I reported a while back that there was a possibility that the phosphatized pre-Cambrian Doushantuo specimens might not be embryos—they might be a particular class of bacteria—but there may be evidence against that hypothesis. John Lynch finds a description of more advanced embryos, intermediate stages that would link at least some of the blastulae described so far to unambiguous multicellular organisms.
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There are these fossilized embryos from the Ediacaran, approximately 570 million years ago, that have been uncovered in the Doushantuo formation in China.
Gah! Just last week I told my students about the Doushantuo embryos and mentioned that they might not actually be metazoan embryos...now I need to go back and qualify that qualification.
Covering cutting-edge research in undergraduate classes is hard. Oh, why do we have to pay attention to new data? It makes things so confusing. Why can't truths just be eternal and unalterable? Oh, right. This is science, and we live in the real world.
We must save the embryos. They are like snowflakes...
I suspect that the truth hasn't changed, but rather our knowledge and understanding is changing. I tend to think of truth as eternal and unalterable.
Sure, sure, you'll gladly kill babies but you want to 'save' a few cell fossils that might be embryos?
I say we ABORT the Doushantuo embryos!
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(oh wait, geology aborted them ages ago ...)
Good clarification. What actually happened is (barring time travel) unalterable and eternal, and what we think we know is just our interpretation based on the evidence we have.
I guess I should've put truths in quotation marks, as in "beliefs that are held no matter how much evidence is amassed against them".
Frank and PZ,
These are interesting specimens no doubt, but they may not be enough to save the embryo hypothesis. Presently there aren't any fossils representing unambiguous multi-cellular organisms in the Doushantuo that haven't been challenged as diagenetic artifacts - nor are there any gastrulas. Pretty surprising given the millions of specimens available isn't it? Also, you can see in these pictures that the fancy-looking holes on the outside are irregularly-spaced and coalesce into grooves, which is more characteristic of taphonomic (preservational) artifacts than primary biological features. It must be remembered that what we are looking at here are phosphatic structures that are commonly encrusted and impregnated with mineralogical features that often have little or nothing to do with the organism's primary biological features. Many of the Doushantuo structures are riddled with internal tunnels and grooves (some of which are spirals) - again artifacts of their preservation (see Xiao and Knoll 1999 Figure 7). When the paper comes out, look carefully and critically at the images and decide for yourselves.
I always thought the Doushantuo embryos were very odd finds. All of this has encouraged me to go through the literature on these fossils in more detail (although I don't have the expertise required to assess possible taphonomic artifacts, etc., so I'm not sure I'll be a good critical reader).
Right. As though I'll ever have time to do all that reading...
Other, admittedly contentious eukaryote fossils are dismissed in a forthcoming paper
Cheers
Joe Meert