According to George and Roberta Poincar,
extinct multicellular life, like dinosaurs, cannot be brought
back to life for two major reasons: DNA extracted from insect
inclusions in Amber are damaged, and certain key components are
missing. There are DNA repair systems, but until what is missing
and what actually needs to be repaired is known, nothing can be
done. Secondly, even if complete DNA from and extinct animal was
obtained, it would have to be inserted into a host egg, and be
convinced that it is in an embryonic state, and the egg would
have to be made to develop normally without it turning into a
mass of undifferentiated tissue.
The oldest ever DNA extracted from an
insect inclusion in Amber is 125 million year old early Cretaceous
Lebanese Amber, (on July 19th, 1992).