5.1 Introduction

The Kingdom Protista consists of single-celled, eukaryotic organisms (plants, animals and fungi are the multicellular eukaryotic kingdoms). Eukaryotic means that each cell contains its DNA within a membrane bound nucleus, and the DNA is organized into strands called chromosomes. Protists utilize a number of different trophic strategies, including autotrophy, heterotrophy, parasitism, and symbiotic relationships.

Although there are numerous protistan groups, only a few are of interest to paleontologists, including the phyla Chrysophyta (containing coccolithophorids, silicoflagellates and diatoms), Pyrrophyta (containing the dinoflagellates), and Sarcomastigophora (containing radiolarians, tintinnids and the foraminifers). The important fossil groups are discussed below. Please note the systematics outline for the classification.

5.2 Systemtatics

5.2.1 Phylum Chrysophyta

Class Coccolithophorida

Coccoliths are very small (3-15 mm) calcareous disks that were once imbedded in the cell wall of a spherical cell. The organism, with its armour of disks, is a free-swimming flagellate most common today in the top 100m of temperate ocean waters. When the organism dies, the plates are usually shed. Coccoliths can be identified microscopically in sediment samples by the pseudouniaxial cross they display under cross-polarized light, but specific classification requires an electron microscope. Coccoliths are very abundant in Mesozoic sediments, forming the main constituents of most Cretaceous chalks. They are quite useful for biostratigraphic analyses of Mesozoic and Cenozoic strata.

Class Silicoflagellata

Silicoflagellates are, as you might expect, flagellated cells with a siliceous skeleton. The skeletons are made of an opal-like material of tubular construction. They are between 20-50 mm across. Like the coccoliths, they are planktic and marine, living mostly in temperate surface waters. Because of their apoarently slow evolutionary rates, silicoflagellates have had only limited application in biostratigraphy.

Class Diatomacea/Bacillariophyceae

Diatoms are generally spherical cells characterized by walls impregnated with silica. This skeleton (frustule) consists of two overlapping valves with a finely reticulate structure. Diatoms are abundant in freshwater and marine environments, usually under temperate conditions. Most planktic diatoms are centric, so they can float better, while most bentic diatoms are pennate, or flat, and live on sediments or other organisms. Diatom frustules are so abundant in some Tertiary deposits that they form entire sedimentary units (diatomites). They are used commercially in scouring powders and toothpaste.

5.2.2 Phylum Pyrrophyta

Class Peridineae

This class includes the dinoflagellates, which are organic-walled, flagellated organisms common in the plankton of marine and fresh waters. They form resistant cysts composed of sporopollenin or (rarely) silica; the cysts are generally the only fossilized traces of these organisms. Dinoflagellates range today from 0.005-2 mm in diameter, but fossil forms are 25-250 mm across. This group has not been studied thoroughly; they may turn out to be quite useful for paleoclimatological studies.

5.2.3 Phylum Sarcomastigophora

Class Granuloreticulosa/Rhizopoda

Order Formanifera

Foraminiferans are unicellular organisms with long, thread-like anastomosing pseudopodia and a test (shell) with a distinct aperture. The test, which may be unilocular (with a single chamber) or multilocular (many-chambered), is either organic-walled, agglutinated, or calcareous. Foraminiferans are found in marine and brackish waters throughout the world. Their abundance, rapic evolution, and sensitivity to environmental conditions has made them excellent index fossils for biostratigraphers, paleoclimatologists and paleoecologists (particularly in Cretaceous and younger rocks).

Foraminifera are either benthic or planktic. In modern waters, benthic forams. are ubiquitous, while planktic forams are found only in open ocean. Far fewer species of planktic forams exist compared to benthic species; but they show the same trend (species diversity) by having the maximum number of species (highest diversity) living in tropical waters. Thus, the ratio of planktic to benthic tests increases with distance from shore. And in the deep sea sediments, planktic tests out number benthic ones by one or two orders of magnitude.

Larger forams, most notably the fusilinids evolved from smaller lenticular forms. These forams are excellent biostratigraphic indicators of Pennsylvanian-Permian rocks because during the late Paleozoic they underwent many evolutionary changes including: increase in the size of the initial chamber, increase in overall size, increase in wall complexity and increase in the intensity of septal fluting. Several of these trends were repeated in different lineages, at different times and at different rates.

Subclass Radiolaria

Radiolarians are amoeboid organisms with long, tapering pseudopodia, an external siliceous skeleton and an internal siliceous capsule. The skeleton is a delicate symmetrical lattice-work, usually with many knobs and spines. They are 40 - 800 mm in length. Radiolarians are plantic, entirely marine group found in both cold and warm waters. Radiolaxians are most abundant in the uppermost few hundred meters of equatorial waters, but some species are also abundant in sub-polar seas. They axe important for biostratigraphy; lately they have been used to correlate the jumble of Paleozoic "microplates" in western North America.

5.3 Taxonomy

Kingdom: Protista Phylum Chrysophyta         Order Centrales* (K-R)         Order Pennales* (Paleocene-R) Phylum Sarcomastigophora     Class Actinopoda       Subclass Radiolaria*     Class Rhizopoda         Order Foraminiferida*           Suborder Allogromina*           Suborder Textulariina*           Suborder Fusilinina*           Suborder Miliolina*           Suborder Rotaliina*

Important foram suborders:

1. Allogromiina

• have a proteinaceous (tectin) test; don't preserve well
• brackish water forams

• have agglutinated tests; cement sand grains or other skeletal fragments with calcareous cements

• extinct; range Ord-Trias
• have a microgranular calcite test wall; appears opaque in reflected light
• fusiform test, often very large
• important index fossils of the Carb. and Perm.

• have a microcrystalline calcite needle test; appears porcelaneous or milky white

• test made of microcrystalline calcite where all crystals are oriented with c-axis perpendicular to wall: appear glassy
• planktonic forms in here
• numulitids; important index fossils in Paleocene and Eocene
• globigerinids- important index fossils in Mesozoic and Cenozoic