Fossils

Men have known fossils since time immemorial. They have been finding them in the areas with outcropping rocks, particularly limestones. In prehistoric times they used them as amulets. And fossils do have a magic power, indeed. They can tell us, for instance, where to find the deposits of coal or petroleum. This, naturally, is not due to any magic, but merely to painstaking work of many generations of geologists and paleontologists.
Chief merit is due primarily to W. Smith, English scientist, who noted as early as last century that some types of fossils appear only in certain strata and that on the basis of these fossils we can pursue and compare geological strata over long distances. W. Smith then formulated the law of stratigraphic correlation providing that the strata containing identical fossils are of the same age.
On the basis of his conclusions he also formulated the so-called Law of Superposition which states simply that the geological strata were deposited successively on top of one another. The strata situated at greater depths are older than those situated on top of them. However, it can happen during orogenic processes that some parts of the Earth crust have been so folded that the strata sequence has been inverted giving rise to the so-called inverted succession.
The study of fossils was of great importance also as a proof of Darwin's evolution theory. It is the very fossils that illustrate in a wonderfully abbreviated form the successive evolution from the simplest forms of life over more complex forms to the so far most advanced organism living on this planet - the man.
The French engineer Joachim Barrande, who acted as tutor to the crown prince of France , was a contemporary of Ch. Darwin. The revolution of July 1830 finally swept Barrande to Bohemia where in 1833 he became acquainted not only with Czech scientists, but also with interresting imprints of long extinct animals. According to the story by J. Arbes, The Trilobite, this happened on the Dívčí Hrady (at present Ctirad, a natural monument). The finds of the trilobites enchanted the learned man so much that he devoted the next fifty years of his life to their study. When he was dying in 1883 at the age of 83 years, he could look with pride at his life's work. In the 22 volumes of his monumental work "Systeme silurien du centre de la Boheme", comprizing more than 6 000 pages and 1 160 plates in colour, he described more than 3 650 species, most of them new to science. This work ranks among the most extensive scientific works of all ages and fields created by a single man.
In his books Barrande describes minutely the trilobites, cephalopods, brachiopods and other families of extinct animals. His work on the bivalves is interesting for Czech science in a particular way. Barrande gave numerous new genera Czech names, such as Synek (Son), Dceruška (Daghter), Královna (Queen). According to the resolution of the geological congress of Bologna in 1881, the names of plants and animal may be only Latin or Latinicized. However, the names given before the Congress remained valid, as a result of which we can still read in scientific literature of the world such Czech names as Panenka (Girl) vendita (in honour of Smetana's opera "The Bartered Bride") of Bábinka ("Old Girl") prima the name with which Barrande called his charwoman - the mother of the great Czech poet, Jan Neruda.
The work of J. Barrande was of enormous significance for Czech and universal science. It is no wonder, therefore, that we encounter his name even at present. The vast area between Kralupy and Klatovy, filled with the deposite of the Proterozoic and Paleozoic seas, is called the Barrandien in his honour. The folded limestones of the Barrandov (Barrande's) rock rank among the remarkable sights of Prague and the Barrandov Film Studio, situated on top of them, is a household world to every Czech cinema goer.
After this historical and biographic digression let us return to the fossils. As we know, the organic remains decompose fast after the death of any organism, and it is actually a favourable coincidence which has preserved at least a small fraction of the immense wealth of extinct plants or animals. Particularly the calcareous tests had a chance of preservation as they sank into the fine mud at the sea floor. That is why most fossils can be found primarily in the marine limestone strata.
The oldest fossils ever have been found in siliceous deposits in South Africa. Bar-shaped formations recalling bacteria and spherical formations similar to cyanophycaea are older than three billions of years. In the Czech Republic minor fossils of unicellular organisms belonging to plants (and, perhaps, some of them also to animals) are known from Proterozoic deposites; they have been found and described i.e. in the Šárka Gorge, i.e. directly in the territory of Prague. Their age is estimated at more than 350 millions of years.
Let us have at least a short glance at some significant groups of extinct organisms.
The most popular fossils indubitably are the remains of the trilobites. They were marine arthropods of the Paleozoic the upper side of which was provided with a chitinous carapace. They had to shed this crust several times during their lifetime, as a result of which we often find their shed carapaces, the so-called exuvia. This also explains the relatively high number of trilobite finds. As they fed primarily on dead organic remains, they are often called ocean floor sweepers.
The number of important Paleozoic fossils in Prague area includes brachiopods. They were sea animals the tests of which recall the bivalves. They too consist of two, the upper and the lower, valves. In contradistinction to bivalves their plane of symmetry proceeds across these valves.
The fauna of Paleozoic seas included also various echinoderms. Characteristic were e.g. the crinoids. In the Dalej profile, a national natural monument, we can find isolated parts of their stems and the name of the local Lobolite Slope is due to the conspicuous floater formations aiding some crinoid species to float freely in sea water.
Of primary importance from the stratigraphic viewpoint are the graptolites. They were minor colonial organisms some 1 mm in size living in small cells of chitinous matter. These cells were ranged in rows on long branches. They can be found in large quantities in fine-grained dark shales rich in pyrite. It is on the basis of the very occurrence of the individual species of graptolites that the Ordovician and the Silurian are divided into zones.
In conclusion of this brief survey let us mention the hyolithids - somewhat mysterious small marine organisms with conical shells, probably near relatives of molluscs. They occur i.a. also in the Ordovician sediments of Prague.
The wealth of fossilized forms of life, however, is not limited to the paleozoic strata of the Prague basin. A large number of deposits has resulted from the activities of the Upper Cretaceous sea. On the Bílá Hora (White Mountain), for instance, as well as in Přední Kopanina, we can find the remains of marine bivalves, most frequently of genus Inoceramus. Even before this sea had flooded Bohemia there was a freshwater lake in the region of Prague in the Upper Cretaceous in which even the imprints of plants have been preserved. The leaves of genus Credneria recall the plane tree. In Prague their imprints can be found e.g. in Chuchle.
Many fossils are aesthetically impressive and most of them are very important to science - not only as a guide when looking for the strata with useful minerals, but also as an instruction on the laws of evolution, when the boom of a species is followed by its decline and extinction. Thus the study of fossils may help mankind to understand better and perhaps even solve the problems of its own.

Reconstruction of life in the Silurian sea in Prague area.

The biggest invertebrates of Paleozoic seas in Prague area were the chelicerates of genus Pterygotus which attained a length of as many as 3 m

Nautiloid cephalopod of genus Hercoceras (Devonian, Hlubočepy).

Baltisphaeridium bohemicus, one of the oldest fossils in the Czech Republic, of only fractions of mm in size (according to M. Konzalová).

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