Taphonomy of fossilized embryos

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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. I've mentioned them before, and as you can see below, they are genuinely spectacular.

parapandorina.jpg
Parapandorina raphospissa

But, you know, I work with comparable fresh embryos all the time, and I can tell you that they are incredibly fragile—it's easy to damage them and watch them pop (that's a 2.3MB Quicktime movie), and dead embryos die and decay with amazing speed, minutes to hours. Dead cells release enzymes that trigger a process called autolysis that digests the embryo from within, and any bacteria in the neighborhood—and there are always bacteria around—descend on the tasty corpse and can turn it into a puddle of goo in almost no time at all. It makes a fellow wonder how these fossils could have formed, and what kind of conditions protect the cells from complete destruction before they were mineralized. Another concern is what kinds of embryos are favored by whatever the process is—is there a bias in the preservation?

Now Raff et al. have done a study in experimental taphonomy, the study of the conditions and processes by which organisms are fossilized, and have come up with a couple of answers for me. Short version: the conditions for rapid preservation are fairly easy to generate, but there is a bias in which stages can be reliably preserved.

Continue reading "Taphonomy of fossilized embryos" (on Pharyngula)

6 Comments

There are these fossilized embryos from the Ediacaran,… they are incredibly fragile—it’s easy to damage them and watch them pop (that’s a 2.3MB Quicktime movie)…

I’ve tried those. Pop Rocks.

Layman question:

How is it known that these were embryos and not just some cell colony?

Some people over at Pharyngula have asked similar questions. Apparently the “casing” that’s visible around some of the cell clusters is pretty definitive of a certain stage of embryo, and may well be what protected the embryos long enough to permit preservation.

PZ added these remarks down in the comment thread at his site:

Could you go into a bit more detail as to how we know these are indeed fossilized embryos rather than fossilized something else or some interesting rock formation?

Size, similarity to extant embryos, regularity, uniformity of blastomere size, and the presence of multiple near-identical exemplars in the same samples. There are also anatomical details like the preservation of the fertilization membrane. The fossils are so well preserved that you can even zoom in with the SEM and see surface featurs. The Raff paper has SEMs of urchin embryos that are in many ways indistinguishable from the fossils.

In the post above, I unnecessarily invented my own term, “casing,” when I should’ve just used PZ’s phrase, “fertilization membrane.”

How is it known that these were embryos and not just some cell colony?

Clearly they can’t be colonies, they must be multi-cells, and those are simply mother cell walls you are seeing that remain due to chemical inducement ;)

/blastfromthepast

Major cool factor 10.

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This page contains a single entry by PZ Myers published on April 3, 2006 11:09 PM.

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