Footprint (geology)

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An imprint in the geological sense is a testimony to primeval life that has been handed down as a hollow form. It can be a trace fossil or a body fossil , depending on whether the imprint was caused by a living animal or whether it depicts a dead living being.

Trace fossil

Single fossil footprint of the trace genus Eubrontes in sandstone of the Moenave Formation (Lower Jurassic), Arizona, USA. Eubrontes may have been caused by larger theropods, in this case probably Dilophosaurus .

Trace fossils handed down as footprints have usually been produced by animals who have walked over a sediment surface and thereby pressed their limbs into the sediment. In principle, it is therefore a fossil-handed step seal . Such a tradition can take place if the step seal was covered with further sediment before wind and weather could destroy it again. If the overlying sediment is completely eroded again after many millions of years , the fossil footprint becomes visible again on the surface of the terrain.

Body fossil

Impression of a small part of the bark of a "shed tree" ( lepidodendron ) in the sandstone of the Upper Carboniferous of Nova Scotia , Canada, pocket knife as a measure of size.

The transmission of the dead body of a living being as an imprint can take place with or without transmission of the actual body. With tradition of the body, an imprint is simply the counterpart or negative of this body. Every geologist and hobby collector knows that when you split a sedimentary rock block and uncover a fossil, ideally the split surface of one half of the block contains the body that has been passed down as positive and the split surface of the other half of the block contains the corresponding negative, the imprint.

Under certain circumstances, however, it can happen that the actual body has been completely dissolved by diagenetic processes or by weathering and only leaves a cavity in the sediment in which it was embedded after its death. Thus, only a hollow form, an impression, is handed down in the sedimentary rock. If a mineral is subsequently precipitated in this hollow form, one speaks of a fossil pseudomorphism .

literature

  • Bernhard Ziegler: Introduction to Paleobiology Part 1: General Paleontology. 5th edition. E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 1992, ISBN 3-510-65316-5 .