tag:blogger.com,1999:blog-3433304117507034540.post6138206129902583454..comments2024-03-27T10:06:07.100-07:00Comments on The Echinoblog: Raiders of the Lost "Ark"arua? The oldest Echinoderm??ChrisMhttp://www.blogger.com/profile/11784970666468925633noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-3433304117507034540.post-57561135538858994862009-06-29T17:11:18.241-07:002009-06-29T17:11:18.241-07:00In my professional opinion, it looks like a smiley...In my professional opinion, it looks like a smiley face, therefore bi-symmetrical.Mary Ellenhttps://www.blogger.com/profile/15001597172789977025noreply@blogger.comtag:blogger.com,1999:blog-3433304117507034540.post-68944011050911160172009-06-17T13:10:42.590-07:002009-06-17T13:10:42.590-07:00Well,
I think that the problem with these very o...Well,<br /> I think that the problem with these very old fossils IS the interpretations of the fossils. Some might argue that the marginal rim IS stereom or stereom-like. I believe Gehling interpreted several of the features as consistent with echinoderm characteristics.<br /><br />The difficulty of your position is the argument of non-presence. The absence of presence is not presence of absence.<br /><br />No worm tracks? Not evidence that they weren't there-only that you don't see them in the fossil record.<br /><br />I honestly have no position on this fossil one way or another-and your arguments are ones I might use if I were attempting to argue against Arkarua as an echinoderm. They are good ones. I'm just playing devil's advocate. :-)ChrisMhttps://www.blogger.com/profile/11784970666468925633noreply@blogger.comtag:blogger.com,1999:blog-3433304117507034540.post-20635190905318844332009-06-17T11:52:48.952-07:002009-06-17T11:52:48.952-07:00If its 5-part symmetry makes it an echinoderm, the...If its 5-part symmetry makes it an echinoderm, then wouldn't it be up there where that synapomorphy evolved? If so, then stereom should have evolved prior to Arkarua. But, there is no stereom anywhere (so far found) in Precambrian rocks.<br /><br />I would conclude that Arkarua cannot readily be interpreted as an echinoderm. <br /><br />Second line of evidence: If Arkarua is an echinoderm, then Bilateria is older than Ediacaran. Early bilaterians were worms. Worms make tracks. No tracks or trails prior to the Ediacaran. Thus, Arkarua probably isn't an echinoderm.<br /><br />For what they are worth, my 2 cents.Tesserahttps://www.blogger.com/profile/04216460189853994672noreply@blogger.com