The Oligocene Bridge Creek Flora of the John Day Formation, Oregon Meyer, H.W. and S.R. Manchester, 1997. University of California Publications in Geological Sciences, Volume 141. ISBN 0520-09816-1 (paper US $50.00) 362 pp. University of California Press, 1445 Lower Ferry Road, Ewing, NJ.- For over forty years the University of California Press has intermittently published two dozen paleobotanically oriented monographs through their "Publications in Geological Sciences" series. Since 1956, two-thirds (16 of 24) of the contributions (including the last eight consecutive issues) relating to fossil plants have been authored by the same individual! Now, a new generation offers this outstanding revision of the 33 Ma Oligocene Bridge Creek Flora of the John Day Formation, Oregon.
Early paleobotanical treatments of the Bridge Creek flora, in the later 1800's and earliest 1900's, were by workers such as Knowlton, Lesquereux, and Newberry. It has been over 70 years since the most recent monographic update of this north-central Oregon flora (Chaney 1927). Thus, the present volume is a long overdue and much needed contribution.
The writing throughout is clean and concise and nearly error free. After the table of contents, acknowledgments, and abstract; the "heart" of the volume is divided into 12 unnumbered, chapter-like, sections. These are followed by an appendix, literature cited, index, and plates. Five of the first six of these 12 central sections are essentially equivalent to the "Introduction" and "Materials & Methods" in a typical report. The fifth (Diversity and Taxonomic Composition) and 12th (Systematic Descriptions) amount to the "Results", and the 7th through 11th sections constitute a "Discussion."
The largest single section of this monograph is the 111 page Systematic Descriptions, wherein the authors present a very careful and thorough approach.
Mechanically, Meyer and Manchester review and revise the previously known and extensive new collections of fossil leaves and reproductive structures from seven of the (at least) ten known Bridge Creek "assemblages", each "...based on one to several localities (e.g., collection sites) in close geographic and stratigraphic proximity" (Meyer and Manchester 1997 (M&M), p. 18). They have also provided a most useful table correlating various locality names to a standard usage (M&M table 3, p. 19). They then revised the systematics to recognize 91 genera and 110 species based on leaves, 52 genera and 58 species based on reproductive structures, and thus, suggest a combined minimum of 125 species. Taxonomically, 41 previously established species are honored, while five new genera (three based on fruits and seeds of undetermined affinity), 25 new species, and 9 new combinations are established. Four taxa are identified at the familial (but not the generic or specific levels), 36 taxa are identified only to the generic level, seven are compared ("cf.") to a given genus, and one taxon is compared ("cf.") to a given species.
It is refreshing to see that the authors have applied what I (and co- authors) recently suggested be called an "honesty policy" in the approach to the naming of plants (Fields, et al. 1998). Rather than misleading themselves, the authors have been honest in identifying isolated plant organs only to the level for which they are taxonomically diagnostic. They have avoided the often misleading practice of applying the same specific epithet to isolated and often specifically undiagnostic organs of the same genus, and instead used separate names or none at all. Consequently, more than three dozen Bridge Creek taxa are generically, but not specifically assigned, and at least half of these are congeneric with other, specifically named taxa in the flora.
Meyer and Manchester have taken a number of difficult groups and treated them most cautiously. Three examples will suffice: 1) In all but one case, the leaves and samaras of Acer are treated as separate taxa. It is explained that they do not entirely accept the treatment of Wolfe and Tanai (1987) that suggests morphologic details can be used to safely combine these isolated organs. Then, Meyer and Manchester provide discussion (M&M, p. 132-133) and tables to distinguish the various maple leaf or fruit taxa (M&M, Tables 7-8, p. 134-135, respectively), that they recognize in the Bridge Creek assemblages. 2) To distinguish the four recognized Ulmus species, they provide a dichotomous key (M&M p.84). And finally, 3) they specifically recognize only two Alnus taxa based on leaves (rather than four or more recognized by others), but then illustrate "...several variant leaf forms that have not been assigned to either species..." (M&M p.91).
Another breath of fresh air is their treatment of the 37 unknown taxa (one monocot and 31 dicot leaf morphotypes and five fruits). Anyone working on a megafossil floral assemblage knows there is always a residuum of unidentified specimens that seem like they are distinctive enough to be taxonomically recognizable, but based on the material at hand and the worker's knowledge, do not appear to be assignable to anything more precise than the Division or Class level. Often these are: 1) never mentioned in a published monograph (only discovered by examining fossils at the backs of museum trays or the backsides of more identifiable specimens); or these specimens are either 2) incorrectly "shoehorned" into existing taxa or 3) discarded as unidentifiable. Each of these numbered approaches loses information. In contrast, Meyer and Manchester have taken the high road by devoting about 8 pages of text and 10 plates towards making these unknowns available to as many workers as possible....... to document the known diversity and to invite comparisons with similar leaves [and fruits] in other Tertiary floras" (M&M p. 150).
The systematics section is followed by an Appendix showing synonymies of taxa recognized in the flora by previous workers, a literature cited, and an index. Both the former and latter are most useful additions to the typical paleobotanical monograph. The volume is concluded with 75 extremely high quality photographic plates. These are much nicer than those of other recent fossil plant volumes in the series and make this monograph all the more useful to future workers. This is especially noticeable in the clean white "blocking" between adjacent figures in each plate (as opposed to gray figure edges casting black shadows). The overall result is a much more professional look (suggesting whatever extra it cost the publishers, it was well worth it).
Whenever something is as well done as this, any minor problems stand out as needing improvement, no matter how insignificant. Of minimal criticism here, but for the record -and knowing that one cannot do everything, I make the following points that range from errors, to "pet peeves", to suggestions:
1) It would be nice if fossil material from all the known Bridge Creek localities could have been incorporated into the present study. The authors state that at least two of the omitted: "...assemblages contain many of the same species found in other assemblages of the Bridge Creek flora..." (M&M, p.19). This leaves one to wonder why then weren't they included in the study.
2) Of concern is the problem of age ranges between the different assemblages, scattered throughout three different facies of the John Day Formation. New incredibly precise, Ar/Ar single crystal laser fusion radiometric dates are presented and summarized for rocks from three of the seven assemblages studied. It is assumed that the remaining four assemblages are essentially the same age, as they have many taxa in common. However, the three dated sites are all clustered within about 30km of one another and removed by some 50km from some of the other assemblages under consideration. The most distant of these are located in a different facies and have a number of taxa that are unique to them. In all fairness, the authors (M&M p. I 1) are well aware of these weaknesses and suggest that: "Further work is needed, particularly within the southern facies, to establish more firmly the age relationships among the different floral assemblages..."
3) The authors recognize only one species of pine (M&M p.66), but illustrate isolated organs of both Hard and Soft pines. Hard Pine (subgenus Pinus or Diploxylon) needles with persistent basal fascicle sheaths and seeds with disarticulating wings (pl.4 f.4, pl.5 f. 1-4, 67), are illustrated next to cones and an isolated cone scale with terminal umbos (pl.4 f.5-7). The latter are of the Soft Pine type (subgenus Strobus or Haploxylon).
4) Leaf margin data suggest mean annual temperatures for six Bridge Creek floral assemblages that vary from 8-12°C (M&M table 5, p.45), but on the accompanying Nomogram (curiously labeled, without explanation, as a "Climagraph" - a new word to the English language), the authors plot the flora at about 9.5-11.5° C (M&M fig.2, p.46). The result is to graphically restrict the flora from the "Mixed Coniferous", "Mixed Northem Hardwood", and "Mixed Mesophytic" forests to just the latter. To their partial redemption, in the text, the authors suggest that the fossils from some assemblages; "...may indicate an ecotonal setting between Mixed Mesophytic and Mixed Northern Hardwood forest (fig.2), although these assemblages contain some genera more typical of Mixed Mesophytic forest." (M&M p.43).
5) The authors do not follow the trend of recent paleobotanical workers in honoring a taxon's authority as part of the Latin name, and thus using the Latin conjunction "et" or an ampersand, rather than the English "and" between multiple authors (i.e., they use "Calocedrus schomii Meyer and Manchester" instead of "C. schomii Meyer et Manchester", in direct contrast to neobotanical practices; see Recommendation 46C of the International Code of Botanical Nomenclature, Greuter 1994).
6) The cited edition of the International Code of Botanical Nomenclature is the superseded "Berlin Code" (Greuter 1988), rather than the most recent "Tokyo Code" (Greuter 1994). This seems especially curious when one considers that they cite 15 other 1994 or later references.
7) I notice very few typographic errors, but two come to mind: line 17 p.61, contains a reference to plate 3, instead of plate 2; and on the explanation page to plate 7, reference is made to fig. 6 in the 8th line (under item #8) instead of fig.7.
8) Text pages are numbered in the upper left (for even numbered pages) or upper right (for odd numbered pages). Unfortunately, this is not continued through the plates section. Users would find it much easier to locate specimen illustrations if the plates (consistently located on the right-hand sides), were directly numbered in their upper right hand corners (as in some past offerings in this series, for example see: Axelrod 1964). Instead the plates section bears no pagination and the plates themselves are unnumbered, but are facing an explanation page on left-handed pages, where plate numbers are centered (i.e., indented) at the top of the page.
Overall, this is a well written and well produced volume on an interesting subject. The Bridge Creek flora's strategic regional position 1) geographically (at paleoelevations ranging from 700 to 1200m above modem sea-level, in the Pacific Northwest between the Cascade Ranges and the Rocky Mountains), and 2) temporally (early Oligocene, right after the terminal Eocene/basal Oligocene cold snap), make this flora an important basis of comparison for earlier, contemporary, or later floras throughout the western U.S. The monograph will also be useful in comparisons to similaraged floras elsewhere in the Northern Hemisphere. I feel that this volume should be called to the attention of librarians, botanists, plant ecologists, plant geographers, paleobotanists, and anyone interested in a longer term view of plants over time. It will be cited by many writers long into the future. - Patrick F. Fields, Department of Botany and Plant Pathology, Michigan State University, East Lansing, Ml 48824-1312