How do dinosaur footprints get fossilised? © Getty

How do dinosaur footprints get fossilised?

A bit of luck, a lot of sediment and time may just result in a stony, fossilised footprint. Okay, make that a lot of luck.

Asked by: Rob French, Sheffield

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Last December, over 80 dinosaur footprints were revealed at a site in East Sussex. They had survived for over 100 million years – and bear witness to the huge amount of luck involved in creating such fossils.

First, the creatures must step through sediment that is pliable enough to record their footprints, but not so pliable it gets washed away before being protected by fresh sediment. Each footprint then has three chances to become a fossil: as the original impression (the ‘true track’), as its fainter impression in the underlying layers (the ‘undertrack’), or by new sediment filling in the original impression (the ‘natural cast’) and hardening. Either way, as the layers of sediment build up, the pressure turns them to rock which – given yet more luck – will preserve the print intact for aeons.

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