Variation and Evolution in Plants and Microorganisms Toward a New Synthesis 50 Years After Stebbins (2000) / Chapter Skim
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14 Toward a New Synthesis: Major Evolutionary Trends in the Angiosperm Fossil Record
14 Toward a New Synthesis: Major Evolutionary Trends in the Angiosperm Fossil Record
Pages 255-270
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From page 255... ...
Three basic nodes of angiosperm radiations are identified: (i) the closed carper and showy radially symmetrical flower, (ii)
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From page 256... ...
This meant that almost no fossil angiosperms were recognized as extinct; it was quite impossible to focus questions of plant evolution on the fossil record of the angiosperms in 1950 as George Gaylord Simpson had done with the fossil vertebrate record in his classic Tempo and Mode in Evolution in 1944 (Simpson, 1944~. Generic Flora Comparisons 90 80 An 60 C 50 ale 40 20 1n O ~ ~ at.
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From page 257... ...
The supposed failure of the fossil record to contribute to understanding the evolution of the early angiosperms was still evident in 1974 when Stebbins published Flowering Plants: Evolution Above the Species Level (Stebbins, 1974~. In chapter 10, "The Nature and Origin of Primitive Angiosperms," there is no substantive use of the fossil record to address this question.
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From page 258... ...
During this time, it became scientifically acceptable to be unable to identify a fossil to a modern genus. Fossil angiosperms were analyzed on the basis of multiple detailed objective characters, and degrees of relationships could be established based on the extent to which these same combinations of characters were found in living families, subfamilies, or genera (Iones and Dilcher, 1980~.
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From page 259... ...
Although the study of angiosperm fossils is only as reliable as the individual investigator, resources are now available, such as cleared leaf collections and cuticular reference slide collections from vast herbarium holdings. This allows angiosperm paleobotanists to survey the nature of
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From page 260... ...
Rapid Changes in the Data The great strides in developing techniques of investigation for understanding Devonian fossil plants, on the basis of seemingly nondescript structurally-preserved compressed remains (Leclercq and Andrews, 1960; Leclercq and Banks, 1962) , and the excellent application of anatomy and morphology to the study of Pennsylvanian age plants (i.e., Delevoryas, 1955, and examples cited in Taylor and Taylor, 1993)
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From page 261... ...
The solid bars extend from the earliest identified fossils of the clades listed on the right side. Modified from Haq and Eysinga, 1998 and Magallon et al., 1999.
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From page 262... ...
The closed carper in a showy flower ensured outcrossing by animal pollinators while increasing pollen exchange with bisexual flowers. The closed carper serves as a plant's control mechanism to guarantee that outcrossing happens.
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From page 263... ...
Therefore, they are examples of some of the most ancient lines of living flowering plants. Those angiosperms that have modified their pollination biology to accommodate new or different animal pollinators are plants that probably have undergone the most extensive changes and whose fossil ancestors should be the most different from their modern descendants.
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From page 264... ...
These nodes include the evolution of showy flowers with a closed carper, the evolution of bilateral flowers, and the evolution of nuts and fleshy fruits. At each of these events, there is a burst of adaptive radiation within the angiosperms that can be interpreted as an attempt to maximize the event for all of the diversity possible and to use the event for increased reproductive potential.
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From page 265... ...
The potential for flowers to further direct the behavior of insects to benefit their pollination had a profound influence on those clades that evolved during the late Upper Cretaceous and early Tertiary. Flowers not only presented their sex organs surrounded by sterile floral organs with attractive patterns and colors, exuding attractive fragrances and filled with nectar and pollen for food, but the bilateral flowers could show the animals which way to approach them and how to enter and exit them.
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From page 266... ...
Each node of angiosperm evolution established genetic systems that favor outcrossing. The showy bisexual flower, the more specialized bilateral flower, and the nutritious nuts and fleshy fruits all are means by which the flowering plants increase their potential for outcrossing.
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From page 267... ...
William Schopf and colleagues who shared perspectives of angiosperm evolution with me. I thank the organizers of the symposium at which this paper was presented: Francisco Ayala, Walter Fitch, and Michael Clegg.
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From page 268... ...
(1935) The systematic value of cuticular characters in recent and fossil angiosperms.
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From page 269... ...
(199Ob) Fossil mimisoid legumes from the Eocene and Oligocene of southeastern North America.
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From page 270... ...
(1990) Cenomanian angiosperm leaf megafossils from the Rose Creek locality of the Dakota Formation, southeastern Nebraska.
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