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Discussion Forum of the International Society for Phylogenetic Nomenclature
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| How should "Aves" be defined? |
| As a crown group (e.g., sensu Gauthier 1986) |
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23% |
[ 3 ] |
| As a total group (e.g., sensu Ax) |
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0% |
[ 0 ] |
| As a non-crown node-based clade (e.g., sensu Chiappe 1997, Sereno 1997) |
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30% |
[ 4 ] |
| As a non-total branch-based clade (e.g., sensu Marjanovic [unpublished]) |
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30% |
[ 4 ] |
| As an apomorphy-based clade (please specify). |
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15% |
[ 2 ] |
| Other (please explain). |
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0% |
[ 0 ] |
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| Total Votes : 13 |
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kinman
Joined: 01 Oct 2006
Posts: 17
Location: Kansas
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 Posted: Sun 01 Oct, 2006 2:47 am Post subject: Apomorphy-based AVES |
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I would prefer an apomorphy-based definition of AVES. However, I would not support such a definition based on "flight feathers", however those might be defined. Instead the apomorphy should be based on one or more osteological characters which are more often preserved in the fossil record. Those which are connected with flight (in the wrist and/or shoulder joint) would be the most likely candidates for apomorphies of AVES. Ideally, it would coincide with (or be slightly more inclusive than) the possession of ornithoid eggshells. Eggshell microstructure is important, but like feathers, is not as well preserved in the fossil record as many osteological characters.
On the other hand, a crown group Aves was and still is a very bad idea, and that clade already has a perfectly good name (Neornithes). Basing Aves on Archaeopteryx is a whole lot better, but I would not favor that if it meant excluding Deinonychus. Given the uncertainty of the splitting of various eumaniraptoran subclades from one another, an apomorphy-based AVES seems the most stable alternative in the long run. The question is what apomorphy is the best.
----Cheers,
Ken Kinman |
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leowsham
Joined: 14 Sep 2006
Posts: 69
Location: Hong Kong
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| Posted: Sun 01 Oct, 2006 6:21 am Post subject: Re: Apomorphy-based AVES |
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| Ken Kinman wrote: | | Given the uncertainty of the splitting of various eumaniraptoran subclades from one another, an apomorphy-based AVES seems the most stable alternative in the long run. |
Well, David's suggestion actually would solve this problem without evoking an apomorphy-based definition. I support a node based definition in the sense that the position of Archaeopteryx is stable (within Aves) - if proven otherwise, a branch-based Aves should be adopted.
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kinman
Joined: 01 Oct 2006
Posts: 17
Location: Kansas
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| Posted: Sun 01 Oct, 2006 1:55 pm Post subject: Re: Apomorphy-based AVES |
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I do not like the idea of excluding Archaeopteryx or Deinonychus from Aves. If that requires that Velociraptor be included (and it probably would), I have no problem with that. Therefore, I would rather have Deinonychus as an internal specifier than an external specifier, but that might make Aves equivalent to one of the other proposed clade names. I still agree with Benton that an apomorphy-based definition for Aves is preferable, but disagree that flight feathers (however defined) should be the apomorphy chosen.
----Cheers,
Ken Kinman |
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tmkeesey
Site Admin
Joined: 14 Aug 2006
Posts: 287
Location: Los Angeles, CA, USA
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| Posted: Sun 01 Oct, 2006 4:20 pm Post subject: Re: Apomorphy-based AVES |
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Using Deinonychus antirrhopus as an internal specifier would be a clear violation of Recommendation 11A:
| Quote: | | Recommendation 11A. Definitions of converted clade names should be stated in a way that attempts to capture the spirit of traditional use to the degree that it is consistent with the contemporary concept of monophyly. Consequently, they should not necessitate, though they may allow, the inclusion of subtaxa that have traditionally been excluded from the taxon, as well as the exclusion of subtaxa that have traditionally been included in the taxon. To accomplish this goal, internal specifiers of converted clade names should be chosen from among the set of taxa that have been considered to form part of a taxon under traditional ideas about the composition of that taxon, and they should not include members of subtaxa that have traditionally been considered not to be part of the taxon. |
(emphasis added)
Marjanovic's definition really does capture traditional usage best, if that is the goal. It is also quite stable under most phylogenies, the only real exceptions being if Archaeopteryx is a deinonychosaur (in which case it just loses archaeopterygids, which weren't always traditionally included, anyway) or if oviraptorosaurs are closer to modern birds than Archaeopteryx is (which isn't widely followed and wouldn't change composition that much, anyway).
Gauthier's (1986) definition works well within a system where widely-known names can be assumed to refer to the crown group, i.e., the least inclusive traditional usage. I do think such a system would make literature more accessible to nonspecialists, and it has a pleasing logic about it. Unfortunately, it is also disruptive and has generated controversy.
Benton's (2000) definition is not admissible under the PhyloCode, since it lacks a species or specimen as a specifier (what if birds were not the first vertebrates to evolve flight feathers?) but it could easily be revised. It would then essentially be identically to Gauthier and de Queiroz' (2001) Aviremigia. But this taxon has not seen much, if any, use, since its content is a bit nebulous. (Would it include ornithomimosaurs? We don't know.)
As Sereno (2005) and others have pointed out, apomorphy-based definitions (even if based on skeletal characters) have a whole host of potential problems. For one, if a specimen is missing that part of its body, then it might be unclassifiable even if its position in the cladogram is well-attested. For another, many characters are not absolute, but appear in gradual stages. Of course, as per PhyloCode, the latter problem can be dealt with by allowing for revisions. But why give the best-known names such issues?
I think apomorphy-based clades have their utility, and there are even some well-known names that might be best defined as apomorphy-based (e.g. Eukaryota). But Aves has never really been tied to an apomorphy; the name just means "birds". The fact that you are uncertain as to which apomorphy to use is evidence of this. Aves, as originally used by Linnaeus, was diagnosed by a huge suite of apomorphies, a suite we now know to have arisen in a mosaic pattern over a very long amount of time. It's a lousy candidate for an apomorphy-based definition (although it does lend itself quite well to a host of eponymous apomorphy-based clades: Avepoda, Averostra, Avepectora, Aviplumosa, Avifiloplumosa, Avipinna, Aviremigia, Avialae [sensu Gauther and de Queiroz 2001], Avebrevicauda).
(I have my own suggestions, but I'm working on the paper....)
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T. Michael Keesey
Director of Technology, Exopolis, Inc.
Last edited by tmkeesey on Tue 03 Oct, 2006 8:52 pm; edited 2 times in total |
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tmkeesey
Site Admin
Joined: 14 Aug 2006
Posts: 287
Location: Los Angeles, CA, USA
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| Posted: Sun 01 Oct, 2006 4:43 pm Post subject: Re: Apomorphy-based AVES |
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| leowsham wrote: | | Well, David's suggestion actually would solve this problem without evoking an apomorphy-based definition. I support a node based definition in the sense that the position of Archaeopteryx is stable (within Aves) - if proven otherwise, a branch-based Aves should be adopted. |
If Archaeopteryx is closer to modern birds than dromaeosaurids and oviraptorosaurs are, then Marjanovic's definition yields the same known content as the node-based definition, anyway. It is slightly more inclusive, but there aren't any known species that are inside Marjanovic's branch-based definition but outside the node-based definition.
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David Marjanović
Joined: 24 Aug 2006
Posts: 137
Location: currently Paris
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| Posted: Sun 01 Oct, 2006 4:52 pm Post subject: |
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| I seem to remember that there are phylogenies under which my definition of Aves would include Rahonavis while Chiappe's would not. (I think this can be considered an advantage for mine, though a small one.) |
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Nescio
Joined: 30 Sep 2006
Posts: 53
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| Posted: Sun 01 Oct, 2006 4:57 pm Post subject: |
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| What is David's list of external specifiers? |
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leowsham
Joined: 14 Sep 2006
Posts: 69
Location: Hong Kong
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| Posted: Mon 02 Oct, 2006 1:28 am Post subject: |
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| David Marjanović wrote: | | I seem to remember that there are phylogenies under which my definition of Aves would include Rahonavis ... |
I thought this idea was gone for some time, was it not? Did you mean the original Science paper in 1997? My own ignorance 
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kinman
Joined: 01 Oct 2006
Posts: 17
Location: Kansas
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| Posted: Mon 02 Oct, 2006 2:20 am Post subject: Re: Apomorphy-based Aves |
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Mike,
Recommendation 11A has as its goal to approximate traditional usage for such taxon names as far as possible. I don't know why you state that Archaeopteryx has danced in and out of Aves over the decades, but as you yourself state, it certainly has been "in" more than it has been "out". Who are some of these traditionalists who excluded Archaeopteryx from Aves?
Therefore, I would predict that David's definition will be rejected by most workers if it fails to include Archaeopteryx as an internal specifier. And given the instability in that area of many cladograms, it would therefore also be inadvisable to use Deinonychus as an external specifier.
----Ken Kinman |
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tmkeesey
Site Admin
Joined: 14 Aug 2006
Posts: 287
Location: Los Angeles, CA, USA
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| Posted: Mon 02 Oct, 2006 3:17 am Post subject: Re: Apomorphy-based Aves |
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| kinman wrote: | | Who are some of these traditionalists who excluded Archaeopteryx from Aves? |
Gregory Paul (1988b) is the most recent and prominent example, I think, although in Dinosaurs of the Air he switched to (more-or-less) cladistic nomenclature and explicitly avoided settling on a definition of Aves, considering the matter too contentious (2002:270-271). Interestingly, the reason he originally excluded Archaeopteryx from Aves is because he found it to be closer to dromaeosaurids than to modern birds. Even in Dinosaurs of the Air he refrained from calling Archaeopteryx a "bird", preferring to reserve that term for Avebrevicauda (an apomorphy-based clade roughly equivalent to Pygostylia or Ornithurae sensu Gauthier and de Queiroz 2001 or Class Aves sensu Paul 1988b). Archaeopteryx is instead referred to as a "dino-bird".
A much less authoritative example is A Field Guide to Dinosaurs (Lambert, 1983). A much earlier example is Andreas Wagner (1862), who considered the animal (which he called Griphosaurus) to be a feathered pterosaur(!)
I'll own that there are far more examples of Archaeopteryx being included. But under the most widely-accepted phylogenies, Marjanovic's definition includes Archaeopteryx, anyway.
| Quote: | | Therefore, I would predict that David's definition will be rejected by most workers if it fails to include Archaeopteryx as an internal specifier. |
It's ahead in the poll so far! 
(That's without my vote, too.)
| Quote: | | And given the instability in that area of many cladograms, it would therefore also be inadvisable to use Deinonychus as an external specifier. |
But no traditional usage of Aves has ever included Deinonychus (with the exception of certain extremely inclusive usages which also included all theropods or all ornithodirans). I think more researchers would rather exclude Archaeopteryx than include Deinonychus, if forced to make a choice. (Of course, that's just my impression.)
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T. Michael Keesey
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tmkeesey
Site Admin
Joined: 14 Aug 2006
Posts: 287
Location: Los Angeles, CA, USA
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| Posted: Mon 02 Oct, 2006 7:18 am Post subject: |
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| Nescio wrote: | | What is David's list of external specifiers? |
I came across the abstracts for this past summer's ISPN meeting while cleaning today. Marjanovic's definition of Aves is branch-based with Passer domesticus internal and Velociraptor mongoliensis, Oviraptor mongoliensis, Segnosaurus galbinensis, Troodon formosus, Sinornithoides youngi, Ornithomimus velox, Tyrannosaurus rex, Compsognathus longipes, Ornitholestes hermanni, Coelurus fragilis, Coelophysis bauri, Hypsilophodon foxii, Crocodylus niloticus, Sphenosuchus acutus, Euparkeria capensis, Megalancosaurus preonensis, and Sorex araneus external.
As you can see he's safeguarded it against all hypotheses, no matter how outdated or poorly supported. Personally, I think the list of external specifiers could be trimmed down a bit (perhaps even to just the first five minus S. galbinensis), but it doesn't matter all that much.
(Incidentally, the reason there are two troodontids in the list is because the type specimen of Troodon formosus is a tooth, so it may be a nomen dubium, although it's usually synonymized with the well-known Stenonychosaurus inequalis these days.)
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David Marjanović
Joined: 24 Aug 2006
Posts: 137
Location: currently Paris
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| Posted: Tue 03 Oct, 2006 8:46 pm Post subject: |
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Thanks for digging this up! 
I agree that people, if forced to make the choice, would rather have Archie out than Deinonychus in; that's why I used Velociraptor as an external anchor and didn't mention Archaeopteryx. Of course, under most published phylogenetic hypotheses Archie would be inside and Deinonychus outside, so the traditional contents would be preserved precisely. |
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Eoraptor
Joined: 13 Sep 2006
Posts: 19
Location: Seattle, WA
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| Posted: Thu 05 Oct, 2006 1:07 pm Post subject: |
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| Quote: | came across the abstracts for this past summer's ISPN meeting while cleaning today. Marjanovic's definition of Aves is branch-based with Passer domesticus internal and Velociraptor mongoliensis, Oviraptor mongoliensis, Segnosaurus galbinensis, Troodon formosus, Sinornithoides youngi, Ornithomimus velox, Tyrannosaurus rex, Compsognathus longipes, Ornitholestes hermanni, Coelurus fragilis, Coelophysis bauri, Hypsilophodon foxii, Crocodylus niloticus, Sphenosuchus acutus, Euparkeria capensis, Megalancosaurus preonensis, and Sorex araneus external.
As you can see he's safeguarded it against all hypotheses, no matter how outdated or poorly supported. |
I don't see Longisquama in the list!  |
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ottscay
Joined: 23 Aug 2006
Posts: 27
Location: Wyoming
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| Posted: Thu 05 Oct, 2006 5:14 pm Post subject: Re: Apomorphy-based Aves |
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| kinman wrote: |
Therefore, I would predict that David's definition will be rejected by most workers if it fails to include Archaeopteryx as an internal specifier. |
I think it should be completely inadmissable to include Archaeopteryx as any kind of specifier for Aves. There are many legitimate lines of arguement that suggest it couldn't fly well, if at all (sorry guys, but there are, even if it isn't the majority opinion). Since we know that maniraptorans in general were winged (but not neccesarily primatively flying) it's an inexcusable example of letting the tradition tail (Archaeopterys is the "first bird") wag the theoretical dog. Look, Archaeopteryx could well be a deinonychosaur exclusive of all other birds, and I could make a case (and may yet) that it's a basal troodontid and that birds are closer to dromaeosaurs, in which case there is no reason to include Archaeopteryx, especially if birds did not inherit flight from it. David's definition allows for eventualites like these.
It's specifically because of the instability of Paraves that we need to allow Archaeopteryx to float into and out of Aves as the evidence dictates. |
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leowsham
Joined: 14 Sep 2006
Posts: 69
Location: Hong Kong
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| Posted: Thu 05 Oct, 2006 5:18 pm Post subject: |
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| Eoraptor wrote: | | I don't see Longisquama in the list! |
Nor any particular pterosaurs e.g. Sordes pilosus...  Though, I think going as far as Coelurus is quite enough. It's good to be prudent, but one has got to make his stance... this echoes much with the case of Orbitoscuta (in the other thread): you just can't play to the gallery each and every time!
And I don't see the PhyloCode recommend anything as per David's style here (no personal offense )
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