Fossils hint at early complexity
Blob-like fossils dating back about 600 million years may
indicate that complex life evolved much earlier on our
planet than had been thought, scientists say. The animals
are less than a fifth of a millimetre long and have a two-
sided body plan previously thought to have existed much
later in Earth's history.
These "bilaterians" have what look like mouths and guts, as
well as internal and external layers of body tissue.
The findings are reported by a US-Chinese team in
Science magazine.
Sensory organs
If the analysis of the fossils by Jun-Yuan Chen and
colleagues is accepted by the scientific community, the
specimens would represent the most ancient evidence yet of
animals complex enough to have the symmetrical two-sided
body plan found in modern creatures, such as humans.
The animals - their scientific name is given as
Vernanimalcula guizhouena - even have what look like
pits in their outer surface that might have contained
sensory organs.
They were discovered in rocks from the Doushantuo
Formation, dated to a time researchers now refer to as the
Ediacaran Period.
This was a period when scientists think our planet was
emerging from a super-glacial event - the so-called
"Snowball Earth" which saw giant ice caps stretch almost to
the equator.
And it is at least 50 million years before the Cambrian
Period, when the fossil record shows there was an explosion
of life - a multiplicity of different shapes and sizes.
But the age of V. guizhouena suggests the roots of this
complexity are much older than had been thought and the
Cambrian explosion may not have been quite the sudden burst
scientists had believed.
Essential 'toolkit'
Professor Chen, from Nanjing University, and his team write
in Science: "The organisation of these fossils, taken
together with their provenance, indicates that the genetic
toolkit and pattern formation mechanisms required for
bilaterian development had already evolved by Doushantuo
times, long before the Cambrian."
However some scientists are sceptical of the claims,
suspecting that what have been characterised as fossils may
in fact be natural mineral formations.
Stefan Bengtson, from the Swedish Museum of Natural History
in Stockholm, said: "These may well have started out as
fossils, but we can't say much about their morphology."
He told Science magazine the presumed tissue layers may be
just thin, banded mineral crusts.
Traces of simple bacteria-like organisms in the fossil
record date back more than three billion years.
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