- Joined
- Jun 8, 2007
- Messages
- 48
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?