BEIJING, Jan. 23 (Xinhuanet) -- A recent fossil
discovery in South China, combined with fossils found in 1998 and 2000 could
reveal how the earliest known egg-laying organism developed from embryo to
Researches discovered thousands of
600-million-year-old fossilized embryos in the Doushantuo Formation nine years
ago. Two years later, the same team unearthed fossils of a tubular coral-like
animal, named Megasphaera ornata, which appeared to be adult versions of the
embryos discovered earlier.
The case for a relationship between the two fossil
types grew stronger following the recent discovery of about 80
intermediate-stage fossils that have traits in common with both groups.
The finding, to be detailed in the February issue of
the journal Geology, could provide the missing link between egg and adult
versions of one of Earth's earliest animals.
"The new fossils provide some suggestive evidence
that these two groups of fossils are linked developmentally," said study team
member Shuhai Xiao of Virginia Tech.
On the outside, the early and intermediate stage
embryos look very similar. They are about the same size -- about 0.02 inches
wide or about as big as a grain of sand -- and both have similar outer
coverings, or embryonic envelopes.
It's what's inside the egg that is different. Using
an imaging technique called microfocus X-ray computed tomography (microCT), the
researchers virtually peeled away the envelope to reveal the new fossils’
What the researchers found were three-dimensional
spiral structures that look like grooves on a screw.
The only signs of these coils on the outside of the
embryos are tiny holes arranged in a pattern resembling stitches on a baseball.
Traces of these coils are also found on the external coverings of the adult
Some of the intermediate embryos also appeared to be
unfurling, encouraging the speculation that if the process had continued, the
embryos would distend like a stretched slinky or a flattened fuselli noodle into
the tubular adult form.
The new embryos could help shed light on how ancient
animals developed and whether the process was similar to that of living
organisms. Ancient embryos and embryos from modern day animals are remarkably
similar, but the developmental journey from egg to adult for ancient organisms
is still cloaked in mystery.
"Now we have isolated dots. We need to connect them
and make a complete story before we can say anything about their evolutionary
relationship," Xiao told LiveScience.
The researchers are hopeful that they can find later
stages of embryo development for M. ornata.
"I think this is an encouraging sign that later
embryonic stages may still be preserved in this rock," Xiao said. "If we keep
looking, we may even find a developmental sequence."