Three-dimensional photographs of fossils (Part 2): Stereophotography of ancient micro-organisms

Dr Robert Sturm (Austria) In the past 60 years, microfossils have increasingly attracted the attention of earth scientists for several reasons. Firstly, they are highly useful in biostratigraphic respects; secondly, they can be easily determined by light- or electron-microscopic studies in most cases; and thirdly, sampling, preparation and storage of microfossils is carried out according to well-defined and mostly simple procedures. By definition, microfossils are the petrified relics of micro-organisms, which have mainly colonised aquatic habitats of the Tertiary or older epochs of earth history. Most of these ancient micro-organisms measured less than 1mm in size, so any scientific documentation of their remains requires a magnifying glass or, better still, a microscope. In certain cases, the size of microfossils is between 10µm and 100µm, which necessitates the use of an electron-microscope to elucidate their structure and to determine the species. Fossils measuring less than 10µm in size chiefly belong to another category of fossils, that is, nannofossils (for example, coccoliths). Typical representatives of microfossils include radiolaria, foraminifera, ostracods and diatoms, which may be used as index fossils within certain local or regional strata. A special role is taken by conodonts, which are small dental structures belonging to the so-called ‘conodont animal’. This is supposed to be distantly related to the lancet fish (Brachiostoma). While foraminifera, radiolaria and ostracods have colonised the earth with varying abundances since the Early Cambrian (570Ma), the occurrence of conodont animals seems to be restricted to the time period ranging from the Middle Cambrian (about 550Ma) … Read More

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Coccoliths: Tiny fossils with immense paleontological importance

Robert Sturm (Austria) Microfossils, such as foraminifera, diatoms, ostracods and conodonts, are usually studied using a magnifying glass or under a stereo-microscope. However, nannofossils, such as coccoliths – with sizes measured in micrometres – are way beyond the resolving power of these optical tools. Fig. 1. Biology of a coccolithophorid alga. Abbreviations: cl — coccolith, cp — chloroplast, f — flagellum, Ga — Golgi- apparatus, hn — haptonema, m — mitochondria, n — nucleus, nl — nucleolus, v — vesicle (modified from Bown, 1998). In general, coccoliths are very regularly shaped, fine calcite platelets that are produced by unicellular, autotrophic (that is, capable of synthesizing their own food from inorganic substances), marine algae – the so-called Coccolithophorida (phylum: Haptophyta; class: Prymnesiophyceae). They are arranged in spheres (coccospheres) that completely enclose the organisms. After the death of the algae, the coccospheres are either preserved entirely or fall to pieces. Then, either way, they settle on the seafloor and can do so continuously over periods of millions of years. Coccoliths are of immense value to the palaeontologist, because of their highly specific shapes. For this reason, they are frequently used for biostratigraphic investigations, where the ages of lithological strata are estimated by using the fossils found in them. Palaeontology distinguishes between two types of coccoliths – the holococcoliths and the heterococcoliths. The first type is composed of calcite crystals of identical size, whereas the second consists of variably-sized calcite crystals. Extant Coccolithophorida preferentially produce heterococcoliths during the phase of their life cycle … Read More

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