Before life exploded in the Cambrian, there were worms

Illustration of a segmented worm leaving traces.

Enlarge (credit: Dr. Zhe
Chen/Nanjing Institute of Geology and Paleontology)

The Cambrian is rightly famous for being the period when animal
life first exploded into a
dizzying diversity of forms
, including some body plans that
remain with us today. But the first animals in the fossil record
predate the Cambrian by tens of millions of years. Entire
ecosystems of creatures appeared over about 50 million years near
the end of the Ediacaran Period and then vanished at the start of
the Cambrian.

But the Ediacaran animals were rather strange, with body plans
that don’t even have the same starting materials as the more
familiar Cambrian forms do. And most of them weren’t mobile,
instead simply attaching themselves to surfaces and staying there.
There were, however, limited indications that the ancestors of
Cambrian animals had already evolved in the Ediacaran. Traces left
in sediments indicated that something was moving through them, and
one odd disk-like creature appeared to have had a bilateral body
plan. But the tracks weren’t left by anything disk shaped, raising
questions about what else might have been moving around in the
Ediacaran.

Those questions have been at least partially resolved with
today’s announcement of Yilingia spiciformis, an Ediacaran worm
that wouldn’t look entirely out of place in today’s oceans.
Yilingia was segmented, it created tracks, and it even appears to
have been able to burrow into sediments. And it managed to do all
that without any prominent structures at its head.

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Source: FS – All – Science – News
Before life exploded in the Cambrian, there were worms