Palynology

The science of palynology or, perhaps in a geologic context, paleopalynology is devoted to the study of pollen grains and spores, and also encompasses the investigation of other organic microfossils, such as chitinozoans, acritarchs (Javaux and Marshall, 2006), scolecodonts, dinoflagellates, certain types of microscopic algae, microforaminifera, rotifers, testate amoebae, chitinous fungal remains, and other forms of organic debris sometimes termed varia. Characteristic features such as grain shape (FIG. 1.58) , wall sculpture, presence or absence of pores, ridges, furrows, or other types of structural features make it possible to distinguish among grains of various kinds and in some instances to assign them to certain groups of plants. The discipline of palynology is a critical component of understanding the biodiversity of the present and the past, and the important volumes by Wodehouse (1965)) Erdtman (1969) (FIG. 1.66), Faegri et al., (1989) (FIG. 1.67), and Traverse (2007) (FIG. 1.68) provided an excellent historical context to the discipline. Palynology has greatly benefited from the introduction of various SEM techniques (Villar de Seoane and Archangelsky, 2008) that have made it possible to image and interpret complex external features on the grains (FIG. 1.69). There has also been an attempt to automate palynology, using texture analysis of SEM images (Langford et al., 1990; Vezey and Skvarla, 1990). This procedure greatly reduces the labor-intensive aspects of palynology and perhaps offers more rapid results, larger data sets, finer resolution of taxa, and possibly greater objectivity in identification (France et al., 2000).

Fossil pollen grains and spores (FIGS. 1.70, 1.71) are now routinely sectioned and examined with the TEM as well.

Erdtman Palynology Images
FIGURE 1.66 Gunnar Erdtman.
Gunnar Erdtman
FIGURE 1.67 Knut Faegri (right) and Ove Arbo H0eg.

These studies have provided a wealth of detailed information about features of the exine (the outer spore or pollen wall that is composed of sporopollenin) that have been useful for systematic studies. Some paleobotanists have combined SEM (FIG. 1.72) and TEM studies of dispersed spores to try to better understand the affinities of these propagules (Edwards et al., 1996), and to more accurately interpret features of the wall (Wellman, 2001). Information on pollen and spore ultrastructure is often determined from single sections

Images Origen Palynology
FIGURE 1.68 Alfred Traverse. (Courtesy M. Streel.)
FIGURE 1.69 Cyathotheca tectata spore viewed with the scanning electron microscope (Pennsylvanian). (From Taylor, 1972.) Bar = 23 |im.

of grains in which the plane of section is not easily determined, but techniques have been developed so that the same grain may be examined and recorded in transmitted light, and then scanning and TEM (Daghlian, 1982). In addition, it is often important to prepare serial sections of the same grain in order to view features, such as lamellae, that may not be consistently present throughout the entire wall (Johnson and Taylor, 2005).

Figure 1.70 Ultrathin section of the spore Horstisporites iri-dodea showing organization of the sporoderm. Bar = 2.5 ^m.
Figure 1.71 Ultrathin section of Cyathotheca tectata spore as viewed with a transmission electron microscope. (From Taylor, 1972). Bar = 12|im.

Fossil pollen and spores that are preserved within the pollen sac or sporangium (in situ) can provide valuable information on developmental patterns in the formation of the pollen grain and spore walls. In certain types of fossils, such as per-mineralizations, it is possible to extract many pollen grains of the same type from a single sporangium, or from multiple sporangia at different stages of development. Study of these grains can thus offer insights into biological processes that took place millions of years ago (Taylor and Alvin, 1984).

The process of identifying numerous palynomorphs, especially those that are dispersed (i.e., not i n situ) can be

Figure 1.72 Fractured surface of Cyathotheca tectata spore. Bar = 3|im. (From Taylor, 1972.)

daunting, and some palynologists have developed automation techniques to assist in the process. For example, image analysis of measurements can be used to quantify shape and ornamentation on SEM images (Treloar et al., 2004). In a companion study, Li et al. (2004) used a neural network to analyze texture and were able to correctly identify four extant pollen taxa.

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