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