University of Leicester eBulletin

Ancient 'Clingfilm' Preserves Fossils

February 2003
No 46


Why are some fossils preserved so beautifully? Dr Jan Zalasiewicz of the University of Leicester Department of Geology believes it is because they were wrapped in a sort of clingfilm, hundreds of millions of years ago. He, together with Helen Jones, a Leicester undergraduate and Professor Barrie Rickards of Cambridge University, have been puzzling over why some graptolites (pictured below) - extinct, ocean-going animals – are so curiously preserved.

These particular graptolites are cone-shaped open spirals. Bury them in sea floor muds and they should fill with mud. Yet many remained empty of mud when they were squashed flat, as if these fossils had been wrapped in clingfilm before they were buried. Dr Zalasiewicz and his co-workers believe that this ancient ‘clingfilm’ was a combination of microbial films and jelly-like particles of ‘marine snow’ which fell from the ocean surface to a deep sea floor. The fossils would have been enveloped in this stuff, which prevented mud and silt from penetrating into their interiors.  

The beautifully-preserved graptolites provide a clue that thick (and probably very smelly) layers of this now-vanished organic matter must have carpeted large areas of sea floors in ancient times. Ocean floors these days are mostly much ‘cleaner’, because such organic gunk quickly decomposes: the nearest comparison in existence today can be found at the stagnant, virtually lifeless bottom of the Black Sea.  

[Photo: graptolites]

This finding will help in the interpretation of other fossils, and may also be of wider significance: for some of the now-vanished ‘clingfilm’ material was likely converted, after millions of years, into oil.

NOTE TO EDITORS:   Further information is available from Dr Jan Zalasiewicz, University of Leicester Department of Geology, telephone 0116 252 3928, fax 0116 252 3918, email

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