Cenomanian Angiosperm Leaf Megafossils, Dakota Formation, Rose Creek Locality, Jefferson County, Southeastern Nebraska AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the cur rent-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Sur vey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. 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E-146, 701 C St. Maps For maps, address mail orders to Maps U.S. Geological Survey, Map Distribution Federal Center, Box 25286 Maps may be purchased over the counter at the U.S. Geologi Denver, CO 80225 cal Survey offices where books are sold (all addresses in above list) and at the following Geological Survey offices: Residents of Alaska may order maps from • ROLLA, Missouri--1400 Independence Rd. Alaska Distribution Section, U.S. Geological Survey, • DENVER, Colorado--Map Distribution, Bldg. 810, Federal New Federal Building -Box 12 Center 101 Twelfth Ave., Fairbanks, AK 99701 • FAIRBANKS, Alaska--New Federal Bldg., 101 Twelfth Ave. Cenomanian Angiosperm Leaf Megafossils, Dakota Formation, Rose Creek Locality, Jefferson County, Southeastern Nebraska By GARLAND R. UPCHURCH, JR. and DAVID L. DILCHER U.S. GEOLOGICAL SURVEY BULLETIN 1915 DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. UNITED STATES GOVERNMENT PRINTING OFFICE: 1990 For sale by the Books and Open-File Reports Section U.S. Geological Survey Federal Center Box 25425 Denver, CO 80225 Library of Congress Cataloging-in-Publication Data Upchurch, Garland A. Cenomanian angiosperm leaf megafossils, Dakota Formation, Rose Creek locality, Jefferson County, southeastern Nebraska I by Garland A. Upchurch, Jr., and David L. Dilcher. p. cm.-(U.S. Geological Survey bulletin; 1915) Includes bibliographical references. Supt. of Docs. no.: I 19.3:1915. 1. Leaves, Fossil-Nebraska-Jefferson County. 2. Paleobotany-Cretaceous. 3. Paleobotany-Nebraska-Jefferson County. I. Dilcher, David L. II. Title. Ill. Series. QE75.89 no. 1915 [QE983] 557.3 s-dc20 90-2855 [561 '.2]CIP CONTENTS Abstract 1 Introduction 1 Acknowledgments 2 Materials and methods 2 Criteria for classification 3 Geological setting and description of fossil plant locality 4 Floristic composition 7 Evolutionary considerations 8 Ecological considerations 9 Key to leaf types at Rose Creek 10 Systematics 12 Magnoliales 12 Laurales 13 cf. Illiciales 30 Magnoliidae order unknown and magnoliid-grade foliage 34 Rosidae 42 Magnoliopsida subclass unknown 45 References cited 49 Index 53 PLATES [Plates follow index] 1. New genus A 2. Extant Magnoliales 3. Crassidenticulum decu1Tens 4. Crassidenticulum decu1Tens 5. DensineJVum kaulii 6. Gomorlega keule and Landonia calophylla 7. Extant Laurales 8. Pabiania variloba 9. Pabiania variloba and extant Laurales 10. Extant Laurales 11. Cuticle of Pabiania variloba and Sassafras albidum 12. Pandemophyllum kvacekii 13. Pandemophyllum kvacekii and Pandemophyllum attenuatum 14. Fossil leaves similar to Pandemophyllum and Pandemophyllum sp. 15. Cuticle of Pandemophyllum kvacekii 16. Cuticle of Pandemophyllum attenuatum and Pandemophyllum sp. 17. Cuticle of Pandemophyllum sp. and extant Lauraceae and Staudtia gabonesis 18. Longstrethia varidentata 19. Cuticle of Longstrethia varidentata 20. Cuticle of Longstrethia varidentata; extant Illiciales 21. Didromophyllum basingerii 22. Didromophyllum basingerii and "Sterculia" towneri var. disjuncta 23. Acritodromum ellipticum and Reynoldsiophyllum masonii Contents Ill PLATES 24. Reynoldsiophyllum nebrascense 25. "Elaeodendron" speciosum, Dicotylophyllum angularis, and New genus B 26. Anisodromum wolfei 27. Citrophyllum doylei and Citrophyllum aligentm 28. Dicotylophyllum myrtophylloides 29. Dicotylophyllum rosafluviatilis 30. Dicotylophyllum aliquantuliserratum 31. Dicotylophyllum expansolobum FIGURES 1. Index map showing location of the Rose Creek locality, Jefferson County, Nebraska 5 2-25. Line drawings showing: 2. New genus A 12 3. Crassidenticulum decurrens 14 4. Ascarina lanceolata 15 5. DensineTVUm kaulii 18 6. Gomortega keule 19 7. Landonia calophylla 19 8. Pabiania variloba 22 9. Pabiania variloba 23 10. Pandemophyllum kvacekii 26 11. Pandemophyllum attenuatum 29 12. Longstrethia varidentata 31 13. Schisandra propinqua 33 14. Didromophyllum basingerii 34 15. Acritodromum ellipticum 36 16. Reynoldsiophyllum masonii 38 17. Reynoldsiophyllum nebrascense 39 18. Dicotylophyllum angularis 40 19. New genus B 41 20. Anisodromum wolfei 42 21. Citrophyllum doylei 43 22. Dicotylophyllum myrtophylloides 45 23. Dicotylophyllum rosafluviatilis 46 24. Dicotylophyllum aliquantuliserratum 41 25. Dicotylophyllum expansolobum 49 TABLES 1. Comparison of Crassidenticulum, DensineTVUm, and related extant taxa 16 2. Comparison of Landonia and related extant taxa 21 3. Comparison of Pabiania, Pandemophyllum, and related taxa 25 IV Contents Cenomanian Angiosperm Leaf Megafossils, Dakota Formation, Rose Creek Locality, Jefferson County, Southeastern Nebraska By Garland R. Upchurch, Jr. and David L. Dilcher1 2 • ABSTRACT INTRODUCTION The leaves described in this report comprise the first assemblage of early flowering plant leaf megafossils to be The mid-Cretaceous was an important period in accorded formal systematic treatment using modern the history of the vascular land plants. During this time, methods of foliar architecture and cuticular anatomy. The 20 the angiosperms began their adaptive radiation, and species of dicotyledonous leaves are described from a new major extant lineages at the level of subclass, order, and locality in the Dakota Formation of Nebraska, near Rose family made their first appearance. (See, for example, Creek (Rose Creek locality). Seventy percent of the species Wolfe and others, 1975; Hickey and Doyle, 1977; represent either subclass Magnoliidae or forms with a similar Dilcher, 1979; Upchurch, 1984; Walker and Walker, grade of foliar architecture. Among Magnoliidae, species are 1984.) Associated with this adaptive radiation were assignable to the orders Magnoliales and Laurales, and one progressive and broad-scale ecological displacements, species shows resemblance to llliciales. Although three wherein cycadophytes, ginkgophytes, and other dominant species have strong similarities to one extant family (Laur groups of gymnosperms declined in relative abundance aceae, or the laurel family), most species of Magnoliidae or magnoliid-grade foliage possess generalized features or and diversity and were replaced in most habitats and combine the characteristics of two or more extant families. geographic regions by angiosperms, especially at lower One species possesses unique features of foliar architecture and middle paleolatitudes (Doyle and Hickey, 1976; that represent an unsuccessful •experimental• design. Two Hickey and Doyle, 1977; Retallack and Dilcher, 1981, species of Rosidae are present in the flora, and these 1985; Crane, 1987; Upchurch and Wolfe, 1987b). combine features of foliar architecture that today are Although some aspects of this transition have been restricted to either compound-leaved or simple-leaved elucidated by recent paleobotanical research, much families. The leaves examined in this study show little remains unknown about this critical interval of Earth evidence for fragmentation prior to burial and are preserved history, particularly with respect to the dynamics of in a sequence of rooted mudstones containing brackish angiosperm diversification and the establishment of water bivalves (including one specimen in life position); thus, major extinct and extant angiosperm lineages. the leaves represent predominantly local, brackish-water vegetation. This indicates that flowering plants evolved the This state of ignorance is largely due to an inade ability to tolerate greater-than-freshwater salinities by the quate taxonomic data base, a problem that is especially Cenomanian. The vegetation represented by the Rose Creek acute for angiosperm leaf megafossils. During the 19th leaf remains shows few similarities to modern mangrove and early 20th centuries, paleobotanists described swamps but instead is most analogous to brackish-water numerous angiosperm leaf remains of Cretaceous age, swamps that occur inland from mangrove swamps. but without a clear understanding of foliar architecture and the systematic distribution of foliar architectural features in extant flowering plants (Wolfe, 1973; Dilcher, 1974; Doyle and Hickey, 1976). Compounding the prob lem was an automatic assignment of most fossil leaves to Manuscript approved for publication, October 20, 1989. extant families and genera, even if these leaves lacked 1Department of Biology, Indiana University, Bloomington, one or more features found in the extant taxa. This Indiana, 47405. "picture matching" (Wolfe 1973; Dilcher, 1974) gave the 2A ddress as of June 1990: Florida Museum of Natural History, University of Florida, Gainesville, Florida, 32611. Cretaceous angiosperm record a falsely modern aspect, Introduction preventing the recognition of extinct evolutionary the manuscript. Mr. and Mrs. Richard DeBoer granted intermediates and disguising similarities that were the permission to collect at the Rose Creek locality, and result of convergent evolution. As a result, even the Roger Judd of the Endicott Clay Products Company oldest known angiosperm leaf assemblages were inferred provided the services of a bulldozer. Field assistance was to show affinities with both primitive and derived taxa, provided by James Basinger, Charles Beeker, Margaret and few angiosperms were thought to represent extinct Bolick, Peter Crane, Peter Dilcher, Martin Farley, Karl intermediate forms. While some authors explained this Longstreth, Greg Retallack, and Michael Zavada. situation by proposing extremely rapid evolution of Insightful comments on the relationships of the Rose flowering plants during the Cretaceous (Scott and others, Creek leaf fossils were provided by Leo Hickey and 1960), others proposed an extensive period of diversi Scott Wing. William Cobban and Douglas Nichols (U.S. fication prior to the group's appearance in the fossil Geological Survey, Denver) provided assistance with record, either in remote geographic regions (Seward, stratigraphic problems. The research for this report was 1931) or in upland regions, where preservation of pre completed while the senior author was a National Tertiary sediments is minimal (Axelrod, 1952, 1970). Research Council Postdoctoral Research Associate at These concepts were consistent with occasional reports the U.S. Geological Survey, Denver. Fieldwork and the of pre-Cretaceous flowering plants (for example, Harris, earlier stages of research were supported by National 1932; Erdtman, 1948; Kuhn, 1955; Brown, 1956; Tidwell Science Foundation Grants DEB-79-10720 and and others, 1970), now either discounted or considered BSR-83-00476 to David L. Dilcher at Indiana problematic on morphological or stratigraphic grounds University, Bloomington. The final stages of data analysis (Read and Hickey, 1972; Scott and others, 1972; Wolfe and writing were supported by National Science and others, 1975; Hickey and Doyle, 1977). Foundation Grant BSR-86--07298 to Garland R. The purpose of this study is to partially redress the Upchurch, Jr. and Erie G. Kauffman at the University of systematic problem for early angiosperm foliage through Colorado, Boulder, and by National Science Foundation analysis of leaf architecture and cuticular anatomy in Grant BSR-85-16657 and a Guggenheim Foundation well-preserved leaf remains from the mid-Cretaceous Fellowship to David L. Dilcher at Indiana University, (uppermost Albian? to middle Cenomanian) Dakota Bloomington. Formation of southeastern Nebraska, along with a few related forms from the classic Dakota assemablages of Kansas. In this report we propose new species and genera MATERIALS AND METHODS that more accurately reflect the interrelationships of mid-Cretaceous angiosperms. We also discuss probable Nearly every specimen examined during this study extant affinities at the level of family, order, and subclass, was collected between June 1978 and October 1983. All based on detailed consideration of foliar architecture and distinctive leaf architectural types and all specimens with cuticular anatomy. These data will serve as a basis for organic preservation were retained for laboratory elucidating the evolutionary status of early angiosperms analysis, and many of the organically preserved speci during the early Cenomanian, approximately 20 million mens were coated with Krylon crystal clear acrylic plastic years into the angiosperm adaptive radiation. spray to prevent cracking of the organic matter. All collected specimens were initially deposited in the Indiana University paleobotanical collections and given ACKNOWLEDGMENTS the locality prefix 15713-. These collections are now housed at the Florida Museum of Natural History in We thank Jack A. Wolfe (U.S. Geological Survey, Gainesville, Florida. Denver) for his discussions concerning the systematic Foliar architecture of fossils was studied through affinities of the Rose Creek foliage, for discussions of the direct observation of specimens and through enhance issues raised in this report, and for critical review of the ment of details by line drawings and high-contrast manuscript. We thank James Basinger (University of photography with Kodak Technical Pan 2415 film. Leaf Saskatchewan, Saskatoon) for his initial research on the architectural terminology largely follows Hickey (1973, Rose Creek leaf flora and for preparing most of the 1979) but incorporates the modifications suggested by cuticles examined during this study. We also thank Roger Wolfe (1977) and Wolfe and Wehr (1987) with three Pabian (Nebraska Geological Survey) for discovery of exceptions. First, we have used Hickey's term "exmedial" the Rose Creek locality, help with geological problems, instead of "abmedial," largely because abmedial is easy and field assistance, and Howard Reynolds (Fort Hays to confuse with admedial. Second, we have used State University, Kansas) for initially informing us about "quaternary" and "quinternary" instead of "quatary" and the Rose Creek locality and for field reconnaissance. We "quintary." Third, we have avoided use of Hickey's terms thank Bruce H. Tiffney for careful and helpful review of "imperfect," "incomplete," and "lacking" for the 2 Rose Creek Locality, Jefferson County, Southeastern Nebraska description of areolation. These three conditions inter architecture are largely confined to line-drawings; the grade and represent a composite of characters (variation interested reader should consult Hickey and Wolfe in areolar size, shape, and degree of branching of the (1975) for photographic illustrations of major tooth types in extant flowering plants. freely ending veinlets ), and we could not be confident that we were always using the terms in the manner intended by Hickey (1973, 1979). Instead, we have CRITERIA FOR CLASSIFICATION described areolation as well developed, moderately developed, or poorly developed, depending on the Angiosperm phylogeny is riddled with examples of regularity in size and shape, and provided illustrations for convergent morphologies, and individual plant organs the reader. We also have added descriptions of the show a large degree of developmental independence general organizational tendencies in festooned brochido relative to one another. Together these create the dromous secondary venation. Readers unfamiliar with potential for strong mosaic evolution. Any classification venational terminology should obtain a copy of Hickey based on a single organ has a greater potential for error (1979) to use while reading species descriptions. than one based on a variety of organs, because whole Cuticles were prepared for light microscopy with a plants contain a larger number of nondevelopmentally combination of standard methods, such as those outlined linked characters than single organs. Hence, the analysis in Dilcher (1974), using bleach for maceration and of whole plants improves the chances of spotting Safranin 0 for staining. When cuticular fragments were convergent similarities. However, while leaves are the large, a piece of 100-mesh screen was sometimes used to most abundant component of the megafossil record, transfer cuticle between solutions. All leaf cuticles were foliar characters have traditionally played a small role in the classification of extant angiosperms, in contrast to photographed with Kodak Technical Pan 2415 film on reproductive structures. Although one solution to this the Zeiss Photoscope I at the Paleontology and Stratigra problem would be to restrict the systematic analysis of phy Branch, U.S. Geological Survey, Denver, using angiosperm megafossils to taxa known from both brightfield and phase-contrast optics. Cuticular termi reproductive and vegetative organs, this approach would nology follows Stace (1965) and Dilcher (1974), except greatly restrict information about the flora as a whole, when the use of terminology would potentially confuse given the dominance of isolated vegetative organs in the the nonspecialist. "Upper" cuticle is used in place of megafossil record. "adaxial" cuticle and "lower" cuticle is used in place of Fortunately, comparative studies of extant angio "abaxial" cuticle. This is because the upper and lower sperms indicate that leaves show a number of features of cuticle in fossils are recognized by an ecologically systematic importance at the levels of genus, family, controlled character (frequency of stomata), while abax order, and subclass; (Wolfe, 1973; Hickey and Wolfe, ial and adaxial denote developmental position. (In the 1975; Roth, 1981; Jones, 1984; Levin, 1986a, b). In particular, features, such as venation pattern, tooth mature leaves of a few extant species, the lower surface structure, and leaf organization, show strong corre actually represents the adaxial side of the developing spondence with recent angiosperm classifications based leaf.) The term "cuticular flange" is used in place of on more traditional botanical characters taken from a "anticlinal cell wall" because the cuticular flanges are the variety of plant organs. (See, for example, Cronquist, only part of the anticlinal walls preserved in most 1968, 1981; Takhtajan, 1969, 1980.) Studies of foliar cuticular preparations. All measurements of cell size are architecture also have resolved the systematic placement for unspecialized cells. Cells from modified areas of the of taxa whose classification proved problematic on the epidermis in proximity to veins ("veinal areas") and basis of reproductive organs. The most prominent stomata were not included in the measurements. · example at the level of subclass is Euphorbiaceae, where Because foliar architecture and cuticular anatomy foliar architecture (Hickey and Wolfe, 1975) strongly in extant flowering plants have not been comprehensively supports Takhtajan's (1969, 1980) placement of the described and illustrated, we have included illustrations family within Dilleniidae, rather than Rosidae, as of extant relatives of the Rose Creek taxa. Complete proposed by Cronquist (1968, 1981). At lower taxonomic illustration of foliar architecture and cuticular anatomy levels, the combination of foliar architecture and epi in the extant relatives would be a major undertaking and dermal anatomy have resolved the systematic placement was not attempted because of limited time and space; of various problematic taxa, including several genera instead, we illustrated only representative taxa. Most within the subfamily Phyllanthoideae of the Euphorbi photographic illustrations of foliar architecture are x 1 aceae (Levin, 1986a, b). Thus, foliar characters have but can be magnified for observation of secondary, much potential for the classification of fossil angio tertiary, and quaternary venation. Illustrations of tooth sperms, especially if venation is combined with Criteria for Classification 3 anatomical features, such as stomatal structure and tri represented by an incompletely preserved specimen that chome type, which are routinely analyzed by systematic had a distinctive suite of leaf architectural features plant anatomists. unknown in any extant family), a generic level taxon was informally recognized, permitting diagnosis when better We followed four major principles to minimize preserved specimens are found. If a leaf type was potential error in our classification of fossil angiosperm distinctive at the species level but had incompletely foliage. preserved venation or a generalized suite of venational First, the only characters used to circumscribe features, the leaf was assigned to Dicotylophyllum. fossil genera were those that have systematic significance In this report we make extensive comparisons in extant angiosperms at the level of genus or family. This between species in the Rose Creek flora and previously was determined by direct study of the foliar architecture reported taxa. The discussion section following most and epidermal anatomy of extant angiosperms and by species descriptions is divided into three parts. The first examination of the literature on foliar architecture (for part compares the taxon with previously described fossil example, Hickey and Wolfe, 1975; Levin, 1986a, b) and genera and discusses the validity of previous generic anatomy (for example, Metcalfe and Chalk, 1950, 1979; assignments, largely to justify the creation of new genera. Wilkinson, 1979). For members of the subclass Magnoli The second part compares the Rose Creek species with previously described species of fossil angiosperm leaves, idae, this comparison was exhaustive and involved exami many of which were invalidly assigned to extant or fossil nation of over 260 extant genera. Approximately 4000 genera. This is done to justify creation of new species and total extant species were examined for foliar architecture. to point out possible congeneric species from other Second, new genera were erected only on the basis floras. The third part provides the basis for assignments of several independent and congruent characters, so as to to extant taxa, starting at the level of class or subclass and avoid the pitfalls of single character taxonomy. In order working down the level of family. to be considered independent, two characters must have Many discussion sections might seem lengthy by a different developmental origin or show distinctly the standards of Tertiary paleobotany. This lengthiness is different constructional principles. For example, both necessitated by the prior identification of species by some foliar venation and cuticular anatomy were used in workers solely on the basis of shape and size and by diagnosing genera because the veins and cuticle have widespread misidentification of mid-Cretaceous angio their developmental origins in different tissue layers of sperm foliage at generic and higher taxonomic levels, the leaf (Fahn, 1967). For another example, the presence practices that, unfortunately, continue to the present day. of two or more vein orders with a particular venational We hope that these comparisons will suggest avenues for pattern (such as reticulate tertiary and quaternary vena future research on the systematics of Cretaceous angio tion) was counted as only a single character, because this sperm foliage. condition could easily result from the iteration of the same developmental pattern at different levels of the venational hierarchy. For the sake of completeness, potentially linked characters were listed separately in the GEOLOGICAL SETTING AND descriptions of species. DESCRIPTION OF FOSSIL PLANT Third, all leaf remains that formed the basis for generic diagnoses had to be known with at least three or LOCALITY four orders of preserved venation and be represented by sufficient specimens to understand the construction of In central Kansas and adjacent regions, the mid the whole leaf. This insured that a large number of Cretaceous sequence comprises five distinct formations, venational characters was considered before erecting a considered to represent the early stages of the Green classification and that all diagnostic features were horn transgression by Kauffman (1969). In ascending present in the type species. This also prevented erro stratigraphic order these units are as follows: (1) the neous assignment of fossil leaves to the most similar Cheyenne Sandstone of middle to late Albian age, (2) the extant taxon, because many times the similarities seen Kiowa Formation of late Albian age, (3) the Dakota between a fossil leaf and an extant taxon were in lower Formation of latest Albian (?) to middle Cenomanian order architectural features and cuticular anatomy, age, (4) the Graneros Formation of middle Cenomanian rather than in fine venation. age, and (5) the Greenhorn Formation of late Ceno Fourth, a leaf taxon had to show either probable manian to Turonian age (Hattin, 1967; Kauffman, 1969; congeneric relationship to other fossil species or a highly Franks, 1975; Ward, 1986). Although the full strati distinctive suite of features before being formally graphic sequence is exposed in central Kansas, older diagnosed at the generic level. If a fossil leaf type met units successively pinch out to the northeast, so that in only three of these criteria (for example, it was southeastern Nebraska rocks of the Dakota Formation 4 Rose Creek Locality, Jefferson County, Southeastern Nebraska