Figure 1: With its five eyes and long, flexible proboscis,
Opabinia resembles a creature out of science fiction. Yet once it
was very real. Its fossilized remains, along with those of hundreds of
other species, are found in ancient marine sediments dating back to a
geological period about 530 million years ago. The diversity of
skeletonized life forms from this time is so spectacular that the period
has been dubbed the Cambrian explosion. Many of the creatures that arose
then are now extinct. But the basic body plans of all animals on earth
today were invented during the Cambrian or the period just preceding it.
Advances in the fields of molecular and developmental biology are allowing
evolutionary biologists to reconstruct basic aspects of the developmental
control systems of long-extinct animals to understand how new forms arose
from existing ones. (Illustration by D. W. Miller.) |