tag:blogger.com,1999:blog-5460788270738656369.post443872587298711579..comments2023-12-24T07:02:43.274+08:00Comments on Catalogue of Organisms: TetragraptinesChristopher Taylorhttp://www.blogger.com/profile/11075565866351612441noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-5460788270738656369.post-7435300681693978632011-11-23T09:42:29.557+11:002011-11-23T09:42:29.557+11:00Thanks a lot for your comments, David!Thanks a lot for your comments, David!Christopher Taylorhttp://coo.fieldofscience.comnoreply@blogger.comtag:blogger.com,1999:blog-5460788270738656369.post-70315429063750186662011-11-23T08:12:46.613+11:002011-11-23T08:12:46.613+11:00I should add that I support the Maletz et al. tree...I should add that I support the Maletz et al. tree as a statement of our current understanding; there will always be more taxon/character sampling to do.<br /><br />Also, not really certain to what extent D. solidus could be said to have a serra proximal end, given that we can't make out the branching order among the thecae. It seems like Fortey and Cooper may have just meant it had a tetragraptus-like branching pattern.<br /><br />Also, one of the odd things about the Maletz et al. tree is how the tetragraptids come out as sister or derived from the paraphyletic didymograptids. Most people previously would have thought it was a simple progression from many-branched dichograptid to four-branched tetragraptid to two-branched didymograptid... The Maletz et al. tree suggests this isn't the case, but again we still have to worry that if we could see more characters on dichograptids we might get a different story.<br /><br />Okay, I'm done. Now the references:<br /><br />Cooper, R. A., and R. A. Fortey. 1982. The Ordovician graptolites of Spitsbergen. Bulletin of the British Museum (Natural History), Geology series 36(3):157-302, pls. 1-6.<br /><br />Maletz, J. 2010. Xiphograptus and the evolution of virgella-bearing graptoloids. Palaeontology 53(2):415-439.dwbapsthttps://www.blogger.com/profile/17606476387441191531noreply@blogger.comtag:blogger.com,1999:blog-5460788270738656369.post-39471648718984967642011-11-23T07:48:24.213+11:002011-11-23T07:48:24.213+11:00Sir-
I am a graptolite worker who is working on th...Sir-<br />I am a graptolite worker who is working on their phylogenetics, so I was pleasantly surprised by your blog post! I don't often get to read blog posts about tetragraptids, unless I write them! I was an undergrad in Chuck Mitchell's lab, which produced the Maletz et al. paper.<br /><br />Just to add some additional information, yes, more taxon sampling would help, however preservation is very poor for most early graptolites, particularly for the dichograptids, a diverse group only represented by Clonograptus on the Maletz et al. tree. So unfortunately, the Maletz et al. represents a statement about what we know of their relationships without adding species that are only poorly preserved.<br /><br />For example, based on Cooper and Fortey (1983) I don't think we even know if D. solidus has a virgella or not... its remains are completely flattened. Fortey and Cooper (1986) included many of these taxa and sorted them along branches based on branching pattern, without regard to the missing data. Yet we know branching pattern can be very homoplastic in groups that we have better character data for. <br /><br />Maletz (2011) looked at the question of the virgella as a general homologous character and found that different lineages have very different constructional approaches to making the spine, suggesting that just knowing a species has a virgella is not very systematically useful.<br /><br />Also, the loss of branches thing is true, but note that graptoloids several times re-figured out how to make new branches via 'cladia'. So, while there was evolution toward losing true dichotomies, there was also evolution to regain multiple-branched colonies. Weird, eh?<br /><br />-Dave Bapst, UChicago Geoscidwbapsthttps://www.blogger.com/profile/17606476387441191531noreply@blogger.com