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Date: Sat, 23 Jun 2001 17:00:42 -0700 (PDT)
From: "Jaime A. Headden" <qilongia@yahoo.com>
To: kinman@usa.net, phylocode@ouvaxa.cats.ohiou.edu
Subject: Re: Crown groups mainstream?
Ken Kinman (kinman@usa.net wrote:) wrote: <Most mammalogists still seem to think that a Mammalia which is cladistically anchored on a monotreme (which still have a miserable fossil record) is a dumb idea. ... I would very HIGHLY recommend that PhyloCode workers NOT define Mammalia as a crown group, because there is a good chance it will end up excluding multituberculates, and it will certainly exclude sinoconodonts, morganucodonts, and docodonts (all of which have the well-known mammalian jaw and three ear ossicles).> Yuk. Poor attitudes about how some groups have less specialized ancestors that must somehow be included because certain classic features are present -- or not, thus excluded -- are in bad taste, in my opinion. The establishment of the taxon Mammalia to include only the smallest group possible including the most recent ancestor of *Ornithorhynchus* [monotreme], *Macropus* [marsupial], or *Canis* [placental] is based on the ability to recognize groups on well-established membership, without fossil taxa literally screwing the tree up. That a fossil's possition may rotate or compeletely squash the proposed phylogeny is anchored on that taxon, this disrupts what is generally perceived of as a stable group. So friggin' what if multis are not member of Mammalia? They can still be mammals. So may anything grouped in Mammaliaformes, which is the stem opposing the cynodonts. If you want to base the name on an apomorphy or two, like three middle ear bones (formed from the jaw, and thus the same character as the dentary-only lower jaw) then go ahead, and see if it survives criticism. Not that I'm arguing against it, but just such a group is bound to be unstable, and would get ripped to shreds the first moment a sphenacodont or less closely related amniote (or more basally!) is found with the same condition. Otherwise, we are left with bounding taxa in terms of their associate taxa, and outgroups, not what they bear. <I think it is pretty obvious a crown group Aves has been rejected already, and who knows what might happen to a crown group Archosauria,> Do you possibly think that birds are not bound within the group defined as being closer to crocodilians than to snakes, lizards, and the like? Otherwise, Archosauria is a real entity, defined on birds and crocs. I have it on good authority (a little bird told me) that Aves being used in tendem with Neornithes will be used to group the Cretaceous/Jurassic fossil birds and the living ones. Thus, hesperornithiforms & ichthyornithiforms become birds by extension, and the name Aves has a broader concept than Neornithes, which is the present broad use of the living membership. Anyways, a crown-group is a node and it stable by its content, now matter how "far" these constituent taxa may be from eachother, intervening taxa ranging in the hundreds or not. <because pterosaurs may not be the only group that gets ejected from that taxon.> Pterosaurs are irrelevant to Archosauria -- they cannot comprise the definition of a crown-group, as they are extinct. As well, Dave Peters quite clearly espouses and convinces the relationship of pterosaurs as basal to archosaurs, as archosauriforms closer to lizards than crocs (lepidosauriforms), as members of Archosauromorpha, and which becomes a senior subjective synonym of Ornithodira by content. <It is perhaps still the best hope that some large crown group within amniotes will become mainstream, but I wouldn't even bet on that one.> Amniota = mammals and reptiles. Mainstream in the sense you've used above. <Crown groups seem to cause more problems than they solve, and if I was a paleontologist I think I would dislike them even more.> Exactly what problem has a crown-group caused for you? ===== Jaime A. Headden Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na Where the Wind Comes Sweeping Down the Pampas!!!! __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail http://personal.mail.yahoo.com/