Judith E. Skog

Biogeography of Mesozoic leptosporangiate ferns related to extant ferns

The paleobiogeography of the extant leptosporangiate fern families present in the Mesozoic is reviewed based mainly on data from megafossils that possess enough characters to be assigned to a family. Times of first appearances are discussed for each family, followed by their distribution throughout the Mesozoic. Paleolatitudes and climatic conditions indicate that first appearances of many fern families occur about or above 30° and in conditions of higher moisture. Much of fern distribution in the past was likely due to long-distance dispersal.

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

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 ac>e) 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.

The lower cretaceous ferns in the genus Anemia (Schizaeceae), Potomac group of Virginia, and relationships within the genus

Abstract Based on characters of the fertile fronds, two species of fossil ferns from the Lower Cretaceous Potomac Group of the U.S.A., originally described as species of Osmunda by Fontaine in 1889, are transferred to the genus Anemia. The two species display primitive characters for that genus. Analysis of these and other characters of Anemia and related species, using parsimony and compatibility programs, suggests possible phylogenetic arrangements and facilitates delimination of three taxonomic units within Anemia that were already distinct during Cretaceous time. The subgenera Coptophyllum and Anemia are shown to be paraphyletic in the suggested phylogenies and the schemes agree with the known stratigraphy of the fossil ferns.

Two early mississippian seeds from the price formation of Southwestern Virginia

Lagenospermum imparirameum Arnold, originally described from a few specimens of cupulate seeds borne on two or three times dichotomous branches, is now shown to be borne on more complex branching systems. Details of the cupule and seed morphology are added and an emended diagnosis of the taxon is given. A new species,Gnetopsis hispida, is described as the third occurrence of this genus and the first occurrence in beds of Lower Mississippian Age in North America. The classification, evolutionary implications, and dispersal biology are discussed for each of the seeds

A new species of Isoëtites from the mid-Cretaceous Dakota group of Kansas and Nebraska

The Isoetaceae is considered to be a monotypic family with about 150 species (Tryon and Tryon, 1982). They note that some authors place fossils in the genus Isoetites Munster (1842). Isoetes as a genus has been assigned to fossil plants that look like Isoetites but differ in stem or leaf morphology or in which some plant part is lacking. Isoetites has been used for compressions of sporophylls which may be isolated or attached to cormlike stems. Megaspores associated with some megafossils resemble the dispersed spore genus Minerisporites (Collinson, in press). Isoetites has been reported from the Triassic and Jurassic; however these earlier fossils are of uncertain relationships. Assignments of fossil material to the Isoetaceae are questionable before the early Cretaceous (Skog & Hill, 1992). The concept of the family may be at variance with that presented by Tryon and Tryon (1982) when fossil forms are included (see Pigg, 1992; Skog & Hill, 1992; for review papers).

Two new fossil matoniaceous stem genera from Tasmania, Australia

Two new genera, Tasmanopteris and Heweria, from Tasmania are the first definite permineralized rhizomes assignable to the Matoniaceae. Tasmanopteris richmondii sp. nov., of mide-Mesozoic age, is from the Lune River site in southwestern Tasmania and is composed of four or more annular solenostelos separated by cortices with an inner mesarch xylem ring and outer exarch xylem rings. Secretory canals occur in the cortices between the protoxylem clusters of its outer xylem rings. The specimen of Heweria kempii sp. nov., which is very similar to extant Matonia, was collected from a Lower Tertiary conglomerate in central Tasmania but was reworked from older sediments. Anatomically, the rhizomes of Heweria consist of 3–6 annular solenosteles with the inner and middle xylem rings being mesarch, whereas the outer ring is exarch. Roots arise opposite the protoxylem clusters of the outermost ring. Epidermal hairs on the stems of this genus are like those of living Matonia in being attenuate, uniseriate, and multicellular. Associated venation pattern of partially preserved leaves, isolated sporangia, annuli, and spores in this specimen provide additional support for the relationships of this fossil to modern Matonia.

Two new species of Solenostelopteris from the Upper Jurassic Morrison Formation in Wyoming and Utah

Abstract Permineralized rhizomes of two new species of Solenostelopteris Kershaw, S. leithii , and S. medlynii , are described from the Upper Jurassic Morrison Formation from the Steiner and Scotts localities north of Greybull, Wyoming, and from Fremont Junction, east of Mt. Ellen, and Mussentuchit Wash sites in Utah. The species are characterized by having a heterogeneous ( S. leithii ) to homogeneous ( S. medlynii ) pith, rhizomes with branches ( S. leithii ), a sclerenchymatous ( S. leithii ) or parenchymatous ( S. medlynii ) inner cortex, and both with a parenchymatous middle cortex. The outer cortex of S. leithii is parenchymatous, whereas in S. medlynii , it is composed of round to irregularly shaped, thick-walled cells. The C-shaped leaf traces in S. leithii usually arise single ranked, sometimes two ranked, with short leaf gaps and short internodes. Although the rhizomes of S. medlynii are incomplete and lack leaf traces, they still suggest very long internodes. Because fronds and epidermal trichomes are lacking in both, the affinity of these species to modern taxa, such as members of the Loxsomaceae, remains uncertain.

Morphology and palynostratigraphy of the genus Camerosporites Leschik 1956

Abstract The genus Camerosporites Leschik 1956 is here emended and the seven species attributed to it are reduced to four. Assemblages of Camerosporites isolated from Upper Triassic strata from sites in the eastern U.S. (the Newark, Culpeper, Richmond, Taylorsville, and Danville basins) and the western U.S. (Chinle Formation) consistently segregate into three recognizable species: C. secatus, C. verrucosus, and C. pseudoverrucatus. Of these, C. secatus and C. verrucosus are more common and more easily recognized. Examination of the morphologic characteristics and regional stratigraphic occurrence of these taxa demonstrates that they can be differentiated by light and electron microscopy, that the enigmatic host plant probably was either a primitive pteridophyte or a primitive gymnosperm, and that C. secatus and C. verrucosus are biostratigraphically useful for differentiating Carnian and Norian (Upper Triassic) continental deposits, especially within the eastern Mesozoic basins. The status of the only rep...

Reexamination of the fossil fern genus Dryopterites Berry based on reproductive characteristics

Abstract The specimens assigned to the genus Dryopterites Berry were reexamined and details of the reproductive characters including the spores are described for the first time. Based upon this new information about the ferns, two species have remained in the genus Dryopterites with one designated as the type species ( D. virginica ) and a lectotype for this species is chosen: one species ( D. dentata ) has previously been reassigned to the family Schizaeaceae, and the remaining species ( D. macrocarpa, D. elliptica, D. cystopteroides ) have been assigned to the genus Delosorus in the family Matoniaceae. This new information and comparisons with Sporae Dispersae suggest a later Cretaceous occurrence of ferns related to the modern dryopterids.

(315–319) Proposals to amend Article 11.8 and its Examples to remove ambiguity in the sanctioning of dual nomenclature for dinoflagellates, and an emendation of Article 11.7, Example 29

1 Department of Earth Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada 2 Natural Resources Canada, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada 3 Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, Illinois 60022, U.S.A. 4 Department of Environmental Science and Policy and Department of Biology, George Mason University, 4400 University Drive, Fairfax, Virginia 22030-4444, U.S.A. Author for correspondence: Martin J. Head, mjhead@brocku.ca