Lower vascular plants of the Dakota Formation in Kansas and Nebraska, USA

Review of Palaeobotany and Palynology, 80 (1994): 1-18 Elsevier Science B.V., Amsterdam

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Lower vascular plants of the Dakota Formation in Kansas and Nebraska, USA* J u d i t h E. S k o g a n d D a v i d L. D i l c h e r

Department of Biology, George Mason University, Fairfax, VA 22030, USA Department of Natural Sciences, Florida Museum of Natural History, Gainesville, FL 32611, USA (Received December 29, 1992; revised and accepted June 24, 1993)

ABSTRACT Skog, J.E. and Dilcher, D.L., 1994. Lower vascular plants of the Dakota Formation in Kansas and Nebraska, USA. Rev. Palaeobot. Palynol., 80: 1-18. This study includes a comprehensive examination of existing collections, extensive field work over two summers and literature searches. Based upon this data source the lower vascular plants of the Dakota Formation (Cenomanian) from five localities in Kansas and Nebraska were studied. Thirteen species can be recognized including one lycophyte, one sphenopyte and eleven pterophytes. Two aquatic plants (Marsilea and Iso~tites) are new reports for the Dakota flora. One new combination is described: Anemia dakotensis (Rushforth) comb. nov. Comparisons are made with fossil plants from the western deposits of the Dakota Formation and also to information from the microfossil record. Distribution of the plants by locality indicates that the ferns were most likely understory plants in or associated with conifer-dominated forests or swamps. Most of the lower vascular plants present in these deposits represent families that are known earlier in the megafossil record. It is suggested that some ferns were common and dominated certain environments as thickets or formed Mesozoic fern prairies.

Introduction C e n o m a n i a n floras have been studied f r o m m a n y areas o f the world resulting in a general impression o f these floras and their relationships to one another (Vakhrameev, 1991). In N o r t h A m e r i c a mid-Cretaceous deposits have received considerable attention (see Retallack and Dilcher, 1986, for summary). M u c h o f this w o r k has emphasized the diverse angiosperms, while the lower vascular plant megafossils have not been as critically reviewed. D u r i n g the Cretaceous, N o r t h America was separated into two land masses by a large epicontinental sea which extended f r o m the Arctic Ocean to the G u l f o f Mexico. Thus there developed the concept o f eastern and western Cretaceous regional floras in N o r t h America. M a n y o f the reports o f the vegetation in the eastern region were *This report is Number 426 in the series University of Florida Contributions to Paleontology.

done during the latter part o f the 1800s and the early part o f the 1900s. Few pteridophytes were reported (Table I) and the flora was considered to consist o f approximately 90% angiosperms. Vakhrameev (1991) reported that the eastern D a k o t a F o r m a t i o n was unusual floristically because o f the paucity o f ferns, Retallack and Dilcher (1986) c o m m e n t e d that fern megafossils were u n c o m m o n , and Lidgard and Crane (1988) did not include data f r o m the D a k o t a flora in their tabulations because o f the great diversity o f angiosperms (more than 400 sp.) when c o m p a r e d to other floras. They considered the D a k o t a flora to be anomalous. There was a need to re-examine the floras o f the D a k o t a G r o u p exposed in its eastern regions with special reference to the lower vascular plants in order to c o m p a r e this area with reports f r o m the western regions o f the D a k o t a F o r m a t i o n (Brown, 1950; Rushforth, 1971; see Table I) and c o m p a r e miospore information f r o m both areas

0034-6667/94/$07.00 © 1994 - - Elsevier Science B.V. All rights reserved. SSDI 0034-6667(93)E0055-A

J.E. SKOG AND D.L. DILCHER TABLE I Reports of the lower vascular plants from the Dakota Formation; each row "refers to the same probable taxon with different nomenclatural assignments Lesquereux (1892)

Rushforth ( 1971 )

This report (1992)

Asplenium dicksonianum Lygodium trichomanoides? Gleichenia nordenskioldii, kurriana G. kurriana (in part) Pteris dakotensis

Asplenium dicksonianum Asplenium dakotensis Gleichenia comptoniaejblia Gleichenia delicatula Cladophlebis constricta

Pecopteris nebraskana

Cladophlebis parva Coniopteris westwaterensis

Anemia dicksoniana Anemia dakotensi,~ Gleichenia comptoniaeJolia Gleichenia delicatula Cladophlebis constrictu Cladophlebis inclinata Cladophlebis parva Coniopteris hymenophylloides Coniopteris simplex Matonidium americanurn Matonidium hrownii

Matonidium americanum Matonidium brownii Hausmannia rigida Astralopteris coloradica Equisetum lvellii

(Pierce, 1961; Hall, 1963; May and Traverse, 1973) with the megafossil record. Retallack and Dilcher (1986) summarized the total flora information up to 1986 and noted environmental differences for the angiosperm remains. Farley and Dilcher (1986) presented data demonstrating the relative abundances of miospore elements for specific localities discussed later in this paper. Cenomanian age sediments of the Dakota Formation preserved in Kansas and Nebraska are an important sequence in the evolutionary history of vascular plants (Upchurch and Dilcher, 1990). Although their paper emphasized the problems related to the identifications of fossil angiosperms, the ferns of the Cretaceous suffer similar problems of identification. Often relationships to extant fern taxa have been made by matching leaf morphology of fossils to modern forms, without detailed analysis of basic characters. Another special problem was created in the identification of the fossil pteridophytes because the leaf matching was often made with previously named taxa from stratigraphically older Mesozoic horizons. This method would tend to obscure any evolutionary changes in these lower vascular plants. Careful analysis is needed to interpret correctly the nature of these leaves. Although only sterile fern foliage was available for this study we can recognize several families

Equisetum burchardlii Marsilea johnhallii Iso6tites phyllophila

and correlate diversity and occurrence of the megafossils and miospores from particular environments in the Dakota Formation.

Localities and stratigraphy The material described in this paper comes from five localities. The Rose Creek locality (UF15713, 18057), is in a clay pit six miles south of Fairbury, Nebraska on Nebraska State Highway 15. A map of all the localities, geology, topography, and stratigraphic columns can be found in Retallack and Dilcher (1981a) (Fig. i). The material was collected from the Janssen Clay Member of the Dakota Formation (see Upchurch and Dilcher, 1990, for a complete description of the locality). This locality has been interpreted as a coastal swamp with periods of inundation that account for evidence of rapid sedimentation. The Hoisington locality was exposed in a clay pit two miles south of Hoisington on State Route 121 (UF 15706). This locality has been interpreted as a fresh water lake or lagoonal environment with river influence (Retallack and Dilcher, 1981a,b; Skog and Dilcher, 1992). Acme Brick Company's Vandra Pit locality three miles east of Kanapolis, Kansas (Retallack and Dilcher, 1981a) may represent flood plain lake and overbank deposits of a

LOWER VASCULARPLANTS OF THE DAKOTAFORMATION IN KANSASAND NEBRASKA,USA

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Fig. 1. Locality map of collections studied. Dakota Formation outcrop (stipple), United States highways (lines) and locality numbers. Map modified from Retallack and Dilcher (1981a).

coastal stream (UF 15708). The Braun Ranch locality (UF 15709) southeast of the intersection of highways 81 and 24 in Kansas is probably a coastal plain fresh-water lake as well (Retallack and Dilcher, 1981a; Farley and Dilcher, 1986). Another locality at Linnenberger Brothers Ranch (UF 15703, 15714) was available for collecting only a few years; recently no collecting has been possible at this site. We mention it here for completeness; very few fragmentary fern remains were recovered from this locality (fig. 23). It represents a swale deposit within a levee (Retallack and Dilcher, 1981a,b; Farley and Dilcher, 1986).

leaf fragments were collected at Hoisington and only leaf fragments were found at Rose Creek (Plate I, 2, 3). This plant was described as a new species by Skog et al. (1992). This genus was documented previously from the Dakota Formation by the presence of megaspores (Kovach and Dilcher, 1988) rather than direct evidence of megafossils. This species documents the presence of Iso~tites megafossils in the formation and confirms the worldwide occurrence of these aquatic heterosporous lycophytes during the late Mesozoic.

Systematic descriptions of the plants

Division SPHENOPHYTA Family EQUISETACEAE

Division LYCOPHYTA Genus Iso#tites Miinster

Isogtites phyllophila J. Skog, Dilcher and Potter (Plate I, 1-3) 1992 Iso~tites phyllophila J. Skog, Dilcher and Potter, Am. Fern. J., 82, p. 152

A complete specimen (Plate I, 1) and isolated

Genus Equisetum L.

Equisetum burchardtii Dunker 1889 Equisetum marylandicum Fontaine, US Geol. Surv. Monogr., 15, p. 65. 1971 Equisetum lyellii Mantell, Rushforth, BYU Sci. Bull. Biol. Ser., 14, p. 14. 1990 Equisetum burchardtii Dunker, Watson and Batten, Bull. Br. Mus. Nat. Hist. Geol., 46, p. 38.

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J.l. SKOGAND D.L. DILCHER PLATE

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I. Whole specimen of lsoe'tites phyllophila J. Skog, Dilcher and Potter. Elongate corm with leaves around sides and top, roots at base. F L M N H 15706-11810. Scale bar = 1 mm divisions. 2. Isolated leaf specimen of Isogtites phyllophila, showing acute apex, entire margins, and lacunae around central vein. U F N M H 15713-11806. Scale bar = 5 ram. 3. Isolated leaf specimen from mid-portion of leaf, showing outer entire margin, outer lacunae, inner thicker portion with lacunae and central vein. U F M N H 15713-11807. Scale b a r = 4 mm. 4. Frond portion of Anemia dicksoniana. U F N M H 15706-11734. Scale bars are 1 mm divisions. 5. Specimen of Anemia dakotensis, showing fronds with slender pinnules as transported into sediment. U F M N H 15709-11909. Scale bar divisions are 1 mm.

LOWER VASCULAR PLANTS OF THE DAKOTA FORMATION IN KANSAS AND NEBRASKA, USA

We found only fragmentary pieces of rhizomes and tubers of this plant at one locality, the Vandra Pit of Acme Brick Company in Kanapolis, KS. Rushforth (1971) also found only the underground stems and tubers in the Utah flora and assigned them to a British species, Equisetum lyellii Mantell, known from the Wealden Formation. He also included Equisetum marylandicum Fontaine in his description. However, in a recent revision of the Equisetales occurring in the Wealden, Watson and Batten (1990) indicated that Equisetum lyellii can be distinguished by its lack of tubers on the rhizome and indicated that Fontaine's various species of Equisetum were probably most similar to the Wealden specimens of E. burchardtii. Therefore we identify this material as E. burchardtii, which is distinguished by many tubers along the rhizome. We indicate that the material from Utah described by Rushforth (1971) represents this species, as both Fontaine's material and our material is similar to it. It is very likely that other specimens of E. lyellii from North America which bear tubers actually represent E. burchardtii. Division PTEROPHYTA Family SCHIZAEACEAE

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to support the presence of this modern genus in the flora and spores of several other genera in Rushforth's lists are present. We believe that the genus Anemia is a better choice for these specimens of ferns because of their similarity to the foliage of many modern species in this genus, the presence of large numbers of spores assigned to the Schizaeaceae in associated sediments, and the documentation of the genus as megafossils in other Cretaceous deposits. The foliage assigned to Asplenium dicksonianum Heer by Rushforth is typical of Anemia foliage and strongly resembles Anemia fremontii foliage described by Andrews and Pearsall (1941) from the Upper Cretaceous of Wyoming. Krassilov (1976) placed the Mesozoic fossil ferns assigned to the species "Asplenium dicksonianum" into the genus Anemia. We have foliage from all localities (Table II) that is identical with this species, thus it appears to be a very common fern of the Dakota flora. Lesquereux (1874, 1883, 1892) described several fern fragments that probably belong to this species. He placed some of them in this species; others he described as Hymenophyllum cretaceum (Lesquereux, 1874) and Sphenopteris corrugata (Lesquereux, 1883). These are better considered as Anemia.

Genus Anemia Swartz

Anemia dicksoniana (Heer) Krassilov (Plate I, 4) 1971 Asplenium dicksonianum Heer, Rushforth. BYU Sci. Bull. Biol. Sci., 14, p. 16. 1976 Anemia dicksoniana (Heer) Krassilov, Tsagayan Flora Amur Region, Moscow, p. 40. 1874 Hymenophyllum cretaceum. Lesquereux, USGS Contrib. Fossil Flora Western Territories, p. 46. 1883 Sphenopteris corrugata Newberry, Lesquereux, USGS Contrib. Fossil Flora Western Territories, p. 26.

Rushforth (1971) assigned two species of foliage to the genus Asplenium, noting that the sterile foliage was difficult to identify and resembled foliage of several ferns, such as Anemia, Onychiopsis, Sphenopteris, Acrostichopteris, Coniopteris, and Dicksonia. Unfortunately Asplenium was chosen mainly based upon Heer's descriptions of the genus from the Cretaceous beds of Greenland. There are no spores of Asplenium

A hernia dakotensis (Rushforth, 1971) Skog and Dilcher, comb. nov. Basionym: Asplenium dakotensis Rushforth, 1971, BYU Sci. Bull. Biol. Ser., 14: 16. The second species probably belonging to this genus has much narrower wedge-shaped pinnules and resembles specimens that have been assigned to Sphenopteris goeppertii in other floras. It is probably the same species that Rushforth assigned to Asplenium dakotensis from Utah, which also belongs to the Schizaeaceae rather than to Asplenium. It is probable that the tiny fragment Lesquereux (1874) described as Lygodium trichomanes also belongs to this species; however, the specimen consists only of a rachis fragment and the base of a single pinnule. Based upon the

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J.E. SKOGAND D.L. DILCHER PLATE

II

6. Specimen of a portion of a frond of Gleichenia comptoniaefolia with variable pinnule shape. Associated conifer remains also can be seen here. U F M N H 18057-11845"d. Scale bar divisions are 1 ram. 7. Portion of frond of G. comptoniaefolia showing rounded pinnule apices and venation pattern. U F M N H 18057-11845'b. Scale bar divisions are 1 ram. 8. Frond of Gleichenia delicatula with narrower pinnules. U F M N H 18057-11834. Scale bar divisions are 1 mm. 9. Enlargement of frond of G. delicatula showing narrower and more angular pinnules. U F M N H I8057-1 I839'a. Scale bar divisions are 1 mm.

LOWERVASCULARPLANTSOF THE DAKOTAFORMATION IN KANSASAND NEBRASKA,USA TABLE II Lower vascular plants listed by the localities in which they occur based upon this study Rose Creek

Braun Ranch

Hoisington

Acme Brick

Linnenberger Brothers

Gleichenia comptoniaefolia Gleichenia delicatula Anemia dakotensis Anemia dicksoniana Coniopteris hymenophylloides Coniopteris simplex? Cladophlebis constricta Cladophlebis parva Cladophlebis inclinata (Osmunda) Matonidium brownii Matonidium americanum Iso(tites phyllophila

G. G. A. A.

G. G. A. A.

G. G. A. A.

G. comptoniaefolia G. delicatula

comptoniaefolia delicatula dakotensis dicksoniana

comptoniaefolia delicatula dakotensis dicksoniana

comptoniaefolia delicatula dakotensis dicksoniana

A. dicksoniana

C. constricta

M. brownii L phyllophila Equisetum burchardtii Marsilea johnhallii

incomplete specimen available, we do not wish to assign it to this species with confidence. Family GLEICHENIACEAE

were placed in the species G. kurriana and G. nordenskioldii; however, Rushforth considers these to be conspecific and in most cases we agree. There are, however, small fragments in the Lesquereux collections that may represent Gleichenia delicatula (see below).

Genus Gleichenia Smith Rushforth (1971) reviews the previously named fossil species within the genus Gleichenia reported from the Mesozoic and reports only two species from the Dakota Formation. Both species are abundant at our localities and we maintain the same specific epithets used by Rushforth. Gleichenia comptoniaefolia (Debenham and Ettinghausen) Heer (Plate II, 6, 7) 1874 Gleichenia comptoniaefolia (Debenham and Ettinghausen) Heer, Flor. Foss. Arct., v. 3 pt. 2, p. 49. 1971 Gleichenia comptoniaefolia (Debenham and Ettinghausen) Heer, Rushforth, BYU Sci. Bull., 14, p. 20.

This species has pinnules that are distinct, with venation from a midvein which then divides into numerous laterals (Plate II, 7). Pinnule size is quite variable (Plate II, 6), but the apex of the pinnules tends to be rounded. These ferns were found as small fragments by Lesquereux in his studies and

Gleichenia delicatula Heer (Plate II, 8, 9) 1874 Gleichenia delicatula Heer, Flor. Foss. Arct., v. 3, pt. 2, p. 54. 1971 Gleichenia delicatula Heer, Rushforth, BYU Sci. Bull., 14, p. 27.

The pinnule morphology of Gleichenia delicatula is very similar to that of G. comptoniaefol& but the pinnules are more angular and the veins reach the pinnule margin after dividing from the midvein; the midvein is distinct at the base but immediately divides into the laterals. These two species of Gleichenia are the most common ferns in the Dakota Formation flora and occur at every locality pterophytes have been collected (Table II), although sometimes the small size of the fragments suggests long distance transport. It is likely that these ferns grew in dense stands as Gleichenia does today, and the tough pinnules were carried along streams to be deposited in areas away from their site of growth. Gleichenia

0 C~ > z

LOWER VASCULAR PLANTS OF THE DAKOTA FORMATION IN KANSAS AND NEBRASKA, USA

may have been a major component of the fern "savannas or prairies" discussed later.

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species is considered to belong to the modern genus Matonia by von Konijnenburg van Cittert (1993) in her study of the genus.

Family MATONIACEAE Family DICKSONIACEAE Genus Matonidium Schenk Genus Coniopteris Brongniart Two species of this genus can be identified in the Dakota flora. Rushforth (1971) also had two other foliage types one of which he assigned to a new variety and the other of which he assigned to a new species with some uncertainty. We do not have enough material to draw such distinctions and therefore recognize only two species in the eastern floral region of the Dakota Formation.

Matonidium americanum Berry (Plate III, 10) 1918 Matonidium americanum Berry, Bull. Torrey Bot. Club, 46, p. 287 1970 Matonidium americanum Berry em. Rushforth, BYU Geol. Stud., 16, p. 25

This species can be distinguished from Matonidium brownii by its regular linear pinnules and pinnae. The pinnules are rounded at the apex and have a prominent midvein.

Matonidium brownii Rushforth (Plate III, 11, 12) 1970 Matonidium brownii Rushforth, BYU Geol. Stud. 16, p. 9 This species has more irregularly shaped pinnules than M. americanum, the apex of the pinnule is acute and the pinnules are longer at the apex of the pinna, whereas at the base of the pinna they are short and rounded. We have fragments that represent the midsection of these pinnae (Plate III, 11) and the basal portions (Plate III, 12). This

Coniopteris hymenophylloides (Brongniart) Seward (Plate III, 13, 14) 1900 Coniopteris hymenophylloides (Brongniart) Seward, Catalogue Mesozoic plants in Dep. Geol., Br. Mus., 3, p. 99

Although Rushforth commented on the large number of species within this widespread Mesozoic genus and noted that not all of them represent good species, he created a new species (C. westwaterensis) for the Dakota material from Utah and compared it to C. bella Harris and C. burejensis (Zalessky) Seward with the difference being that C. westwaterensis has the fertile portion of the foliage occurring as apically reduced pinnae. Only one small foliage fragment is illustrated and the fertile pinnules are difficult to distinguish. LaPasha and Miller (1985) found Coniopteris in the Kootenai Formation of Montana that exhibited variability in pinnule form that included C. hymenophylloides, C. bella and C. burejensis. They placed their material in the species C. hymenophylloides. It is likely that our material is the same as the Utah specimen (Plate III, 14), but we do not have fertile material. We do have variable pinna sizes in our collections that could be due to the differences in sterile and fertile material or to the presence of two separate species, but lacking better material we assign all our specimens to Coniopteris hymenophylloides (Brongniart) Seward. The best

PLATE III Pinna fragment of Matonidium americanum. U F M N H 15713-11106. Scale bar divisions are 1 mm. Pinna fragment of Matonidium brownii showing irregularly sized pinnules. U F M N H 15706-11732. Scale bar divisions are 1 mm. Basal portion of pinna o f M. brownii. U F M N H 15706-11730. Scale bar = 5 mm. Pinna fragment of Coniopteris hymenophylloides (C. simplex?) with narrower pinnules. U F M N H 18057-11830. Scale bar divisions are 1 mm. 14. Pinna tip of Coniopteris hymenophylloides with broad pinnules narrowing to the tip of the pinna. U F M N H 15713-11105'. Scale bar divisions are 1 mm. I0. 11. 12. 13.

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J t SKOGAN[) D.L. DILCHER

PLATE IV

15. Bipinnate frond portion of Cladophleb& parva, showing venation pattern in pinnules. U F M N H 15713-1t 104. Scale bar divisions are I ram. 16. 17. 18. 19.

Bipinnate frond tip of Cladophleb& constricta, showing pinnule venation. U F M N H 15709-3117. Scale bar divisions are 1 mm. Pinna fragment of Cladophleb& inclinata showing pinnute venation. U F M N H 18057-11811. Scale bar divisions are 1 mm. Pinna fragment of smaller pinnules (fertile?) of C. inclinata. U F M N H 18057-11841. Scale bar = 5 ram. Bipinnate frond portion of C. incl&ata. U F M N H 15713-12646. Scale bar = 5 mm.

LOWER VASCULARPLANTSOF THE DAKOTAFORMATION IN KANSASAND NEBRASKA,USA

specimens of this fern occur at the Rose Creek locality. We note, however, that the difference between the narrow pinnules (Plate III, 13) and the wider pinnules (Plate III, 14) could have been considered distinct and there may be a second species represented by the narrower lobed pinnules, Coniopteris simplex (Lindley and Hutton) Harris. LaPasha and Miller (1985) suggest that ~his species is a swamp dweller which is supported by our finding it only at Rose Creek. However, some modern dicksoniaceous ferns (e.g. Culcita) form thickets of undergrowth in drier regions. INCERTAE SEDIS

Genus Cladophlebis Brongniart These three species of fern foliage are most likely representatives of the Matoniaceae or Osmundaceae, both of which occur in the Dakota Formation microfossil flora. However, since we have only sterile fragments of foliage, we are not assigning them to a particular family but retain them within this form genus. All three species are abundant at the Rose Creek locality and are occasionally found at other localities.

Cladophlebis parva Fontaine (Plate IV, 15) 1889 Cladophlebis parva Fontaine, USGS Monogr., 15, p. 73. 1971 Cladophlebis parva Fontaine, Rushforth, BYU Sci. Bull., p. 36. 1874 Pecopteris nebraskana Heer, Lesquereux, USGS Contrib. Fossil Flora Western Territories, p. 46.

In the Utah deposits, Rushforth (1971) recognized small pinnules with slightly undulate margins and distinctive venation as Cladophlebis parva. This fern clearly has a bipinnate frond.

Cladophlebis constricta Fontaine (Plate IV, 16) 1889 Cladophlebis constricta Fontaine, USGS Monogr., 15, p. 68. 1971 Cladophlebis constricta Fontaine, Rushforth, BYU Sci. Bull., p. 36. 1893 Pteris dakotensis Lesquereux, USGS Mon. 17, p. 24.

The other species recognized by Rushforth is Cladophlebis constricta with lobed pinnules larger

I1

than C. parva. The midvein in this species is strong and the lateral veins divide dichotomously ending at the margin.

Cladophleb& inclinata Fontaine (Plate IV, 17-19) 1889 Cladophlebis inclinata Fontaine, USGS Monogr., 15. p. 47 1985 Cladophlebis inclinata Fontaine, LaPasha and Miller, Palaeontographica B, 196, p. 17.

LaPasha and Miller (1985) noted that this species in the Kootenai Formation is similar to Cladophlebis acuta, C. oblongifolia and C. virginiensis, which were also described by Fontaine (1889). All these species are similar in pinnule morphology and venation and may simply be variations found in different localities or sediment or from different parts of the plant. We find some smaller pinnules (Plate IV, 18) that might have been fertile pinnules but could not determine this because of poor preservation. Most commonly our specimens are single pinnae (Plate IV, 17), but occasionally we find bipinnate portions of a frond (Plate IV, 19). This species most closely resembles fronds of the Osmundaceae.

Family MARSILEACEAE

Genus Marsilea L.

Marsileajohnhallii J. Skog and Dilcher (Plate V, 20-22) 1992 Marsileajohnhallii J. Skog and Dilcher, Am. J. Bot., 79, p. 983.

This fern definitively documents the presence of the genus Marsilea in the Dakota Formation confirming previous references based on megaspores (Kovach and Dilcher, 1988). Skog and Dilcher (1992) published a complete description of this fern based on whole plants (Plate V, 20, 22) and several specimens of individual leaflets (Plate V, 21). The fern is known only from Hoisington in a probable pond or levee swale deposit.

12 PLATE

J l SKOGAND I).L. DILCHER V

20. Whole plant of Marsilea johnhallii. Rhizome, roots at nodes, and one set of leaflets can be seen. U F M N H 15706-8273. Scale bar divisions are 1 mm. 21. Isolated leaflet of M. johnhallii showing typical venation pattern and crenate margin. U F M N H 15706-8272. Scale bar = 5 m m 22. Rhizome, with attached roots and frond with four pinnules of M. johnhallii. U F M N H 15706-8274. Scale bar divisions are 1 mm. 23. Piece of matrix from Linnenburger Brothers locality showing very fragmentary remains of ferns (arrows indicate two of the larger remains). U F M N H 15714-12644. Scale b a r = 1 cm.

LOWER VASCULAR PLANTS OF THE DAKOTA FORMATION IN KANSAS AND NEBRASKA, USA

General discussion

Distribution oflower vascular plant species by localities Five localities - Rose Creek, Braun Ranch, Hoisington, Acme Brick and Linnenberger Brothers - were studied in this investigation (Table II) but the first four supplied most of the data for the following discussion. The Rose Creek locality, which represents a shallow lake or swamp flora, has the most diverse and abundant lower vascular plant flora. The species of lower vascular plants found at Rose Creek are listed in Table II. Rose Creek has been the most intensely studied of any of the Dakota Formation plant-bearing localities and detailed data are now available for both the miospores (Farley and Dilcher, 1986) and the angiosperm megafossils (Upchurch and Dilcher, 1990). Upchurch and Dilcher (1990) concluded that the angiosperm leaves from Rose Creek were probably deposited in brackish water and probably represented plants that were present in the local flora. Whether the ferns reported here are also of local origin is questionable, particularly because the sediment yielding the most ferns is a darker clay seam interbedded with sandier layers. This is in a new area of the pit that was only partially exposed before 1990. These fern-rich sediments may reflect deposition about 20 to 30 m further inland. The same species of plants are found in both the initial excavations of the pit and the later excavations. The only difference in the megafossils from the different parts of the pit appears to be the size and completeness of the megafossils recovered which probably correlate to the size of the blocks exposed while collecting. This larger size of specimens allowed for more complete specimens and thus more precise identification of the species. Rose Creek has the highest percentage diversity of lower vascular plants of all the microfossil floras reported by Dilcher and Farley (1988). Thus the pteridophyte spore diversity (59%) far surpasses that of pollen types (16.7% angiosperm pollen, 24.4% gymnosperm pollen) (Fig. 2). With the increased number of fern species known as megafossils the great differences between micro-

13

fossil and megafossil floral diversity as reported by Dilcher and Farley (1988) and Lidgard and Crane (1988) are reduced. Rather than 75-95% of the megafossils being angiosperm species as previously reported, in the Rose Creek locality (Fig. 2), the angiosperms now represent 55% of the flora (21 species of Upchurch and Dilcher, 1990) and the pteridophytes 33% (12 species reported here). Angiosperms dominate the megafossil record while the pteridophytes dominate the microfossil record when total number of species are considered. This difference between the megafossil and microfossil data might be explained by the inflated taxonomic differences in miospores of pteridophytes compared to the angiosperms and the more dominant leaf representation of the angiosperms (Farley and Dilcher, 1986). The other localities are not nearly as rich in species as Rose Creek, nor are thorough analyses of the angiosperm species complete. Ferns from Braun Ranch include the two Anemia species, Cladophlebis constricta, and the Gleichenia species. This locality also has been analyzed for the miospore species present (Fig. 2) and currently the large number of reproductive parts of angiosperms are being studied. Dilcher and Farley (1988) noted that at this locality the small number of miospore species may cause the percent values to be unreliable. With increased studies of the Braun locality a better estimate of the total flora composition will result. Hoisington clay pit species are listed in Table II and include two aquatics, Iso~tites phyllophila and Marsilea johnhallii, indicating its probable origin as a pond deposit. The presence of these two aquatic genera along the eastern coastal areas of the midcontinent seaway is interesting. There is evidence for Iso~tites in other Cretaceous deposits throughout the world but the genus is spread more widely later in the Cretaceous. Marsilea also becomes more common in the late Cretaceous. The occurrence of this aquatic fern as a megafossil is very rare and most often it is the presence of the megaspores that document its presence. Today these plants are dispersed by aquatic birds and we suggest that the shore birds of the Cretaceous (for examples, see Brodkorb, 1963; Olson, 1985) could be responsible for increasing the distribution of

14

•.v_ SKOG AND D.L. DILCHER

PERCENT MEGAAND MICROFOSSILSPECIES 120-

100-

80O3

©

60-

Z 40

20,

RC+

RC-

BR+

BR-

LB+

LB-

Fig. 2. Graph of percent megafossil species present ( + ) and percent miospore species ( - ) at Rose Creek (RC), Braun Ranch (BR) and Linnenberger Brothers (LB) based upon our megafossil information and miospore information from Dilcher and Farley (1988).

these two plants. Unfortunately it has been impossible to successfully prepare miospores from the sediments at Hoisington; however, many additional megafossil specimens of gymnosperms and angiosperms were collected and are being studied. Acme Brick clay pit has both species of Gleichenia and both species of Anemia. Rhizomes and tubers of Equisetum burchardtii, a plant that would probably be found along the banks of streams, occur in this deposit. This locality has been suggested as an overbank deposit (Retallack and Dilcher, 1981 a). Linnenburger Brothers locality is extremely poor in pteridophytes despite extensive collections and the very small fragments collected there represent the two species of Gleiehenia and one probable Anemia dicksoniana (Plate V, 23). This locality has miospores representing 54% pteridophytes, with the angiosperm and gymnosperm pollen being about equal, 24.5 and 21.4%, respectively (Fig. 2). The depauperate flora of lower vascular plants from some of these localities is most likely related to the depositional environments. These localities are streams or lakes where the fragments of plants

would have drifted into the stream or lake from shore plants or been carried in with streams flowing into the lakes and larger tributaries. Most of the plant parts carried into these lakes and rivers were deciduous organs such as leaves, floral parts, fruits and twigs. The fern leaves were probably not deciduous. This would reduce the number available to be dispersed into the sedimentary environment. Also complete fern fronds are unlikely to survive much abrasion as they were carried by the streams, as indeed are compound angiosperm leaves (Retallack and Diicher, 1981a). The common fern species tend to have thick pinnules and be thicket formers probably with more sclerenchymatous rachides. Rose Creek, on the other hand may have been a shallow lake or a swamp environment, where the leaves would have dropped into a muddy and probably more acidic environment and there was most likely a thicker layer of humus built up under the vegetation. Conditions were probably more favorable for fossilization there. Thus, the Rose Creek flora is more reliable for comparative purposes in an overall assessment of the lower vascular plants present during the mid-Cretaceous.

LOWER VASCULAR PLANTS OF THE DAKOTA FORMATION IN KANSAS AND NEBRASKA, USA

Only three of these localities have been examined for miospores (Farley and Dilcher, 1986; Dilcher and Farley, 1988). The environments as interpreted in their papers were a levee swale at Linnenberger Ranch, lake deposits at Braun Ranch and distributary margin at Rose Creek. They note that the sediments are dominated by fern spores in the microfossil data whereas the megafossil dominants are the angiosperms. Figure 2 summarizes the percent species from their data for the miospores and our data for the megafossils. Reasons they suggest for the difference in miospore data and megafossil data are: the local abundance and fecundity of ferns for spores while megafossils are biased by greater production of dedicuous leaves and reproductive organs of angiosperms, and by lower susceptibility of angiosperm fragments to decay (Farley and Dilcher, 1986). Their data also show that some miospore taxa occur preferentially in some environments: e.g. Gleicheniidites confossus in swamp or levee swale at Linnenberger Brothers' Ranch. Megafossil plant debris studies by Kovach and Dilcher (1988) and Kovach (1988) also show locality differences. Two isoetalean megaspores and one species of Arcellites (a megaspore of Marsilea) were found at several localities where transport along rivers is inferred.

Comparisons to other published research Our recent studies on the lower vascular plant flora from the Dakota Formation sediments in central Kansas and Nebraska provides further clarification of several points raised in previous studies. The earliest concept of the Dakota flora was that it was essentially a modern flora lacking fossils of antecedent floristic types. Conifers and ferns were few in number and a minor component of the flora (Lesquereux, 1874) and even with later additions (Lesquereux, 1883, 1892) angiosperms represented 92.6% of the total flora. Even for the angiosperms this was a "falsely modern aspect" (Upchurch and Dilcher, 1990) and led to numerous misinterpretations in the understanding of angiosperm evolution. Previous research of the Dakota Formation ferns had been done mainly on localities in Utah,

15

west of the inland sea that spanned the central portion of North America. The vegetation of the eastern and western shores of this seaway were thought to be distinct due both to the separation and supposed isolation created by the sea barrier and also to the unique environment in the western area because of mountains forming nearby (Vakhrameev, 1991). Vakhrameev (1991) noted the different floristic nature of the Dakota flora in the eastern deposits from those to the west, commenting that in the eastern region ferns were extremely rare. He postulated that the climate of the eastern region was less humid than other areas to explain this difference. CockereU (1916), Berry (1919, 1922), and Brown 0950) presented Matoniaceae and Gleicheniaceae as very common components of the flora in the western deposits of the Dakota Formation. Rushforth (1971) concluded that the fern component was representative of an Early Cretaceous/Jurassic vegetation that was more dominant in the west than in the east where he suggested that the angiosperms dominated while ferns and gymnosperms were minor components. Rushforth based his conclusions on the large numbers of matoniaceous and gleicheniaceous ferns that are present in many of the deposits west of the Rocky Mountains and their apparent paucity in the east. Microfloral analysis (May and Traverse, 1973) in the western area indicated that during the later Cenomanian the abundance of spores dropped below 50% in the microflora and that the dominance of groups of plants changed from locality to locality. This decrease in pteridophyte groups and increase in angiosperm groups, although not at all localities, was reflected in the diversity of megafossils (Crane, 1987). Miospore analyses (Pierce, 1961, Hall, 1963) indicated that ferns and gymnosperms were much more dominant in the eastern flora than was indicated by the megafossils. Pierce (1961) suggested that the disagreement between the Cretaceous microflora (gymnosperms dominant) and the megaflora (angiosperms dominant) may have been due to the dissection of the Dakota Formation into plant communities in stages of succession. The angiosperms from the primary communities of the river banks, lakes, and deltaic areas were preserved as leaves in the megafossil

16

record. The climax and other diverse communities of the area were mixed in the microfloral record where the conifers appear dominant. More recent work on miospores of the eastern Dakota flora supports the dominance of ferns and gymnosperms in both abundance and diversity and indicates that various environments had a distinct miospore flora (Farley and Dilcher, 1986; Dilcher and Farley, 1988) supporting the work done in the western deposits (May and Traverse, 1973). However, the megafossil reports for floras in the western areas of the North American continent (summarized by Rushforth, 1971) suggests that ferns may be more dominant in the flora in some localities and the angiosperms may dominate at other localities. He contrasted this with the work done on the flora of the eastern coastal plain of the continental seaway, where in the megafloral studies it appears that the angiosperms form the dominant part of the flora. In this paper we document the presence of the lower vascular plants at several localities in Kansas and Nebraska and try to emphasize that the eastern coastal plain Dakota flora is not as distinct from the western regions as previously suggested by Rushforth (1971) (Table I). Furthermore, there is less discrepancy between the presence of the pteridophytes found in the microfloral record and the megafloral record than has been reported earlier (Fig. 2). The megafossil record indicates that the Rose Creek locality, where we have 12 species of ferns documented in the megafossils, has the highest diversity of pteridophytes (Table II). The other localities have fewer pteridophytes represented by the megafossil record and we propose that these differences are a reflection of the environment of deposition and not caused by a depauperate flora that existed in the eastern area of the Dakota Formation as was suggested by Vakhrameev (1991). In fact both prior and new collections indicate few differences between the lower vascular plants present in the Utah deposits and those in the Kansas/Nebraska deposits. Of the 12--14 species described by Rushforth (1971) in the western regions all but two are probably present in the Dakota Formation collections from Kansas and Nebraska. There are two additional species (the aquatics) present in the eastern region not yet

J l : . S K O G A N D D.L. D I L C H E R

reported in the western area (Table I). It should be noted that the Rushfortb report was based upon ash deposits and the difference is likely due to the environment rather than the geography. The two species found in Utah and not present in our collections are Hausmannia rigida in the Dipteridaceae and Astralopteris coloradica placed in the Polypodiaceae by Rushforth (1971). The description of the latter suggests that this fern might be better placed in the Matoniaceae and the spore record of this family is also diverse. The Matoniaceae and Dipteridaceae survive together today at high altitudes in southeast Asia (Bower, 1926). There are also locality differences reflected in the megafossil data that parallel those suggested by Kovacb (1988) and Farley and Dilcher (1986) for the palynological record. The Rose Creek locality, which is the most diverse, is very likely swamp and swale deposits: the lake deposits have far fewer pteridophyte species represented. The Linnenberger locality has Gleichenia delicatula represented as a common megafossil and commonly had Gleicheniidites found as a microfossil. The clay pit at Hoisington, which is probably a pond and swale area has the aquatic pteridophytes Marsilea and IsoO'tites as megafossils and aquatic angiosperms represented (Retallack and Dilcher, 1981b). The swamp locality at Rose Creek has several species of Cladophlebis that probably represent the Osmundaceae or Matoniaceae and Coniopteris representing the Dicksoniaceae. The most commonly found ferns are the Gleicheniaceae and the genus Anemia in the Schizaeaceae which agrees with the widespread abundance of these two families in the microfossil record. Changes of the pteridophyte flora in the forest/ swamp localities do not appear to have happened prior to the Cenomanian, and May and Traverse (1973) report that during the middle of the Cenomanian the pteridophyte miospore record dropped below 50% of the flora as the relative abundance of angiosperm pollen increased. The dominance of plant types changed from area to area in the younger deposits considered in their study. Our megafossil diversity supports this view, as the numbers of species reported at Rose Creek (lowermost Cenomanian) show higher percentages

LOWER VASCULAR PLANTS OF THE DAKOTA FORMATION IN KANSAS AND NEBRASKA, USA

of pteridophytes and lower percentages of angiosperms than the typical Cenomanian floras (as defined by Lidgard and Crane, 1988). The advent of new fern types suggests that a more modern vegetation can occur later in the fossil record than these deposits reflect or in communities further removed from these swamp and swale areas. The families of pteridophytes that were dominant during the earlier Mesozoic are still dominant at this point in these communities, even though angiosperms were becoming more diverse. We support the idea of a major dominance of ferns as understory and thicket-forming plants at this time ("fern savannas and prairies"; Coe et al, 1987). Those fern families that we find in greatest abundance, Gleicheniaceae, Matoniaceae, and to a lesser extent Schizaeaceae are ferns that today have species which can form expanses of vegetation in open areas or as undergrowth in more open forests. Even the Dicksoniaceae today contains species that may form an undergrowth thicket. Direct evidence for fern "savannahs" has been noted by Wing (1992) for the Maastrichtian. He concludes that angiosperms may be taxonomically dominant, but not ecologically so. Our evidence from the Dakota Formation indicates that the same taxa of pteridophytes were distributed widely over the eastern coastal plain in numerous localities during the Cenomanian. These same species were reported from the Cenomanian western land masses of North America, often in abundance (Rushforth, 1971). It is quite probable that these fern savannas remained as a vegetation type throughout the Cretaceous.

Acknowledgments The authors thank numerous colleagues for help with the previous field collections and the new collections made for this project. Help with the new collections was provided by: Terry Lott, Michael Muller, Alicia Lesnikowska, James Landon, John Jones, Stephan Imhof, and Francis Raven. We thank Donald Suciu for aid in data collection of the number of megafossil species at each locality and J. Galtier and P. Crane for helpful comments on the manuscript. This research

17

was supported by NSF grants RII-9002663 to JES and DEB 7910720 to DLD.

References Andrews, H.N. and Pearsall, C.S., 1941. On the flora of the Frontier Formation of southwestern Wyoming. Ann. Mo. Bot. Gard., 28: 165-192. Berry, E.W., 1919. A new Matonidium from Colorado, with remarks on the distribution of the Matoniaceae. Bull. Torrey Bot. Club, 46: 285-294. Berry, E.W., 1922. The flora of the Cheyenne Sandstone of Kansas. US Geol. Surv. Prof. Pap., 129-1: 199-226. Bower, F.O., 1926. The Ferns, Vol. II. Cambridge Press, Cambridge, 344 pp. Brodkorb, P., 1963. Birds from the Upper Cretaceous of Wyoming. Proc. 13 Ornithol. Congr. Baton Rouge, LA, pp. 55-70. Brown, R.W., 1950. Cretaceous Plants from Southwestern Colorado. US Geol. Surv. Prof. Pap., 221-D: 45-66. Cockerell, T.D., 1916. A lower Cretaceous flora in Colorado. J. Wash. Acad. Sci., 6: 109-112. Coe, J.J., Dilcher, D.L., Farlow, J.O., Jarzen, D.M. and Russell, D.A., 1987. Dinosaurs and land plants. In: E.M. Friis, W.G. Chaloner and P.R. Crane (Editors), The Origins of Angiosperms and their Biological Consequences. Cambridge Univ. Press, Cambridge pp. 225-258. Crane, P.R., 1987. Vegetational consequences of the angiosperm diversification. In: E.M. Friis, W.G. Chaloner and P.R. Crane (Editors), The Origins of Angiosperms and their Biological Consequences. Cambridge Univ. Press, Cambridge, pp. 107 144. Dilcher, D.L. and Farley, M.B., 1988. Cenomanian miospores and co-occurring megafossils in the midcontinent of North America. 7th Int. Palynol. Congr., Brisbane, Abstr., p. 39. Farley, M.B. and Dilcher, D.L., 1986. Correleation between miospores and depositional environments of the Dakota Formation (mid-Cretaceous) of north-central Kansas and adjacent Nebraska. Palynology, 10: 117-134. Fontaine, W.M., 1889. The Potomac or younger Mesozoic flora. US Geol. Surv. Monogr., 15, 377 pp. Hall, J.W., 1963. Megaspores and other fossils in the Dakota Formation (Cenomanian) of Iowa. Pollen Spores, 5: 425-443. Heer, 1874. Die Kreideflora der arctischen zone. Flora Fossil. Arctic, 3, 2, 138 pp. Kovach, W.L., 1988. Quantitative palaeoecology of megaspores and other dispersed plant remains from the Cenomanian of Kansas, USA. Cretaceous Res., 9: 265-283. Kovach, W.L. and Dilcher, D.L., 1988. Megaspores and other dispersed plant remains from the Dakota Formation (Cenomanian) of Kansas, U.S.A. Palynology, 12: 89-119. Krassilov, V.A., 1976. Tsagayan Flora of Amur Region. Nauka, Moscow, 92 pp. (in Russsian). LaPasha, C.A. and Miller, C.N., 1985. Flora of the early Cretaceous Kootenai Formation in Montana, Bryophytes and Tracheophytes excluding conifers. Palaeontographica B, 196: 111-145.

18 Lesquereux, L., 1874. Contributions to the fossil flora of the Western Territories - Part 1, the Cretaceous flora. US Geol. Geogr. Surv. Terr. Rep., 6: 1-136. Lesquereux, L., 1883. The Cretaceous and Tertiary floras. US Geol. Geograph. Surv. Terr. Rep., 9: 1-283, Lesquereux, L., 1892. The flora of the Dakota Group. US Geol. Surv. Monogr., 17: 1-256. Lidgard, S. and Crane, P.R., 1988. Quantitative analyses of the early angiosperm radiation. Nature, 331:344 346. May, F.E. and Traverse. A., 1973. Palynology of the Dakota Sandstone (Middle Cretaceous) near Bryce Canyon National Park, southern Utah. Geosci. Man, 7: 57-64. Olson, S.L., 1985. The fossil record of birds. In: D.S. Farner, J.R. King and K.C. Parkes (Editors), Avian Biology. Academic Press, New York, NY, Vol. 8, pp. 79-238. Pierce, R.L., 1961. Lower Upper Cretaceous plant microfossils from Minnesota. Minn. Geol. Surv. Bull., 42: 1-86. Retallack, G. and Dilcher, D.L., 1981a. A coastal hypothesis for the dispersal and rise to dominance of flowering plants. In: K.J. Niklas (Editor), Paleobotany, Paleoecology and Evolution. Praeger, New York, NY, Vol. 2, pp. 27-77. Retallack, G. and Dilcher, D.L., 1981b. Early angiosperm reproduction: Prisca reynoldsii, gen. et sp. nov. from midCretaceous coastal deposits in Kansas, U.S.A. Palaeontographica B, 179: 103-137. Retallack, G. and Dilcher, D.L., 1986. Cretaceous angiosperm invasion of North America. Cretaceous Res., 7: 227-252. Rushforth, S.R., 1971. A flora from the Dakota sandstone

J.E. SKOGAND D.L. DILCHER formation (Cenomanian) near Westwater, Grand County, Utah. Brigham Young Univ. Sci. Bull. Biol. Ser., 14:1 44. Seward, A.C., 1900. The Jurassic Flora. 1. The Yorkshire Coast. Catalogue of the Mesozoic Plants in the Department of Geology, British Museum (Natural History), 3. London, 341 pp. Skog, J.E. and Dilcher, D.L., 1992. A new species of Marsilea from the Dakota Formation in central Kansas. Am. J. Bot., 79: 982-988. Skog, J.E., Dilcher, D.L. and Potter, F.W., 1992. A new species of IsoYtites from the mid-Cretaceous Dakota Group of Kansas and Nebraska. Am. Fern J., 82: 151-16l. Upchurch, G.R. Jr. and Dilcher, D.L., 1990. Cenomanian angiosperm leaf megafossils, Dakota Formation, Rose Creek locality, Jefferson County, Southeastern Nebraska. US Geol. Surv. Bull., 1915: 1-55. Vakhrameev, V.A., 1991. Jurassic and Cretaceous Floras and Climates of the Earth. Cambridge Univ. Press, Cambridge, 318 pp. Van Konijnenburg-van Cittert, J.H.A., 1993. A review of the Matoniaceae based on in situ spores. Rev. Palaeobot. Palynol., 78:235 267. Watson, J. and Batten, D.J., 1990. A revision of the English Wealden Flora, II. Equisetales. Bull. Br. Mus. Nat. Hist. Geol., 46: 37-60. Wing, S.L., 1992. Exceptional Maastrichtian flora shows that high diversity does not imply ecological dominance. Geol. Soc. Am. Abstr. Prog., 1992: 271.