shakeup for the tree of life

:bonk: Yeah, it's a mess fitting spirula in... but it's got pair 4 as tentacles, rather than the octopod/vampy other pair modification (is that pair 2?) which would seem to put it after the octo/deca split.

see also Fossil Cephalopods FAQs - The Cephalopod Page

I also worry a bit about the tendency to use Nautilus as representative of fossil shelled cephs, since it seems plausible that the reason it's the only one to survive the k/T extinction event is that it had a different lifestyle that kept it safer: a deep water scavenger might have done particularly well when all the shallow-water animals were dying and sinking, for example.
 
cuttlegirl;117466 said:
Once again Monty, you get me thinking... Here is an abstract on the siphuncle of Spirula. I have a hard time thinking that Spirula is a weird coleiod - but I never really considered it a squid :bonk:.

http://www.blackwell-synergy.com/doi/abs/10.1111/j.1475-4983.2006.00533.x

? Phylogeny based on connecting rings.

Architeuthoceras;85774 said:
Oops!:oops:

Looks like what I remember isnt what I remember at all. An orthocone formerly referred to Bactritida (?Ammonoidea) is referred to Spirulida (Coleoidea) because of the lack of a nacreous layer. Seems the Spirulida and this Orthocone have 2 prismatic layers.

Doguzhaeva, L., Mapes, R., and Mutvei, H., 1999, A Late Carboniferous Spirulid Coleoid from the Southern Mid-Continent (USA) Shell Wall Ultrastructure and Evolutionary Implications, in: Advancing Research on Living and Fossil Cephalopods, edited by Oloriz and Rodriguez-Tovar. Kluwer Academic/Plenum Publishers

? Phylogeny based on shell layers


monty;117474 said:
:bonk: Yeah, it's a mess fitting spirula in... but it's got pair 4 as tentacles, rather than the octopod/vampy other pair modification (is that pair 2?) which would seem to put it after the octo/deca split.

see also Fossil Cephalopods FAQs - The Cephalopod Page

I also worry a bit about the tendency to use Nautilus as representative of fossil shelled cephs, since it seems plausible that the reason it's the only one to survive the k/T extinction event is that it had a different lifestyle that kept it safer: a deep water scavenger might have done particularly well when all the shallow-water animals were dying and sinking, for example.

? Phylogeny based on arms (no fossil record). Is not the shell of Nautilus the only (?) thing that connects ammonoidea (and 99% of all other fossil shelled cephalopods) to the cephalopoda at all?

:cool2:
 
for extra chaos, I just re-read Spirula spirula

4 rows of arm suckers (how many rows of hooks did belemnites have?) and tentacle clubs covered in just a "lawn" of suckers. No corneas (Sepia have corneas) Both arms IV hectocotylized.

And I'd point out that another view is that, because of the lack of fossil arms, comparison to the extant arms may be the only way to fit the coleoids in with the shelled fossils.

And the shell: coiled opposite ammonites (and we know that from cameral fluid, of course) and Nautilus. Siphuncle marginal, not central. Simple sutures. No ornamentation. No living chamber. No aptychi.

"Spirula is able to withdraw its head and arms completely within the mantle; the mantle opening can then be closed by folding over the large dorsal and ventrolateral extensions (= flaps) of the mantle margin"

Switching to Nixon & Young:

Giant fiber system like the other decabranchia (lacking in octopods and Vampyroteuthis). Arm suckers have peduncles like other decabranchians with "an inner ring which has blunt teeth of almost uniform height and size." Tentacle suckers similar but smaller. Beaks: lower rostrum "protrudes and is sharp." Radula vestigial, lateral buccal flaps with stout teeth. Eye muscles resemble Sepia and Sepiola. "The central nervous system follows the general plan found in other decabranchians, but is without special similarity to Sepiolidae or Sepiidae." "Discriminant analysis of several parameters of the statocyst place Spirula amongst the buoyant squids."

Which brings up an unrelated question for Kevin and the other fossil hunters: does anyone ever sift through the matrix of ammonites looking for the statolith? Obviously, it's a needle-in-a-haystack proposition, but there are a lot of ammonite beds out there, one might think that the statolith is occasionally preserved-- it's pretty much a rock, after all. Assuming ammonites even had them (quite likely, both given their presumptive lifestyle and because Nautilus and all coloeoids have statocysts, although Nautilus lacks a statolith ad rather has "statoconia," which are crystals that are ovoid or spherical.) Knowing what ammonite statoliths looked like would be interesting in light of the extensive studies of how coleoid statocysts match their lifestyles.

:confused::hmm::bonk:

We need laboratory cultures of Spirula and a Spirula genome project and several squid, octopus, vampyrotetuhis, and nautilus genome projects for comparison. And make sure to do an argonaut genome as well, for comparison. Any takers?
 
p.s. I was also curious about what "fossil ancestors" are referred to by this ToLweb bit:

The large posterior guard-like sheath of fossil relatives of Spirula seems to be designed to function as a counterweight to maintain the animal in a horizontal position. Such an orientation is particularly important for a bottom-associated animal that swims just above the ocean floor (Naef 1921-23). Presumably the ancestors of Spirula were bottom associated and some remnants of this behavior apparently remains in their life history and distribution (Young, et al., 1998). A small remnant of the sheath exists on the Spirula shell and a remnant of the ancestral habitat remains in Spirula's apparent benthic spawning (Young, et al., 1999).

they seem to have left the 1999 article out of the references list, but the 1998 is in the South African Journal of Marine Science, which I don't have access to, anyone got this?

Young, R. E., M. Vecchione and D. Donovan. 1998. The evolution of coleoid cephalopods and their present biodiversity and ecology. South African Jour. Mar. Sci., 20: 393-420.

or, for that matter, this:

Monks N, Wells S (2000) A new record of the Eocene coleoid Spirulirostra anomala (Mollusca: Cephalopoda) and its relationships to modern Spirula. Tert Res 19: 47-52

I did find this: http://userpage.fu-berlin.de/~jevers/data/palbio3/22.pdf when looking for those. It adds ribosomal DNA to Kevin's list of possible things to use for the phylogeny....

Edit: and http://userpage.fu-berlin.de/~jevers/data/palbio3/12.pdf this one adds "loss of the right oviduct" to lump spirulida with myopsida.

BTW, does anyone know if any of the versions of cephbase are currently working?
 
Jean;117531 said:
I have the the Young Vecchione & Donovan one, I bought that issue. I'll try to find the volume and pdf you a copy.

The former in your last post is on it's way!

J

Cool! Thanks!
 
Well, after reading the links - and have to admit, I like the idea of "No predators and lost of sex" part - I have to say this sounds interesting.

I wish I could get institutionalized so I could get a copy of this paper. :tongue:

Well, the Onycophora (Velvet Worms) as a sister group to the Arthropods is kinda old news. From what I know Ecdysis is a pretty much straightforward hormal process (even then its an AWESOME evolutionary process to study), and many phyla share this trait. I'm glad they are no longer trying to sell the coelom as the end-all of evolutionary traits, because while body cavities are a novel concept, there's a bit of evidence that covergence tends to play a role here.

Hmm... The Sipuncula and Echiura... trochophore larva and all... Well, I am all for Mollusca and Annelida having a common ancestry.

I worry, though, about the treatment of molecular phylogeny as the holy grail of classification. Somehow, I get the impression that rates of mutation are treated as constant, and that seems a little too Schroedinger's Cat for me to be completely at ease.

Oh well, good show. I need to find a copy of that paper...

- John

Oh, and Velvet Worms are awesome. Their mode of attack is just sweet. Check out "Life in the Undergrowth" from BBC. David Attenborough is my master, I am his padawan.
 

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