A Much Earlier Start for Animals
Where did all the animals come from? … The problem with the earliest animals, from a paleontologist’s perspective, is that they lacked hard parts.
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The answer lies in the unique molecules they left behind…. one such molecule [c]alled 24-IPC, … is only produced by Demospongiae, a class of animals that includes most modern sponges and is thought to constitute the roots of the animal family tree. The researchers acquired 30 pristine drill cores removed from underneath the southern Arabian Peninsula by the oil company Petroleum Development Oman. The cores ran through sedimentary layers and extended back beyond the Cambrian Explosion into the Cryogenian Period, about 635 million years ago near the end of a long, global ice age.
And what did they find? Read about it here.
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OK, I don’t get this. The article quotes “paleobiologist Kevin Peterson” as saying that this confirms that “we animals can all trace our origins back to sponges.” — although this is not in quotes so may be a misrepresentation. Now, if Demospongiae have 24-IPC and other animals don’t, they must either have developed it after the separation of lineages or it’s a plesiomorphy that all other animals have lost. The quote is obviously relying on the second alternative being true. But in that case, what indicates that these 635-million-year-old animals were “sponges”, let alone Demospongiae? For all we know, 24-IPC could have first arisen in single-celled organisms and subsequently been lost once or several times. We now know just one (molecular) character of these old organisms, which they happen to share with extant animals that are on a basal branch; it’s a big leap to assuming that they were similar in other ways.
Vasha – The “News and Views” article that accompanies the Nature paper (see http://tinyurl.com/bldepx) makes pretty much those points, and gives a more “biological” view of the finding.
Robert
Everyone knows that cold climates encourage industriousness and thrift.
Thanks Robert, but that article is behind the paywall. The headline does say that the find “places the rise of the sponge lineage more than 635 million years ago” — what reasons do they give for thinking that the molecule does belong to the sponge lineage? When were the Demospongiae previously thought to have separated from the other animals?