Browsing by Subject "DAKOTA FORMATION"

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    Marsileaceae sporocarps and spores from the late cretaceous of Georgia, U.S.A.
    (International Journal of Plant Sciences, 2000-01-01) Lupia, R; Schneider, H; Moeser, GM; Pryer, KM; Crane, PR
    A new species provisionally assigned to the extant genus Regnellidium Lindm. (Regnellidium upatoiensis sp. nov.) is established for isolated sporocarps assignable to the heterosporous water fern family Marsileaceae. Three sporocarps and hundreds of dispersed megaspores were recovered from unconsolidated clays and silts of the Eutaw Formation (Santonian, Late Cretaceous) along Upatoi Creek, Georgia, U.S.A. The sporocarps are ellipsoidal and flattened, contain both megasporangia and microsporangia, and possess a two-layered wall - an outer sclerenchymatous layer and an inner parenchymatous layer. In situ megaspores are spheroidal, with two distinct wall layers - an exine, differentiated into two layers, and an outer ornamented perine also differentiated into two layers. The megaspores also possess an acrolamella consisting of six (five to seven) triangular lobes that are twisted. In situ microspores are trilete and spheroidal, with a strongly rugulate perine, and show modification of the perine over the laesura to form an acrolamella. Comparison of the fossil sporocarps with those of four extant species of Marsileaceae reveal marked similarity with Regnellidium diphyllum Lindm., particularly in megaspore and microspore morphology. If found dispersed, the in situ megaspores would be assigned to Molaspora lobata (Dijkstra) Hall and the microspores to Crybelosporites Dettmann based on their size, shape, and ornamentation. Regnellidium upatoiensis sp. nov. extends the stratigraphic range of the genus back to the Santonian, nearly contemporaneous with the first evidence of Marsilea, and implies that the diversification of the Marsileaceae into its extant lineages occurred in the mid-Cretaceous.
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    Phylogeny of Marsileaceous Ferns and Relationships of the Fossil Hydropteris pinnata Reconsidered.
    (International journal of plant sciences, 1999-09) Pryer, KM
    Recent phylogenetic studies have provided compelling evidence that confirms the once disputed hypothesis of monophyly for heterosporous leptosporangiate ferns (Marsileaceae and Salviniaceae). Hypotheses for relationships among the three genera of Marsileaceae (Marsilea, Regnellidium, and Pilularia), however, have continued to be in conflict. The phylogeny of Marsileaceae is investigated here using information from morphology and rbcL sequence data. In addition, relationships among all heterosporous ferns, including the whole-plant fossil Hydropteris pinnata are reconsidered. Data sets of 71 morphological and 1239 rbcL characters for 23 leptosporangiate ferns, including eight heterosporous ingroup taxa and 15 homosporous outgroup taxa, were subjected to maximum parsimony analysis. Morphological analyses were carried out both with and without the fossil Hydropteris, and it was excluded from all analyses with rbcL data. An annotated list of the 71 morphological characters is provided in the appendix. For comparative purposes, the Rothwell and Stockey (1994) data set was also reanalyzed here. The best estimate of phylogenetic relationships for Marsileaceae in all analyses is that Pilularia and Regnellidium are sister taxa and Marsilea is sister to that clade. Morphological synapomorphies for various nodes are discussed. Analyses that included Hydropteris resulted in two most-parsimonious trees that differ only in the placement of the fossil. One topology is identical to the relationship found by Rothwell and Stockey (1994), placing the fossil sister to the Azolla plus Salvinia clade. The alternative topology places Hydropteris as the most basal member of the heterosporous fern clade. Equivocal interpretations for character evolution in heterosporous ferns are discussed in the context of these two most-parsimonious trees. Because of the observed degree of character ambiguity, the phylogenetic placement of Hydropteris is best viewed as unresolved, and recognition of the suborder Hydropteridineae, as circumscribed by Rothwell and Stockey (1994), is regarded as premature. The two competing hypotheses of relationships for heterosporous ferns are also compared with the known temporal distribution of relevant taxa. Stratigraphic fit of the phylogenetic estimates is measured by using the Stratigraphic Consistency Index and by comparison with minimum divergence times.