species are present. They include both trees (Eristophyton, Bilignea) and shrubs/pseudoherbs (e.g. Tetrastichia and the Triradioxylon–Calathopteris–Oxroadopteris–‘Tristichia’ plexus), suggesting a range of life strategies. Their diversity has complicated attempts to reconstruct whole-plants, though attachment is demonstrated between several ovules and cupules, and several ovules and pollen-organs are correlated using shared microspores. Elements of particular evolutionary significance include the ‘megacupule’ Calathospermum and a structurally similar pollen-organ aggregate, a bisexual Pullaritheca cupule, and a complete ontogenetic sequence of Hydrasperma ovules. Comparable Dinantian floras are reviewed. © 1990, Royal Society of Edinburgh. All rights reserved.