S.No.

Fossil

Example

Mode of formation

1

Unaltered

(Preservation)

Wooly mammoths, 25,000 years

old, ice in Siberia, mummies, insect.

Whole bodies are found frozen in ice.

2

Altered or

petrified fossils

Bones, shell, teeth, wood etc.

Replacement of organic parts by mineral

deposits is called petrification.

3

Coprolite

Coenozoic mammals

Faecal pellets buried in sediments.

4

Moulds and

Casts

Gastropods (Mullusca)

from Portland

Moulds of hardened and fossilized mud that surround an extinct individual, the burried individuals have been completely destroyed but the moulds retained true

copies of their shape.

5

Impressions

Archaeopteryx feather, leaf

Remains in fine grained sediments on

which organisms died.

6

Imprints

Dinosaur footprints, prints of leaf,

skin, wing etc.

Footprint trails, tract of

organism.

7

Compression

Plants

Main tissues part disappears and only the outer tough parts remains intact covering into rock.