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they have an uncanny resemblance to the human male reproductive
organ, and hence their informal name of 'penis worms'. Jean dredged
up some penis worms from a Swedish fjord along with some of the
mud from the bottom. Back in the laboratory he observed the action
of the worms as they moved across this mud. The worms had a very
distinctive motion, anchoring themselves by means of small spines in
their cuticle and then projecting themselves forward in a series of
peristaltic waves. The pattern they produced in the mud was remark-
able, in that it closely resembled the patterns of Treptichnus in rocks 541
million years old (Fig. 14). Here then, was evidence of worms begin-
ning to burrow into sediment and the opening up of a new world of
opportunities for life in the sea.
This explosion of life at the beginning of the Phanerozoic Eon ( our
eon) transformed the oceans. It was the third pivotal biological event,
the first being the origin of life itself, the second being photosynthe-
sis, and then this one, often named the Cambrian Agrarian Revolu-
tion. As animals began to burrow into the seabed, new sources of
food became available, including a vast untapped resource of organic
carbon. There were new homes for living in and hiding in, and new
patterns of moving and feeding. There are remarkable similarities
between this Cambrian Agrarian Revolution and its near namesake,
the human agrarian revolution that took place 541 million years later.
Both involved new patterns of making food, releasing a surplus of
energy that allowed complex new systems to develop. What began
with organisms burrowing into the sediment cascaded rapidly into a
series of steps towards complexity—and transformation of the ocean
environment.
The first Cambrian animals were essentially soft-bodied, and left
only the traces of their activity. Then, as competition for resources
increased and animal ate animal, mineralized skeletons evolved for
protection, and also to support new ways of living. A variety of
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