Edited by C. J. Cleal. Special Papers in Palaeontology no. 55, £45. ISBN 0-901702-59-5. ISSN 0038-6804. Members of the Palaeontological Association can purchase a single copy for a 25% discount (+£1-50 P&P) from the Marketing Manager. Non-members can obtain copies from Blackwell Publishers, Journals, P.O. Box 805, 108 Cowley Road, Oxford, OX4 1FH, UK.
This 145 page publication of the Palaeontological Association contains four papers which deal with aspects of Ordovician, Silurian and Devonian spores from the United Kingdom. As the preface (by C. J. Cleal) points out, an understanding of the development of terrestrial vegetation is important to the study of the evolution of higher plants, the development of the terrestrial environment and, thus, the evolution of the higher animals.
The first paper, by John Richardson, deals with the taxonomy and classification of some early Devonian (Gedinnian) cryptospores from England. The paper proposes the division of the cryptospores into two major informal groups, the eucryptospores and paracryptospores, as well as describing several new taxa, suprageneric groupings (turmae, suprasubturmae etc.) and proposing a revised cryptospore classification scheme. Paracryptospores possess an identical sculpture on a variety of spore units (tetrads, triads, dyads and hilate monads), whereas each eucryptospore species usually have a sculptural type restricted to a single spore unit (tetrads, pseudodyads, dyads or monads, but never triads). Richardson likens paracryptospores to similar abnormal spore associations in modern hybrid ferns and suggests that if hybridization were a common and recurrent theme (only a single species of paracryptospore is described) it would have had a considerable impact on the pattern and rates of early land plant evolution. The paper concludes with some biological considerations on the paracryptospores and eucryptospores and the plants which produced them.
The sporomorphs of the ‘Lower Old Red Sandstone’ of Lorne, Scotland, are discussed in the next paper by Charles Wellman and John Richardson. Well preserved cryptospores and miospores are described from probable lacustrine deposits (hopefully giving a true reflection of the local flora) lying beneath the radiometrically aged Lorne lavas. The sporomorph assemblages have allowed an earliest Devonian age to be proposed (based on the presence of crassitate trilete spores with large distinct apiculae and the absence of various taxa and morphological characteristics) and have brought into question previously proposed correlations between the island of Kerrera and mainland Scotland. The Lorne assemblages are compared with other late Silurian-early Devonian assemblages from Southern Britain, Scotland, the Ardennes-Rhenish area, Amoricain Massif, Cantabrian Mountains, Podolia and Bolivia.
Charles Wellman goes on to describe cryptospores from the generally near shore marine sequences of the type Caradoc area, Shropshire, providing further insight into the sparsely documented Ordovician cryptospores. Wellman also examines aspects of cryptospore classification, morphology, affinity and evolution and details previous reports of Ordovician sporomorphs from around the globe. The stratigraphical distribution and zonation of Ordovician and early Silurian sporomorphs is discussed, as is the phytogeographical scheme of Gray et al., which divides Ordovician and early Silurian sporomorph assemblages into Malvinokaffric and extra-Malvinokaffric Realms.
The final paper by Cedric Shute, Alan Hemsley & Paul Strother reassesses dyads contained in a late Silurian (Prídolí) sporangium from the Welsh Borderland by using both transmitted light and confocal laser scanning microscopy (CLSM). A rhyniophytoid affinity is suggested for the sporangium and numerous dyads were noted to contain granular bodies (interpreted as mineralization products of the degredational remnants of the entire cell contents) and have inner membranes, which CLSM work suggests are of a non-sporopollenin composition, surrounding organic rich regions. Shute et al. conclude that the dyads represent meiospores.
I have only one gripe. The revised classification scheme proposed for the cryptospores in the first paper is not used in the systematic sections of the second and third papers. That over, I can only say that the material throughout this Special Paper is beautifully illustrated by transmitted light and scanning electron microphotographs and as a whole attains the very high standards one expects from a Palaeontological Association publication.
Gary Mullins, Department of Geology, University of Portsmouth, Burnaby Building, Burnaby Road, Portsmouth PO1 3QL, UK.