shakeup for the tree of life

Discussion in 'Physiology and Biology' started by monty, Apr 11, 2008.

  1. monty

    monty Colossal Squid Staff Member Supporter

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    There's a paper in Nature this week that is full of interesting stuff, including several curve-balls, resulting from a very comprehensive molecular evaluation of relationships between animal groups.

    On topic first: molluscs are monophyletic.

    Now that I got that out of the way, the non-ceph but most astounding part: Ctenophores (comb jellies) are a separate group from the rest of the metazoans, including sponges. So the metazoa/eumetazoa split is wrong.

    In other words, we're more closely related to sponges than to comb jellies. In fact, jellyfish are more closely related to us and sponges than they are to comb jellies.

    The article also resolves controversies and validates morphological taxons to some extent: Protostomia, Ecdysozoa, and Lophotrochozoa come out winners, spiral cleavage not so much (in terms of clades, anyway). And the coin "clade A," "clade B," and "clade C" where "clade C" contains our friends the molluscs and clade B, which is a bunch of worms and brachiopods and stuff. Clade C is all the animals that have or whose ancestors had shell-like bits of a certain sort, including mollusc shells. Read the paper if you know/care about these details, 'cause I'm not really qualified to discuss 'chitinous chaetae.' Also, some juggling of the arthropods is described (sorry, Roy, no stomatopods).

    The abstract is at

    http://www.nature.com/nature/journal/v452/n7188/abs/nature06614.html

    and if you have institutional access, the PDF is at

    http://www.nature.com/nature/journal/v452/n7188/pdf/nature06614.pdf

    There's a mainstream science press article that's got some horrible misrepresentation in it here:

    http://www.livescience.com/animals/080410-first-animal.html

    but while reading that one, keep in mind that their use of "first animal" is horrible misleading... what they really mean is "last common ancestor between comb jellies and other animals," which was certainly not anywhere close to a "first animal," and shared common traits between apes, octopuses, sponges, and comb jellies, so may not have looked any more like a comb jelly than like an ostrich. Anyway, there were certainly many ancestors leading up to that last common ancestor, and we even know a little about what some (the Edicarian fauna) looked like... like these, for example:

    http://www.reuters.com/article/scienceNews/idUSN2040405820080320?sp=true
     
  2. Heather Braid

    Heather Braid O. vulgaris Supporter

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    I just finished my exam for invertebrate zoology, and in it we learned all of what you are saying has changed. As upsetting as it may seem to have my knowledge of inverts be based on false assumptions, I think it's really cool how they can use molecular evidence to sort it out.
     
  3. Steve O'Shea

    Steve O'Shea Colossal Squid Supporter

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    ..... Heather, what we were taught years ago differs from what you were taught, and from that presented in this Nature article.

    There never is a 'last word' in phylogenetic matters. Believe me, this will all change again. If we were to uncritically accept everything that was published, even in Nature, we'd go ever-so-slightly insane.
     
  4. monty

    monty Colossal Squid Staff Member Supporter

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    Yeah, this is a sign that you're not in a boring, stagnant, stodgy field. But rather a wet, squishy, and slimy one. Er, as well as a vibrant, growing, exciting one!

    Plus, you probably didn't have to look up the Latin names for water bears and velvet worms and such like I did...
     
  5. Tintenfisch

    Tintenfisch Architeuthis Staff Member Moderator

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    Cool about the velvet worms being a sister-group to arthropods! I'll have to see if I can get hold of this.
     
  6. monty

    monty Colossal Squid Staff Member Supporter

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    I suspect Hallucigenia would have preferred to be a sister to cephalopods, but so it goes. The water bears being so far separate is interesting as well.
     
  7. Heather Braid

    Heather Braid O. vulgaris Supporter

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    On the last day my professor told us not to look at our notes 20 years from now expecting them to still be valid because things would have changed by then. I just didn't expect this to happen so soon. Really all it means is that there is always going to be a lot of opportunities in science, which is nice.
     
  8. Jean

    Jean Colossal Squid Supporter

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    I have the pdf if you want it

    J
     
  9. Octodude

    Octodude Blue Ring Registered

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    You know, I was about to leave for class, it got cancelled, I came on here and stumbled across this, and am a much happier person. This great reading I have to say, thanks for posting.
     
  10. Tintenfisch

    Tintenfisch Architeuthis Staff Member Moderator

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    Got it, but thanks! :smile:
     
  11. monty

    monty Colossal Squid Staff Member Supporter

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    This slightly older (2006) paper used monoplacophoran genetics to re-jigger the mollusca in ways I hadn't realized obsoleted some of my books:

    http://www.pnas.org/cgi/content/full/103/20/7723

    Maybe all of you taxonomists and paleontologists already knew about this, though... pretty much says chitons and monoplacophorans are a derived clade, which I guess (?) casts some doubt on a segmented origin for the last common mollusc ancestor... as well as splitting the gastropods up.
     
  12. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Nice cladogram in that article. Thanks Monty :notworth:

    Surprising to me that Spirula is closer to Architeuthis than it is to Nautilus. 8-)
     
  13. monty

    monty Colossal Squid Staff Member Supporter

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    Interesting. So you're in the "more than a weird coleoid" camp for Spirula, eh?

    I figured just from the siphuncle placement it would have to be heavily diverged from nautiloids... and the arm/tentacle anatomy would suggest that it's in some sense closer to the decapodiformes. I'm pretty shocked that it's lumped in more with squids that sepia, though. I suspect the ceph section is pretty uncertain, though: they don't number the branches, and they sure chose one weird examples to be representative of the octopods-- I had to look up what the heck Bathypolypus was. Since there are no numbers on the really weird ceph distribution, and the paper doesn't mention much about them, I'm going to go out on a limb and say the weird branching within the decapodiformes is arbitrary for the markers they used. I am curious about the 70 on the sepiolida branch (I had to look up all 3 species on that branch, though... so it's not like I knew much about them).
     
  14. Tintenfisch

    Tintenfisch Architeuthis Staff Member Moderator

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    Although I haven't included a genetic component in my thesis (not enough tissue samples available), recently I've been looking up some genetic studies that have been done on the past for the Onychoteuthidae at different levels, and in short, no two studies say the same thing. There are some overall trends that support some of my observations, but there are other results in individual studies that I don't even want to think about. :roll: The same seems true at the family level - three different studies looking at relationships between oegopsid families give three different closest relatives to the Onychoteuthidae; in Lindgren et al 2004 the onychos fall out with the Enoplos, Gonatids and Ancistrocheiros, while Carlini & Graves (1999) group the onychos with the ommastrephids. :bugout: So... looks like at many levels your results depend on which sequences you're using and from which taxa (Lindgren et al (2004) used one of the weirder onychoteuthids, 'M.' knipovitchi, as their token onychoteuthid).
     
  15. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    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
     
  16. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    I was, I was hoping to see it closer to the octopods so I could squeeze ammonoids in between somewhere. Now I think I'll take Kats advice and not put to much into any of it... yet. :wink:
     
  17. monty

    monty Colossal Squid Staff Member Supporter

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    :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 http://www.thecephalopodpage.org/FosCephs.php#8

    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.
     
  18. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    ? Phylogeny based on connecting rings.

    ? Phylogeny based on shell layers


    ? 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?

    8-)
     
  19. monty

    monty Colossal Squid Staff Member Supporter

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    for extra chaos, I just re-read http://tolweb.org/Spirula_spirula/19989

    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?
     
  20. monty

    monty Colossal Squid Staff Member Supporter

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    p.s. I was also curious about what "fossil ancestors" are referred to by this ToLweb bit:

    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?
     

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