COMPARATIVE PALEOBIOCHEMISTRY OF SOME FOSSIL AND EXTANT FAGACEAE

A Fagus-like leaf fossil (cuticular compression) with an attached fruit, differing from any known Fagus species (fossil or extant) or other fagoid taxa, has been discovered from the Miocene Clarkia Lake deposits of northern Idaho. Because of its unusual morphology (especially the fruit) the fossil taxon has been described as a new genus and species, Pseudofagus idahoensis Smileky and Huggins. The successful previous use of paleobiochemistry in studies of fossil taxa from the Miocene Succor Creek Flora of Oregon suggested that chemical data might help clarify the taxonomic affinities of Pseudofagus. Indeed, examination of the chemistry of the fossil, Pseudofagus idahoensis, and comparison with extant Fagus species and related fagoid genera indicate that: 1) based on steroid chemistry, Pseudofagus idahonesis does belong in the Fagaceae; 2) like all extant species of Fagus, the fossil lacks the tannin component, ellagic acid, which separates it from other extant fagoid genera, and 3) its simple flavonoid pigment profile places it closest to the extant North American Fagus grandifolia or the European/Eurasian Fagus sylvatica. However, the exclusive presence of an isorhamnetin (3'-methoxyquercetin) 3-0-glycoside, onocerane, and 5a-cholestane imparts a species-specific chemical character to Pseudofagus idahoensis, which also sets it apart from extant species of Fagus. While the chemistry does not decide the taxonomic level to be accorded to the fossil, it certainly supports, along with morphology and anatomy, the distinctness of Pseudofagus and its proposed relationships within the Fagaceae. RECENT WORK by Niklas (1976) and Niklas and Gensel (1976, 1977, 1978) has shown the taxonomic and systematic utility of using the paleobiochemistry of fossil plants in comparative chemical studies with putative extant relatives. Steroids, fatty acids, alkanes, and phenolics from fossil plants have proven to be the most useful compounds in these studies. Extracts of extant plants are subjected to artifical thermolytic diagenesis and then directly compared to extracts of the fossil taxa which have themselves undergone "natural" diagenesis (i.e., fossilization). Congruence in chemical data between unequivocally identified fossil plants and their contemporary counterparts is quite high, contributing to the utility of the approach. Further, statistical analysis of these chemical ' Received for publication 9 October 1979; revision accepted 10 December 1980; held in abeyance for publication with the preceding manuscript by Smiley and Huggins. The authors thank Professor T. Tanai, Hokkaido University, for providing samples of several species of Fagus. Thanks also are extended to Mr. T. Delendick, Brooklyn Botanic Garden, for collecting other specimens of Fagus from various arboreta and the Brooklyn Botanic Garden. As always, we are indebted to Dr. Pat Holmgren, the New York Botanical Garden, for access to herbarium material. Mrs. Regilda Foscaldi provided invaluable technical assistance during the chromatographic analyses. This work was supported by NSF grant DEB-7904551 awarded to the authors. data via suitable computer programs produce three-dimensional clusters of taxa (fossil and extant) remarkably similar to taxonomic arrangements based on morphology and other paleobotanical evidence (Niklas and Gensel, 1978). With the discovery of flavonoids preserved in fossil angiosperm leaves, i.e., Zelkova (Ulmaceae, Succor Creek Flora), Niklas and Giannasi (1977a) have extended this paleochemotaxonomic approach to the study of angiosperm systematics, phylogeny, and phytogeography. The occurence of flavonoids in the angiosperm leaf compressions is quite significant since these compounds are already used in contemporary plant chemosystematics at all taxonomic levels and in nearly all plant groups (Smith, 1976; Alston, 1967). Thus they provide a broadly based set of chemical data that can be readily compared between fossil and extant taxa. Subsequent work (Giannasi and Niklas, 1977) showed that the fossil flavonoid find was not a "freak" occurrence since distinct flavonoid profiles were found in additional fossil taxa (e.g., Celtis and Ulmus). Further, thermolytic studies on authentic flavonoids indicated that they do not undergo diagenesis (other than terminal destruction) and thus if found in fossils, represent original, unaltered constitu-