Trilobite Olenoides erratus. Source: Mark A.Wilson A fossil is
the preserved remain of a lifeform that lived in prehistoric
times. Most commonly fossils are mineralized parts or a whole
organism which is no longer alive. In other cases the fossil may
contain actual remains of the dead organism; in particular, DNA
may be preserved over long periods of time under the right
conditions, since DNA is fundamentally an inanimate molecule.
While the most familiar fossils are those derived from animals
and plants including such exotic species as dinosaurs and woolly
mammoths, there are also fossils from ancient bacteria. There
are several methods of fossil formation including re-
crystallization, permineralization, compression, molding and
entombment. Examination of fossils was the earliest technique of
palaeoentology, the study of ancient lifeforms, and it continues
as the companion of molecular biology, to be key in the
elucidation of phylogenies (ancestral relationships of species).
The earliest animal fossils date