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| Ghost lineages! | |
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| Topic Started: Jun 21 2017, 06:59 AM (1,827 Views) | |
| Nembrotha | Jul 25 2017, 06:58 AM Post #31 |
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Adolescent
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Nudibranchs are some of my all time favourite animals (That I somehow didn't know had eyes...). So why am I bringing them up here? Because, as far as I know, we know nothing about their evolutionary history. I have yet to have ever come across a single description of a nudibranch fossil. The only thing I could find is that they evolved from shelled ancestors, and that the ancestors of most living gastropods lived in the Mesozoic. I suppose it makes sense, considering their lack of a shell, that would make them extremely difficult to fossilize. If there are any fossil nudibranchs you know of, hit me up! |
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| kusanagi | Jul 25 2017, 07:27 AM Post #32 |
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Adolescent
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1. Its actually because it is easier to spot morphological convergences I prefer morph data. And do people honestly not realise there are molecular homoplasies too? 2. Sorry theres no way you can get a brachiozoan from a trochozoan. The development of the lophophore is inconsistent (among things). People in the past pointed out similarities between phoronids and pterobranchs, things such as that - its not just about the blastopore. There are in fact likely synapomorphies between brachiozoans, enteropneusts and chrordates for esample giant nerve cells in all three groups. Although the morphological tree in Glenner et al does place brachiozoans as deuterostomes stemwards of (pterobranchs + echinoderms + cytrotretes). Other morphological trees have supported Ambulacraria but fossils such as Mitrates might rule out certain typologies. If stylophores are regarded as total group echinoderms then they might drag echinoderms closer to Chordates and Enteropneusts than are Pterobranchs because the gills of Jaekelocarpus are very chordate-like (remember only Mitrates and Chordates show dexothetism). The possible stem echinoderm Vetulocystidae resemble the Cornutes and might be decalcified stylophorans(?) but their anatomy remains uncertain and to my knowledge it is unclear if they have gills. They remain incertae sedis owing to a lack of data but otherwise interpreting them as the most basal of the ecinoderms would be appealing. fossils change a lot but thats why the homologies need to be certain. http://www.sciencedirect.com/science/article/pii/S0960982204007031 I find the polytomy in that morphological tree interesting. Intuitively ctenophores should be stemward of the polytomy but they are neotenous planulae and so might have a bilaterian origin. Ectoprocts (bryozoans) are possibly related to spiralians within the protostomes but they have no close relatives, and their aberrant position in morphological trees probably results from their specialisation and lack of close relatives. If the true platyhelminthes are recovered as simplified protostomes then xenacoelamorphs might also be secondarily simplified nephrozoans, and including "flatworms" probably affected the tree typology else a Nephrozoa ought to have resulted. Myxozoans, catenulids, orthonectids, rhombozoans and Salinella are all missing from the tree, maybe justifiably in the last case as it may not have existed and coding could not be checked. All of them may be degenerated decendants of "normal" bilaterian ancestors or cnidarians in the case of myxozoans, but it cannot be ruled out that any of them are genuinely intermediates between nephrozoans and stemward eumetazoans. The living problematica Lobatocerebrum, Diurodrilus and Limnognathia were skipped but probably the latter genus would have been recovered as a gnathiferan and the other two at the very least are spiralian. Edited by kusanagi, Jul 25 2017, 12:08 PM.
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| IIGSY | Jul 25 2017, 05:28 PM Post #33 |
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A huntsman spider that wastes time on the internet because it has nothing better to do
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Why are you saying enteropnuesta and pterobranchia seperatly? They are both hemichordates. And if the supposed morphological synaphomorphies between brachiozoans and dueterostomes are true, then how do you explain the molecular data that points to them being protostomes? Catenulids are basal flatworms, orthonectida and rhombozoa are somewhere within spiralians, diurodrilus is an annelid, and limnognathia is a sister to rotifers. |
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Projects Punga: A terraformed world with no vertebrates Last one crawling: The last arthropod ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess) Potential ideas- Swamp world: A world covered in lakes, with the largest being caspian sized. Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal. Tri-devonian: A devonian like ecosystem with holocene species on three different continents. Quotes Phylogeny of the arthropods and some related groups In honor of the greatest clade of all time More pictures Other cool things All African countries can fit into Brazil
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| kusanagi | Jul 25 2017, 05:44 PM Post #34 |
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Adolescent
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1. I was repeating th argument presented in the paper, but in either the Ambulacraria or Cytrotreta hypotheses the hemichordates are paraphyletic. I don't have to defend hypotheses from one line of data if it conflicts with data from another method as the test of conscilience is should they independently converge upon the same conclusion: morphological and developmental data stand for themselves though they run into problems without intermediate forms explaining the difficultties regarding secondarily degenerated or otherwise ultra-specialised forms. 2. There is no such thing as a basal flatworm if platyhelminthes proper are degenerated spiralians and the classic flatworm form taxons was polyphyletic. (In any case I ws contemplating the effects missing taxa might have on the typology rather than making a taxonomic argument per se.) Yes orthonectida have spiralian tissue homologies but the plcement of rhombozoans is even more mysterious. Of the definite spiralians Diurodrilus is not an annelid and nor are the flatworm-like myzostomida (except in the waste bin sense) whereas Lobatocerebrum can't be proved to be an annelid because of relevant character states are missing and is more basal by default. All such problematica are ghost lineages. Edited by kusanagi, Jul 25 2017, 05:45 PM.
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| IIGSY | Jul 25 2017, 05:54 PM Post #35 |
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A huntsman spider that wastes time on the internet because it has nothing better to do
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What the hell do you mean by 'no such thing as a basal flatworm'? Platyhelminthese (excluding xenacoelamorpha) are monophyletic, and catenulida is the basal most member of the clade. ![]() And how are myzostomids "flatworm like". Even if they aren't annelids (which they most likely are, if not please tell me otherwise), they sure as hell aren't flatworms. |
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Projects Punga: A terraformed world with no vertebrates Last one crawling: The last arthropod ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess) Potential ideas- Swamp world: A world covered in lakes, with the largest being caspian sized. Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal. Tri-devonian: A devonian like ecosystem with holocene species on three different continents. Quotes Phylogeny of the arthropods and some related groups In honor of the greatest clade of all time More pictures Other cool things All African countries can fit into Brazil
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| kusanagi | Jul 25 2017, 06:09 PM Post #36 |
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Adolescent
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Flatworm is the equivalent to a paleontological form taxon for a group of simlar animals that share a broadly similar morphology and in the earlier days of cladistics they were found to be a paraphyletic grrade of stemward bilaterians in the order of Acoela + (Rhabditophora + (Catenulida + Nephrozoa) because all of them lack the full suite of traits inferred for the nephrozoan LCA and the old Platyhelminthes phylum lacked unifying synapomorphies among themselves. Myzostomids are incompletely segmented acoelomates with chaetae and a trochophore larva as though a normal spiralian is degeneratng into the flatworm morphotype. This paper presents molecular data that myzostomids are a sister taxon to regular flatworms but it is more interesting that a normal protostome was caught in the act of becoming a flatworm, giving a window into how a drastic suite of reversal happens in nephrozoans. The same caveat applies to flatworm taxa as to mesozoans, that it would be risky to interpret aberrant and anatomically simple forms as most stemward. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1690696/ Edited by kusanagi, Jul 25 2017, 06:44 PM.
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| IIGSY | Jul 25 2017, 06:21 PM Post #37 |
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A huntsman spider that wastes time on the internet because it has nothing better to do
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That phylogeny you presented is wrong. Very wrong. Acoelamorpha are basal bilaterians and are no longer part of platyhelminthese. Rhabditophora and catenulida are sister groups that make up platyhelminthese and are part of spiralia. And of course they lacked traits inferred in the nephrozoan ancestor. They are degenerate. And being acoelomate means practically nothing, as groups with varying coelomic development are spread across bilateria. Ecdysozoa contains both coelomate and pseudocoelomate animals for example. And if myzostomids aren't annelids, why do they have chetae? |
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Projects Punga: A terraformed world with no vertebrates Last one crawling: The last arthropod ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess) Potential ideas- Swamp world: A world covered in lakes, with the largest being caspian sized. Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal. Tri-devonian: A devonian like ecosystem with holocene species on three different continents. Quotes Phylogeny of the arthropods and some related groups In honor of the greatest clade of all time More pictures Other cool things All African countries can fit into Brazil
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| kusanagi | Jul 25 2017, 06:59 PM Post #38 |
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Adolescent
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I was not claiming the phylogeny is correct: but the traditional platyhelminthes was polyphyletic like (probably) the non-triploblastic mesozoa. Chetae and homologous structures seem to be scattered across protostomia and obviously to be without a body cavity is to either be pristinely primitve or to have undergone a reversal. Like the diploblasty of mesozoans any acoelomate character state in a bilaterian is a warning sign of sorts it may in fact be deceptively crownwards and yet you cannot assume such reversals knowing the acoelomate and diploblastic conditions were at one point present in nephrozoan ancestors. (Although ctenophores are triploblastic and cnidarian triploblasty is noted in Buddenbrockia, Polypodium and in non-hydrozoan polyps and medusae suggesting all total group bilaterans may be primitively triploblastic, meaning diploblasty in any bilaterian would be a reversal.) To my knowlede there are no definite non-nephrozoan bilaterians even in the fossil record (saltation?). Just odds and ends that could be secondarily simplified but who knows? Edited by kusanagi, Jul 25 2017, 07:09 PM.
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| IIGSY | Jul 25 2017, 07:06 PM Post #39 |
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A huntsman spider that wastes time on the internet because it has nothing better to do
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Well, platyhelminthese is now correct as it no longer includes xenacoelamorpha. And that last sentance isn't true. Xenacoelamorphs are non-nephrazoan bilaterians. If they where placed in nephrozoa, that would just make it the same as bilateria. |
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Projects Punga: A terraformed world with no vertebrates Last one crawling: The last arthropod ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess) Potential ideas- Swamp world: A world covered in lakes, with the largest being caspian sized. Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal. Tri-devonian: A devonian like ecosystem with holocene species on three different continents. Quotes Phylogeny of the arthropods and some related groups In honor of the greatest clade of all time More pictures Other cool things All African countries can fit into Brazil
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| kusanagi | Jul 25 2017, 07:19 PM Post #40 |
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Adolescent
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I am not saying that xenocoelomorph flatworms are definitely not non-nephrozoan biaterians only that their functional and anatomical similarities to other flatworms within spiralia suggests their own primitiveness cannot be assumed. To that ends I am drawing the comparison between flatworms and mesozoans which also may also not be assumed a priori to lie stemward. Even if the molecular data is correct to place xenocoelomorphs stemward of nephrozoans their ancestor still might have been more complex than a flatworm. Besides, Janvier at least seems to think xenocoelomorphs are still probable deuterostomes with a question mark but he presented no argument so. The importance of the myostomids is that they capture the process of flatworm-isation in action as a result of a mode of life. Though it probably had a flattened planula larva. In th past there was an assumption a flatworm would be most primitive but even though there are possible flatworms in the Precambrian such as Brabbinthes and Plexus they are all controversial in some way so there is no reason to interpret the urbilaterian as a flattened worm at all. Edited by kusanagi, Jul 26 2017, 11:03 AM.
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| IIGSY | Jul 27 2017, 05:21 PM Post #41 |
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A huntsman spider that wastes time on the internet because it has nothing better to do
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I am still skeptical of conodonts not being vertebrates. There are several specimens that preserve soft tissue that have eyes. Eyes are completely absent in other chordates. |
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Projects Punga: A terraformed world with no vertebrates Last one crawling: The last arthropod ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess) Potential ideas- Swamp world: A world covered in lakes, with the largest being caspian sized. Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal. Tri-devonian: A devonian like ecosystem with holocene species on three different continents. Quotes Phylogeny of the arthropods and some related groups In honor of the greatest clade of all time More pictures Other cool things All African countries can fit into Brazil
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| kusanagi | Jul 27 2017, 05:28 PM Post #42 |
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Adolescent
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Eyes are convergently evolved easily and you have no answer to their near-lack of cephalisation compared to vertebrates. Even the tullimonster is more encephalised, and still might be a gastropod. On balance eucondonts (not simply conodonts, they are polyphyletic and the word refers only to the hard parts) lack craniate synapomorphies unless you assume a priori there are homologies that have been questioned. Did you read the skeptical paper I directed you to? Though their analysis constrained euconodonts to be chordates they found them to be non-vertebrate and non-craniate when the matrix was corrected for questionable homologies. Besides Murdock argued that teeth cannot be derived from conodont structures and refuted the inside out model. A lot of these taxa (euconodonts, Tullimonstrum, vetulicolida) should be put into a morphological matrix of Metazoa like the one I directed you to. Unfortunately there is no access to cladistic software, here. But somehow the relative probability of proposed relationships has to be weighed more scientifically, as was done with vetulicolidans. And for euconodonts a run using pterobranchs an outgroup would probably work fine since there is hardly a reason to think euconodonts are non-chordates. Edited by kusanagi, Jul 27 2017, 05:51 PM.
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| IIGSY | Jul 27 2017, 06:06 PM Post #43 |
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A huntsman spider that wastes time on the internet because it has nothing better to do
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I see now. I have been lied to. Euconodonts really aren't vertebrates after all. But hey, at least they're still definitely chordates (looking at you Pikaia). So what are their "teeth"? Possible homologous to the feeding structures of modern lancelets? If you look at a lancelets head, it's mouth kinda looks like a tentacle-y version of a conodont mouth. Maybe it's just me though. Something about tullimonstrum still doesn't seem right. No craniate, living or extinct, has a mouth that even resembles that of the tully monster. But then again, it may also be a gastropod. And I still don't see the difference between craniata and vertebrata. They are essentially the same thing. And since when are hemichordates paraphyletic? |
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Projects Punga: A terraformed world with no vertebrates Last one crawling: The last arthropod ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess) Potential ideas- Swamp world: A world covered in lakes, with the largest being caspian sized. Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal. Tri-devonian: A devonian like ecosystem with holocene species on three different continents. Quotes Phylogeny of the arthropods and some related groups In honor of the greatest clade of all time More pictures Other cool things All African countries can fit into Brazil
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| kusanagi | Jul 27 2017, 08:54 PM Post #44 |
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Adolescent
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Well I do not know if you have been lied to about conodonts but such debates have gone on since conodontophores were discovered in the 1980s. No gastropod has a mouth like Tullimonstrum either, but loosey defined a proboscis is widely found among animals from worms to elephants. Craniata is one node back from Vertebrata, its about the naming of nodes. And I explained this about hemichordates I am sure. Just google Nielsen on the cytrotrete hypothesis or for that matter a good deal on the ambulacraria hypothesis, which often suggests paraphyly of hemichordata with regards to echinoderms and sometimes of enteropneusts with regards to pterobranchs (harrimanid enteropneusts as the pterobranch sister or parent group). Morphological trees do not recover them as monophyletic under either hypothesis and nor has all of the molecular data. Cripps and Schram independently in 1991 foung hemichordate paraphyly/polyphyly when hemichordate monophyly was first tested and Cripps even found Cephalodiscus crownwards of Rhabdopleura and therefore closer to enteropneusts, chordates and echinoderms. The most recent tree of morphological data I showed you favoured clade Cytrotreta but papers after 2000 were recovering Ambulacraria. And I admit to being neutral until more fossil taxa are added to the matrices without constraining problematica like vetulicolidans, Pikaia and Yunnanozoon to a deuterostome placement by coding or choice of taxa. Both the pterobranchs and crown echinoderms lack gills that are homologous with those of chordates and enteropneusts. The water vascular system of echinoderms nonetheless evolved from the lophohore of hemichordates by distortion through torsion, involving the same supression of structures on the right side of the body that is oddly favoured in chordates such as Amphioxus. In chordates the endostyle replaced the lophophore organ at least if cytrotreta hypothesis stands up. (In any case enteropneusts lack a lophophore as do the chordates.) But muddying it is that mitrates at the base of echinoderms(?) have clearly cytrotrete-like gill slits. If the gene for them can be lost in crown echinoderms why not in the pterobranchs? But there is no evidence pterobranchs have ever possessed cytrotrete-like gills. Yunnanozoon blends the traits of chordates (mostly superficial ones mind) and the anatomical traits of enteropneusts. Enteropneust larvae so closely resemble those of echinoderms they were initially misidentified as such. Who knows? But I know what there is little evidence for: a holophyletic Phylum Hemichordata. In 2001 Peterson and Eernisse found only two hemichordate synapomorphies, the stomochord and the mesocoelomic ducts. How hard is it to modify or lose both? This is messing with my head if you can't tell and if it looks like I'm listing facts istead of making a coherent argument, thats because I am. Deuterostomes are a mess even without inclusion of possible but non-definite deuterostomes (brachiozoans, chaetognaths, Xenoturbella) or the fossils. I still think brachiozoan lophophores are homologous with those of pterobranchs with an added mystery that they share character states with the cytrotrete phyla but not the pterobranchs. Edited by kusanagi, Jul 27 2017, 09:08 PM.
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| IIGSY | Jul 27 2017, 09:26 PM Post #45 |
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A huntsman spider that wastes time on the internet because it has nothing better to do
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One node back? Hagfish have remnants of vertebra and are vertebrates. So if so much evidence points to hemichordates being an invalid clade, why don't they change it? We finally establish acanthocephala as a part of rotifera*, so why not this? But xenoturbellids are basal bilaterians* and chaetognaths are basal protostomes*. Dammit. DAMMIT! I though protostomes where the confusing one! Deuterostomes where supposed to be the fine and dandy ones while protostomes kept hopping around. BuT nOoOoOoOoO! Stupid hemichordates had to mess everything up! You know what we need? A big, wide scale cladistic analysis of dueterostomes and possible dueterostomes. It needs to include homalozoans, enteropneusts, pterobranchs, pikia, cephalochordates, tunicates, euconodonts, paraconodonts, brachiozoans, hagfish, lampreys, ,some gnathostomes, tullimonstrum, vetulicolians, chaetognaths, xenacoelamorphs, some protostomes, and a cnidarian outgroup. *lemme guess, that's not true either Edited by IIGSY, Jul 27 2017, 09:27 PM.
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Projects Punga: A terraformed world with no vertebrates Last one crawling: The last arthropod ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess) Potential ideas- Swamp world: A world covered in lakes, with the largest being caspian sized. Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal. Tri-devonian: A devonian like ecosystem with holocene species on three different continents. Quotes Phylogeny of the arthropods and some related groups In honor of the greatest clade of all time More pictures Other cool things All African countries can fit into Brazil
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7:51 PM Jul 10