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| How should "Dinosauria" be defined? |
| 1. Node-based definition using a herrerasaurid, a saurischian, and an ornithischian (sensu Novas 1992). |
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| 2. Node-based definition using Triceratops horridus and Fringilla domestica (=Passer domesticus) (sensu Sereno 2005; similar to Padian and May 1993, Sereno 1998, Fraser et al. 2002). |
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| 3. Node-based definition using Triceratops horridus and Vultur gryphus (not published but similar to #2 except that it uses the first avian species listed by Linnaeus). |
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| 4. Node-based definition using Megalosaurus bucklandii and Iguanodon bernissartensis (sensu Olshevsky 2000, Clarke 2004) |
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| 5. Node-based definition using Triceratops horridus and Tyrannosaurus rex (sensu Holtz and Osmólska 2004). |
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| 6. Node-based definition using Megalosaurus bucklandii and Hylaeosaurus armatus (sensu Kischlat 2002). |
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| 7. Node-based definition using Megalosaurus bucklandii, Hylaeosaurus armatus, and Iguanodon bernissartensis (not published, but somewhat suggested in the draft PhyloCode). |
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| 8. No definition. "Dinosauria" should be used as a paraphyletic group, excluding avialans. |
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| 9. Other (please explain). |
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| Total Votes : 9 |
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tmkeesey
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 Posted: Fri 13 Apr, 2007 10:57 pm Post subject: Definition of Dinosauria |
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All published definitions of Dinosauria, to my knowledge, have been node-based heterodefinitional synonyms of each other. The real question is: which specifiers should be used?
(I left an option for those who do not think "Dinosauria" should be converted as a clade, too.)
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tmkeesey
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| Posted: Fri 13 Apr, 2007 11:00 pm Post subject: |
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It should be noted that options #2 and #3 violate PhyloCode Recommendation 11A (and are explicitly noted as an example of a violation).
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dinoguy2
Joined: 22 Aug 2006
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| Posted: Sat 14 Apr, 2007 3:46 am Post subject: |
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| Quote: | | "Dinosauria" should be used as a paraphyletic group, excluding avialans. |
I chose other, because of I just posted in the Aves definition thread. Paraphyletic excluding aves, but with a definition (why can't paraphyletic groups be defined? Clades must be monophyletic, but this is PhyloCode not CladoCode, right?  )
So, in my ideal world where PC doesn't convert traditional names but invents all new ones, Dinosauria = "Perforate acetabulum (+whatever other universal dinosaurian apomorphies you like, I'm just under the impression this one has always been seen as the biggie) as in the MRCA of Iguanodon, Megalosaurus, and Hylaeosaurus, plus all its descendants, excluding pennaceous feathers as in Passer."
So, basically, Apo-Dinosauria (which will self-destruct if I. + M. + H. are polyphyletic, especially if you throw in some Crurotarsans, etc. as external specifiers) minus Avipluma. Plesio-Dinosauria.
The CLADE Dinosauria (whcih should have a variant name like Dinosauriclae to avoid confusion) should be "The ancestor of Iguanodon + Megalosaurus + Hylaeosaurus and all its descendants."
Dinosauria and Dinosauriclae would name different groups. Dinosauria is anything that would traditionally be a dinosaur, possibly basal things that aren't members of the clade, and no birds, since BAD only came about post-Phylo. The clade is how everyone uses it nowadays.
Or, chuck out the entire first part of this post and pretend I nominated the I.+M.+H. node-based definition |
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tmkeesey
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| Posted: Sat 14 Apr, 2007 5:29 am Post subject: |
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| dinoguy2 wrote: | | Or, chuck out the entire first part of this post and pretend I nominated the I.+M.+H. node-based definition ;) |
I just might.
One reason not to name paraphyletic groups (apart from species) is clarity. If I see something written Alphoidea I automatically know it's a clade, not some grab-bag taxon that's an accident of history.
Another reason: why recognize non-avialan Dinosauria? Why not non-ceratopsian Dinosauria, or non-tetanuran Archosauria, or non-neoavian Theropoda, or non-maniraptoran Bilateria, or non-avian Eukaryota? Objectively, they're all equally valid.
The number of paraphyletic groups is an order of magnitude greater than the number of clades. Rather than waste names on them, if we just name clades, we can actually discuss paraphyletic groups with more precision. You can discuss Mesozoic Ornithodira or ectothermic Tetrapoda or pre-Cretaceous Archosauria or non-chiropteran Theria all with equal ease. Naming clades is actually better for discussing paraphyletic groups.
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David Marjanović
Joined: 24 Aug 2006
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| Posted: Sat 14 Apr, 2007 11:19 am Post subject: |
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If it were still 1986, I'd have chosen 8, and said that a new name should be coined for traditional dinosaurs + birds. But it's too late for that. Dinosauria now has at least as much usage including birds as excluding them, so I go with current usage and the overwhelming historical usage of the last 10 to 20 years. To be precise, I voted 7.
It still happens a lot, however, that people talk about "dinosaurs" and mean "Mesozoic dinosaurs" or "non-neornithean dinosaurs" or "nonavian dinosaurs". The nomenclature problem has become an education problem. In general we should avoid that. |
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tmkeesey
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| Posted: Sat 14 Apr, 2007 2:55 pm Post subject: |
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I completely agree with you, David.
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tmkeesey
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Nick Gardner
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| Posted: Sat 14 Apr, 2007 7:31 pm Post subject: |
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Personally, I prefer 7 (and voted as much). If not 7, I'd readily go for 2 or 3 though.
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dinoguy2
Joined: 22 Aug 2006
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| Posted: Sun 15 Apr, 2007 3:17 am Post subject: |
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| One thing about 7, something like Crocodilus should be included as external in case Dinosauria somehow turns out not to be monophyletic after all (werid things like Silesaurus, etc.). |
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tmkeesey
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| Posted: Sun 15 Apr, 2007 3:47 am Post subject: |
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That is not actually a bad idea. The monophyly is pretty well-established now, but was doubted for some time.
Then again it does clutter up the definition, and there's no real doubt about the monophyly nowadays. Eh, could go either way.
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dinoguy2
Joined: 22 Aug 2006
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| Posted: Sun 15 Apr, 2007 7:02 am Post subject: |
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| tmkeesey wrote: | That is not actually a bad idea. The monophyly is pretty well-established now, but was doubted for some time.
Then again it does clutter up the definition, and there's no real doubt about the monophyly nowadays. Eh, could go either way. |
I think it's always useful to include a fw outside specifiers, even for clades where monophyly seems air tight, just in case. At least in cases like this. If extant groups like Crocodilia were to fall inside Dinosauria, it would pretty much obliterate original usage (though, I guess like having birds in there, we'd get used to it...). Having some odd fossil groups like Pterosauria or what have you wouldn't be such a big deal, so I think only modern species neec to be used in cases like this. |
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David Marjanović
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| Posted: Sun 15 Apr, 2007 10:29 am Post subject: |
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| What's so bad about Silesaurus? It either is a dinosaur (a basal ornithischian) or not (in which case it is part of the sister-group of Dinosauria). |
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tmkeesey
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| Posted: Sun 15 Apr, 2007 3:24 pm Post subject: |
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I think another good point is that, if by some crazy occurrence Dinosauria were shown to include crocodylians, it would always be possible to petition for an emendation to the definition. Right now it's really, really not looking likely.
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T. Michael Keesey
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Nescio
Joined: 30 Sep 2006
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| Posted: Wed 18 Apr, 2007 11:43 am Post subject: |
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I voted 7 as a nod to Owen, but I'm basically fine with any of the definitions.
Just a question - is it certain these days that Herrerasauridae are inside ornithischia+saurischia? I thought I heard they might be non-dinosaurian ornithodires. |
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tmkeesey
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| Posted: Wed 18 Apr, 2007 2:46 pm Post subject: |
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As far as I know, herrerasaurids are more and more being considered non-avepod, non-sauropodomorph saurischians, not non-dinosaurian dinosauriforms. But there's still work being done in this area.
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