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I always wonder if fossils preserve the original size of the former animal. I can easily imagine that trough pressure the original animal is compressed and appe

I always wonder if fossils preserve the original size of the former animal. I can easily imagine that trough pressure the original animal is compressed and appears smaller as a fossil afterwards.

londons_explore 3y ago
Most fossils are two rocks - one around the animal, and one that fills the cavity of the animal later. The 'filler' usually isn't sedimentary - it tends to be formed by something that seeps through then crystalizes. Those crystals are super hard, and generally won't be compressible at all. Although there is a good chance the cavity compressed a bit before being filled.
- laszlojamf 3y ago
  TIL So is there like a flat imprint of all the biological residue or is it more like a shell, if you know what I mean? Also, what kind of crystals are w usually talking about?
  - systems_glitch 3y ago
    Depends on the fossil and enclosing material. A lot of the fossils we found as kids in slate were flattened, but sandstone fossils tended to be more like injection molded.
- jacquesm 3y ago
  A fantastic example of this is 'the petrified forest'. https://www.nps.gov/pefo/index.htm https://www.nps.gov/pefo/index.htm Straight from the Triassic.
andrewflnr 3y ago
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.

I always wonder if fossils preserve the original size of the former animal. I can easily imagine that trough pressure the original animal is compressed and appears smaller as a fossil afterwards.

londons_explore 3y ago

Most fossils are two rocks - one around the animal, and one that fills the cavity of the animal later. The 'filler' usually isn't sedimentary - it tends to be formed by something that seeps through then crystalizes. Those crystals are super hard, and generally won't be compressible at all. Although there is a good chance the cavity compressed a bit before being filled.

laszlojamf 3y ago
TIL So is there like a flat imprint of all the biological residue or is it more like a shell, if you know what I mean? Also, what kind of crystals are w usually talking about?
- systems_glitch 3y ago
  Depends on the fossil and enclosing material. A lot of the fossils we found as kids in slate were flattened, but sandstone fossils tended to be more like injection molded.
jacquesm 3y ago
A fantastic example of this is 'the petrified forest'. https://www.nps.gov/pefo/index.htm https://www.nps.gov/pefo/index.htm Straight from the Triassic.

andrewflnr 3y ago

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.