The Palaeozoic - era of the trilobite empires !

Trilobites, as we know them from their fossilized remains, existed in the Palaeozoic only and became extinct at the end of the Permian, some 250 million years before our time. The reasons for their evolutionary defeat are not entirely clear. There are strong indications (some scientists talk of evidence) that early trilobites or their immediate ancestors may have existed in the late Precambrian already, but we have not yet found fossilized remains of these animals. This may be due to the fact that early trilobites may have had a soft, non-calcified exoskeleton that hardly stood a chance of getting preserved. More information can be found here.

The Palaeozoic, like all other geologic eras, is sub-divided into periods and epochs. Here is a simplified breakdown of the geologic eras as is currently accepted. Please bear in mind that this information is subject to constant change, as improving knowledge leads to corrective amendments of this chart pretty much every year. Time spans may shrink or grow, start dates may climb and fall on our time ladder, the treacherous steps of which being but slippery marks. The datings shown in our chart are, to a large extent, in accordance with the findings of the International Subcommission on Global Stratigraphy as published in 2004. This document can be downloaded in our Document-Section as a PDF-file.

Hereafter you can find a more detailed breakdown of the Palaeozoic. This chart shows the international chronostratigraphic units of the Palaeozoic, as approved by the ICS and ratified by the IUGS (2004).

Sometimes you may come across different descriptions for the very same subdivisions in stratigraphic charts. For example, some charts list the Middle Devonian as a "Series" while others list it as an "Epoch". The reason for that can be found in two different approaches used: One is based on chronostratigraphy, the other on geochronology. While the first refers to subdivisions based on the age of rock strata in relation to time, the latter determines the absolute age of rocks by various methods like radiometry and the like. To quote from Wikipedia:

"It is important not to confuse geochronologic and chronostratigraphic units. Geochronological units are periods of time, thus it is correct to say that Tyrannosaurus rex lived during the the Late Cretaceous Epoch. Chronostratigraphic units are geological material, so it is also correct to say that fossils of the genus Tyrannosaurus have been found in the Upper Cretaceous Series. In the same way, it is entirely possible to go and visit an Upper Cretaceous Series deposit - such as the Egyptian mangrove deposit where the Tyrannosaurus fossils were found - but it is naturally impossible to visit the Late Cretaceous Epoch as that is a period of time."

© Images of Perisphinctes, Odontochile and Cambropallas on this page courtesy of PaleoDirect, exclusive provider of trilobite images in support of this web site.

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