Burgess Shale Cephalopod

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?
 
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.
 
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?
 
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:
 

Shop Amazon

Shop Amazon
Shop Amazon; support TONMO!
Shop Amazon
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.
Back
Top