Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Lisa was hiking in a rocky area and in a rock, she saw what looked like footprints made by a bird. But weirdly, they were in a rock. Where did they come from?
The footprints were originally in mud or peat, but after a lot of time, the substance had been changed into rock
Birds do not make footprints in rocks.