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The Fossil Monocot Limnobiophyllum scutatum: Resolving the Phylogeny of Lemnaceae
No full textMore than 200 specimens of Limnobiophyllum scutatum (Dawson) Krassilov have been recovered from lacustrine claystones in the Paleocene Paskapoo Formation near Red Deer, Alberta. The plant was a floating, aquatic angiosperm with helically arranged, ovate leaves attached in small rosettes. Rosettes are interconnected by stolons and bear simple adventitious roots as well as larger branching roots that appear to have vascular tissue. Leaves are pubescent, aerenchymatous, with 12– 14 campylodromous primary veins that curve toward the apex, joining a fimbrial vein, often an apical notch. Staminate flowers with two, four-loculate stamens, are borne in the axils of second leaves. Anthers contain monoporate, globose, echinate pollen, 20–25 mm in diameter. The pollen wall is 0.8 mm thick, with a homogeneous foot layer, granular to slightly columellate infratectal layer and an echinate tectum. Pollen most closely resembles the sporae dispersae genus Pandaniidites Elsik. The completeness of L. scutatum has allowed for its inclusion in a numerical cladistic analysis to resolve relationships among taxa of the Lemnaceae, Pistia, and selected genera of Araceae. Results of the analysis indicate that the Lemnaceae plus Pistia form a monophyletic group within the Araceae
Tree of death: The role of fossils in resolving the overall pattern of plant phylogeny
Get PDFSystematics has a long history of conficting results arising from analyses of diferent categories of biologically informative data and difering analytical methods. Until the advent of numerical methods in systematics in the 1960s, evolutionary relationships were most ofen inferred from a small subset of available characters (e.g., foral structure, fruit type, pollen characters, leaf form, cuticular anatomy), and hypotheses of relationships were not routinely tested against the results from other subsets of the data (see Nixon, 1996). In retrospect, we now realize that only partly accurate “phylogenies” became widely accepted, through either relatively universal popularity or by the force-of-will of infuential authors (e.g., Haeckel, 1876). For example, while both the Takhtajan (1969) and Cronquist (1981) systems of classifcation for fowering plants have been extremely useful in a taxonomic context, they now are recognized to be collections of systematic hypotheses that were largely untested scientifcally.Fil: Rothwell, Gar W.. Ohio University; Estados Unidos. State University of Oregon; Estados UnidosFil: Escapa, Ignacio Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; ArgentinaFil: Tomescu, Alexandru M. F.. Humboldt State University; Estados Unido
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Permineralized Mesozoic Moss Gametophytes and their Implications for Bryophyte Evolution
Get PDFMosses (Phylum Bryophyta) are widely considered to be among the most ancient groups of land plants (embryophytes) and they are the second most speciose embryophyte phylum with ~13,000 extant species. Despite their diversity and antiquity, mosses have a limited fossil record, which primarily consists of gametophytes entombed in Cenozoic amber. However, surveys of Mesozoic floras from North and South America have recently uncovered a wealth of permineralized moss gametophytes. These fossils present the first opportunity to explore macroevolutionary trends in mosses over deep geologic time, with rich sampling of pre-Cenozoic diversity.
The over-arching goal of this dissertation is to explore moss evolution over geologic time, using these recently discovered permineralized gametophytes. There are four main objectives: 1) document moss diversity in Late Jurassic and Cretaceous deposits by characterizing anatomically preserved fossil mosses, 2) investigate patterns in moss biogeography using data from the fossil record, 3) understand the longevity of moss genera over geologic time, and 4) explore the hypothesis that modern moss lineages diversified as part of the Cretaceous Terrestrial Revolution using paleontological data. Herein, six new taxa are characterized based on permineralized gametophytes from one Late Jurassic and three Cretaceous deposits. All fossils were studied using light microscopy.
In Chapter 2, a permineralized acrocarpous moss gametophyte from the Late Jurassic of Patagonia, Argentina, is described. This fossil was prepared using the petrographic thin sectioning technique. The gametophyte shoot is unbranched, and leaves have a broad sheathing leaf base that narrows distally, forming a free leaf blade. Costa is strong, with an adaxial epidermis of bulging-mammillose cells, subtended by guide cells and a single abaxial stereid band. An abaxial epidermis is lacking. In the free leaf blade, the lamina is bistratose, with an adaxial layer of bulging-mammillose cells. This fossil gametophyte displays a novel combination of characters that suggest basal affinities within the families Timmiellaceae or Polytrichaceae. Both of these families are members of a grade within Subphylum Bryophytina basal to Subclass Bryidae. Therefore, this fossil is described as a new genus and species assignable to Subphylum Bryophytina, Heinrichsiella patagonica gen. et sp. nov. Heinrichsiella is the oldest evidence of this basal grade within Subphylum Bryophytina by at least 15 Ma.
In Chapter 3, a permineralized moss gametophyte assignable to the extant genus Cynodontium is described from the Late Cretaceous of the North Slope of Alaska. This fossil was permineralized in a terrestrial limestone and prepared using the cellulose acetate peel technique. The moss gametophyte branches irregularly and has leaves with a broad base, narrow blade, and excurrent costa. Leaf margins are narrowly recurved basally, becoming bistratose and denticulate distally. Costa is strong and composed of a poorly defined epidermis, guide cells, and thin-walled substereids. Leaf blade is keeled basally, becoming channeled distally. Laminar cells are subquadrate or rectangular proximally, becoming quadrate distally. This fossil has a combination of gametophytic characters diagnostic of the extant genus Cynodontium, but displays a novel combination of characters that are distinct from any extant species of that genus. Therefore, this fossil is described as Cynodontium luthii sp. nov. This species is the oldest evidence for Cynodontium by at least 15 Ma and reveals that some genera found in the High Arctic today also lived in the region during the Late Cretaceous, when it experienced a temperate climate.
In Chapter 4, three new species of the extant genus Sphagnum are described based on permineralized gametophytes from the Late Santonian to Campanian of Vancouver Island, Canada. These fossils were permineralized in near-shore marine calcareous concretions and prepared using the cellulose acetate peel technique. All three species have unistratose leaves that are composed of smaller cells (chlorocysts) that alternate with larger, porose cells (hyalocysts). Collectively, these features are diagnostic of Sphagnum. The three species are most easily distinguished based on their stem anatomy. Stems of Sphagnum species one have a unistratose hyalodermis, while stems of Sphagnum species two have a multistratose hyalodermis, and stems of Sphagnum species three completely lack a hyalodermis. Taxonomic comparisons with extant species of Sphagnum are difficult due to the fragmentary nature of the specimens. Sphagnum species one and two have combinations of features found in several extant sections of Sphagnum. However, the absence of a hyalodermis is a character that is only found in some species of Sphagnum Section Cuspidata. Therefore, Sphagnum species three can be assigned to Section Cuspidata and is the only pre-Pleistocene evidence for that section. These fossils also represent the first reports of permineralized Sphagnum gametophytes and reveal that Sphagnum was anatomically diverse by the Late Cretaceous, which is far earlier than predicted by some molecular dating analyses.
In Chapter 5, permineralized moss gametophytes assignable to the family Leucobryaceae are described from the Valanginian (~136 Ma) of Vancouver Island, Canada. These fossils were permineralized in near-shore marine calcareous concretions and prepared using the cellulose acetate peel technique. The gametophyte shoots are irregularly branched, leaves are almost entirely comprised of an expanded costa. Lamina is restricted to the sheathing leaf base and composed of small-diameter porose cells that are isodiametric in cross section. Anatomically, the costa is comprised of larger porose cells that are rectangular in cross section (leucocysts) and much smaller, thicker-walled cells, which are triangular in cross section for most of the leaf (chlorocysts). Costa is typically homostrosic, with a single layer of leucocysts on either side of centric chlorocysts. The unusual leaf anatomy of these fossils is diagnostic of the leucobryoid clade within the family Leucobryaceae. However, the fossils display a mosaic of characters, combining features of two leucobryoid genera (Leucobryum and Steyermarkiella). Therefore, they will be assigned to a new genus and species. These fossils are the oldest evidence of the family Leucobryaceae by at least 88 Ma and the oldest evidence of the leucobryoid clade within this family by >115 Ma.
In Chapter 6, the role of paleontological data in bryophyte systematics is summarized based on a comprehensive review of the paleobryological literature, considering techniques for integrating fossils into evolutionary analyses with extant plants as well as aspects of bryophyte structure and ecology relevant to taphonomy. Bryophytes are unusual in that the group has a deep evolutionary history, but a sparse fossil record. The paucity of bryophyte fossils is driven by phenotypic and ecological features related to the small size and patchy ecological distributions of most members of the group as well as incomplete exploration of the fossil record. However, fossils provide unique insight on the evolution of organisms (including bryophytes), over deep time. They are the only means to independently test hypotheses about evolution generated from extant bryophytes and are essential for making accurate inferences regarding speciation and extinction rates, patterns of morphological evolution, and biogeography. The review concludes that development of robust morphological datasets for bryophytes, that would allow fossils to be integrated into macroevolutionary analyses alongside extant plants as well as focused efforts to uncover and describe pre-Cenozoic bryofloras are essential for bringing deep-time evolutionary perspectives to bryophyte systematics
Large Permineralized Seeds in the Jurassic of Haida Gwaii, Western Canada: Exploring the Mode and Tempo of Cycad Evolution
Get PDFPremise of research. Numerous large permineralized fossil seeds from the Jurassic of Haida Gwaii, western Canada, provide evidence for the mode and tempo of cycad evolution.Methodology. Fossil seed specimens are studied from external morphology and serially sectioned by the classic cellulose acetate peel technique to reveal anatomical features of the integument, vascular system, nucellus, and gametophyte. Fossils are compared to living cycad seeds that are also examined from external views, dissections, and anatomical preparations.Pivotal results. The fossil seeds are described as Traskia maahlae gen. et sp. nov. Features of the integument and vascular system reveal that T. maahlae is a stem group cycad that shares seed architecture and mode of germination with living Cycas spp.Conclusions. Traskia maahlae adds to a growing body of paleontological data on stem and crown group cycads. Results suggest that modern pollination and postpollination biology and the two contrasting modes of cycad seed germination evolved during the Mesozoic but that crown group cycad species may not have appeared until the Cenozoic
Developmental programmes in the evolution of Equisetum reproductive morphology: a hierarchical modularity hypothesis
Get PDFBackground: The origin of the Equisetum strobilus has long been debated and the fossil record has played an important role in these discussions. The paradigm underlying these debates has been the perspective of the shoot as node-internode alternation, with sporangiophores attached at nodes. However, fossils historically excluded from these discussions (e.g. Cruciaetheca and Peltotheca ) exhibit reproductive morphologies that suggest attachment of sporangiophores along internodes, challenging traditional views. This has rekindled discussions around the evolution of the Equisetum strobilus, but lack of mechanistic explanations has led discussions to a stalemate.Fil: Tomescu, Alexandru M F. Humboldt State University; Estados UnidosFil: Escapa, Ignacio Hernán. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rothwell, Gar W.. State University of Oregon; Estados Unidos. Ohio University; Estados UnidosFil: Elgorriaga, Andres. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cúneo, Néstor Rubén. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Stockeystrobus gen. nov. (Cupressaceae), and the evolutionary diversification of sequoioid conifer seed cones
Get PDFAn anatomically preserved seed cone from Late Cretaceous (Santonian-Coniacian) sediments of the Yezo Group on the Japanese Island of Hokkaido documents additional diversity among sequoioid conifers, and reveals previously unknown mechanisms for pollination and post-pollination seed enclosure in the conifer family Cupressaceae. The cylindrical seed cone of Stockeystrobus interdigitata gen. et sp. nov. consists of a central axis bearing helically arranged bract-scale complexes. Individual complexes are tightly packed and peltate in form, with completely fused bracts and scales. Peltate heads of adjacent complexes are attached to each other by elongated interdigitating epidermal trichomes. Each complex bears 6 â 8 inverted seeds on the adaxial surface of the inside of the peltate bract/scale complex head. Seeds occur in a single row, are roughly disk shaped, with broad wings in the major plane of symmetry. The nucellus is attached to the seed integument at the chalaza and free distally, with a convoluted apex. This cone reveals greater diversity of sequoioid reproductive biology than is represented among living species, and demonstrates that completely enclosed cones with well protected seeds were produced by Late Cretaceous fossil conifers of the Cupressaceae.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Paleobotany in Canada papers presented at a symposium sponsored by the Canadian Museum of Nature, October 5 - 6, 1989
No full textA new pteropsid fructification from the Middle Pennsylvanian of Kansas
No full textVolume: 19Start Page: 307End Page: 31
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