Press release/science journalism hype again. Sigh.
@John_Harshman Thanks. Can you give a few words on what the paper shows and doesn’t show.
Isn’t Kimberella, which is certainly also a bilaterian, already as old as that? And of course, we have no idea whether this creature is an ancestor of anything now living, though early bilaterians are always interesting…
What Puck said. This may be more certainly a bilaterian than Kimberella; at least the evidence is different. However, it’s simply impossible to impute ancestry to any fossil species.
What does it say about the Cambian explosion ?
I can’t even find the article. May not be published yet.
Obviously if you mean what does the paper say, I guess nobody knows yet. But if you mean “what are the implications of such a find for the Cambrian explosion,” not much. We already knew that bilaterians must have started diversifying before the explosion because we see bilaterians in the SSF (small shelly fauna) in the early Cambrian, and because trace fossils – as the article mentions – have strongly suggested it. The Erwin and Valentine book on the Cambrian is quite a nice read if you’re interested – E&V place the origins of the eumetazoa and the first bilaterians well before the Cambrian, but of course we don’t start seeing a lot of critters until the Cambrian because body sizes were constrained (E&V think this had a lot to do with oxygen levels, since most of these simple creatures get their oxygen through diffusion and therefore can’t support large body sizes) and because hard, easily fossilizable body parts weren’t plentiful, either.
The creationist take on the Cambrian, of course, is that you need a huge burst of special creation – this is what Meyer argues, and it’s just wrong. In order to make that argument you’ve got to treat the explosion fauna as though it poofed into existence ex nihilo, but that requires ignoring quite a bit of evidence. One notable example is Meyer’s omission (except from a deeply buried end-note) of any reference to the SSF.
Thanks to Paul Nelson for sending me the actual PNAS paper. Oddly, I still can’t find it anywhere on the PNAS web site.
To those who are wondering about Kimberella, there’s this:
“We propose that Ikaria is the trace maker of Helminthoidichnites [an ichnofossil] and potentially the oldest, definitive bilaterian, at least as represented in the fossil record of South Australia. Kimberella, the only other taxon from the Ediacara Member that is consistently reconstructed as a bilaterian, occurs significantly higher stratigraphically than the earliest appearance of Helminthoidichnites”
The DOI in the sciencedaily article worked for me:
I have never really understood how YEC’s can conclude that the Cambrian fauna is older than the Ordovicium to Pleistocene fauna. Since they don’t accept that fossils are diagnostic for formation age they really have no basis for biostratigraphic correlation at all. For them, all fossils are equally young and were pretty much created at the same time, and died at the same time, certainly so geologically speaking.
What then is the significance that in some places in the world in some rocks that we call Cambrian this particular fauna is present? There is really nothing unique about Cambrian rocks merely containing Cambrian fauna - elsewhere, Jurassic rocks merely contain Jurassic fauna, Devonian rocks merely contain Devonian fauna, Miocene rocks contain merely Miocene fauna and so on and on. Why single out the Cambrian for special significance?
In the creation ‘model’, what needs explaining is the exquisite sorting of the fossil assemblages - why is it that we don’t find fossils of all species mixed together? After all, they all were created together, lived together and died together. How did they end up being separated in the sediments if time is not a factor for this?
What they need to be thinking about is separation of contemporary assemblages by environment and/or climate, but I never see that. They are fixated by separation in time, a concept that doesn’t even exist in the YEC ‘model’!
When have they done this? I don’t think they do. Incidentally, the particular fauna this thread is about is Precambrian.
Don’t they do it every time they talk about the Cambrian explosion? As in, that is when life went from practically nothing to many new forms?
I don’t think YECs talk about the Cambrian explosion. Are you referring to anything or anyone specific?
David Tyler’s post-flood recolonisation model includes that Pleistocene fauna spread out later than Ordovician fauna which spread out after Cambrian fauna, so while technically they are all the same age, in most of the world Ordivician and then Pleistocene fossils post date Cambrian ones.
However, his model has major issues - such as the Silurian being only 22 years long. That’s probably less than the lifespan of individual eurypterids.
I’m not familiar with David Tyler. What does he consider to be Flood deposits?
IIRC everything above the Precambrian.
That makes no sense. If everything above the Precambrian is a Flood deposit, there can’t be any fossils involving “recolonization” and there can’t be any order.
That is pretty much what I meant. I don’t have anyone particular in mind, and perhaps I am mixing up YEC and ID here.
I think somebody’s mixing up something. Without specifics, there’s no way to know who or what.