Burgess Shale Cephalopod

DWhatley

Cthulhu
Staff member
Moderator
#2
Thanks Roy!

Here is a link to a UK announcement:
Newly discovered fossil revealed as the mother of modern-day molluscs

"Our discovery allows us to push back the origin of cephalopods by at least 30 million years, to the famous Cambrian explosion about a half-billion years ago," said Jean-Bernard Caron of the Royal Ontario Museum in Toronto.
An abstract from Charles D. Walcott and the discovery of the Burgess Shale the might have additional info to interest our fossil members.
 

OB

Colossal Squid
Staff member
Moderator
#4
I'll be very VERY interested to see how this affects the whole idea of nautiloids to coleoids transition.
 

Phil

Colossal Squid
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Registered
#5
It all seems very odd to me - the thing looks so advanced, akin to a modern coleoid. What on earth is it doing so far back in time?

According to the conjectured time line available at Pharyngula it is a dead-end lineage sharing a common ancestor with the nautiloids and others in the early Cambrian. It didn't lead to the squid and ammonites at all. So where does this leave our small creeping shelled early nautiloids such as Plectronoceras?

http://scienceblogs.com/pharyngula/upload/2010/05/mother_of_all_squid/nectocaris_phylo.php

Can a syphon really be interpreted? What form did it's own ancestors take, shelled or not? Where is the radula? Isn't a dead-end lineage all to easy to place an unfamiliar animal in?

Something is not right here...
 

OB

Colossal Squid
Staff member
Moderator
#6
How sure are they that the funnel is indeed that, a funnel, and not a mouth of sorts, there's a bit too much Anomalocaris going on here, from my perspective...
 

cuttlegirl

Colossal Squid
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#7
Ob,
That was I was thinking, especially since the fossils seem to show segmentation. I wish I could access the full article - I would like to see how the internal shell compares to cuttlefish.
 

willsquish

Blue Ring
Supporter
#14
Yeah, that looks really like a larval dinocarid/anomalocarid. (Hence 2 arms and a 'funnel' that looks very like an anomalocaris mouthplate, segmentation, and projections that look like fins along the sides) In fact, stratocladistically speaking it has very little to do with cephalopoda. None of the ancient cephs have much in common. It shares 5 times as many characters with anomalocarids as it does with cephalopods. It would be weird for it to lose the shell, then evolve a specialized shell with air chambers, then slowly lose the shell again. Not the most parsimonious solution. And the segmented body structure isn't even seen in modern cephalopods, or any molluscs, except maybe chitons, but that's mostly a hard tissue/gill pairing. It's convergent evolution only. It had a similar lifestyle to modern squids. How many months would a paleontologist have to wait before publishing a paper reclassifying it?

Here's another link with another picture of a different fossil specimen.

http://blogs.discovermagazine.com/n...tually-a-500-million-year-old-squid-relative/

You can clearly see the 'funnel'. It looks much like a mini anomalocarid mouth to me. Anomalocaris mouth below for comparison.

http://ircamera.as.arizona.edu/NatSci102/NatSci102/text/cambrian_files/burgess22.jpeg
 

willsquish

Blue Ring
Supporter
#15
Also, why no radula? We see radulichnites as far back as the pre-cambrian mollusc kimberella, and the radula's one of the easiest spotted features of pohlsepia (soft bodied octopod ancestor from Mazon Creek).
 

willsquish

Blue Ring
Supporter
#16
Phil;156293 said:
According to the conjectured time line available at Pharyngula it is a dead-end lineage sharing a common ancestor with the nautiloids and others in the early Cambrian. It didn't lead to the squid and ammonites at all. So where does this leave our small creeping shelled early nautiloids such as Plectronoceras?


Yeah, the tree just doesn't line up at all. Spirula, rostrospirula, belemnites, all tie coleoidea together, and have chambered shells, like nautiloids. They're difficult to unlink from the internal shell of cuttlefish and the pen of squids. Goniatites, ceratites, and prolecanitids all tie nautiloids to ammonoids. It's practically a continuum of a record there.

According to that tree, aulacocerids, belemnite phragmocones, and goniatites must have nothing to do with nautiloids...which doesn't add up at all. And the chambered shell would have to convergently be evolved by both nautiloidea which came from shelled creatures looking much more like monoplacophorans of their time than nectocaris, and this segmented squishy nectocaris' ghost lineage, only to lose it quickly thereafter. *edit* It should have to evolve convergently 3 times. The tree shows ammonoidea and coleoidea split back in the Ordovician too. */edit The nectocaris should have more in common with nautiloidea than gastropoda, and it clearly doesn't. Did they try cladistic analysis?
 

OB

Colossal Squid
Staff member
Moderator
#17
Yet more sceptics leaning towards the alternative hypothesis as presented here on Tonmo... Most interesting feature of this particular discussion; a distally expanding syphon is of no use whatsoever for jet propulsion.
 

willsquish

Blue Ring
Supporter
#18
ob;156573 said:
[ a distally expanding syphon is of no use whatsoever for jet propulsion.
Well, as an aerospace engineer, I can say you're practically correct. However, there are one or two situations where expanded siphons are perfect for jet propulsion. The vacuum of space or otherwise high pressure ratio rocket engines like Apollo and the shuttle. I think it is fair to conclude that nectocaris lived on the moon.

Now do I submit this idea to the AIAA journal of propulsion, or Nature?
 

OB

Colossal Squid
Staff member
Moderator
#19
Maybe, then, Nectocaris used steam, rather than water, giving rise to the notion of it foraging down towards ocean floor vents, taking in superheated water at high pressure and let the ascent back up the watercolumn do the rest? :wink: I assume the Moon theory offers better prospects... Ah well, back to serious, I guess...
:feet:
 

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