Press release/science journalism hype again. Sigh.
@John_Harshman Thanks. Can you give a few words on what the paper shows and doesnât show.
Isnât 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 interestingâŚ
What Puck said. This may be more certainly a bilaterian than Kimberella; at least the evidence is different. However, itâs simply impossible to impute ancestry to any fossil species.
What does it say about the Cambian explosion ?
I canât 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 May not be published yet.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 âwhat are the implications of such a find for the Cambrian explosion,â 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 â as the article mentions â have strongly suggested it. The Erwin and Valentine book on the Cambrian is quite a nice read if youâre interested â E&V place the origins of the eumetazoa and the first bilaterians well before the Cambrian, but of course we donât 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 canât support large body sizes) and because hard, easily fossilizable body parts werenât plentiful, either.
The creationist take on the Cambrian, of course, is that you need a huge burst of special creation â this is what Meyer argues, and itâs just wrong. In order to make that argument youâve 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 Meyerâs 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 canât find it anywhere on the PNAS web site.
To those who are wondering about Kimberella, thereâs this:
âWe 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 Helminthoidichnitesâ
The DOI in the sciencedaily article worked for me:
I have never really understood how YECâs can conclude that the Cambrian fauna is older than the Ordovicium to Pleistocene fauna. Since they donât 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 âmodelâ, what needs explaining is the exquisite sorting of the fossil assemblages - why is it that we donât 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 doesnât even exist in the YEC âmodelâ!
When have they done this? I donât think they do. Incidentally, the particular fauna this thread is about is Precambrian.
Donât 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 donât think YECs talk about the Cambrian explosion. Are you referring to anything or anyone specific?
David Tylerâs 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. Thatâs probably less than the lifespan of individual eurypterids.
Iâm 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 canât be any fossils involving ârecolonizationâ and there canât be any order.
That is pretty much what I meant. I donât have anyone particular in mind, and perhaps I am mixing up YEC and ID here.
I think somebodyâs mixing up something. Without specifics, thereâs no way to know who or what.