When a rock is squished, it's usually compressed in one direction but spreads out in the other. You do get fossils that are completely flattened in one directio

When a rock is squished, it's usually compressed in one direction but spreads out in the other. You do get fossils that are completely flattened in one direction, but the other dimensions will be pretty much original. I don't think you'll ever see a rock or fossil just get smaller in every dimension under pressure. At minimum you would see really obvious distortion. Ed: to clarify my first two sentences, when you see a flattened fossil, IIRC they were already flat before they turned to rock, by relatively light forces acting on the body. It wouldn't spread out sideways unless the whole rock it was fossilized in was later squished by geologic forces.