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PANGEA Ltd
14 St Mary's
Place, Chippenham, Wilts,
SN11 1EN, UK
Telephone: +44 (0) 1249 462677
Fax:+44 (0) 1249 463841
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406.10
71.07We have a variety of rock and mineral collections available in boxed display trays. The specimens in these collections may be removed from the trays for hands-on examination and study.
MICROFOSSILS ARE the tiny remains of bacteria, protists, fungi, animals, and plants. Microfossils are a heterogeneous bunch of fossil remains studied as a single discipline because rock samples must be processed in certain ways to remove them and microscopes must be used to study them. Thus, microfossils, unlike other kinds of fossils, are not grouped according to their relationships to one another, but only because of their generally small size and methods of study. For example, fossils of bacteria, foraminifera, diatoms, very small invertebrate shells or skeletons, pollen, and tiny bones and teeth of large vertebrates, among others, can be called microfossils. But it is an unnatural grouping. Nevertheless, this utilitarian subdivision of paleontology, first recognized in 1883, is very significant in geology, paleontology, and biology.
Microfossils are perhaps the most important group of all fossils — they are extremely useful in age-dating, correlation and paleoenvironmental reconstruction, all important in the oil, mining, engineering, and environmental industries, as well as in general geology. Billions of dollars have been made on the basis of microfossil studies. Because they usually occur in huge numbers in all kinds of sedimentary rocks, they are the most abundant and most easily accessible fossils. Indeed, some very thick rock layers are made entirely of microfossils. The pyramids of Egypt are made of sedimentary rocks, for example, that consist of the shells of foraminifera, a major microfossil group.
Microfossils can also be very useful in teaching science at all levels. Students are commonly fascinated by things they cannot see with their naked eyes, especially when the objects are beautiful or interesting in their own right. Furthermore, collection of microfossils is usually possible close to many schools — in fact, some schools are built right on top of microfossil-bearing sedimentary rocks! Processing the rock samples is usually easy and safe enough for children to do themselves, or at least to watch. Prepared samples can be purchased or obtained from museums and some universities. Because so many microfossils are usually found in any sample, the students can even keep their own finds!
MICROFOSSILS
Although plants and animals are the most obvious life around us today, they are not the most numerous nor the most important contributors of microfossils. Bacteria (prokaryotes) and protists far outnumber them, live in more diverse habitats, and leave a greater diversity of microfossils. Today these organisms live from Antarctic ice deserts to steaming volcanic hot springs, and from the highest mountains to the deepest sea. Some cause diseases, such as malaria which infects 350-400 million people today; others are useful to humans. Most simply live their lives unknown to us but contributing enormously to our well being through the production of oxygen, the degradation of waste materials, recycling of nutrients, production of food, and a multitude of other functions, some of which take place in our own bodies. Fungi, another group in modern environments that both benefit and plague humans, have a long, but mostly unstudied, microfossil record.
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Prokaryotes and protists are very well represented in the fossil record. Prokaryotes are the oldest known fossils, and they were the only life on Earth for most of its history — from 3.5 to 1.5 billion years ago. Protists joined them at least 1.5 bya, and animals and plants were latecomers at less than .55 bya. All these microfossils provide insights to Earth and life history, and so are important to study in paleontology. The single-celled forms help to develop and test evolutionary models using organisms that are not multicellular or sexual in all cases, and with greater ecological variety.
Generally prokaryotes and protists are single-celled. Yet the most significant contrast among life forms separates them. Prokaryotes have their DNA loosely organized within the cell and not in the cell nucleus, and chromosomes are absent. All protists, fungi, animals and plants are eukaryotes and have chromosomes made of DNA, RNA, and proteins in a nucleus. Many other very important differences occur too (Table 1). Animals, plants and fungi are multicellular; protists are generally unicellular and include all other eukaryotes.
Table 1. Some primary differences between prokaryotes and eukaryotes (from Lipps, 1992, p. 2).
PROKARYOTES EUKARYOTES
Nucleus absent Nucleus present
Meiosis absent Meiosis
1 basic genome Chromosome number 2-600
Mitochondria absent Mitochondria present
Chloroplasts absent Chloroplasts may be present
Endoplasmic reticulum absent Endoplasmic reticulum present
Vacuoles absent Vacuoles present
Prokaryotes and protists are often called "simple", but this is just not true. Each one must do everything with just a single cell that higher plants or animals do with millions of cells. Single-celled organisms have many different kinds of specialized organelles within their cells that function in extraordinary ways. Prokaryotes, protists, fungi, animals, and plants are all very successful at making a living, and that is all that evolution requires. Although prokaryotes and protists seem simpler, they arose much earlier than their multicellular descendants and so might be considered more primitive, but some have also existed for at least 3.5 billion years and must therefore be considered very successful indeed.
Fungi, plants, and animals contribute a vast multitude of small parts to the microfossil record. Fungi are found as isolated microscopic filaments and spherical spores, usually associated with larger fossil plant material. As such, they have largely been ignored by paleontologists. Many plants have small pieces and parts that can be found as microfossils. Most important of these are pollen and spores which can be very abundant in terrestrial and nearshore marine deposits. Just about any animal with skeletal parts also contributes to the microfossil record.
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Protists
FORAMINIFERA — Foraminifera, usually called "forams" or "bugs", comprise a large group. Some 60-80,000 species have been described from Cambrian through Recent age sediments. The species generally have shells made of silt and sand particles or secreted calcium carbonate that range in size from less than .1 mm to 10 cm. Most are about the size of a pin head. Each shell has one or more chambers in which the protoplasm of the living protist resided.
Forams live today from the shallowest intertidal zones to the deepest trenches of the oceans. A very few live in salty lakes and springs, where they have been transported by birds or other means. About 4,000 species are alive today. Of these, only 40 float in the water and are planktonic, the rest are benthic and live on the bottom of the ocean or on plants or animals. Some even live on other forams! Forams eat a wide variety of food, from bacteria through algae to various kinds of animals and other protists.
Forams are among the most abundant fossils. They first occur as simple tubes of sand in the Cambrian. Later more complex tubes and coils appear, even developing chambers in the Ordovician. In the Silurian, secreted calcium carbonate types appear; these diversify into many different shapes and kinds. Like animals and plants, they undergo extinctions at particular times in the geologic past, but radiate again into new, but similar shaped, forms. They remain abundant and diverse. Because of this, forams are the principal microfossil used to age-date and correlate marine sedimentary rocks — they are particularly useful in the oil industry. A single oil company, during the boom days of exploration for new deposits, might have employed 40 or 50 micropaleontologists to study forams. They are used also to decipher ancient environments, climates and oceanography. They are probably the most important fossils of any, simply because they are so useful.
RADIOLARIA — "Rads", a
DIATOMS — Diatoms
Diatoms
USEFUL REFERENCES
Blome, C. E., Whalen, P. M., and Reed, K. M. (Convenors). 1995. Siliceous Microfossils. Short Courses in Paleontology Number 8. Paleontological Society. 185 p.
Boardman, R. S., Cheetham, A. H. and Rowell, A. J. (Editors). 1987. Fossil Invertebrates. Blackwell Science, 238 Main St., Cambridge, MA 02142. 713 p. An advanced college-level text on fossil invertebrates with exellent descriptions and good illustrations.
Brasier, M. D. 1980. Microfossils. George Allen & Unwin, London. 193 p. Brief overview of major groups of microfossils. Simple drawings of each kind of microfossil.
Haq, B. U., and Boersma, A. (Editors). 1978. Introduction to Marine Microfossils. Elsevier, New York. 376 p. A college text describing important microfossils found in marine rocks, excluding fish parts. Good illustrations.
Lipps, J. H. 1981. What, if anything, is micropaleontology? Paleobiology, vol. 7, p. 167-199. An essay on the history, use, and potential of microfossils in paleontology.
Lipps, J. H. (Editor). 1992. Fossil Prokaryotes and Protists. Blackwell Science, 238 Main St., Cambridge, MA 02142. 342 p. A college-level text on microfossils of single- celled prokaryotes and protists. Good illustrations showing the variety of forms and their terminology, as well as detailed descriptions of their paleobiology, biostratigraphy, and evolutionary history.
Foraminifera or foraminifers or forams (for short) generally very common in marine post-Palaeozoic rocks. They are quite easy to get out of soft rocks such as clays and marls, but can also be found in loose oolites, shell sands and chalks.
From a practical point of view, forams can be divided into four main categories: the agglutinated forms (agluts for short), the benthic calcareous forams, the planktonic calcareous forams and large benthic foraminifera.
he Agglutinated Foraminifera build their test from grains of sediment. The grains could be quite small, giving it a smooth appearance, or larger with the individual grains being visible under the low power binocular microscopes we use to study them. The test can have just one chamber or many chambers arranged in different patterns.
Calcareous Benthics
The Planktonic forams
NEOGENE FORAMINIFERA FROM JAPAN
Foraminifera from the Gault Clay
Foraminifera at the Smithsonian Museum of Natural Hustory
Plaeontologia Electronica
Pictures of Forams at the Natural History Museum (London)
Late Quaternary microfossils of the Gulf of St Lawrence
Modern Formainifera from Norfolk
Studying microfossils
Micropalaeontology involves the study of foraminifera, ostracods and calpionellids, which mainly have a calcareous composition; diatoms and radiolaria, which are composed of silica; and conodonts, which are phosphatic. Routine identifications employ incident light microscopy. In some cases, thin-section analysis is required, as in the case of the study of larger foraminifera and calpionellids.
Nannopalaeontology covers the study of nannofossils, which are the smallest of the microfossil groups examined routinely. This group includes coccoliths and nannoliths, and also calpionellids. Nannofossils are calcareous and examined in transmitted light. They need polarisation techniques for positive identifications to be made.
Palynology was once limited to the study of spores and pollen. However, in the last fifty years, the field has been extended to encompass other organic-walled microfossils, collectively termed palynomorphs. The groups studied include dinoflagellate cysts (dinocysts), acritarchs, marine prasinophyceaen algae and various freshwater algae, chitinozoa, as well as spores and pollen. Palynomorphs are examined in transmitted light. In addition to palynomorphs, palynological preparations often yield a variety of other fossil remains (foraminiferal test-linings, arthropod fragments and fungal material) and organic debris (amorphous organic matter and a range of structured phytoclasts). These components, together with the specific palynomorphs present, are important in palynofacies analysis.
1. Uniserial test (Hormosina)
2. Biserial test (Palaeotextularia)
3. Planospiral test (Nonion)
4. Trochospiral test (Ammonia)
1. Centric diatom (Coscinodiscus)
2. Pennate diatom (Achnathes)
Radiolaria
Radially symmetrical Spumellarian form (Belonapsis)
Helmet-shaped Nassellarian form (Podocyrtis)
Radiolaria occur from the Ordovician and range to the present day. They are unicellular, planktonic, marine protists. They are characteristic of the open ocean, living mainly at the surface, but capable of surviving at almost any depth. Their skeletons are composed of opaline silica and accumulate in sea-floor sediments. Spumellarian forms have a radial symmetry, sometimes discoidal or ellipsoidal, with latticed, perforated or spongy walls. Nassellarian forms have latticed walls with a helmet-shaped, bilaterally symmetrical morphology.
1. Simple cone element (Oistodus)
2. Compound blade (Ozarkodina)
3. Platform (Polygnathus)
Conodonts range from the Cambrian to the Triassic, being particularly prominent in the Ordovician and Late Devonian. Their affinity is uncertain, but they are now generally considered to represent the jaw apparatus belonging to a group of marine worm-like animals. Phosphatic in composition, and tooth-like in appearance, conodont elements exhibit just a few basic components - cones, bars/blades and platforms.
Calpionellids
Calpionella
Calpionellids are best known from Mesozoic pelagic limestones of the Tethyan realm. However, they are related to the tintinnid ciliates, which have a longer history from the Ordovician to the present day. Calpionellids are small calcareous, cup-shaped microfossils.
1. Coccosphere of living coccolithophore (Cyclococcolithina)
2, 3. Distal and proximal views of single coccolith (Pseudoemiliana)
4. Coccolith with bars crossing central area (Prediscosphaera)
Coccoliths appear in the Late Triassic and range to the present day. They are found in marine carbonate sediments. Coccoliths are plates formed of calcium carbonate, together forming a coccosphere, which envelopes a single flagellate cell - the coccolithophore. The coccolithophore is a primary producer in modern oceans. Some freshwater forms are known. However, coccoliths are found extensively in marine carbonate sediments. Most coccoliths are elliptical or circular discs, called shields, with plates arranged radially around a central area, which may be a void, crossed by bars, filled with a lattice or extended into a spine. The outer, distal side of the coccolith is generally more convex, with a pronounced sculpture, whereas the inner, proximal side is flat or concave and may have a different sculptural arrangement. Coccoliths are prone to the effects of calcite overgrowth and recrystallisation. Coccoliths, together with nannoliths (see below), constitute the group of small fossils termed nannofossils.
1. Pentagonal nannolith (Braarudosphaera)
2. Stellate nannolith (Discoaster)
Nannoliths are known from the Early Jurassic to the present day. They occur commonly in nannofossil assemblages. However, their relationship to coccoliths and coccolithophores is unclear. They have a wide variety of morphologies including polygonal to stellate forms. As with coccoliths, they are susceptable to calcite overgrowth and recrystallisation.
Dinoflagellate cysts
1. Proximate cyst with precingular archaeopyle (Gonyaulacysta)
2. Chorate cyst with apical archaeopyle (Hystrichosphaeridium)
3. Cavate cyst with intercalary archaeopyle (Deflandrea)
Dinoflagellate cysts first appear in the Late Triassic and become common from the Middle to Late Jurassic. They range to the present day, although they are much less diverse now than in the past. These unicellular organic-walled microfossils represent benthic resting cysts, which are produced within motile planktonic cells. The planktonic phase is a biflagellate cell composed of a series of plates forming a tabulate theca. In this phase, dinoflagellates, together with diatoms, form the basis for the marine food chain. They are the cause of red tides and can produce luminescence. The resting cysts reflect the tabulation of the thecate phase to a greater or lesser extent. The varying cyst paratabulation is important in classification, as is the overall cyst morphology. Proximate cysts may exhibit ridges and other forms of low ornamentation along paraplate boundaries or within paraplate areas. In a similar manner, chorate cysts develop a more extensive ornamentation including long, solid or tube-like processess. Cavate cysts are similar to proximate cysts but develop inner and outer layers, which may be in contact to varying degrees. All cysts types develop an aperture, called the archaeopyle, through which the cell contents excyst to produce a new motile cell. The archaeopyle is manifested in a variety of ways, related to paratabulation, and is a prime taxonomic feature.
1. Triangular cyst (Veryhachium)
2. Circular cyst (Micrhystridium)
3. Ovoidal cyst (Acanthodiacrodium)
3. Fusiform cyst (Leiofusa)
Acritarchs are known from Precambrian to Recent sediments, but develop their greatest diversity during the Lower Palaeozoic. They are unicellular marine cysts of unknown affinity. However, many acritarch groups may well serve a similar function to dinoflagellate cysts and occupy comparable niches. The cysts are generally triangular, circular, ovoidal or fusiform in outline, and often exhibit spines or septa. An excystment aperture, or pylome, is occasionally developed as either a circular opening, a cyclopyle, or median split.
Prasinophyceaen algae. Spheroidal cyst showing folds due to compression (Leiosphaeridia)
2. Thick-walled cyst with median split (Tasmanites)
3. Cyst with septa (Cymatiosphaera)
4. Cyst with equatoral flange (Pterospermella)
Prasinophyceaen algae developed in the Late Precambrian and range to the present day. They are marine planktonic cysts (phycomas) of unicellular green algae. The several groups included here have been previously assigned to the acritarchs. The cysts are spheroidal or ovoidal (Leiosphaeridia) and may be relatively thick-walled with pores (Tasmanites), or develop septa (Cymatiosphaera) or flanges (Pterospermella). The excystment aperture may be either a circular pylome or median split.
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