Scientists move closer to linking embryos of the Earth's first animals to adult form

Virginia Tech News ^ | 11-3-04 | Susan Trulove

[beavus]

Blacksburg, Va., November 3, 2004 -- In 1998, Shuhai Xiao and colleagues reported finding thousands of 600-million-year-old embryo microfossils in the Neoproterozoic Doushantuo Formation, a fossil site near Weng''an, South China (Xiao, S., Zhang, Y., and Knoll, A.H., 1998, "Three-dimensional preservation of algae and animal embryos in a Neoproterozoic phosphorite," Nature, v. 391). Within the egg cases they examined at that time, they discovered animals in the first stages of development - from a single cell to only a few dozen cells. "The cellular preservation is amazing," said Xiao, assistant professor of geosciences in the College of Science at Virginia Tech.

But what kind of adult would these ancient embryos have hatched into?

In 2000, Xiao's team reported the discovery of a coral-like animal that might be a candidate for parenthood (Xiao, S., Yuan, X., and Knoll, A.H., 2000, "Eumetazoan fossils in terminal Proterozoic phosphorites?" Proceedings of the National Academy of Sciences, USA, v. 97). "It was tubular, not spherical. But in some of the best specimens, we could see that the tube branches and has cross-walls," Xiao said. "But can it be linked to the embryos?"

Upon examination of more embryos collected from the original site, Xiao's research team has discovered some embryos that may be at the hatching stage. He will report on this latest finding at the Geological Society of America meeting in Denver, Nov. 7-10.

"Looking now at these egg cases, we can see clockwise spiral grooves, as if a knife sliced the egg open," Xiao said. "The embryo was beginning to hatch. When we removed the egg case, we found that the post blastula but pre-hatching embryo at this stage is beginning to transform into a spiral animal. Each such animal had three clockwise spires. After hatching, the spiral organism began to uncoil slightly," Xiao said.

"They look as if they can unwind to a tube structure. We are looking for more evidence, but if that is true, it might link the embryo fossils to the tubular coral-like animal."

The researchers will slice open a hatched embryo specimen that appears to be unwinding to see if it has cross-walls. "That would indicate it is related to the tubes," Xiao said.

"These organisms lived 600 million years ago – before big animals. This the very first moment of animal evolution preserved in the fossil record."

The research, "Animal Embryos from the terminal Neoproterozoic Doushantuo Formation: How did they hatch?," written by Xiao, and Chuanming Zhou and Xunlai of the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, will be presented at 1:30 p.m. Wednesday, Nov. 10, in rooms 108/110/112 of the Colorado Convention Center.

Xiao's research is supported by the National Science Foundation. Images and information about the Doushantuo project are at http://www.geol.vt.edu/paleo/Xiao/#Research.

[beavus]

Embryogenesis was a very very early evolutionary development.

[Popman]

Pictures

[js1138]

ping

[ClearCase_guy]

"This the very first moment of animal evolution preserved in the fossil record."

Evolution implies change. More specifically, change from one species into a different species. To see a 600 million year old fossil and say "this is change" seems silly. Do they know what came before? Do they know what came after? How can they recognize this "moment of animal evolution"?

They found an interesting thing which they had not found before. That's all.

[beavus]

How can they recognize this "moment of animal evolution"?

The article is a bit hyped, but looking beyond the hype, it does show us the earliest fossil evidence for embryogenesis, and at 600 million years, it is very old. It seems logical that embryogenesis would have evolved at a time when young and adult were morophologically very similar, and that is kind of what we have here.

Of course, the fossil record can only demonstrate disconnected points along the evolutionary continuum. There is no continuus fossil movie of evolutionary change. Unless you are a poofist, this causes no particular intellectual difficulty.

[beavus]

Thanks, Popman.