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The word fossil literally means something dug up from the ground. Preservation as a fossil is a very unusual occurrence; if every dead animal was fossilised we would long ago have been buried by them. Recycling is what ecosystems are all about, that way all the elements and minerals are available for new animals and plants. So how are fossils preserved.

Fossilisation is a very complex process; it can take many different forms and we don't understand everything about it. The thing that has to be ensured for every fossil is that the recycling process is interrupted at some stage - precisely when can vary. The way this is achieved is by burying the remains of the animal. The burial process may be what kills the animal, or at the other extreme may only happen long after the animal is dead and its remains have been broken and scattered.

Mere burial, however does not ensure an animal's fossilisation. Subterranean conditions must also be favourable; the activity of worms or bacterial action can destroy bone and water in the sediment can disintegrate it. Providing the bone survives all this it is still not plain sailing. The sediment in which it is buried could be eroded before the fossil is found or it could be buried so deep or folded so strongly that the rock is metamorphosed and the organic remains destroyed. Even if the Mesozoic sediments in which the fossils are are at or near the surface now it does not mean that the fossil will ever be discovered and excavated.

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15y ago

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