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THE ENIGMA OF ANGIOSPERM ORIGINS

Norman F. HUGHES

Cambridge University Press, 1994, Cambridge Paleobiology Series I, ISBN 0-521-41145-9.

GEOBIOS, 28-5 - Ana lyse d 'ouvrage

This excellent and very original book represents a complete work dealing with the problematic enigma of angiosperm origins. It summarizes the results of forty years of systematical studies done by a paleobotanist-palynologist, evolutionist and geologist, Norman F. Hughes. With this book he closed his scientific career. He passed away on September 17th 1994 in Cambridge.

I agree with Norman Hughes' opinion that the book may be considered as a sequel to his previous book "Paleobiology of angiosperm origins", published in 1976 (C.U.P), but it is not in any sense a second edition. During the last twenty years, a lot searching has been done and the still unsolved problem of angiosperm origins has progressed in terms of interest and general attention, but remains in some respects as wide open as ever. The author believes that the failure is not due primarily to lack of application on the part of any one of us, and that consequently there is a significant error of method concealed somewhere. He also believes that reliable evidence can only come from the fossil record and not from neontologic procedure and that the compromise between both is no longer of value here. It is in this way of thinking that this book is written.

On 303 pages richly i l lustrated by drawings, diagrams and photographic documentation, the book is divided into three parts with fifteen chapters, a glossary, references and, an index.

Part I - The setting of the problem includes seven general and methodical chapters : 1, outline history of investigations ; 2, contributions on origin ; 3, challenges to customary procedures ; 4, working principles ; 5, stratigraphic framework ; 6, general Mesozoic palynologic evidence ; 7, integration of Mesozoic floras and faunas.

Part II - The evidence for Cretaceous origins includes chapters 8-11. In Chapter 8 - Mesozoic megafossils - the author critically evaluates the record of megafossils as known to date. In the comprehensive chapter 9 - English Barremian monosulcate pollen - the author presents from a methodological point of view the Lower Cretaceous angiosperm pollen from the Hauterivian, Barremian and Aptian of southern and eastern England. This chapter is il lustrated with 56 scanning electron micrographs of the oldest of record angiosperm pollen. The author describes in great detail the research project including the geological circumstances, method of preparation, microscope examination, information dealing with results of research in succession phase examination, comparison with North America, Gondwana as well as the scope of present understanding of MTC (monosulcate, collumellate-tectate) pollen, and the regional palynologic characters and botanical affinities of MTC pollen. In chapter 10 - First convincing angiospermous fossils - the author critically evaluates from stratigraphical, paleogeographical and paleoenvironmental points of view all fossil records so far known of leaves, pollen and flowers. Chapter 11 - Cretaceous angiosperm consolidation - deals with the late Cretaceous paleoenvironment, late Cretaceous "dicotyledonous" fossils, fossil leaves, late Cretaceous palynomorphs, the Maastrichtian floral radiation, "monocotyledonous" fossils, the existing theory of origin of "monocotyledons", the suggested separate origin for palms, the strong radiation of ferns in Early Cretaceous time, fossil palms, Pandan group fossils and general comments on the Late Cretaceous.

Part I I I - Consequences and conclusions - comprises four chapters (12-15). Chapter 12 - Cenozoic angiosperm radiation - deals with "paleobotanical indigestion, climate patterns and angiosperm radiation, the Cretaceous / Tertiary boundary phenomena, Eocene floras, taxonomy, nomenclature and evolution, avoidance of the use of Quaternary methodology and the Cenozoic contribution". Chapter 13 - Research unattained but possible - deals with the research problems. In chapter 14 - Principles, t ime and choice - the author discusses" fossil record paramount, relevance of Holocene studies to the past, paleobotanical and botanical baggage, time and the angiosperm definition, the plant beginnings of the Mesozoic era, Triassic diversity, the "Mesophyticum", the use of period classifications, Cretaceous floral changes, Cenozoic speciation, explosion and major geologic events. The last chapter 15 - General biological conclusions - is very contrary to a tradition of definition that has persisted for many decades with little change according to the opinion of the author, presumably because it was locked on to the concept of an evolutionary event of probable monophyletic nature. He continues in a discussion of so called "older" characters and "newer" characters of the proposed fossil angiosperms, proposed convention, Mesozoic Pollenifera and dicotyledonous angiosperms, pteridophyte evolution, animal integration and concludes with the resolution : "The future appears to lie in gradual mastery and integration of the whole of the available fossil record including paleopalynology, and especially in unbiased data handling of the products".

It is not easy to review this book, where every sentence, written in good English style, carries important information. The work abounds with new and provocative thoughts in an effort to find an effective method and to resolve the enigma of angiosperm origins.

I suspect that this book of Norman F. Hughes is ahead of its time and was written for the next scientific generation, which will be less imbued with deep-rooted conventional thinking.

Analyse Blanka PACLTOVA