Definition: Palynology

Abstract

xxx

Keywords: palynology, palynomorph, acritarch, dinoflagellate, dinocyst, spore, pollen

Introduction

To a first-order approximation, palynology is the study of four major groups of ‘things’ - namely acritarchs, dinoflagellate cysts, spores, and pollen. But at a more practical level, palynology is defined by the broad methodology by which its subject material is prepared for study: digestion of clastic materials with various acids to yield an organic residue amenable to microscopic scrutiny.

Taxonomy

“Palynomorphs may represent parts of a sexual life cycle (spores and pollen of embryophytes, some Fungi), parts of an asexual propagation strategy (other fungal spores), parts of a single animal organ (scolecodonts), animal remains of as yet unknown function or status (chitinozoans), algal reproductive parts (probably most acritarchs, some zygospores), algal colonies or coenobia (Botryococcus, Pediastrum), and protist ‘whole skeleton’ remains (dinoflagellate cysts, prasinophytes, and foraminiferal linings = ‘microforams’)” (Traverse 1996, p. 11).

Form Taxa

"Fossil dinoflagellate cysts are whole-organism "skeletal" remains. Their taxonomy therefore approximates normal biological classification, with not only genera and species, but also families and classes. Dinoflagellate cyst fossil taxa are therefore, in some sense, not form-taxa (fragmentary genera, "not assignable to a family," are called "form-genera"; note, however, that in the classification of asexual fungi, form-taxa may be used at any rank). A family name can be based on a "cyst genus" name, and can be typified by the type of that generic name, as is the normal procedure for whole plants. The taxonomic-nomenclatural situation for prasinophytes (Tasmanites, etc.) is essentially the same as that just described for fossil dinoflagellates. Artificial classifications for convenience are of course also possible; one can set up groups with or without processes, more than 50 J.lm in maximum dimension, etc.

"Fossil spore and pollen genera (e.g. Cicatricosisporites, Thomsonipollis, Geminospora), on the other hand, are form-genera, the names of which are typified by dispersed specimens of fossil spores and pollen (of "fragmentary nature," in the words of Art. 3.3, ICBN). As such, sporomorph genera cannot, per the ICBN, be grouped under supra generic names at the family level, though they may be referred to taxa of higher rank, such as class Angiospermae, for example. Still, a genus such as Caryapollenites, used as a form-genus, is referable beyond reasonable doubt to the extant plant family Juglandaceae. Per ICBN Art. 3.3, that would make Caryapollenites not a form-genus, which is an unresolved problem with the ICBN" (Traverse 1996, p. 16).

The Principal Types of Palynomorphs

Spores and Pollen

xxxyyyzzz

Dinoflagellates

"Dinoflagellates are nomenclaturally a difficult problem. Traditionally they were regarded as protozoans (one-celled animals) by some scientists, and as one-celled algae (plants) by others. In current biological thinking they are regarded as protists, and hence as neither animals nor plants, but fortunately that classification has not yet caused production of an additional nomenclatural code. If, as generally has been the case in the last twenty years, dinoflagellates are handled nomenclaturally as algae (= plants), there are some interesting results.

"[D]inoflagellate cysts (and also prasinophytes such as Tasmanites) are "special" in that the fossils are "skeletal" remnants of whole organisms at one stage of their life cycle. They have a high degree of integrity in architecture ("Bauplan"). Thus, for dinoflagellates, there is a reasonable expectation that evolutionary progression can be traced backward in time, from extant species of extant genera to extinct species of extant genera to extinct genera of extant families, to extinct families. This means that integration of names of fossil forms into a classification scheme including modern taxa is to be expected" (Traverse 1996, p. 15).

(Read more.)

Acritarchs

Acritarchs are organic-walled, acid-resistant micorfossils of uncertain biological affinities that are classified on the basis of their morphology.

"Some acritarchs resemble dinoflagellate cysts (Margulis & Schwartz 1982; Tappan 1980; Mendelson 1993), but they do not show paratabulation and they have excystments that are different from classical archeopyles of recognised Mesozoic and younger dinocysts. Many acritarch specimens have no excystment structure. However, most modern dinocysts reach sediments before germination (Anderson et al. 1985), and some of these can fossilize without excystment structure formation. Some Ordovician acanthomorphic acritarchs have a double-wall structure (Martin & Kjellström 1973) comparable with that of dinoflagellate cysts. Certain cysts of living dinoflagellates from the order Gymnodiniales lack clearly defined archeopyles or reflected tabulation (Wall & Dale 1968). ... [But, on balance,] the morphological evidence has not been sufficient to establish links between acritarchs and dinoflagellates" (Moldowan & Talyzina 1998, pp. 1168-1169).

Acritarchs are widely distributed in sedimentary rocks from the Proterozoic and Phanerozoic. They were the principal victims of the Varanginian mass extinction, around 610 Ma, when perhaps 70% of taxa became extinct.

Conclusion

References

Anderson, D.M.; Lively, J.J.; Reardon, E.M.; Price, C.A. 1985: Limnol. Oceanogr. 30: 1000.

Margulis, L.; Schwartz, K.V. 1982: Five Kingdoms: An Illustrated Guide to the Phyla of Life. Freeman.

Martin, F.; Kjellström, G. 1973: Neusser Jahrb. Geol. Palaeontol. Monatsh. 1973: 44.

Mendelson, C.V. 1993: In Lipps, J.H. (ed.) 1993: Fossil Prokaryotes and Protists. Blackwell, pp. 77-104.

Moldowan, J.M.; Talyzina, N.M. 1998: Biogeochemical Evidence for Dinoflagellate Ancestors in the Early Cambrian. Science 281: 1168-1169.

Tappan, H. 1980: The Paleobiology of Plant Protists. Freeman.

Traverse, A. 1996: Nomenclature and Taxonomy: Systematics. In Jansonius, J.; McGregor, D.C. (eds.) 1996: Palynology: Principles and Applications. American Association of Stratigraphic Palynologists Foundation, v. 1: 11-28.

Wall, D.; Dale, B. Micropaleontology 14: 265.