tag:blogger.com,1999:blog-5460788270738656369.post3859698352608285538..comments2023-12-24T07:02:43.274+08:00Comments on Catalogue of Organisms: Arthropods in the Precambrian?Christopher Taylorhttp://www.blogger.com/profile/11075565866351612441noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-5460788270738656369.post-90123427329064025972015-03-15T16:32:48.347+08:002015-03-15T16:32:48.347+08:00Is it possible that no one who specializes in Edia...Is it possible that no one who specializes in Ediacaran has ever looked at a Triops specifically the ventral surface or that of any of the animals that are members of the order Notostraca?<br /><br />I don't think I am exaggerating when I say they are virtually a perfect fit for Spriggina fossils, with spriggina being the earliest identifiable ancestor of modern Notostraca, which are themselves considered living fossils, appearing in the fossil record about the same time when spriggina fossils disappear from the record.<br /><br />I wish I could send you the specific photo that I am using to compare to various spriggina fossils. I'm certain you'd see what I see.<br /><br />Realizing just how similar spriggina is to modern triops does take looking at more than just one or two spriggina, because every fossil seems to show a different feature more clearly than the others. <br /><br />Still, I can say in spriggina examples where the headshield area is clear, the features on the headshield of the spriggina lose their ambiguity completely. The only difference between the headshield of the two is the triops has one that is larger while still maintaining the same shape as on spriggina.<br /><br />Oh by looking at the triops you can positively identify the mouth on the spriggina, because on the triops it is identically shaped and in the exact same position relative to the head shield on the spriggina and the food groove. <br /><br />The food groove of the spriggina along with the rows of appendages also is a near perfect match to the triops especially just below the head shield area.<br /><br />What differences there are could easily be explained by the modern triops being very much an aquatic acrobat, and to swim like it does it does the ends of its middle parts of many legs broaden out to flat paddles. <br /><br />The spriggina could have been strictly a bottom crawler, and thus lacked that on their legs.<br /><br />If you assume that, it becomes pretty obvious that if the spriggina is the earl ancestor of any modern organism it would be for Notostraca.<br /><br />If you get a moment I'd love to hear what you think provided you can find that photo. If not I can send it. <br /><br />Thanks<br />JohnnyJohnn Moraleshttps://www.blogger.com/profile/18410754869779549100noreply@blogger.comtag:blogger.com,1999:blog-5460788270738656369.post-64666597540522596392014-05-16T15:20:38.966+08:002014-05-16T15:20:38.966+08:00My inclination would be towards the latter, if Spr...My inclination would be towards the latter, if <i>Spriggina</i> was a stem-nephrozoan (Nephrozoa = deuterostomes + ecdysozoans + lophotrochozoans) and acoels are non-nephrozoans. Of course, if <i>Spriggina</i> is a crown-nephrozoan then the question becomes a lot less relevant.Christopher Taylorhttps://www.blogger.com/profile/11075565866351612441noreply@blogger.comtag:blogger.com,1999:blog-5460788270738656369.post-5081524256015798132014-05-16T14:11:42.060+08:002014-05-16T14:11:42.060+08:00Where does that leave "minor" bilaterian...Where does that leave "minor" bilaterians, like acoels? Secondarily reduced, or outside a deuterostome-ecdysozoan-lophotrochozoan-<i>Spriggina</i> clade?Andreas Johanssonhttps://www.blogger.com/profile/08802392912541974977noreply@blogger.comtag:blogger.com,1999:blog-5460788270738656369.post-52595606626029248992014-05-15T08:28:54.402+08:002014-05-15T08:28:54.402+08:00And in reply to Allen: Yes, I believe it was the l...And in reply to Allen: Yes, I believe it was the late 1980s/early 1990s when the concepts of 'Ecdysozoa' and 'Lophotrochozoa' originated, though it wouldn't be for another decade or so before they became the default paradigm. Placement of sprigginids and the like on the bilaterian stem would correlate with the suggestion that has been made that, rather than being flatworm-like as was assumed in the past, the earliest bilaterians may have been relatively large, probably coelomate, probably pseudo-segmented. Each of these are features that are found in all three of the main bilaterian lineages of ecdysozoans, lophotrochozoans and deuterostomes.<br /><br />And yes, by 'basal chordates' I primarily meant amphioxus (and also, I believe, lampreys). Amphioxus go through a glide-reflective stage during development, though by maturity they have mostly returned to symmetry.Christopher Taylorhttps://www.blogger.com/profile/11075565866351612441noreply@blogger.comtag:blogger.com,1999:blog-5460788270738656369.post-46068410433313896282014-05-15T08:18:03.105+08:002014-05-15T08:18:03.105+08:00Comment from Allen Hazen, who has apparently been ...Comment from Allen Hazen, who has apparently been having trouble getting his comments to load:<br /><br />"Thank you for this post!<br />The placement of the Ediacaran "weird wonders" is a fascinating problem.<br />-<br />Note that, had you been writing this few decades back, the fact that these critters resemble both arthropods and annelids would not have seemed problematic: at that time (up, I think, until the ??? late 1980s ??? when molecular phylogenies started assigning arth and ann to very different supra-phylem groups (arth to the ecdysiasts, and annelids to… are they lophotrochozoans? anyway, closer to mollusks and brachiopods than to arthropods despite the superficial resemblance given by their segmentation) arth and ann were thought to be closely related. But now resemblance to these two phyla just dramatizes their strangeness!<br />--<br />To be sure I am following you: when you speak of "basal chordates" as having "glide reflectional symmetry" … are you thinking of Cephalochordates like amphioxus?<br /><br />PPS: One of the options for commenting given by your page was a Google one. Note that I am now writing you from a Google mail account: posting to your site didn't work either before or after I logged in to my Google mail..."Christopher Taylorhttps://www.blogger.com/profile/11075565866351612441noreply@blogger.comtag:blogger.com,1999:blog-5460788270738656369.post-41431186487539390292014-05-15T01:17:00.233+08:002014-05-15T01:17:00.233+08:00Paleontological Rorschach tests? Somebody must ha...Paleontological Rorschach tests? Somebody must have made that observation: ah, a google search for that plus ediacaran find 85 hits.Mike Hubenhttps://www.blogger.com/profile/01371469964446567690noreply@blogger.comtag:blogger.com,1999:blog-5460788270738656369.post-37179458972514767582014-05-14T17:14:15.089+08:002014-05-14T17:14:15.089+08:00Ediacaran critters are fascinating and frustrating...Ediacaran critters are fascinating and frustrating.Andreas Johanssonhttps://www.blogger.com/profile/08802392912541974977noreply@blogger.com