Doushantuo Formation is a recently discovered lagerstätte
in Guizhou Province, China that is most notable for its
contributions in the hunt for Precambrian
is of particular interest because its fossils, dating from
565 to 590 million years ago, predate the Cambrian
Explosion by at least 20 million years. The most fossiliferous
zones are estimated to be 570 million years old.
Doushantuo fossils are so exquisitely preserved through
fossilization that cellular structures are visible under magnification,
including soft tissues of putative metazoan embryos and
Perhaps the most significant and still contentious finding
from the Doushantuo fossils is evidence of bilateral symmetry,
key characteristic in many modern animals. Just when bilateral
symmetry appears (Precambrian or during the Cambrian) is
important question in evolution.
Vernanimalcula (meaning springtime micro-animal) has been
suggested as the oldest known bilateral
animal in the fossil record. If so, the fossils would validate
the widely held view that the major evolutionary diversification
of animals already had occurred prior to the Cambrian period
where a explosion
of metazoan life-forms apparently occurred.
Other researchers such as Bengtson and Budd (2004) offer evidence
that Vernanimalcula may be a taphonomic artifact produced by
growth of phosphate within a spherical object such as an acritarch.
biota of Doushantuo comprises algae, multi cellular thallophytes
(seaweeds), acritarchs, and cyanophytes, poriferans (sponges),
cnidarians, including possible tabulate corals. Most important
are the putative bilateral animal embryos. Some of these
animal embryos apparently record the early stage of cellular
division. There are also putative bilateral animal embryos,
some of which appear to be in an early stage of cellular
This is also in dispute, as Baily and co-workers, (2007) argued
that the putative embryos, Parapandorian, and putative eggs,
Megasphaera, could be fossils of giant sulfur bacteria similar
to Thiomargarita, a bacterium so large that it is visible
the naked eye. Baily's interpretation also provides a mechanism
for phosphatic fossilization found at Doushantuo through
mediated phosphate precipitation by the bacteria.
particular interest is that putative embryos from Doushantuo
Formation can be digitally dissected into their component cells,
and even the
examined. The fossils bear similarities to modern organisms
at early stages of development. However, they lack The absence
of ectodermal and mesodermal sheets of tissue at later stages,
suggesting that these animals are very primitive,
that they are preserved remains of
the embryos of a stem group of metazoans.